Category Archives: Plant Pathogens

Plant Pathology (plant diseases)

Fungi, Plant Pathogens

Calonectria pseudonaviculata (Crous, J. Z. Groenew. & C. F. Hill) L. Lombard, M. J. Wingf. & Crous, 2010

California Pest Rating for
Calonectria pseudonaviculata (Crous, J. Z. Groenew. & C. F. Hill) L. Lombard, M. J. Wingf. & Crous, 2010
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

On November 22, 2016, non-official samples of diseased boxwood plants collected by a landscaper from a private property in Hillsborough, San Mateo County, were sent through the San Mateo County Agricultural Commissioner’s office to the CDFA Plant Pathology Lab for diagnosis.  The samples were examined by Kathy Kosta CDFA plant pathologist, and the associated pathogen was cultured and identified by Cheryl Blomquist CDFA plant pathologist, as Calonectria pseudonaviculata (Kosta, 2016).  Subsequently, on November 29, 2016, official samples were collected from the same private property by Kathy Kosta (CDFA) and Fred Crowder (San Mateo County) and processed at the CDFA Plant Pathology Lab for pathogen diagnosis.  The official identification of Calonectria pseudonaviculata was made by Cheryl Blomquist on December 7, 2016.  This detection marked a first record of the pathogen in California.  Consequently, the pathogen was assigned a temporary ‘Q’ rating.   The risk of introduction and establishment of the pathogen is assessed here and a permanent rating is proposed.

History & Status:

Background:  Calonectria pseudonaviculata is the fungal pathogen that causes boxwood blight or box blight disease.  The pathogen is also known by its asexual (anamorph) stage as Cylindrocladium pseudonaviculatum.  The disease was first reported in the United Kingdom in the early to mid-1990s and the pathogen was given the name Cylindrocladium buxicola.  The origin of C. pseudonaviculatum is not known.  The pathogen was considered an exotic species that had been introduced to the UK and by 1998, it had spread to Europe and New Zealand.  (CABI, 2016; Crous et al., 2002; Dart et al., 2012).  While most published literature refers to the fungus as C. buxicola, this pathogen was not formally reported in the literature until 2002 as Cylindrocladium pseudonaviculatum which later became synonymous with Calonectria pseudonaviculata, the sexual (teleomorph) stage of the fungus (Lombard et al., 2010).  The current scientific name of the pathogen is Calonectria pseudonaviculata (CABI, 2016; Crous et al., 2002; Ivors & LeBude, 2011).

Disease cycle:  The pathogen infects host plants rapidly in warm (18-25°C) and humid conditions and has a life cycle that is completed in one week (Henricot, 2006; Henricot et al., 2008).  The primary inoculum of spores are sticky and therefore, are best transmitted to healthy host plants by water-splash or carried by insects, birds or infested plants.  Spores germinate three hours after inoculation and penetrate leaves in as little as five hours (Henricot, 2006).  Hyphae penetrate through stomata on lower surface of leaves, or directly through the cuticle on upper surface of leaves without appressorium formation (specialized attachment and penetration structure).  The fungus continues to grow intercellularly in the mesophyll layers of the plant (Henricot, 2006).  Two to three days after infection, the fungus produces conidiophores and conidia (asexual spores) through stomata and after seven days, these cover the lower surface of the leaf.  Leaves are eventually killed (Henricot, 2006).   The fungus can form resting structures (microsclerotia) which can survive on leaf material and in the soil in the absence of a susceptible host (Henricot, 2006).  However, in a 5-year study on the survival of the fungus on decomposing plant material, Henricot et al., (2008) did not detect the presence of microsclerotia.  Apparently, the pathogen is able to survive as mycelium within decomposing plant tissue.   No sexual stage structures have been observed in nature or in culture (CABI, 2016).

C. pseudonaviculata is a low temperature fungus that can grow below 10°C but is inhibited at 30°C and killed at 33°C (Henricot, 2006).

Dispersal and spread: The pathogen is spread by wind-driven rain and splashing water over short distances.  Long distance spread occurs by movement of infected plants/nursery stock, infested plant debris, soil, contaminated tools and equipment, insects or birds.  The pathogen can survive in leaf debris on or beneath the soil surface for up to 5 years (Dart et al., 2012; Henricot, 2006; Henricot et al., 2008).  The disease may also be spread is through the movement of asymptomatic (or with very limited outward symptoms) boxwood plants or plants treated with fungicides that suppress but do not kill or eliminate the inhabiting pathogen (Douglas, 2011).

Hosts: Buxaceae: Buxus microphylla (little-leaf box), B. microphylla var. japonica, B. sempervirens (syn. B. colchica; common boxwood), B. sinica (Chinese box), B. sinica var. insularis (Korean boxwood), Buxus sp. (box), Pachysandra procumbens, P. terminalis (Japanese spurge), Sarcococca sp. (sweet box) (CABI, 2016; EPPO, 2016; Farr & Rossman, 2016).

The full host range of this pathogen is not currently known however, none of the Buxus species are immune to boxwood blight and susceptibility to the pathogen may vary among cultivars (Henricot et al., 2008).  Sarcococca sp. (sweet box) and Pachysandra terminalis (Japanese spurge) are experimental hosts (Henricot et al., 2008; LaMondia et al., 2012).

Symptoms:  Infections by Calonectria pseudonaviculata result in the production of dark brown or lighter brown leaf spots surrounded by a dark border.  Stems are also infected exhibiting characteristic black streaks.  Eventually severe defoliation and dieback occur.  The fungus does not infect the roots.  Entire foliage typically becomes blighted causing the leaves to turn ‘straw’ to light brown in color and defoliate.  Stems of blighted plants may remain green under the outer bark until infected by secondary or opportunistic pathogens and diseases resulting in decline and eventual death of entire plants.  Young seedlings can be killed by this pathogen (Henricot, 2006; Henricot et al., 2008; USDA-NCSU).

Damage Potential:   The disease has been described as ‘devastating’ to boxwood plants (Henricot et al., 2008). Foliage of infected plant is eventually killed and blighted plants are predisposed to infections by secondary pathogens also resulting in their eventual death.  At particular risk are boxwood plants grown in nurseries, commercial landscapes, parks and gardens, and at private residences under warm and wet climates conducive for the development and spread of the pathogen.  Rapid and widespread infection including over 10,000 American boxwood plants and 150,000 plants in production nurseries in North Carolina and Connecticut were reported (Ivors et al., 2012).  Buxus spp. (boxwood) are not native to the United States, and are widely cultivated as ornamental plants.  In California, depending on plant species and cultivar, boxwood is commonly grown throughout the State except in cold, mountainous regions, and are likely to prefer cooler climates in the State (Sunset Western Garden Book, 1992).  Three main species are grown as ornamentals in the USA, B. sempervirens, B. microphylla, and B. sinica var. insularis, all which are known hosts of C. pseudonaviculata (USDA-NCSU).

Worldwide Distribution: Asia: Iran, Republic of Georgia, Turkey; North America: Canada (restricted distribution in British Columbia, few occurrences in Ontario and Quebec), USA; Europe: Austria, Belgium, Croatia, Czech Republic, Denmark, France, Germany, Ireland, Italy, Netherlands, Norway, Slovenia, Spain, Sweden, Switzerland, United Kingdom; Oceania: New Zealand (CABI, 2016; EPPO, 2016; Farr & Rossman, 2016).

In the USA, C. pseudonaviculata has been reported from Alabama, Connecticut, Delaware, Kentucky, Maryland, Massachusetts, New Jersey, New York, North Carolina, Ohio, Oregon, Pennsylvania, Rhode Island, Virginia (CABI, 2016; EPPO, 2016; Farr & Rossman, 2016), and by this report from California.

Official Control:  Cylindrocladium buxicola (synonym C. pseudonaviculata) is on the ‘Harmful Organism Lists’ for the Republic of Korea (USDA PCIT, 2016).  Presently, it has a temporary Q rating in California.

California Distribution:   San Mateo County.

California Interceptions:  None reported.

The risk Calonectria pseudonaviculata would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: The boxwood blight pathogen, Calonectria pseudonaviculata rapidly infests host plants under humid and warm (18-25°C) climates – being inhibited at 30°C and killed at 33°C. Spores are transmitted to healthy host tissue under wet conditions, requiring wind-driven rains and water splash from overhead irrigation systems. Depending on species and cultivar selection, Buxus are grown throughout California, except in mountainous regions, and are likely to do best in cool climates, such as coastal regions of the State.  Plants grown in warm and humid climates are at possible risk of infection by the pathogen.  The pathogen may be able to establish in a larger but limited region in the State, suitable also to the growth of its host plants.  Therefore a ‘medium’ rating is given to this category.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: The host range of Calonectria pseudonaviculata is currently limited to few Buxus species (boxwood) and several cultivars, as well as Sarcococca (sweet box) and Pachysandra spp. (Japanese spurge).

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Calonectria pseudonaviculata has high reproductive potential.  Although its dispersal and spread over short distances to non-infected plants depends on wind-driven rain and water-splash, long distance spread occurs by movement of infected plants/nursery stock, infested plant debris, soil, contaminated tools and equipment, insects or birds. The disease may also be spread through the movement of asymptomatic (or with very limited outward symptoms) boxwood plants or plants treated with fungicides that suppress but do not kill or eliminate the inhabiting pathogen.  These modes of spread, plus the ability of the pathogen to survive in leaf debris on or beneath the soil surface for up to 5 years, places it as a ‘high risk’ in this category.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: Boxwood blight disease could result in lower crop value, loss of foliage and plants, increased production costs, loss of markets, and changes in delivery of irrigation water so to avoid water splash and wetness of foliage.  Also, insects and birds could aid in spread of the pathogen to non-infected plants.  Therefore, economic impact, caused by the boxwood blight pathogen, is given a ‘High’ score.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, C, D, E.

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: Infections of Calonectria pseudonaviculata could significantly affect private and commercial plantings of boxwood plants commonly used as hedge and shrub ornamentals and result in additional treatments against the pathogen.  Therefore, risk on environmental impact is scored as ‘High’.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: D, E.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact.

Environmental Impact Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Calonectria pseudonaviculata: Medium (11)

Add up the total score and include it here.

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

6) Post Entry Distribution and Survey Information: Presently, the boxwood blight pathogen has only been officially reported from one region, namely, San Mateo County. California.

Score: (-1)

-Not established (0) Pest never detected in California, or known only from incursions.

–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = Medium (10)

Uncertainty:  

None.                              

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Calonectria pseudonaviculata is B.

References:

CABI, 2016.  Calonectria pseudonaviculata (buxus blight) full datasheet. http://www.cabi.org/cpc/datasheet/17414.

Crous, P.W., J. Z. Groenewald, and C. F. Hill.  2002.  Cylindrocladium pseudonaviculatum sp. nov. from New Zealand, and new Cylindrocladium records from Vietnam. Sydowia 54: 23-34.

Dart, N., M. A. Hansen, E. Bush, and C. Hong.  2012.  Boxwood blight: a new disease of boxwood found in the eastern U.S.  Virginia Cooperative Extension, Virginia State University Publications and Educational Resources PPWS-4.  http://pubs.ext.vt.edu/PPWS/PPWS-4/PPWS-4.html

Douglas, S. M.  2011.  Boxwood blight – a new disease for Connecticut and the U. S.  The Connecticut Agricultural Experiment Station.  www.ct.gov/caes .

Farr, D.F., and A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved December 1, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Henricot, B., C. Gorton, G. Denton, and J. Denton. 2008. Studies on the control of Cylindrocladium buxicola using fungicides and host resistance. Plant Disease, 92(9):1273-1279.  http://www.apsnet.org

Ivors, K. and A. LeBude.  2011.  A new pest to the U. S. ornamental industry: the “box blight” pathogen Cylindrocladium pseudonaviculatum = Cylindrocladium buxicola.  NC Pest Alert. http://plant-clinic.bpp.oregonstate.edu/files/plant_clinic/webfm/NC_pest_alert_box_blight1-1.pdf

Ivors, K. L., L. W. Lacey, D. C. Milks, S. M. Douglas, M. K. Inman, R. E. Marra, and J. A. LaMondia.  2012.  First report of boxwood blight caused by Cylindrocladium pseudonaviculatum in the United States.  Plant Disease.  96: 1070. http://dx.doi.org/10.1094/PDIS-03-12-0247-PDN.

Kosta, K.  2016.  Personal communication to J. Chitambar, CDFA Primary Plant Pathologist/Nematologist via email on November 30, 2016, 5:03:15 pm.

LaMondia, J. A., D. W. Li, R. E. Marra, and S. M. Douglas.  2012.  First report of Cylindrocladium pseudonaviculatum causing leaf spot of Pachysandra terminalis.  Plant Disease 96: 1069. http://dx.doi.org/10.1094/PDIS-03-12-0235-PDN.

Lombard, L., P. W. Crous, B. D. Wingfield, and M. J. Wingfield.  2010.  Phylogeny and systematics of the genus Calonectria.  Studies in Mycology. 66: 31-69.  www.studiesinmycology.org , doi:10.3114/sim.2010.66.03

USDA-NCSU.  (Date not known).  The ‘box blight’ pathogen: Cylindrocladium pseudonaviculatum = Cylindrocladium buxicola (Teleo.  Calonectria pseudonaviculata).  Datasheet developed by USDA-APHI-PPQ-CPHST and NCSU Department of Plant Pathology, Mountain Horticultural Crops Research and Extension Center (MHCREC) staff. caps.ceris.purdue.edu/dmm/1603

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

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Pest Rating: B

Posted by ls

Bacteria, Plant Pathogens

Candidatus Liberibacter solanacearum Liefting, Perez-Egusquiza & Clover, 2009

California Pest Rating for
Candidatus Liberibacter solanacearum Liefting, Perez-Egusquiza & Clover, 2009 
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

None.  The risk of entry and establishment of Ca. Liberibacter solanacearum in California is assessed and a permanent rating is proposed.

History & Status:

Background:  Candidatus Liberibacter solanacearum was first identified in 2008 simultaneously in the United States and New Zealand. In New Zealand, Liefting et al., (2008, 2009), detected the bacterial pathogen first in tomato and pepper and then in potato and other solanaceous plants.  The pathogen was tentatively named Candidatus Liberibacter solanacearum.  In the United States, the pathogen was detected in tomato plants and the potato/tomato psyllid Bactericera cockerelli and tentatively named Candidatus Liberibacter psyllaurous because of its association with psyllid yellows (Hansen et al., 2008; CABI, 2016).  Ca. L. psyllaurous is now considered a synonym of Ca. L. solanacearum.  The pathogen is the cause of ‘Zebra chip disease’ in potatoes, named because of the presence of dark stripes and blotches that develop from the rapid oxidative darkening of freshly cut tubers and become more distinct after frying infected potato chips (Crosslin, 2009).  Zebra chip disease of potatoes was first observed in the 1990s in Mexico and parts of Central America.  Foliar symptoms resembled those caused by phytoplasmas.  The disease is now widespread in south-western, central, and north-western USA, Mexico, Central America, New Zealand and restricted regions within Europe (see “Worldwide Distribution’ below).

In the United States, zebra chip disease of potatoes was first identified in 2000 in commercial potato fields in Texas and by 2004-2005, was reported to cause serious economic damage in parts of Southern Texas.  By 2007, zebra chip disease was observed in Nebraska, Colorado, Kansas, New Mexico, Arizona, Nevada, and California causing losses in the millions of dollars to potato producers and processors in affected regions.  Infested fields were often abandoned (Munyaneza et al., 2007b).

In California, while potato crops exhibiting symptoms of zebra chip disease were observed previously (Munyaneza et al., 2007b), the bacterium Ca. L. psyllaurous was first identified in 2009 from diseased potatoes grown in commercial fields in Lancaster, Los Angeles County (Crosslin, 2009; Crosslin et al., 2010).   Since then, the presence of Ca. L. solanacearum was also detected, in plant tissue and psyllid vector with real time PCR, in Riverside, Santa Barbara, Orange, and San Diego Counties (Trumble, 2015).  Substantial crop losses have occurred in southern California that resulted in abandonment of commercial fields, decline in potato and tomato productions, and significant increases in disease control costs (Trumble, 2015).  The pathogen is considered to be of rare occurrence and less of a problem in northern California (Nunez, 2015; Davis, 2015).   The psyllid can be found throughout southern California, in Kern County, on the coast up to Sacramento, and within the Sacramento Valley.  In the Sacramento area, dense psyllid populations have been reported on bell peppers.  For reasons not known, the peppers do not show symptoms of Ca. L. solanacearum (unlike peppers infested with psyllids in Utah, Arizona, New Mexico and New Zealand), and therefore, the presence of the bacterial pathogen in the populations cannot be definitely stated (Trumble, 2015).  Also, the psyllid vector is kept in control by growers, through routine insecticide applications primarily against aphid-vectored viruses (Nunez, 2015).

Biology: Candidatus Liberibacter solanacearum is a phloem-limited, insect hemolymph-limited, gram-negative, unculturable bacterium that is primarily spread from infected to healthy plants by psyllid insect vectors.  Presently, there are five known geographic haplotypes (a specific group of genes that are inherited together from a single parent) designated A, B, C, D, and E.  Haplotypes A and B are associated with Bactericera cockerelli and the diseases caused by this bacterium in potatoes and other solanaceous plants.  Haplotypes C and D are associated with diseased carrots, and Trioza apicalis and Bactericera trigonica respectively, and haplotype E is associated with diseased celery and carrot.  The five haplotypes are not yet known to elicit biological differences in plant or insect hosts.  Haplotype A has been found primarily from Central to North America (from Honduras and Guatemala through western Mexico to Arizona, California, the Pacific Northwest) and in New Zealand.  Haplotype B has been found in Mexico and North America (from eastern Mexico and northwards through central USA through Texas).  Some overlap of haplotypes A and B occurs in Texas, Kansas, and Nebraska.  Haplotype C occurs in Finland, Sweden, and Norway and is associated with T. apicalis. Haplotype ‘D’ was found in mainland Spain and the Canary Islands.  Haplotype E is present in mainland Spain, France, and Morocco (EPPO, 2013; Tahzima et al., 2014; Teresani et al., 2014, 2015).  Teresani et al., (2015) recently reported two additional new psyllid species, Bactericera tremblayi and B. nigricornis, as potential vectors of Ca. L. solanacearum that were detected with B. trigonica during surveys conducted from 2011 to 2014 in carrot, celery and potato plots in mainland Spain and the Canary Islands.

While there is not much known on the effects of environment on Ca. L. solanacearum, temperature is known to have a significant effect on the development of this bacterial pathogen.  Compared to the citrus greening Huanglongbing Liberibacter species, Ca. L. solanacearum appears to be heat sensitive and does not tolerate temperatures above 32°C

Dispersal and spread:  Ca. L. solanacearum is transmitted by its psyllid insect vector, Bactericera cockerelli, in a persistent (transovarially or vertically) way and during feeding on infected plant hosts (horizontally).  However, vertical transmission of the pathogen in the other psyllid species, Bactericera trigonica and Trioza apicalis, is currently not known.  The pathogen is also spread by grafting and infected plants, but not true seed (EPPO, 2013).  However, Bertolini et al., (2014) reported the detection of Ca. L. solanacearum in carrot seeds using real-time PCR thereby, indicating that seed transmission is involved in the natural spread of the bacterium via carrot seed in distant regions and countries in Europe.  Usually infected seed potatoes do not germinate but may occasionally produce infected plants which are often weak and short-lived and therefore, not a significant mode for spreading the disease (EPPO, 2013).

Hosts: Hosts are included in the plant families Apiaceae and Solanaceae.  Main hosts include, Capsicum annuum (bell pepper), Solanum lycopersicum (tomato), S. tuberosum (potato), and Datura stramonium (jimsonweed).  Other wild and incidental hosts include Solanum melongena (eggplant), S. pseudocapsicum (Jerusalem-cherry), S. dulcamara (climbing nightshade), Cyphomandra betacea (syn. Solanum betacea; tree tomato/tamarillo), Apium graveolens (celery), Daucus carota (carrot), Physalis peruviana (Cape gooseberry/tomatillo), and Nicotiana tabacum (tobacco) (CABI, 2016, EPPO, 2016).

Symptoms:  Characteristic above-ground symptoms in potato and other solanaceous host plants include stunting, erectness of new foliage, chlorosis and purpling of foliage with basal cupping of leaves through entire plant, resetting due to shortened and thickened terminal internodes, enlarged nodes, axillary branches or aerial tubers, leaf scorching, disruption of fruit set, and production of numerous small, misshaped and poor quality fruits. Below-ground symptoms in potato include collapsed stolons, browning of vascular tissue concomitant with necrotic flecking of internal tissues and streaking of the medullary ray tissues, all of which can affect the entire tuber.  These symptoms become more distinct upon frying and potato chips processed from affected tubers show very dark blotches, stripes or streaks thereby making them unacceptable for marketing.  It is due to the symptoms produced in potato tubers that the disease was named ‘zebra chip’ (EPPO, 2013).

Damage Potential: In potato, plant growth is affected.  Potato chips produced from zebra ship-infected tubers have dark stipes that are more distinct upon frying and therefore, not commercially acceptable. Infected tubers often do not sprout or produce hairy sprouts and weak plants.  Damage is also caused to other economically important solanaceous plants including tomato, pepper, eggplant, tamarillo, and tobacco.  Fields with infected crops may be rejected resulting in their abandonment (EPPO, 2013).  Ca. Liberibacter solanacearum can cause significant damage to crop quality and yield.  In the Americas and New Zealand, losses in millions of dollars have been caused by the pathogen and psyllid complex and to the carrot industry in Europe (Crosslin et al., 2010; Munyaneza 2007a, 2007b).  In Texas and New Zealand, annual potato yield losses at approximately US $22 million and US $40 million respectively were due to Ca L. solanacearum (Soliman, 2012 in CABI, 2016).  In Europe, up to 100% crop losses in carrot production due to Ca. L solanacearum – infected carrot psyllid were reported (CABI, 2016).

Worldwide Distribution: Africa: Morocco; North America: Mexico, USA; Europe (restricted distributions within): Finland, Germany (few occurrences), Norway, Spain, Spain – Canary Islands, Sweden; Central America:  Guatemala, Honduras, Nicaragua; Oceania: New Zealand (CABI, 2016; EPPO, 2013, 2016).

In Europe, Ca. L. solanacearum has not been detected in potato and tomato crops but has been detected mainly in carrot crops and to a lesser extent in celery in association with other psyllid species, Bactericera trigonica and Trioza apicalis (EPPO, 2013). Ca. L. solanacearum is considered “transient, under eradication” in Austria and France.

In the USA, the pathogen is present in Arizona, California, Colorado, Idaho, Kansas, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oregon, Texas, Utah, Washington, and Wyoming (CABI, 2016; EPPO, 2016).

Official Control: Candidatus Liberibacter solanacearum is on the Harmful Organisms Lists for Argentina, Australia, Brazil, Chile, Costa Rica, Guatemala, Honduras, Republic of Korea, Panama, and Taiwan (USDA PCIT, 2016).

California Distribution: Los Angeles, Riverside, Orange, San Diego, and Santa Barbara Counties.  The pathogen is considered to be of rare occurrence in northern California.

California Interceptions:  There are no reports of the detection of Ca. Liberibacter solanacearum in plant shipments imported to California.

The risk Ca. Liberibacter solanacearum would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 3

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is High (3): Ca. L. solanacearum appears to be heat sensitive and does not tolerate temperatures above 32°C.  Presently, its distribution has been confirmed in some counties in southern California, while its occurrence in northern California is rare.  While the potato/tomato psyllid vector can be found on Ca L. solanacearum host plants throughout southern California, in Kern County, on the coast up to Sacramento, and within the Sacramento Valley, the presence of the bacterial pathogen has only rarely been found in the northern regions.  Furthermore psyllid populations are kept in check by growers through insecticides routinely applied primarily to control aphid-vectored viruses. In the absence of vector control measures, the bacterial pathogen is expected to establish a widespread distribution on prime hosts including, tomatoes, potatoes, peppers and eggplant.

2) Known Pest Host Range:  Evaluate the host range of the pest.

Score: 2

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Medium (2):  The pathogen has a medium host range that includes major host plants such as tomatoes, potatoes, and peppers, cultivated under significant acreage in California.

3) Pest Dispersal Potential:  Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3):  Ca. L. solanacearum is primarily transmitted by its psyllid insect vector, Bactericera cockerelli.  The bacterium has high reproduction and is dependent primarily on its vector for short and long-distance spread. The bacterium is also spread by grafting and infected plants.  [Usually infected seed potatoes do not germinate but may occasionally produce infected plants which are often weak and short-lived and therefore, not a significant mode for spreading the disease.]

4) Economic Impact:  Evaluate the economic impact of the pest to California using the criteria below.

Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is High (3): Ca. L. solanacearum causes zebra chip disease of potatoes and has resulted in significant crop damage and economic loss in production and marketability. Significant losses have also been caused in other economic host crops.  The pathogen is vectored by the potato/tomato psyllid vector in California. 

5) Environmental Impact:  Evaluate the environmental impact of the pest on California using the criteria below.

The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

The pest could directly affect threatened or endangered species.

The pest could impact threatened or endangered species by disrupting critical habitats.

The pest could trigger additional official or private treatment programs.

The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact.

Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2): Infestations of the bacterial pathogen could significantly impact home/urban gardening.

Consequences of Introduction to California for Candidatus Liberibacter solanacearum:

Add up the total score and include it here. (Score)

-Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 13.

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Score:  -1

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Low (-1): Presently, Ca. L. solanacearum is distributed within few counties of southern California, namely, Los Angeles, Riverside, Orange, San Diego, and Santa Barbara Counties and is considered to be only of rare occurrence in northern California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 12.

Uncertainty:  

Not much is known on the effects of environment on Ca. L. solanacearum.   Also, its presence in vector populations in northern California cannot be definitively stated.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the zebra chip pathogen, Ca. Liberibacter solanacearum is B.

References:

Bertolini, E., G. R. Teresani, M. Loiseau, F. A. O. Tanaka, S. Barbé, C. Martínez, P. Gentit, M. M. López, and M. Cambra.  2014.  Transmission of ‘Candidatus Liberibacter solanacearum’ in carrot seeds.  Plant Pathology: http://dx.doi.org/10.1111/ppa.12245 .

Crosslin, J. M.  2009. First report of ‘Candidatus Liberibacter psyllaurous’ in zebra chip symptomatic potatoes from California.  Plant Disease 93: 551. http://dx.doi.org/10.1094/PDIS-93-5-0551B .

Crosslin, J. M., J. E. Munyaneza, J. K. Brown, and L. W. Liefting.  2010.  Potato zebra chip disease: A phytopathological tale. Online. Plant Health Progress doi: 10.1094/PHP-2010-0317-01-RV.

Davis, M.  2015.  Email from M. Davis, Professor Emeritus, Plant Pathology Department, UC Davis, to J. Chitambar, Primary Plant Pathologist/Nematologist, CDFA, sent Wednesday, November 11, 2015, 7:13:45 pm.

Farr, D.F., & A. Y. Rossman.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved January 28, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

EPPO.  2013.  Candidatus Liberibacter solanacearum.  EPPO Data Sheets on pests recommended for regulation, European and Mediterranean Plant Protection Organization.  Bulletin OEPP/EPPO Bulletin 43: 197-201.  DOI: 10.1111/epp.12043.

EPPO.  2016.  Liberibacter solanacearum (LIBEPS).  New PQR database.  Paris, France:  European and Mediterranean Plant Protection Organization.  http://newpqr.eppo.int

Hansen, A. K., J. T. Trumble, R. Stouthamer, and T. D. Paine.  2008.  A new huanglongbing species, “Candidatus Liberibacter psyllaurous,” found to infect tomato and potato, is vectored by the psyllid Bactericera cockerelli (Sulc). Applied and Environmental Microbiology, 74(18):5862-5865. http://aem.asm.org .

Liefting, L. W., Z. C. Perez-Egusquiza, G. R. G. Clover, and J. A. D. Anderson.  2008.  A new ‘Candidatus Liberibacter’ species in Solanum tuberosum in New Zealand. Plant Disease, 92(10):1474.

Liefting, L. W., B. S. Weir, S. R. Pennycook, and G. R. G. Clover.  2009.  ‘Candidatus Liberibacter solanacearum’, associated with plants in the family Solanaceae. International Journal of Systematic and Evolutionary Microbiology, 59(9):2274-2276.

Munyaneza, J. E.  2012.  Zebra chip disease of potato: biology, epidemiology and management.  American Journal of Potato Research 89: 329-350.  http://dx.doi.org/10.1007/s12230-012-9262-3.

Munyaneza, J. E., J. M. Crosslin, and J. E. Upton.  2007a. Association of Bactericera cockerelli (Homoptera: Psyllidae) with “zebra chip”, a new potato disease in southwestern United States and Mexico.  Journal of Economic Entomology 100, 656–663.

Munyaneza, J.E., J. A. Goolsby, J. M. Crosslin, and J. E. Upton.  2007b.  Further evidence that zebra chip potato disease in the lower Rio Grande Valley of Texas is associated with Bactericera cockerelli.  Subtropical Plant Science 59, 30–37.

Nunez, J.  2015.  Email from J. Nunez, Vegetable/Plant Pathology Farm Advisor, UC Cooperative Extension, to J. Chitambar, Primary Plant Pathologist/Nematologist, CDFA, sent Wednesday, November 11, 2015, 4:35 pm.

Tahzima, R., M. Maes, E. H. Achbani, K. D. Swisher, J. E. Munyaneza, and K. De Jonghe.  2014.  First Report of “Candidatus Liberibacter solanacearum’ on carrot in Africa.  Plant Disease 98: 1426.  http://dx.doi.org/10.1094/PDIS-05-14-0509-PDN .

Teresani, G. R., E. Bertolini, A. Alfaro-Fernández, C. Martinez, F. A. O. Tanaka, E. W. Kitajima, M. Roselló, S. Sanjuán, J. C. Ferrándiz, M. M. López, M. Cambra, and M. I. Font.  2014.  Association of ‘Candidatus Liberibacter solanacearum’ with a vegetative disorder of celery in Spain and development of a real-time PCR method for its detection.  Phytopathology 104: 804-811.

Teresani, G., R. Hernández, E. Bertolini, F. Siverio, C. Marroquin, J. Molina, A. Hermoso de Mendoza, and M. Cambra.  2015.  Search for potential vectors of ‘Candidatus Liberibacter solanacearum’: population dynamics in host crops.  Spanish Journal of Agricultural Research, 13 (1): e10-002. http://dx.doi.org/10.5424/sjar/2015131-6551 .

Trumble, J. T.  2015.  Email from J. T. Trumble, Distinguished Professor of Entomology, University of California, Riverside, to J. Chitambar, Primary Plant Pathologist/Nematologist, CDFA, sent Thursday, November 12, 2015, 5:28:41 pm.

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment:
Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

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♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

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♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Coleophoma empetri (Rostr,) Petr. 1929

California Pest Rating for
Coleophoma empetri (Rostr,) Petr. 1929
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

On April 27, 2016 a mail shipment containing cut foliage of Galax sp. was intercepted by the Santa Barbara County Dog Team, at the FedEx Service Center in Goleta, Santa Barbara County.  The shipment had originated in Florida and was destined to a nursery in Carpinteria, Santa Barbara County.  Samples of diseased leaves exhibiting leaf spots were collected by the County and sent to the CDFA Plant Pathology Laboratory for disease diagnosis.  On April 29, 2016 Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen, Coleophoma empetri, as the cause for the disease.   The pathogen has not been previously reported in California and therefore, was assigned a temporary Q rating.  Subsequent action taken by the County resulted in the destruction of the intercepted shipment of Galax sp. foliage (CDFA, 2016). The risk of infestation of Coleophoma empetri in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background: Originally described as Septoria empetri, the fungal pathogen Coleophoma empetri is also known by other synonyms, Rhabdostromina empetri, Sporonema oxycocci, and Coleophoma rhododendri, and Coleophoma ericae.  The pathogen is widely distributed and found on living and dead leaves and fruit of many different plant species (Farr & Rossman, 2016; Sutton, 1980).

Disease cycle:   There is a paucity of specific information on Coleophoma empetri.  However, it is likely that the development of disease caused by the pathogen would be similar to other pycnidia-forming fungal pathogens.   The pathogen overwinters as mycelium or immature pycnidia in infected fruit and diseased plant debris. Under high moisture and cool temperature conditions, pycnidia swell and release conidia which are spread by splashing rain, irrigation, water, and so on.  Seed transmission is not known for C. empetri.  Infection of host plants and severity of disease development is likely to require high moisture and cool temperatures.  In the development of fruit rot of berries, conidia initiate infection during bloom and early berry development.  As infected fruit mature, hyphae continue to invade the fruit and rot symptoms do not develop until the late growing season and mostly in storage (Kusek, 1995).

Dispersal and spread: Splashing rain and irrigation water, air currents, infected plants, infected plant debris, cultivation tools, animals, and contaminated clothing.

Hosts:  Archontophoenix alexandrae (Alexander palm), Arctostaphylos sp. (Manzanita), A. uva-ursi, Arctous alpine (bearberries), Betula sp. (birch), Camellia sp., Cajanus cajan (pigeon pea), Canavalia ensiformis (Jack bean), Capsicum annuum (bell peppers), Croton sp., Diapensia sp., D. obovata (pincushion plant), Elaeagnus sp. (oleaster), E. macrophylla, Empetrum sp., E. nigrum (black browberry), Erica carnea (winter heath), Eucalyptus sp. E. tereticornis (forest red gum), Ficus sp., Fraxinus sp. (ash), Galax aphylla (beetleweed/coltsfoot), Gaultheria shallon (shallon), Gaylussacia brachycera (box huckleberry), Juniperus sp. (juniper), Kalmia angustifolia (sheep laurel), Laurus sp., L. nobilis (sweet bay), Leucothoe sp., Loiseleuria sp., L. procumbens, Lonicera sp. (honeysuckle), L. periclymenum, Malus sylvestris (European crab apple), Paxistima canbyi (Canby’s mountain-lover), Plea europaea, Prunus laruocerasus (cherry laurel), P. ponticum, Rhododendron sp., R. maximum, Solanum tuberosum (potato), Stransvaesia sp., Taxus baccata (English yew), Vaccinium sp. (blueberry), V. macrocarpon (American cranberry), V. ovatum (California huckleberry), V. oxycoccos (bog cranberry), V. vitis-idaea (lingonberry) (Farr & Rossman, 2016; Kusek, 1995; Sutton, 1980).

Symptoms:  Coleophoma empetri causes leaf spot, fruit rot and tuber skin spot disease on numerous hosts in numerous families.  Symptoms of ripe rot on cranberry fruit initially appear as a small soft area which expands over the entire fruit.  Diseased fruit appear off-red or reddish orange, and internally watery, squirting a watery fluid when squeezed.  However, as not all watery-soft fruit is caused by the pathogen, the latter must be isolated from the diseased fruit to confirm an association with the symptoms (Kusek, 1995).

Disease Potential:  Specific information on quantitative crop losses caused by Coleophoma empetri has not been reported. Photosynthetic area can be reduced due to leaf spotting.  In severe infections, leaf wilt and drop may be expected. Symptomatic host plants infected with the pathogen may be more of a serious problem for nursery greenhouse productions where favorable wet requirements for disease development and spread are more likely to occur under controlled environments than in open field environments in California.  The disease could negatively impact value and marketability of nursery-grown plants including ornamental and landscape plants such as Manzanita, Camellia, Rhododendron, and Eucalyptus. The pathogen causes fruit rot that is apparent during late growing season and mainly in storage.

Worldwide Distribution: Coleophoma empetri is globally widely distributed.  Asia: India, USSR; Europe: Finland, Lithuania, Poland, USSR, United Kingdom, Ukraine, Scotland, Germany; North America: Alaska, Maryland, Massachusetts, Maine, Michigan, New Jersey, Oregon, Tennessee, Virginia, Washington, Wisconsin, and Northwestern states (Farr & Rossman, 2016).

Official Control:  Currently, has a temporary Q rating in California.

California Distribution:  is not established in California.

California Interceptions: A single shipment of Coleophoma empetri-infected Galax sp. foliage was intercepted on April 27, 2016 at the FedEx Service Center in Goleta, Santa Barbara County (see ‘Initiating Event’).

The risk Coleophoma empetri would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California:

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2): Coleophoma empetri may be able to establish on suitable host plants growing in high moisture and cool to warm climate conditions.  These conditions would likely limit natural establishment to northern coastal regions of California.

2) Known Pest Host Range: Evaluate the host range of the pest:

Score: 2

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Medium (2):  Coleophoma empetri has a moderate host range that includes many host species in different plant families.  Most hosts grow under cool and wet climates.  In California, main hosts include ornamental, landscape, and fruit berry plants such as, Manzanita, Camellia, Rhododendron, Eucalyptus, blueberry, and cranberry.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest:

Score: 2

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (2): Coleophoma empetri has high reproduction and dispersal potential.  The pathogen can be spread over short and long distance by splashing rain and irrigation water, air currents, infected plants, infected plant debris, cultivation tools, animals, and contaminated clothing.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Score: 2

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Medium (2):  The pathogen may be more of a serious problem for nursery greenhouse productions where favorable wet requirements for disease development and spread are more likely to occur under controlled environments than in open field environments in California.  The disease could negatively impact value and marketability of nursery-grown plants including ornamental and landscape plants.  Also, the pathogen may cause fruit rot that is apparent during late growing season and mainly in storage.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below:

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact:

Score: 3

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

 Risk is High (3): Severe infections caused of Coleophoma empetri could impact ornamental plantings.  Under suitable conditions that result in severe disease, threatened or endangered plant species, namely, manzanita (Arctostaphylos spp.) could be affected and disrupt critical habitats.  

Consequences of Introduction to California for Coleophoma empetri:

Add up the total score and include it here:

-Low = 5-8 points

–Medium = 9-12 points

        -High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 11 (Medium).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included:

Score: 0

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Not Established (0).  Coleophoma empetri is not established in California.   

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 11 (Medium).

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Coleophoma empetri is B.

References:

Agrios, G. N.  2005.  Plant Pathology (Fifth Edition).  Elsevier Academic Press, USA.  922 p.

CDFA.  2016.  Santa Barbara County Dog Team Interception.  CDFA AQW Pest Report No. 18-2016, weekly AQW report: for the week of April 28 to May 04, 2016.

Duan, J. X., W. P. Wu, and X. Z. Liu.  2007.  Reinstatement of Coleonaema for Coleophoma oleae and notes on Coleophoma.  Fungal Diversity 26: 187-204.

Farr, D. F. and A. Y. Rossman.  2016.   Fungal databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved August 24, 2016 from http://nt.ars-grin.gov/fungaldatabases/.

Kusek, C. C.  1995.  Cranberry Ripe Rot.  In Compendium of Blueberry and Cranberry Diseases Edited by F. L. Caruso and D. C. Ramsdell.  APS Press, The American Phytopathological Society, page 43.

Sutton, B. C. 1980. The Coelomycetes. Fungi Imperfecti with pycnidia, acervuli and stromata. Commonwealth Mycological Institute, Kew, Surrey, England, 696 pages

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment:
Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

Violates agency regulations prohibiting sexual harassment or other forms of discrimination;

Violates agency regulations prohibiting workplace violence, including threats.

♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: B

Posted by ls

Phytoplasmas, Plant Pathogens

Candidatus Phytoplasma pruni

California Pest Rating for
Candidatus Phytoplasma pruni
(= Peach X-disease, Peach Rosette, Peach Red Suture, and Little Peach Phytoplasmas)
Pest Rating: C
PEST RATING PROFILE
Initiating Event: 

CDFA regulations require imported peach nursery stock to be certified free from Peach Rosette, Peach Yellows, Little Peach and Red Suture Diseases.  These diseases are caused by phytoplasmas which are named accordingly.  Presently, all four phytoplasmas are A-rated pathogens in California.  However, research has shown that these phytoplasmas are actually strains of Candidatus Phytoplasma pruni.  Therefore, the status of the four phytoplasmas and their current rating in California are reviewed herein and a new permanent rating is proposed.

History & Status:

Background:  In 1933, a disease of peach was discovered in Connecticut and called the “X-disease of Peach” because of its unknown cause and mysterious nature.  For several years following its discovery, X-disease was believed to be caused by a virus that was mainly vectored by insects from nearby forests to peach orchards and seldom passed from tree to tree in the eastern USA.  Wild chokecherry (Prunus virginiana), growing in forests, was found to be an important natural host of the pathogen.  By the early 1950s, X-disease was also discovered in several US north eastern states and western states, including California, as well as in Canada (Stoddard, et al., 1951).   Subsequently, based on slightly different symptoms, two forms of peach X-disease were initially distinguished in the USA, namely, eastern X-disease and western X-disease, however, based on serological, nucleic acid and graft-transmission studies the eastern and western forms were found to be similar and recognized as strains of the pathogen. The pathogen was soon discovered to be widely distributed in fruit trees in the USA and can be transmitted by species of leafhopper.  X-disease is now known to be caused by a phytoplasma (formerly, mycoplasma-like organism or MLO).  In Eastern USA, peach rosette, peach yellows (also called little peach) and peach red suture were associated with the presence of peach X-disease phytoplasma.  Cherry albino disease, once found in the Rogue River Valley of Oregon in 1937 but now no longer found, was suspected to be caused by a strain of peach X-disease phytoplasma.  In California, Cherry buckskin disease on cherry had been known since the early 1920s and later the pathogen that caused this disease was also discovered to cause lethal decline disease of peach or “lethal casting yellows’.  Both diseases were later considered to be caused by strains of peach X-disease. Also in California, peach yellow leaf roll disease is caused by several genetically unrelated phytoplasmas of which only one is similar to, and a strain of peach X-disease phytoplasma (CABI, 2016; Davis et al., 2013; Kirkpatrick, 1995; Larson & Waterworth, 1995; 1995 Kirkpatrick et al., 1995).

Based on gene analysis, namely, restriction fragment length polymorphism (RFLP) analysis of 16S rRNA gene sequences, strains of peach X-disease phytoplasma from eastern and western USA and eastern Canada were classified in phytoplasma 16S rRNA gene RFLP group 16 SrIII, subgroup A.  Davis et al., (2013) found gene sequences of peach X-disease phytoplasma strains to be distinct from other previously described Candidatus Phytoplasma species and therefore, formally described Candidatus Phytoplasma pruni (Ca. Phytoplasma pruni) as a new species group or taxon of phytoplasma associated with X-disease of stone fruits to include geographically diverse X-disease phytoplasma strains that shared similar nucleotide sequence (16S rRNA gene sequences) alignments.  These strains include X-disease phytoplasma (cause of peach yellows disease), peach rosette, peach red suture, and little peach phytoplasmas.

Hosts: Peach (Prunus persica) is the principal host of the pathogen.  Other hosts include species of the genus Prunus, including, cherry (P. avium and P. cerasus), Japanese plum (P. salicina), almond (P. dulcis), apricot (P. armeniaca), nectarine (P. persica var. nectarine), Chinese bushcherry (P. japonica), Bessey cherry (P. besseyi), wild American plum (P. americana), wildgoose plum (P. munsoniana) and European plum (P. domestica). Common chokecherry (P. virginiana) is a wild host species that serves as an important natural reservoir of peach X-disease phytoplasma in many states of USA.  Bur clover (Medicago polymorpha) is also a wild host of the pathogen.  Also, switch sorrel (Dodonaea viscosa) and lucerne (Medicago sativa) (CABI, 2016; EPPO, 2014; Davis et al., 2013; Douglas, 1986; Stoddard et al., 1951).

Symptoms: Symptoms of X-disease on peach (Ca. Phytoplasma pruni) include: tattered, shot-holed leaves, chlorosis, loss of severely affected leaves leaving a cluster of leaves at the terminal tips of shoots (rosettes), dieback of branches and death of trees (Davis, et al., 2013; Douglas, 1986; Stoddard, et al., 1951).  Younger peach trees die within 1-3 years after the first appearance of symptoms.  The first symptoms of X-disease in peach on leaves of some or all branches appear as reddish purple spots which later die and fall out (shot-holes). The leaves turn reddish and curl upwards.  Older trees may survive longer but bear little or no fruit.  Fruit usually shrivel and drop, but those remaining on the trees ripen prematurely, have an off-taste and are not marketable. No seeds develop in infected fruit.  The phytoplasma can be irregularly distributed in the trees therefore fruit on healthy-appearing parts of a tree do not show signs of disease (Agrios, 2005; CABI, 2014).  Infected cherry trees on resistant Prunus mahaleb rootstock die rapidly due to hypersensitive reaction that occurs at the graft union. Other rootstocks die slower (Kirkpatrick et al., 1995).

Damage Potential:  Peach X-disease is one of the most important diseases of peach.  Infected trees become commercially useless in 2-4 years (Agrios, 2005). The degree of damage depends on the strain of the pathogen and development stage of the infected host.  Also, it can cause serious losses to cherry production.

Transmission: The pathogen is transmitted by several species of leafhopper, including Colladonas clitellarius, C. montanus, C. geminatus, Euscelidius variegates, Fieberiella florii, Graphocephala confluens, Gyponana lamina, Keonella confluens, Norvellina seminude, Osbornellus borealis, Paraphlepsius irroratus, and Scaphytopius delongi (S. acutus) (CABI, 2014; Davis, et al., 2013).  The leafhopper vectors overwinter on herbaceous weeds that act as reservoir of the pathogen in orchards, and infect trees in spring and summer. The latency period, or the time between when a vector acquires the pathogen while feeding on an infected host and when the vector is able to inoculate the pathogen into a non-infected, susceptible host, is 22-35 days for Colladonas geminatus and 45 days for Scaphytopius delongi (S. acutus) (CABI, 2016).

The pathogen is also transmitted over long distances through infected plant materials that were propagated by budding and grafting of infected plant material.  Infected plant parts at risk of spreading the phytoplasma include all plant parts with the exception of fruit (CABI, 2016).

Worldwide Distribution: Asia: India (EPPO, 2016); North America: Canada, USA (California, Colorado, Connecticut, Georgia, Hawaii, Massachusetts, Michigan, Minnesota, Missouri, Nebraska, New York, North Dakota, Oregon, Pennsylvania, South Carolina, South Dakota, Utah, Virginia, Washington, West Virginia) (CABI, 2016; EPPO, 2016; Thakur et al., 1998).

Official Control: Currently, the listed diseases and strains of Ca. Phytoplasma pruni are on the ‘Harmful Organism Lists’ for the respective countries.  Peach X-disease phytoplasma: Argentina, Brazil, Canada, Chile, China, Colombia, Guatemala, Japan, Jordan, Republic of Korea, Mexico, Morocco, Norway, Paraguay, Peru, and Turkey; Peach X-disease mycoplasma: European Union, Holy See (Vatican City State), Monaco, San Marino, and Serbia; Peach X phytoplasma: Israel and Japan; Peach rosette mycoplasma: European Union, Holy See (Vatican City State), Monaco, San Marino, and Serbia; Peach rosette phytoplasma: Argentina, Brazil, Guatemala, Israel, Japan, Mexico, Morocco, Paraguay, and Turkey; Peach yellow MLO: Mexico; Peach yellows mycoplasma: European Union, Holy See (Vatican City State), Madagascar, Monaco, San Marino, Serbia, and Ukraine; Peach yellows phytoplasma: Brazil, Chile, Colombia, Israel, Japan, Jordan, Republic of Korea, Mexico, Morocco, Paraguay, Peru, and Turkey (PCIT, 2016).

Ca. Phytoplasma pruni is an EPPO A1 quarantine pest.  It is a quarantine pest in Israel, and Norway (EPPO, 2016).

Currently, diseases and strains of Ca. Phytoplasma pruni, namely, X-disease phytoplasma causing cherry buckskin, cherry albino and peach western X diseases are already present in California and rated ‘C’, while peach red suture, peach rosette, little peach and X-disease (causing peach yellows disease) phytoplasmas are quarantine pathogens rated ‘A’.

California Distribution:  Western X-disease phytoplasma (now, Ca. Phytoplasma pruni) is generally distributed throughout California and has been detected on plum, cherry, apricot, peach, nectarine, almond and celery (California Plant Disease Host Index by French, A. 1989, Updated 2014).

California Interceptions: The risk Ca. Phytoplasma pruni would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California:

Score: 3

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is High (3) – Strains of Ca. Phytoplasma pruni are already established and widespread within California.

2) Known Pest Host Range: Evaluate the host range of the pest:

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1) – The host range is limited to Prunus spp. of which peach (P. persicae) is the principal host.  Peach is a major stone fruit crop in California, cultivated in significant acreage throughout the State.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest:

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3) – The pathogen is artificially transmitted mainly by a number of leafhopper species thereby marking it as having a high potential for increase and spread.  It is also spread in infected plant materials through grafting and budding operations.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is High (3) – Ca. Phytoplasma pruni has the potential to seriously damage peach (and stone fruit) production by lowering crop yield and value, requiring changes in cultural management practices to maintain disease free plants, trigger loss of markets possibly through further impositions of quarantines by importing countries and increase costs in production of clean crops.  The pathogen is vectored by many species of leafhopper.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below:

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2) – There is a medium impact to the environment expected. The pathogen is limited to Prunus spp. of which a few serve as wild hosts.  These wild hosts may also serve as reservoirs from which the vectors can acquire and transmit the pathogen to non-infected main hosts.  Home grown peach trees may be infected thereby requiring specific treatment measures.

Consequences of Introduction to California for X-disease phytoplasma:

Add up the total score and include it here. (Score)

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction of X-disease phytoplasma to California = (12).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included:

Score: 3

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is High (3). 

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 9.

Uncertainty:

Continued survey of stonefruit production for all strains of Ca. Phytoplasma pruni will lend more knowledge to the distribution of this pathogen in California.  This information can result in further lowering the overall score but will not lower the proposed C rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Ca. Phytoplasma pruni (containing peach X-disease, peach rosette, peach red suture, and little peach strains) is C.

References:

Agrios, G. N.  2005.  Plant Pathology fifth edition.  Elsevier Academic Press, Massachusetts, USA.  922 p.

CABI.  2016.  Phytoplasma pruni (peach X-disease) full datasheet report.  Crop Protection Compendium.  www.cabi.org/cpc/ .

Davis, R. E., Y. Zhao, E. L. Dally, Ing-Ming Lee, R. Jomantiene and S. M. Douglas.  2013.  ‘Candidatus Phytoplasma pruni’, a novel taxon associated with X-disease of stone fruits, Prunus spp.: multilocus characterization based on 16S rRNA, secY, and ribosomal protein genes.  International Journal of Systematic and Evolutionary Microbiology, 63:766-776.

EPPO.  2016.  Phytoplasma pruni (PHYPPN).  European and Mediterranean Plant Protection Organization PQR database.  http://www.eppo.int/DATABASES/pqr/pqr.htm .

Douglas, S. M.  1986.  Detection of mycoplasma-like organisms in peach and chokecherry with X-disease by fluorescence microscopy.  Phytopathology 76:784-787.

Kirkpatrick, B. C.  1995.  Diseases caused by mycoplasma-like organisms: Cherry Albino, Peach Rosette, Peach Yellows.  In Compendium of Stone Fruit Diseases.  Edited by J. M. Ogawa, E. I. Zehr, G. W. Bird, D. F. Ritchie, K. Uriu and J. K. Uyemoto.  APS Press, The American Phytopathological Society, Minnesota, USA, pg. 55-59.

Kirkpatrick, B. C., J. K. Uyemoto and A. H. Purcell.   1995.  Diseases caused by mycoplasmalike organisms: X-Disease.  In Compendium of Stone Fruit Diseases.  Edited by J. M. Ogawa, E. I. Zehr, G. W. Bird, D. F. Ritchie, K. Uriu and J. K. Uyemoto.  APS Press, The American Phytopathological Society, Minnesota, USA, pg. 57-59.

Larsen, H. J., and H. E. Waterworth.  1995.  Diseases caused by mycoplasmalike organisms: Peach Red Suture.  In Compendium of Stone Fruit Diseases.  Edited by J. M. Ogawa, E. I. Zehr, G. W. Bird, D. F. Ritchie, K. Uriu and J. K. Uyemoto.  APS Press, The American Phytopathological Society, Minnesota, USA, pg. 55-56.

PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp .

Stoddard, E. M., E. M. Hildebrand, D. H. Palmiter and K. G. Parker.  1951.  X-disease.  In Virus Diseases and Other Disorders with Viruslike Symptoms of Stone Fruits in North America, United States Department of Agriculture Handbook, Washington: US Government Printing Office. 10:37-42.

Thakur, P. D., A. Handa, S. C. Chowfla, and G. Krczal.  1998.  Outbreak of a phytoplasma disease of peach in the northwestern Himalayas of India.  Acta Horticulturae, No. 472: 737-739.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health@cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment:
Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

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♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

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Pest Rating: C

Posted by ls

Fungi, Plant Pathogens, Ratings

Pseudocercospora purpurea (Cooke) Deighton 1976

California Pest Rating for
Pseudocercospora purpurea (Cooke) Deighton 1976
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

On November 17, 2016, USDA APHIS PPQ inquired if CDFA had conducted a pest risk assessment of the fungal pathogen, Pseudocercospora purpurea on avocados in California.  Subsequently, the risk of infestation of P. purpurea in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background:  Pseudocercospora purpurea is a fungal plant pathogen that causes Pseudocercospora (Cercospora) spot (blotch) disease exhibiting leaf and fruit spot symptoms in Persea spp., including avocado (P. americana) plants. The pathogen was originally known as Cercospora purpurea. In South Africa, the disease is known as black spot or Cercospora spot and is the most serious pre-harvest disease affecting all cultivars of avocado, particularly, cv. Fuerte (Crous et al., 2000; Pohronezny et al., 1994).  The disease occurs in warm, humid and rainy climates and is found in southeastern USA, South America, northern Australia, Asia, Africa, and the Caribbean (CABI, 2016; Menge & Ploetz, 2003).  The pathogen has not been reported from California.

Disease cycle:  Initial inoculum of conidia (asexual spores) mostly comes from infected leaves.  New shoot tissues are infected wherever this disease occurs.  The pathogen penetrates host tissue either directly or through wounds. Conidia are easily detached and blown by wind often over long distances.  On landing on surfaces of a plant host, conidia require water or heavy dew to germinate and penetrate the host.  In South Africa, the pathogen remains latent for about 3 months after penetration.  Infected plants produce conidiophores (specialized hypha) that arise from the plant surface in clusters through stomata and form conidia successively.  Substomatal stroma (compact mycelial structure) may form from which conidiophores develop.  Fruit are susceptible when developed to a quarter to three-quarter of their full size.  Very small fruit (< 4 cm diameter) and those at or near maturity are almost immune.  Disease development is severe during warm, rainy weather when fruit are about a quarter size (Agrios, 2005; Menge & Ploetz, 2003; Pohronezny et al., 1994).  High relative humidity is necessary for conidial germination and plant infection.  The pathogen can overwinter as mycelium (stromata) in old infected leaves (Agrios, 2005).  

Dispersal and spread: Wind, rain, irrigation water, infected nursery plants, infected leaves, insects (Menge & Ploetz, 2003).

Hosts: Avocado is the main host; Persea spp. in the family Lauraceae, namely, P. americana (syn. P. gratissima, avocado), P. borbonia (redbay), P. drymifolia (Mexican avocado), P. palustris (swamp bay), and Persea sp. (Farr & Rossman, 2016).

Symptoms: Symptoms occur on leaves, stems, and fruit (Pohronezny et al., 1994).  On leaves, lesions initially appear as small (1-5 mm) angular, purple to purplish brown flecks or spots near leaf margins.  Over time, chlorotic halos surround older spots and are visible on both leaf surfaces.  The fungus sporulates under high humid conditions, appearing as gray, felty mycelial growths in the center of lesions. Individual lesions may coalesce forming larger regions of necrotic tissue.  Leaves become curled, deformed and may fall.

On fruit, lesions initiate as small flecks which later become slightly sunken, expand or coalesce becoming somewhat circular, and turn brown to brownish black in color.  Fissures or cracks usually develop in fruit lesions and serve as avenues for infection by other pathogens.  In certain cases, if the disease is temporarily arrested, the lesions appear as minute, raised, shiny, black specks associated with the corking of lenticels.  While blotch is usually confined to the rind of fruit, in advanced cases, the flesh may be invaded.  Once defoliation occurs, fruit may turn chlorotic, shrivel and drop.  Dark brown to black, 2-10 mm lesions may also form on green twigs and fruit pedicels (Pohronezny et al., 1994; Menge & Ploetz, 2003).

Damage Potential:  Pseudocercospora spot (blotch) is one of the most common diseases of avocado in Florida (Pohronezny et al., 1994).  Losses in avocado production may be severe and have been reported to be up to 69% in non-sprayed orchards in South Africa (Pohronezny et al., 1994; Menge & Ploetz, 2003).  Photosynthetic area can be reduced due to leaf spotting.  In severe infections, leaf wilt and drop may be expected.  In California, avocado production is a major industry producing 75% and 92% of the nation’s avocado fruit supplies (Lazicki et al., 2016).  Therefore, losses due to this pathogen is of particular concern.

Worldwide Distribution: Pseudocercospora purpurea is widespread in subtropical and tropical regions.  Asia:  India, Japan, Philippines; Africa: Cameroon, Democratic Republic of Congo, Côte d’Ivoire, Guinea, Kenya, South Africa; North America: Bermuda, Mexico, USA; Central America and Caribbean: Dominica, El Salvador, Honduras, Jamaica, Nicaragua, Panama, Puerto Rico, Trinidad and Tobago, United States Virgin Islands; South America: Argentina, Bolivia, Brazil, Chile, Guyana, Peru, Venezuela; Oceania: Australia, Palau (CABI, 2016; Farr & Rossman, 2016).

In the USA, the pathogen has been found in the states of Florida, Georgia, and Mississippi (CABI, 2016).

Official Control:  Presently, Cercospora purpurea (syn. Pseudocercospora purpurea) is on the ‘Harmful Organism Lists’ for Namibia and South Africa and P. purpurea is on the ‘Harmful Organism Lists’ for French Polynesia and New Caledonia (USDA PCIT, 2016).

California Distribution: Pseudocercospora purpurea has not been reported from California.  The pathogen is not known to be established in California.

California Interceptions:  None reported.

The risk Pseudocercospora purpurea would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California:

Score: 2

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2): In California, Pseudocercospora purpurea may be able to establish on avocado, under high moisture and warm climate conditions.  In the State, avocados are grown mostly along the southern coast (Lazicki et al., 2016).

2) Known Pest Host Range: Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1):  The host range for Pseudocercospora purpurea is limited to Persea spp. with avocado being the main host.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3):  Pseudocercospora purpurea has high reproductive potential resulting in the successive production of conidia which are mainly dependent on wind, rain, and infected plants for dispersal and spread.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Score: 3

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is High (3):  Infected host plants with leaf and fruit spot symptoms caused by Pseudocercospora spot (blotch) disease could lower value and yield of commercially produced avocado plants as well as affect nursery productions resulting in loss of markets.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below:

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact:

Score: 2

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2):  The pathogen could significantly impact avocado plants grown for fruit and aesthetic value in private residential and public environments.

Consequences of Introduction to California for Pseudocercospora purpurea:

Add up the total score and include it here:

-Low = 5-8 point

–Medium = 9-12 point

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 11

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.

Score: 0

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is not established (0):  Pseudocercospora purpurea is not established in California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score:

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 11

Uncertainty:  

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Pseudocercospora purpurea is B.

References:

Agrios, G. N.  2005.  Plant Pathology (Fifth Edition).  Elsevier Academic Press, USA.  922 p.

CABI.  2016.  Pseudocercospora purpurea (spot blotch) (basic) datasheet.  Crop Protection Compendium.  http://www.cabi.org/cpc/datasheet/12266 .

Crous, P.W., A. J. L. Phillips, A. P. and Baxter.  2000.  Phytopathogenic fungi from South Africa. University of Stellenbosch, Department of Plant Pathology Press, 358 pages (referenced by Farr & Rossman, 2016).

Farr, D. F., & A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved August 18, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Lazicki, P., D. Geisseler, and W. R. Horwath.  2016.  Avocado production in California. https://apps1.cdfa.ca.gov/FertilizerResearch/docs/Avocado_Production_CA.pdf. (Last updated April, 2016.)

Menge, J. A., and R. C. Ploetz.  2003.  Disease of Avocado.  In Diseases of Tropical Fruit Crops, Edited by R. C. Ploetz, CABI Publishing, CAB International, UK, USA, 527 p.

Pohronezny, K. L., G. W. Simone, and J. Kotzé.  1994.  Pseudocercospora spot (blotch).  In Compendium of Tropical Fruit Diseases, Edited by R. C. Ploetz, G. A. Zentmeyer, W. T. Nishijima, K. G. Rohrbach, and H. D. Ohr, APS Press, The American Phytopathological Society, 79-80 p.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment: 

Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

Violates agency regulations prohibiting sexual harassment or other forms of discrimination;

Violates agency regulations prohibiting workplace violence, including threats.

♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Phakopsora phyllanthi Dietel 1910

California Pest Rating for
Phakopsora phyllanthi Dietel 1910
Pest Rating: C
PEST RATING PROFILE
Initiating Event:

On December 4, 2015, a shipment of cut foliage of an unidentified plant species was intercepted at the USPS West Sacramento Distribution Center by the CDFA Dog Team.  The shipment had originated in Florida and was destined to a private owner in Merced County, California.  A sample of the symptomatic foliage was collected from the shipment and sent to the CDFA Plant Pathology Laboratory for pathogen diagnosis.  On January 20, 2016, Suzanne Latham, CDFA plant pathologist, identified the rust fungal pathogen, Phakopsora phyllanthi associated with the diseased leaves and confirmed the identification by PCR sequencings.  Subsequently, the shipment was destroyed (Martyn, 2016).  On further investigation, USDA APHIS PPQ and Florida Department of Agriculture and Consumer Services communicated to Suzanne Latham, CDFA, that P. phyllanthi had been detected in three locations in Florida on February 18, 2016 (Latham, 2016).  The risk of introduction and establishment of this pathogen in California is assessed and a permanent rating is proposed.

History & Status:

Background:  Phakopsora phyllanthi is a fungal pathogen that causes rust disease in Phyllanthus spp. (‘gooseberry’).  The pathogen has only been detected on certain species of the plant genus primarily grown in tropical and subtropical regions of the globe.  In 2015, Phakopsora phyllanthi was first reported in the USA from Hawaii (Dietrich & Ko, 2015), and later in 2016, from Florida (Latham, 2016).  The pathogen is not known to be present in California and was detected for the first time in an intercepted shipment of cut foliage from Florida, which was subsequently destroyed (see ‘Initiating Event’).  The plant genus, Phyllanthus (Phyllanthaceae) contains several hundred species, however, only one species, P. caroliniensis subsp. caroliniensis (Carolina leaf-flower) native to the eastern United States, is known to be present in San Diego County as an introduced annual plant (Calflora, 2016).

Disease cycle:  The life cycle of Phakopsora phyllanthi is not fully known.  Teliospores (the sexual, overwintering stage of the fungus), have not been observed nor is it known if the pathogen needs an alternate host to complete its life cycle (Dietrich & Ko, 2015).  It is likely, but not proven, that P. phyllanthi is spread to non-infected hosts via production of urediniospores only.

Dispersal and spread: Urediniospores are spread by wind and splashing rain.  Insects, animals, and humans may also aid in spreading spores to non-infected plants. Infected nursery plants also aid in introducing and spreading the pathogen.

Hosts:  Phyllanthus acidus (synonyms: Cicca acida, P. distichus; Tahitian gooseberry), P.benguetensis, P. emblica (Indian gooseberry), P. niruri (gale of the wind), P. phyllanthi, Phyllanthus sp. (Dietrich & Ko, 2015; Farr & Rossman, 2016).  Some Phyllanthus species such as, P. emblica and P. acidus are cultivated for fruit in warm climates, while other species are pantropical weeds or grown for medicinal uses – but these species are not present in California.

Symptoms:  Rust-infected Phyllanthus acidus (Tahitian gooseberry) trees may exhibit a general unthrifty appearance with thinning canopy, and barren branches or twigs.  Leaves exhibit discolored chlorotic or necrotic spots on upper and lower surfaces.  Small white-brownish raised spots or pustules containing numerous powdery urediniospores are produced on lower leaf surfaces.  Affected leaves eventually drop off.  Rust pustules and lesions are also formed on the surface of fruit (Dietrich & Ko, 2015).

Disease Potential:  Phyllanthus species, such as P. acidua (Tahitian gooseberry) and P. emblica (Indian gooseberry) grown for their fruit in tropical climates, are not commercially cultivated in California, but are probably sold by rare fruit nurseries within the State.  Infections of this rust pathogen could negatively impact production and value of plants.  In general, severe infestation of rust can result in defoliation and reduction in plant growth, vigor and stand.  Containment and management of the rust pathogen can be difficult as masses of air-borne spores produced can spread over long distances.  Backyard growers, other small, rare fruit production growers, hobbyists, and rare plant nurseries in warm and wet climates of southern California may be at particular risk.

Worldwide Distribution: Asia: China, India, Indonesia, Malaysia, Philippines, Thailand; North America: USA (Florida, Hawaii); South America: Brazil, Ecuador, French Guyana, Venezuela (Dietrich & Ko, 2015; Farr & Rossman, 2016).

Official Control: None reported.  Presently, Phakopsora phyllanthi has a temporary Q rating in California.

California Distribution:  The gooseberry rust pathogen, Phakopsora phyllanthi is not established in California.

California Interceptions:  The pathogen has only been detected once in a single intercepted quarantine shipment of unidentified cut foliage that originated in Florida (see “Initiating Event”).

The risk Phakopsora phyllanthi would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Low (1):  Phakopsora phyllanthi may establish in very limited areas within southern California that have warm and wet climates where the tropical host, Phyllanthus spp. is able to grow.  Presently, only one species, Phyllanthus caroliniensis subsp. caroliniensis (Carolina leaf-flower) native to the eastern United States, is known to be present in San Diego County’s coastal region as an introduced annual plant. 

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1):  The host range for the pathogen is very limited and comprises of some species non-native, tropical plants belonging to the genus Phyllanthus.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3): Phakopsora phyllanthi has high reproduction and dispersal potential.  Spores are spread by wind and splashing rain.  Insects, animals, and humans may also aid in spreading spores to non-infected plants. Infected nursery plants also aid in introducing and spreading the pathogen.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Low (1): Reported hosts of the gooseberry rust pathogen are not to be present in California and therefore, no major economic impact of this pathogen is expect within California.  However, if the pathogen was introduced, growers of rare, imported fruit plants, such as backyard growers, hobbyists, and rare plant nurseries in warm and wet climates of southern California may be at particular risk of reduced crop value.  The economic impact is evaluated to be low.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2):  Backyard growers, other small, rare fruit production growers, hobbyists, and rare plant nurseries in warm and wet climates of southern California may be at particular risk, if the pathogen were introduced into the State.

Consequences of Introduction to California for Myrtle Rust:

Add up the total score and include it here. (Score)

–Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 8 (Low).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is ‘Not established’ (0).  

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 8.

Uncertainty:

Details of the pathogen’s complete life cycle including the need of an alternate host to complete its life cycle are not presently known.  However, it is unlikely that this information will alter the proposed rating for the pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for gooseberry rust pathogen, Phakopsora phyllanthi is C.

References:

Calflora.  2016.  Calflora: Information on California plants for education, research and conservation [web application].  Berkeley, California: The Calflora Database [a non-profit organization].  http://www.calflora.org/

Dietrich, B., and M. Ko.  2015.  Phyllanthus Rust Phakopsora phyllanthi Dietel.  New Pest Advisory No. 15-02 October 2015, State of Hawaii Department of Agriculture.

Farr, D. F. and A. Y. Rossman.  2016.   Fungal databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved October 17, 2016 from http://nt.ars-grin.gov/fungaldatabases/.

Khan, S.  2016.  Email from K. Martyn, Yolo County, to S. Khan, CDFA, subject: “RE: Information request for A/Q/W reports”, dated February 11, 2016, forwarded to J. Chitambar, CDFA, by T. Walber, CDFA on October 18, 2016.

Latham, S.  2016.  Email from S. Latham (CDFA) to J. Chitambar (CDFA), subject: “FW: confirmed ID: Positive for gooseberry rust (Phakopsora phyllanthi) from St. Petersburg, Pinellas Co., FL.”, sent October 17, 2016.

USDA-PCIT.  2016.  United States Department of Agriculture, Phytosanitary Certificate Issuance & Tracking System (PCIT). https://pcit.aphis.usda.gov/PExD/faces/ViewPExD.jsp .

Responsible Party: John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment: 

Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

Violates agency regulations prohibiting sexual harassment or other forms of discrimination;

Violates agency regulations prohibiting workplace violence, including threats.

♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: C

Posted by ls

Fungi, Plant Pathogens

Pseudocercospora myrticola (Speg.) Deighton 1976

California Pest Rating for
Pseudocercospora myrticola (Speg.) Deighton 1976
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

None.  The risk of infestation of P. myrticola in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background:  Pseudocercospora myrticola is a fungal plant pathogen that belongs to a larger group of Cercospora-like fungi most of which cause leaf spot symptoms in host plants. The pathogen was originally named Cercospora myrticola, and since then has also been known by several synonyms: Cercospora myrti, C. saccardoana, C. amadelpha and Fusariella cladosporioides (Crous et al., 2013; Farr & Rossman, 2016).   The pathogen is widely distributed globally and infects myrtle and several species within the family Myrtaceae, with few in Melastomataceae (Farr & Rossman, 2016). In the USA, P. myrticola has only been reported from myrtle (Myrtus communis).  In 1984, P. myrticola was first reported in the USA from Florida (Alfieri et al., 1984) and from San Diego, California in 2006 (CPPDR, 2007).  On December 4, 2013, the pathogen was detected in a decorative wreath comprising of symptomatic leaves of an unknown plant, most likely to be myrtle that had been shipped from the State of Nevada and intercepted in Sonoma County, California.

Disease cycle: Infected plants produce conidiophores (specialized hypha) that arise from the plant surface in clusters through stomata and form conidia (asexual spores) successively.  Conidia are easily detached and blown by wind often over long distances.  On landing on surfaces of a plant host, conidia require water or heavy dew to germinate and penetrate the host.  Sub-stomatal stroma (compact mycelial structure) may form from which conidiophores develop.  Development of the pathogen is favored by high temperatures and the disease is most destructive during summer months and warmer climates.  High relative humidity is necessary for conidial germination and plant infection.  The pathogen can overwinter in or on seed and as mycelium (stromata) in old infected leaves (Agrios, 2005).  

Dispersal and spread: air-currents, infected nursery plants, infected leaves, seeds.

Hosts: Blepharocalyx divaricatus, Metrosideros excela (New Zealand Christmas tree), M. parkinsonii (Parkinson’s rata), Monochaetum polyneurum, Myrciaria cauliflora (jaboticaba), Myrtus communis (common myrtle), M. communis var. latifolia, M. communis var. laurifolia, M. divaricata, Tristania suaveolens (swamp mahogany) (Farr & Rossman, 2016).

Symptoms:  Infected host plants exhibit irregular to angular, leaf spots on both leaf surfaces.  Spots are 2-4 mm in diameter, rusty-brown, abundant on the lower leaf surface, usually confluent.  Lesions or spots may be surrounded by a diffuse lighter halo (Nakashima et al., 2004).

Damage Potential: Specific losses due to Pseudocercospora myrticola have not been reported.  Photosynthetic area can be reduced due to leaf spotting.  In severe infections, leaf wilt and drop may be expected.  However, damage potential due to this pathogen is likely to be similar to other Cercospora diseases which is usually low (Agrios, 2005).  In California, myrtle is not native to California and is grown in lower coastal and some inner valley regions of the State (Calflora, 2016) in landscapes, commercial and private gardens.  Also, young branches and foliage are used in floral decorations and therefore, diseased plants could be of particular concern to production nurseries.

Worldwide Distribution: Africa: South Africa, Cape Province; Asia:  India, Japan; Europe: Cyprus, England, Republic of Georgia, Germany, Greece, Israel, Italy, Sicily, Scotland, Sweden, Yugoslavia; North America: USA (Florida, California); South America: Brazil, Chile, Paraguay; Oceania: Australia, New Zealand (Crous et al., 2013;  Farr & Rossman, 2016).

Official Control: None reported.  Presently, Pseudocercospora myrticola has a temporary ‘Q’ rating in California.

California Distribution: Pseudocercospora myrticola has been found in San Diego Counties (CDFA Plant Pest and Damage Records).

California Interceptions:  Pseudocercospora myrticola was detected in 2013 in an intercepted quarantine shipment of a plant wreath that originated in Nevada.

The risk Pseudocercospora myrticola would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2): Pseudocercospora myrticola may be able to establish wherever myrtle and other hosts plants are able to grow.  Myrtle is a non-native plant in California and is grown in lower coastal and some inner valley regions in warm and humid climates.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Medium (2):  Pseudocercospora myrticola has a moderate host range that comprises common myrtle and other species within Myrtaceae, plus few species in Melastomataceae.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3):  Pseudocercospora myrticola has high reproductive potential resulting in the successive production of conidia which are dependent on air currents and infected plants and seed for dispersal and spread.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Medium (2):  Infected host plants with leaf spot symptoms could lower value of nursery-produced plants and trigger the loss of markets.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

 Risk is Medium (2): Pseudocercospora myrticola infections could significantly impact home/urban gardening and aesthetic plantings of myrtle in commercial environments, such as parks and public gardens.

Consequences of Introduction to California for Pseudocercospora myrticola:

Add up the total score and include it here. (Score)

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 11

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

-Not established (0) Pest never detected in California, or known only from incursions.

–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Low (-1): Pseudocercospora myrticola has been found in San Diego County only.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 10

Uncertainty:  

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Pseudocercospora myrticola is B.

References:

Agrios, G. N.  2005.  Plant Pathology (Fifth Edition).  Elsevier Academic Press, USA.  922 p.

Alfieri Jr., S. A., K. R. Langdon, C. Wehlburg, and J. W. Kimbrough.  1984.  Index of Plant Diseases in Florida (Revised). Florida Department of Agriculture and Consumer Service, Division of Plant Industry Bulletin 11: 1-389.  In [Farr, D. F.  & A. Y. Rossman, 2016. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved October 19, 2016, from http://nt.ars-grin.gov/fungaldatabases/ ].

Crous, P.W., U. Braun, G. C. Hunter, M. J. Wingfield, G. J. M. Verkley, H. D. Shin, C. Nakashima, and J. Z. Groenewald.  2013.  Phylogenetic lineages in Pseudocercospora. Studies in Mycology 75: 37-114.

Calflora.  2016.  Information on California plants for education, research and conservation. [Web application].  Berkeley, California: The Calflora Database [a non-profit organization]. http://www.calflora.org/

CPPDR.  2007.  Plant pathology A & Q rated pathogen & hosts detected by county.  California Plant Pest & Disease Report, California Department of Food and Agriculture July 2005 through December 2006 23(1): 113-115.

Farr, D.F., & A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved October 19, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Nakashima, C., H. Horie, and T. Kobayashi.  2004.  Addition and reexamination of Japanese species belonging to the genus Cercospora and allied genera.  VI. Four Pseudocercospora species from Ohshima Island, Tokyo.  Mycoscience 45: 49-55.  DOI 10.1007/s10267-003-0151-y

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Comment Format:

♦  Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.

Example Comment: 

Consequences of Introduction:  1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]

♦  Posted comments will not be able to be viewed immediately.

♦  Comments may not be posted if they:

Contain inappropriate language which is not germane to the pest rating proposal;

Contains defamatory, false, inaccurate, abusive, obscene, pornographic, sexually oriented, threatening, racially offensive, discriminatory or illegal material;

Violates agency regulations prohibiting sexual harassment or other forms of discrimination;

Violates agency regulations prohibiting workplace violence, including threats.

♦  Comments may be edited prior to posting to ensure they are entirely germane.

♦  Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.

Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Neofusicoccum mangiferae (Syd. & P. Syd.) Crous, Slippers & A. J. L. Phillips, 2006

California Pest Rating for
Neofusicoccum mangiferae (Syd. & P. Syd.) Crous, Slippers & A. J. L. Phillips, 2006
Pest Rating: C
PEST RATING PROFILE
Initiating Event:

The current status and rating of Neofusicoccum mangiferae in California is reassessed and a permanent rating is proposed.

History & Status:

Background:  Neofusicoccum mangiferae is a fungal plant pathogen belonging to the family Botryosphaeriaceae.  The species was originally named Dothiorella mangiferae but since then has undergone several taxonomic revisions and is also been known as Nattrassia mangiferae, Fusicoccum mangiferae, and Hendersonula cypria (Crous et al., 2006; Farr & Rossman, 2016).

In California, Neofusicoccum mangiferae is widespread and has been found in different hosts including walnut and fig causing branch wilt and limb dieback (Michailides et al., 2007), in citrus causing branch and trunk canker (Eskalen et al., 2011) and Indian leaf-laurel fig causing ‘Sooty Canker’ disease (as syn. Nattrassia mangiferae) which severely damaged street plantings of Indian leaf-laurel fig in southern California (Hodel, et al., 2009; Mayorquin et al., 2012).  In addition, during 2015-16, CDFA plant pathologists identified the pathogen from diseased mango and avocado fruit that were intercepted in shipments from Florida to California. In natural infestations, the pathogen is often found in combination with other fungal species.

Disease development:  In Indian laurel-leaf fig and other host plants, Hodel et al., (2009) reported that the pathogen enters the tree primarily through bark wounds produced by mechanical damage, pruning, freezing weather, sunburn, insects, or other diseases.  Smooth, thin-barked trees or those stressed from insufficient water and other factors are especially susceptible to the disease.  The fungus and disease develops most rapidly in warm temperatures (85-105°F) under high humidity. Slightly sunken cankers develop at the wound and point of infection on branches and may expand as the disease progresses.  Once the disease expands to the trunk, the tree dies.  Small, black, pencil-point size fungal fruiting bodies are formed on the cankers while the underlying infected sapwood inside the bark is stained grey to black and sharply demarcated from adjacent light-colored, healthy tissue.   Masses of dark spores are produced by the fruiting bodies and dispersed by wind, rain splash, pruning tools, and insects.

Dispersal and spread: Wind, rain, water-splash, pruning tools, insects, and animals can spread fungal spores to non-infected plants.

Hosts: Agathis spp. (kauri; Araucariaceae), Castanea sativa (European chestnut; Fagaceae), Dioscorea rotundata (white yam; Dioscoreaceae), Eucalyptus grandis (flooded/rose gum; Myrtaceae), Mangifera indica (mango; Anacardiaceae), Manihot esculenta (cassava; Euphorbiaceae), Persea americana (avocado; Lauraceae), Prunus armeniaca (ansu apricot; Rosaceae), Phoenix dactylifera (date palm; Arecaceae), Cupressus (cypress; Cupressaceae), Robina pseudoacacia (black locust; Fabaceae), Tibouchina urvilleana (glory bush/purple glory tree; Melastomataceae), Ficus microcarpa (Indian laurel-leaf fig; Moraceae)) F. carica (edible fig: Moraceae), Juglans regia (English walnut; Juglandaceae), Citrus sp. (citrus; Rutaceae) (El-Trafi, 2010; Farr & Rossman, 2016; French, 1989; Heath et al., 2011; Mayorquin et al., 2012; Michailides et al., 2007; Nazerian et al., 2015).  Vitis vinifera (grape: Vitaceae) was reported as a host of Neofusicoccum mangiferae in China (Dissanayake et al., 2015).

Symptoms: Neofusicoccum mangiferae causes blight of inflorescences, rachis, and branches of infected host plants.  Symptoms include branch and trunk cankers, branch wilt and dieback, lesions and rot of fruit, rachis and flower discoloration and necrosis.

The pathogen has been reported to be associated with rachis necrosis and inflorescence blight in mango in Puerto Rico (Serrato-Diaz et al., 2014), lesions and progressive rot in mango and avocado fruit in Taiwan (Ni et al., 2009, 2010), Walnut branch wilt, fig branch dieback, citrus branch and/or trunk cankers, branch dieback and tree death symptoms of sooty canker disease in Indian laurel-leaf fig trees in California (Eskalen et al., 2011; Michailides et al., 2007; Hodel et al., 2009). In China, symptoms associated with grapevine dieback were characterized by partial or total death of affected cordons, with brown U-shaped necrotic sectors and brownish-black spot in cross-sections of affected trunks and arms (Dissanayake et al., 2015).

Damage Potential: In mango, disease incidences of 20-100% have been reported (Serrato-Diaz et al., 2014; El-Trafi, 2009) as well as 30-72% rot disease in stored mango fruit (Ni et al., 2010).  In several cities in Los Angeles County, California, the pathogen has devastated landscape plantings of Indian laurel-leaf fig tree by causing severe damage and death (Hodel et al., 2009).  Branch and trunk canker of citrus and other tree hosts may lead to decline or death of branches and whole plants (Eskalen et al., 2011; Michailides et al., 2007).

Worldwide Distribution: Asia: India, Iran, Myanmar, Pakistan, Taiwan; Africa: Benin, Nigeria, South Africa, Sudan; Europe: Cyprus; North America: Arizona, California, Hawaii, Washington, West Virginia; South America: Uruguay; Caribbean: Puerto Rico; Australia (CABI, 2016; USDA ARS, 2016; Farr & Rossman, 2016).

Official Control: None reported.

California Distribution: Neofusicoccum mangiferae is widespread in California in northern and southern coastal and valley counties including, Fresno, Los Angeles, Riverside, San Diego, San Luis Obispo, Tulare, and Ventura Counties (Eskalen et al., 2011; French, 1989; Hodel et al., 2009; Mayorquin et al., 2012).

California Interceptions:  From June 2014 to August 2016, Neofusicoccum mangiferae has been detected in eight shipments of mango and one shipment of avocado fruit imported to California (CDFA Pest and Damage Records).

The risk Neofusicoccum mangiferae would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2):  Neofusicoccum mangiferae is able to establish in California under warm to hot and very humid climates.  Already, it is distributed within the State in certain southern and northern coastal and valley counties.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Medium (2):  Neofusicoccum mangiferae has a moderate and diverse host range. In California it has been found in Indian laurel-leaf fig tree, edible fig, citrus, avocado, and chestnut.  It has been detected in intercepted shipments of mango and avocado fruit.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is Medium (2): Numerous numbers of spores are produced by this pathogen due to its high reproduction.  However, spore dispersal to non-infested hosts is dependent on external factor such as wind, water-splash, rain, infected pruning tools, insects, and animals. Therefore, it is given a Medium score.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is High (3): Neofusicoccum mangiferae could lower crop yield, value, increase production costs, require changes in normal pruning practices, and can be spread by insects and animals, thereby, qualifying it for a high score for economic impact.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is High (3): Infections of tree hosts used as commercial landscape, ornamental and private gardens plantings could result in disrupting natural communities in those environments, subsequently requiring official or private treatments.

Consequences of Introduction to California for Neofusicoccum mangiferae:

Add up the total score and include it here. (Score)

-Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 13

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is High (-3): Neofusicoccum mangiferae has been reported from certain southern and northern coastal and valley counties.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 9.

Uncertainty:  

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Neofusicoccum mangiferae is C.

References:

CABI.  2016.  Neofusicoccum mangiferae datasheet (basic).  http://www.cabi.org/cpc/datasheet/115758 .

Crous, P. W., B. Slippers, M. J. Wingfield, J. Rheeder, W. F. O. Warasas, A. J. L. Philips, A. Alves, T. Burgess, P. Barber, and J. Z. Groenewald.  2006.  Phylogenetic lineages in the Botryosphaeriaceae.  Studies in Mycology 55: 235-253.

Dissanayake, A. J., W. Jhang, X. Li, Y. Zhou, T. Chethana, E. Hukeatirote, K. D. Hyde, J. Yan, G. Zhang, and W. Zhao.  2015.  First report of Neofusicoccum mangiferae associated with grape dieback in China.  Phytopathologia Mediterranea temp25-30.  DOI: 10.14601/Phytopathol_Mediterr-15159.

El-Trafi, M. A.  2010.  Studies on mango branch wilt disease caused by Neofusicoccum mangiferae.  FAO Agris Records.  http://agris.fao.org/openagris/search.do?recordID=SD2010000222 .

Eskalen, A., A. Adesemoye, and D. Wang.  2011.  Identification of different species causing Botryosphaeriaceae canker in citrus reveal Neofusicoccum mangiferae with Scytalidium-like synanomorph.  Phytopathology, 101: S49.

Farr, D.F., & A. Y. Rossman.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved January 28, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

French, A.M. 1989. California Plant Disease Host Index. California Department of Food and Agriculture, Sacramento, 394 pages.

Heath, R.N., J. Roux, B. Slippers, A. Drenth, S. R. Pennycook, B. D. Wingfield, and M. J. Wingfield.  2011.  Occurrence and pathogenicity of Neofusicoccum parvum and N. mangiferae on ornamental Tibouchina species. Forest Pathology, 41: 48-51.

Hodel, D. R., A. J. Downer, and D. M. Mathews.  2009.  Sooty canker, a devastating disease of Indian laurel-leaf fig trees.  Western Arborist 35: 28-32.

Mayorquin, J. S., A. Eskalen, A. J. Downer, D. R. Hodel, and A. Liu.  2012.  First report of multiple species of the Botryosphaeriaceae causing bot canker disease of Indian laurel-leaf fig in California.  Plant Disease, 96:459. http://dx.doi.org/10.1094/PDIS-08-11-0714.

Michailides, T. J., D. P. Morgan, D. Felts, and H. Reyes.  2007.  Emerging fungal diseases in fruit and nut crops in California.  Phytopathology, 97: S170.

Nazerian, E., H. R. Naji, H. Abdul-Hamid, and M. Moradi.  2015.  Phenotypic and molecular characterization of Neofusicoccum mangiferae, the causal agent of black locust decline.  Journal of Plant Pathology and Microbiology, 6: 1. http://dx.doi.org/10.4172/2157-7471.1000250 .

Ni, H. F., R. F. Liou, T., H. Hung, R. S. Chen, and H. R. Yang.  2010. First report of fruit rot disease of mango caused by Botryosphaeria dothidea and Neofusicoccum mangiferae in Taiwan.  Plant Disease 94: 128. http://dx.doi.org/10.1094/PDIS-94-1-0128C

Ni, H. F., R. F. Liou, T., H. Hung, R. S. Chen, and H. R. Yang.  2009.  First report of a fruit rot disease of avocado caused by Neofusicoccum mangiferae.  Plant Disease 93: 760. http://dx.doi.org/10.1094/PDIS-93-7-0760B

Serrato-Diaz, L. M., L. I. Rivera-Vargas, and R. D. French-Monar.  2014.  First report of Neofusicoccum mangiferae causing necrosis and inflorescence blight of Mango (Mangifera indica) in Puerto Rico.  Plant Disease 98: 570. http://dx.doi.org/10.1094/PDIS-08-13-0878-PDN

USDA ARS.  2016.  Fungi on Mango in India, but not found in the U.S.A.  U.S. Department of Agriculture, Agricultural Research Service, Systematic Mycology and Microbiology Laboratory – Nomenclature Fact Sheets.  July 7, 2016. http://nt.ars-grin.gov/sbmlweb/onlineresources/nomenfactsheets/rptBuildFactSheet_onLine.cfm?thisName=Fungi%20on%20Mango%20in%20India&currentDS=specimens .

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

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Pest Rating: C

Posted by ls

Fungi, Plant Pathogens

Cercospora coniogrammes Crous & R. G. Shivas 2012

California Pest Rating for
Cercospora coniogrammes Crous & R. G. Shivas 2012
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

On June 14, 2016, a shipment of silver lady fern (Blechnum gibbum) plants from Florida, destined to a nursery in Nippomo, San Luis Obispo County, was intercepted by San Luis County officials.  Diseased plants exhibiting leaf spot symptoms were collected and sent to the CDFA Plant Pathology Laboratory for disease diagnosis.  Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen, Cercospora coniogrammes, by culturing and multigene sequencing.  On July 19, 2016, the pathogen was detected in another shipment of silver lady fern plants from Florida and destined to the same nursery in San Luis Obispo County. The identity of the pathogen was confirmed on August 19, 2016 by the USDA PPQ PM National Identification Services in Beltsville, Maryland.  This detection marked a new US record and is reportable/actionable by the USDA (Bowers, 2016).    The pathogen was given a temporary Q rating and consequently, the shipment of Blechnum gibbum was placed on hold, treated with fungicides, and is currently undergoing 30-day inspections (Schnabel, 2016).  The risk of infestation of C. coniogrammes in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background:  Cercospora coniogrammes is a fungal pathogen that causes leaf spots on fern.  The pathogen was first reported in 2012 from infected bamboo fern, Coniogramme japonica var. gracilis, in Brisbane, Queensland, Australia (Groenewald et al., 2012), and in 2016 from Brazil (Guatimosim et al., 2016).  The detection of C. coniogrammes in California marked a new record of the pathogen in the USA (Bowers, 2016; see ‘Initiating Event’).  Presently, not much is known about the distribution and ecology of the pathogen.

Disease cycle:  In general, in infected plants, Cercospora species produce conidiophores (specialized hypha) that arise from the plant surface in clusters through stomata and form conidia (asexual spores) successively.  Conidia are easily detached and blown by wind often over long distances.  On landing on surfaces of a plant host, conidia require water or heavy dew to germinate and penetrate the host.  Substomatal stroma (compact mycelial structure) may form from which conidiophores develop.  Development of the pathogen is favored by high temperatures and the disease is most destructive during summer months and warmer climates.  High relative humidity is necessary for conidial germination and plant infection.  The pathogen can overwinter in or on seed and as mycelium (stromata) in old infected leaves (Agrios, 2005).  

Dispersal and spread: air-currents, infected nursery plants, infected leaves, seeds (Agrios, 2005).

Hosts: Fern species, namely, Blechnum gibbum, Coniogramme japonica var. gracilis, Hypolepis mitis, Macrothelypteris torresiana (Groenewald et al., 2012; Guatimosim et al., 2016).

Symptoms: Infected host plants exhibit leaf spots on upper and lower sides of leaves and are sub-circular to angular, 1-3 mm in diameter, grey to pale brown, surrounded by a broad brown margin up to 4 mm in diameter (Groenewald et al., 2012).

Damage Potential: Quantitative losses due to Cercospora coniogrammes have not been reported.  Photosynthetic area can be reduced due to leaf spotting.  In severe infections, leaf wilt and drop may be expected.  However, damage potential due to this pathogen is likely to be similar to other Cercospora diseases which is usually low (Agrios, 2005).

Worldwide Distribution: Australia: Queensland; South America: Brazil; North America: USA (Groenewald et al., 2012; Guatimosim et al., 2016).

Official Control: None reported particularly for Cercospora coniogrammes, however, the following countries have Cercospora spp. on their ‘Harmful Organism Lists’: French Polynesia, Madagascar, South Africa, and Sri Lanka (USDA PCIT, 2016).

California Distribution: Cercospora coniogrammes is not known to be established in California.  Interceptions of infected plants in a San Luis Obispo nursery were placed on hold, treated with fungicide, and is currently undergoing 30-day inspections (see, ‘Initiating event’).

California Interceptions:  Cercospora coniogrammes was detected in only two shipments of Blechnum gibbum intercepted by San Luis Obispo County officials during June and July 2016.

The risk Cercospora coniogrammes would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2):  Cercospora coniogrammes may be able to establish in large but limited regions in California wherever fern plants are able to grow naturally under high humid and cool to warm temperatures. Silver lady fern, Blechnum gibbum, is cultivated indoors and outdoors in coastal parts of California.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1): Presently, the host range for Cercospora coniogrammes is limited to few species of fern, namely, Blechnum gibbum, Coniogramme japonica var. gracilis, Hypolepis mitis, and Macrothelypteris torresiana.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3):  Cercospora coniogrammes has high reproductive potential resulting in the successive production of conidia which are dependent on air currents and infected plants and seed for dispersal and spread.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Medium (2):  Infected host plants with leaf spot symptoms could result in lowered value and loss of markets of nursery-produced fern host plants.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Low (1): The pathogen could significantly impact ornamental plantings in home/ urban and commercial gardens and recreational environments.

Consequences of Introduction to California for Cercospora coniogrammes:

Add up the total score and include it here. (Score)

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 9

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is not established (0):  Cercospora coniogrammes is not established in California and has only been detected in intercepted shipments of fern to the State. 

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 9

Uncertainty:  

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Cercospora coniogrammes is B.

References:

Agrios, G. N.  2005.  Plant Pathology (Fifth Edition).  Elsevier Academic Press, USA.  922 p.

Bowers, J. H.  2016.  Email from J. H. Bowers, USDA, to H. R. Wright, USDA APHIS, forwarded to U. Kodira, CDFA on September 2, 2016.

Farr, D.F., & A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved September 22, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Groenewald, J. Z., C. Nakashima, J. Nishikawa, H. D. Shin, J. H. Park, A. N. Jama, M. Groenewald, U. Braun, and P. W. Crous.  2013.  Species concepts in Cercospora: spotting the weeds among the roses. Studies in Mycology 75: 115-170.

Guatimosim, E., P. B. Schwartsburd, R. W. Barreto, and P. W. Crous.  2016.  Novel fungi from an ancient niche: cercosporoid and related sexual morphs on ferns.  Persoonia 37: 106-141.

Schnabel, D. L.  2016.  Email from D. L. Schnabel, CDFA Pest Exclusion, to J. Chitambar, CDFA on September 28, 2016.

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System. Sept. 23, 2016.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Pest Rating: B

Posted by ls 

Fungi, Plant Pathogens

Fusarium brachygibbosum Padwick 1945

California Pest Rating for
Fusarium brachygibbosum Padwick 1945
Pest Rating: C  
PEST RATING PROFILE
Initiating Event: 

On July 18, 2016, CDFA plant pathologists were notified by Dr. R. Bostock, Professor, Department of Plant Pathology, University of California, Davis, of a fungal pathogen, Fusarium brachygibbosum, detected in cold-stored, bare-root nursery almond trees in California. This detection marked a first report of the pathogen in California.  Therefore, a risk analysis of F. brachygibbosum to California agriculture and environment was conducted and a permanent rating is proposed here for the otherwise non-rated pathogen.

History & Status:

Background: In California, Seidle et al. (2016) reported the first detection of Fusarium brachygibbosum from asymptomatic, cold-stored, bare-root propagated almond (Prunus dulcis) trees.  Samples had been collected in fall 2013, from a nursery in Sutter County.

In 2011, that same nursery had experienced the re-emergence of a canker disease that occurred in the late 1900s.  During the winter of 1997-98, a severe canker disease developed during cold storage of dormant almond trees and other fruit tree species in several nurseries in California.  Fusarium acuminatum and F. avenaceum were identified as the primary causal agents of the disease.  The predominant symptoms were necrosis of the inner bark, cambium, and sapwood, which in severe cases, resulted in girdling and death of trees. However, in the absence of external symptoms, internal necrosis was not readily evident in dark-bark trees, but detectable in light-bark trees.  Notably, the canker phase of Fusarium-infected young trees did not become apparent unless predisposed by some physiological stresses.  Consequently, infected trees were distributed to growers and the disease that developed under abiotic stress factors, including desiccation and variable cold storage temperatures, resulted in loss of thousands of trees, newly planted orchards, and millions of dollars (Marek et al., 2013). Fusarium acuminatum and F. avenaceum were also detected along with F. brachygibbosum in the 2013 almond samples reported by Seidle et al. (2016).  The ability to detect F. brachygibbosum during the last few years than earlier was likely due to the availability of molecular tools for distinguishing this pathogen from other Fusarium species associated with nursery trees and storage/processing facilities and fields (Personal communication: Dr. R. M. Bostock, Professor, Department of Plant Pathology, University of California, Davis).

Fusarium brachygibbosum has been found on diverse host species within five plant families and reported from few countries in Asia, Africa, and North America (see ‘Worldwide Distribution’).

Hosts: Citrullus lanatus (watermelon; Cucurbitaceae), Euphorbia larica (spurge; Euphorbiaceae), Sorghum vulgare (broom corn; Poaceae), Triticum spp.  (wheat; Triticeae), Prunus dulcis (syn. P. amygdalus, almond; Rosaceae) (Al-Mahmooli et al., 2013; Farr & Rossman, 2016; Mirhosseini et al., 2014; Renteria-Martinez et al., 2015; Seidle et al., 2016; Van Coller et al., 2016).

Symptoms:  Fusarium brachygibbosum is associated with symptoms of wilting, dieback, and cankers and has often been found infecting plants with a complex of fungi species.  Therefore, symptoms particular to the species have only been demonstrated experimentally through pathogenicity tests.  In pathogenicity tests using almond branches inoculated with F. brachygibbosum and incubated at 15°C for two weeks, Siedle et al. (2016) found that canker lesions (area: 26.7 mm2 to 83.0 mm2) developed, comparable to those produced by F. acuminatum and F. avenaceum. Additionally, F. brachygibbosum was found in asymptomatic almond rootstock.  Experimentally in watermelon, F. brachygibbosum produced variable sized light brown colored lesion at neck and root causing wilting of leaves or whole plants (Renteria-Martinez et al., 2015). The pathogen produced dark brown to black, circular to elliptical leaf spots in oleander (Mirhosseini et al., 2014).  In South Africa, F. brachygibbosum was isolated along with several other Fusarium species from kernels of field-grown wheat exhibiting symptoms of Fusarium head blight disease (Van Coller et al., 2013).

Disease cycle: While the disease cycle has not been reported specifically for Fusarium brachygibbosum, it is likely that it is similar to other Fusarium species causing canker and wilt disease.  Generally, Fusarium species inhabit soils and plants.  They can exist saprophytically, but can also act as opportunistic pathogens.  On hosts predisposed by stress, as in cold storage temperatures, or in combination with other pathogens, symptoms may become severe.  The pathogen overwinters as mycelium or spores in infested crop residues and seed, or as chlamydospores (thick walled asexual spores) in soil, and produces asexual spores (microconidia and macroconidia) which are dispersed to plants and other plant debris by wind or rain-splash. Generally, under warm and humid conditions, sexual spores are produced which are forcibly discharged into the air and transmitted by wind currents to susceptible plants where infection and further development of the pathogen occur.

Damage Potential: Precise losses due to Fusarium brachygibbosum have not been reported.  More than one Fusarium species and/or other fungal species may be present in cold-stored canker diseased nursery stock (Marek et al., 2013).  Fusarium brachygibbosum may remain cryptic and asymptomatic within the host, and the canker phase does not become apparent unless young trees are subjected to some physiological stress. Asymptomatic, infected nursery trees may result in the development of the disease and losses in production in the field.

Transmission: Infected plants, roots, stems, leaves, seeds (Van Coller et al., 2016), plant debris, soil, air currents, rainwater splash, and contaminated equipment.

Worldwide Distribution: Asia: India, Iran, Oman; Africa: South Africa; North America: Mexico, USA (California) (Al-Mahmooli et al., 2013; Farr & Rossman, 2016; Mirhosseini et al., 2014; Renteria-Martinez et al., 2015; Seidle et al., 2016; Van Coller et al., 2016).

Official Control: None reported.

California Distribution: Sutter and Stanislaus Counties (Seidle et al., 2016). However, suspected to be widespread in California (R. M. Bostock, Professor, Department of Plant Pathology, University of California, Davis: personal communication).

California Interceptions:  None reported.

The risk Fusarium brachygibbosum would pose to California is evaluated below.

Consequences of Introduction:  

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2) – In California, Fusarium brachygibbosum was detected in young almond nursery rooting predisposed to cold storage temperatures.  It was also isolated from soil under almond production (Seidle et al., 2016), and is suspected to be widespread within California.  The disease is likely to establish primarily in nurseries with bare-root propagative almond plants predisposed to abiotic stresses – including temperature variations in cold storage, and in almond production fields within California.  Watermelon is a reported host of the pathogen (although not reported from California) and may also be affected by the disease.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1) – Presently, the known host range of Fusarium brachygibbosum is limited to watermelon, almond, wheat, spurge, and broom corn.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3) – Fusarium brachygibbosum has high reproduction and dispersal potential through infected plants, roots, stems, leaves, seeds, soil, plant debris, air currents, rainwater splash, and contaminated equipment.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is High (3) – Quantitative estimates of losses in crop yield have not been reported, however, based on losses caused by the complex of other Fusarium species also detected in cold-stored almond tree seedlings in California (Marek et al., 2013), significant loss in crop production, value and yield is possible. However, development of the pathogen and production of visible disease symptoms in young trees is subject to predisposing physiological stresses.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

 Risk is Low (1) – The pathogen has not been reported to significantly impact the environment.  However, leaf spots caused by the pathogen in infected ornamental oleander have been reported (but not from California). 

Consequences of Introduction to California for Fusarium brachygibbosum:

Add up the total score and include it here. (Score)

-Low = 5-8 points

  –Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Fusarium brachygibbosum to California = (10).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

–Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Medium (-2).  Fusarium brachygibbosum has been detected in cold-stored young almond rootings in Sutter and Stanislaus Counties, however, the pathogen is suspected to be widespread in California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 8

Uncertainty:

The full distribution of Fusarium brachygibbosum in California needs to be confirmed.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Fusarium brachygibbosum is C.

References:

Al-Mahmooli, I. H., Y. S. Al-Bahri, A. M. Al-Sadi, and M. L. Deadman.  2013.  First report of Euphorbia larica dieback caused by Fusarium brachygibbosum in Oman. Plant Disease, 97(5):687. http://apsjournals.apsnet.org/loi/pdis.

CABI.  2016.  Fusarium brachygibbosum basic datasheet.  Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/119707.

Farr, D.F., and A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved January 28, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

Marek, S. M., M. A. Yaghmour, and R. M. Bostock.  2013.  Fusarium spp., Cylindrocarpon spp., and environmental stress in the etiology of a canker disease of cold-stored fruit and nut tree seedlings in California.  Plant Disease 97: 259-270.  http://dx.doi.org/10.1094/PDIS-04-12-0355-RE .

Mirhosseini, H. A., V. Babaeizad, and L. Hashemi.  2014.  First report of Fusarium brachygibbosum causing leaf spot on oleander in Iran. Journal of Plant Pathology, 96(2):431. http://www.sipav.org/main/jpp/.

Renteria-Martinez, M. E., A. Meza-Moller, M. A. Guerra-Camacho, F. Romo-Tamayo, A. Ochoa-Meza, S. F. Moreno-Salazar.  2015.  First report of watermelon wilting caused by Fusarium brachygibbosum in Sonora, Mexico. Plant Disease, 99(5):729. http://apsjournals.apsnet.org/loi/pdis.

Seidle, A. J., M. A. Yaghmour, S. C. Kirkpatrick, T. R. Gordon, and R. M. Bostock.  2016.  First report of Fusarium brachygibbosum causing cankers in cold-stored, bare-root propagated almond trees in California.  (Submitted for publication: Plant Disease, shared with J. Chitambar, CDFA, August, 2016).

Van Coller, G. J., A. -L. Boutigny, L. Rose, T. J. Ward, S. C. Lamprecht, and A. Viljoen.  2013.  Head blight of wheat in South Africa is associated with numerous Fusarium species and chemotypes.  Conference paper: 12th European Fusarium Seminar, at Palais de la Bourse, Bordeaux, France, May 2013.  https://www.researchgate.net/publication/269700231_Head_blight_of_wheat_in_South_Africa_is_associated_with_numerous_Fusarium_species_and_chemotypes

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

Pest Rating: C

Posted by ls 

Fungi, Plant Pathogens

Podosphaera xanthii (Castagne) U. Braun & Shishkoff 2000

Watermelon leaf showing an even distribution of powdery mildew (Podosphaera xanthii) over the entire leaf surface. June 1995 Photo by Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org
Watermelon leaf showing an even distribution of powdery mildew (Podosphaera xanthii) over the entire leaf surface. June 1995.  Photo by Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org
California Pest Rating for
Podosphaera xanthii (Castagne) U. Braun & Shishkoff 2000
Pest Rating:  C
PEST RATING PROFILE
Initiating Event:

On July 13, 216, diseased leaves of Calibrachoa sp. plants exhibiting powdery mildew symptoms were collected during a regulatory nursery inspection, from a nursery in San Luis Obispo County, by San Luis Obispo County officials and sent to the CDFA Plant Pathology Laboratory for diagnoses.  Suzanne Latham, CDFA plant pathologist, identified the powdery mildew pathogen, Podosphaera xanthii, as the cause for the disease.  The pathogen was assigned a temporary “Z” rating as it has been reported earlier in California and is considered widely distributed.  That rating is reassessed here and a permanent rating is proposed.

History & Status:

Background: Podosphaera xanthii causes powdery mildew disease primarily in cucurbits under field and greenhouse conditions.  The pathogen has a wide host range which includes several ornamental plants, including Verbena. There are several pathogenically distinct races of P. xanthii, and plant resistance-breaking races are present in California.  The pathogen is widely distributed throughout the world (see ‘Worldwide Distribution’ below) as well as in California.  Within California, powdery mildew may be common in coastal and desert production areas, but is more common in fall in the San Joaquin Valley and Sacramento Valley (Davis, et al., 2012).

Podosphaera xanthii was previously known by several names including Sphaerotheca fuliginea and S. fusca.  In 2012, P. caricae-papayae was synonymized with the morphologically similar species P. xanthii (Braun & Cook, 2012) however, the synonymy of P. xanthii and P. caricae-papayae is in question given the molecular work of Takamatsu et al., (2010) who also inferred that further molecular and morphological studies would help to determine the correct taxonomic position of P. caricae-papayae within the genus Podosphaera in the family Erysiphaceae of the order Erysiphales.  (The CDFA risk assessment and rating for P. caricae-papayae is published separately.)

Hosts: Podosphaera xanthii has a wide host range which includes agricultural crops, ornamentals, few fruit, and weed plant species within eight or more families. Hosts include, Citrullus lanatus (watermelon), Cucumis melo (melon), C. sativus (cucumber), Cucurbita (pumpkin), C. maxima (giant pumpkin, C. moschata (pumpkin), C. mixta (pumpkin), C. pepo (synonym: C. ovifera; ornamental gourd), C. vulgaris, Lagenaria siceraria (bottle gourd), Luffa acutangula (angled luffa), L. aegyptiaca (loofah), L. cylindrica, Momordica charantia (bitter gourd), M. cochinchinensis (gac), Sechium edule (chayote), Cyamopsis tetragonoloba (guar), Phaseolus aconitifolius (synonym: Vigna aconitifolia; moth bean), P. coccineus (runner bean), P. vulgaris (common bean), Vigna mungo (black gram), V. radiata (mung bean), V. umbellata (rice-bean), V. unguiculata (synonym: V. catjang; cowpea), Cajanus cajan (pigeon pea), Sesamum indicum (sesame), Capsicum frutescens (chili), Solanum melongena (eggplant),  Hibiscus mutabilis (cottonrose), H. syriacus (shrubby althaea), Hoheria lyallii (synonym: H. populnea; lacebark), Malva pusilla (round-leaved mallow), Carica papaya (papaya), Coriaria arborea (tree tutu), Kalanchoe blossfeldiana (flaming katy), Petunia x hybrid, , Verbena bonariensis (purpletop vervain), V. brasilensis (Brazilian verbena), V. canadensis (clump verbena), Verbena x hybrida (synonym: V. hortensis; garden verbena), V. incisa, V. lasiostachys (western vervain), V. litoralis (blue vervain),V. macdougalii (MacDougal verbena), V. officinalis (common verbena), V. phlogiflora, V. rigida rigid verbena), Calendula sp. C. arvensis (field marigold), C. officinalis (pot marigold), C. palaestina (Palestine marigold),  Cosmos bipinnatus (garden cosmos), Calibrachoa sp.,  Cephalotus follicularis (Albany pitcher plant), Farfugium japonicum (leopard plant), Glandularia pulchella (South American mock vervain), Gynostemma pentaphyllum (jiagulan), Gerbera jamesonii (African daisy), Gynura bicolor (Okinawan spinach), Helianthus annuus (sunflower), Heteropogon contortus (black speargrass), Jatropha gossypiifolia (bellyache bush), Ligularia sibirica, Medusagyne oppositifolia (jellyfish tree), Melampyrum nemorosum (wood cow-wheat), Melothria japonica (Japanese wild cucumber), Melothria sp. Parasenecio hastatus subsp. tanakae, Pericallis cruenta (common cineraria), Physalis alkekengi (Chinese lantern), Pisum sativum (pea), Pulicaria dysenterica (meadow false fleabane), Senecio chrysanthemoides , S. grahamii, S. hercynicus, S. nemorensis, Impatiens hawker (New Guinea impatiens), Ageratum conyzoides (billy goat weed), Bidens bipinnata (Spanish needles), B. cernua (nodding beggarticks), B. frondosa (devil’s beggartick), B. pilosa (blackjack), B. tripartita (three-lobe beggarticks), Boehmeria nivea (Chinese grass), Buddleja brasiliensis, B. salviifolia, Xanthium californicum (synonym: X. strumarium var. canadense; Canada cocklebur), Xanthium italicum, X. pensylvanicum, X. spinosum, X. strumarium (common cocklebur), X. spinosum (spiny cocklebur) Zinnia elegans (zinnia), (CABI, 2016; Farr & Rossman, 2016).

Symptoms:  Powdery mildew symptoms on cucurbits: the disease first appears as pale yellow spots on stems, petioles, and leaves.  These spots enlarge as white powdery fungal growth comprising primarily of asexual spores (conidia) develops on upper and under leaf surfaces, petioles, and stems of infected plants, usually developing first on crown leaves, shaded lower leaves, and leaf undersurfaces.  Affected leaves become dull, chlorotic and may wilt and eventually turn brown and papery (Davis et al., 2012).  Older plants are initially infected and infected leaves usually wither and die.  Premature senescence may occur.  Fruit infection occurs rarely in cucumber and watermelon.  Minute dark brown chasmothecia (sexually produced, closed fruiting structures) have been rarely observed in infected cucurbits in the USA and may be easily overlooked. They may develop late in the season, and the sexual spores within the structures are protected from adverse conditions.  Symptoms are less common on cucumber and melon as many commercial cultivars are resistant to the pathogen (McGrath, 2011).

Disease cycle:  Podosphaera xanthii is an obligate parasite.  Primary sources of inoculum include conidia which can be dispersed over long distances and remain viable for 7-8 days.  The fungus grows on the surface of plant tissue and invades by sending feeding organs (haustoria) into the plants epidermal cells only in order to obtain nutrients.  Mycelium produces conidiophores on the plant surface.  Each conidiophore produces chains of conidia (spores) that are dispersed by air currents.  Powdery mildew develops quickly under favorable conditions of dense plant growth and low light intensity.  High relative humidity is favorable for infection and conidial survival, and infection can occur as low as 50% relative humidity.  Dry conditions favor colonization, sporulation, and dispersal, however, rain and free moisture on plant surfaces are unfavorable.  Optimum temperature for disease development is 20-27°C with infection occurring at 10-32°C.  Powdery mildew development is arrested at 38°C and higher temperatures.  As an obligate parasite, P. xanthii requires living host plants for survival, however, it may also survive as chasmothecia which have been reported rarely in the United States (CABI, 2016; McGrath, 2011).

Damage Potential:  Powdery mildew can diminish the photosynthetic regions of cucurbit leaves. Severely infected leaves turn brown and shriveled.  Fruit quality and yield are reduced.  In squash, fruit quality is reduced by sunscald and premature ripening resulting in poor storability, in melon, incomplete ripening and poor flavor occurs, and pumpkin fruit may be shriveled and discolored (CABI, 2016).  Late fruit usually fail to mature and are small and misshapen.  Stress from disease can result in speckling and oedema on fruit rind.  Powdery mildew-infected plants can be weakened and predisposed to other diseases.  Podosphaera xanthii can be a major production problem of cucurbits in field and greenhouse conditions (McGrath, 2011).

Transmission:  Conidia (spores) are airborne and dispersed by wind currents.  Laboratory studies have shown that conidia remain viable for 7-8 days. On cucurbits in greenhouses conidia are released and spread from plant to plant via irrigation or air currents.  Conidia can overwinter on cucurbit plants in a greenhouse and then be dispersed from greenhouse to field crops during spring and summer.  Non-cucurbit hosts are not a major source of inoculum due to pathological specialization (CABI, 2016; McGrath, 2011).

Survival:  During cool weather, conidia production ceases and powdery mildew fungi overwinter as chasmothecia and mycelium in weeds and dormant plant tissue. However, the sexual (teleomorph) stage has only been found in California greenhouses and reported for the first time in greenhouse grown squash and melons in Salinas, California (Ramos et al., 2010-2011).  Constant greenhouse growth conditions could perpetuate the asexual stage of the fungus.

Worldwide Distribution: Asia: Armenia, Azerbaijan, Bangladesh, China, Republic of Georgia, India, Iran, Iraq, Israel, Japan, Republic of Korea, Kyrgyzstan, Lebanon, Myanmar, Oman, Pakistan, Saudi Arabia, Singapore, Taiwan, Turkey, Turkmenistan Uzbekistan, Vietnam; Africa: Egypt, Ethiopia, Libya, Somalia, South Africa, Sudan, Tunisia; North America: Canada, Mexico, USA; Central America and Caribbean: Cuba, Puerto Rico; South America: Argentina, Bolivia, Brazil, Nicaragua, Uruguay, Venezuela; Europe: Austria, Bulgaria, Czech Republic, (former) Czechoslovakia, Denmark, Estonia, Finland, Former USSR, Romania, France, Germany, Greece, Hungary, Ireland, Italy, Lithuania, Netherlands, Norway, Poland, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, United Kingdom, Ukraine, Yugoslavia (Serbia and Montenegro); Oceania: Australia, New Zealand, Samoa (CABI, 2016; Farr & Rossman, 2016).

Official Control: Podosphaera xanthii is on the ‘Harmful Organism List’ for Guatemala (USDA-PCIT, 2016).

California Distribution: San Luis Obispo, Solano, and Yolo (CDFA Pest and Damage Records); San Joaquin Valley and Sacramento Valley counties, coastal and desert cucurbit production areas (Davis, et al., 2012).

California Interceptions:  None reported.

The risk Podosphaera xanthii would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2) – Powdery mildew of cucurbits Podosphaera xanthii can occur in coastal and desert production regions, and is common in fall in the San Joaquin Valley and Sacramento Valley. Powdery mildew thrives in warm and humid environments. Low light levels, high humidity, and moderate temperature enhance disease development.  Dry conditions favor conidia production and dispersal.  The pathogen is already widely distributed within cucurbit production regions of the state.   

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is High (3) – Podosphaera xanthii has a wide host range that includes agricultural crops – primarily cucurbits, ornamentals, few fruit and weed plants.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is High (3) – Under suitable climate conditions, airborne conidia are produced in abundance and readily spread by wind currents to non-infected sites.  Within and outside greenhouse environments, the pathogen is capable of rapidly spreading to non-infested host plants as well as other sites where host plants are grown.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is High (3) – The pathogen can potentially cause significant losses in plant growth and crop yield. Powdery mildew infections could lower crop yield and value causing significant losses in production – especially with use of protective and eradicative fungicides.  It could result in loss of markets, and change in cultivation practices to prevent the spread of inocula to non-infected, healthy plants.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2) – The powdery mildew pathogen could significantly impact home/urban gardening and/or ornamental plantings.  

Consequences of Introduction to California for Podosphaera xanthii:

Add up the total score and include it here. (Score)

-Low = 5-8 points

-Medium = 9-12 points

–High = 13-15 points

Total points obtained on evaluation of consequences of introduction of P. xanthii to California = (13).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

-Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is High (-3).  Powdery mildew of cucurbits caused by Podosphaera xanthii is widely distributed in California. 

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 10

Uncertainty:

None.

Remark:

The assessment of risk of Podosphaera xanthii distinctly documents its economic importance to California agriculture and environment and its widespread distribution within cucurbit production regions of the State.  Due to its biological capacity for rapid spread and its current widespread instate status, it is highly unlikely that the powdery mildew pathogen of cucurbits can be eradicated from California.  However, control measures, including use of protectant fungicides and resistant varieties, have proven successful in significantly reducing disease intensities and spread (CABI, 2016).  Therefore, a ‘C’ rating is proposed for this pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Podosphaera xanthii is C.

References:

Braun, U. and R. T. A. Cook.  2012.  Taxonomic manual of the Erysiphales (Powdery Mildews).  Centraalbureau voor Schimmelcultures, vol. 11, 707 p.

CABI.  2016.  Podosphaera xanthii (powdery mildew of cucurbits) full datasheet.  http://www.cabi.org/cpc/datasheet/50922.

Davis, R. M., T. A. Turini, B. J. Aegerter, and J. J. Stapleton.  2012.  Cucurbits powdery mildew pathogens: Sphaerotheca fuliginea (=Podosphaera xanthii) and Erysiphe cichoracearum (=Golovinomyces cichoracearum).  UC IPM Pest Management Guidelines: Cucurbits UC ANR Publication 3445. http://ipm.ucanr.edu/PMG/r116100711.html .

Farr, D.F., and A. Y. Rossman.  2016.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved January 28, 2016, from http://nt.ars-grin.gov/fungaldatabases/.

McGrath, M. T.  2011.  Vegetables: powdery mildew of cucurbits.  Vegetable MD Online, Cooperative Extension, New York State, Cornell University.  Fact sheet Page: 732.30 Date: June 2011.  http://vegetablemdonline.ppath.cornell.edu/

Ramos, C. B., K. Maruthachalam, J. D. McCreight, and R. S. Garcia Estrada.  2010-2011. Podosphaera xanthii but not Golovinomyces cichoracearum infects cucurbits in a greenhouse at Salinas, California.  Cucurbit Genetics Cooperative Report 33-34: 24-28.

Takamatsu, S., S. Ninomi, M. Harada and M. Havrylenko.  2010.  Molecular phylogenetic analyses reveal a close evolutionary relationship between Podosphaera (Erysiphales: Erysiphaceae) and its rosaceous hosts.  Persoonia, 24, 38-48.

USDA PCIT.  2016.  USDA Phytosanitary Certificate Issuance & Tracking System.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

 PEST RATING:  C

Posted by ls

Fungi, Plant Pathogens

Phyllosticta yuccae Bissett 1986

California Pest Rating for
Phyllosticta yuccae Bissett 1986
Pest Rating: C
PEST RATING PROFILE
Initiating Event:

On June 17, 2016 Yucca elephantipes (Adam’s needle) plants exhibiting leaf spot symptoms were intercepted at a nursery in San Diego County by San Diego County officials.  The shipment had originated in Florida.  Samples of symptomatic leaves were collected by the County and sent to the CDFA Plant Pathology Laboratory for disease diagnosis.  On July 17, 2016 Suzanne Latham, CDFA plant pathologist, identified the fungal pathogen, Phyllosticta yuccae, as the cause for the disease.   The pathogen has not been previously reported in California and therefore, was assigned a temporary Q rating.  Subsequent action taken by CDFA resulted in prevention of the shipment from introduction to California. The risk of infestation of Phyllosticta yuccae in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background:  Phyllosticta yuccae causes leaf blotch disease in Yucca plants.

Disease cycle:  It is likely that Phyllosticta yuccae has a similar life cycle to that of other Phyllosticta species and overwinters as conidia (asexual spores) in pycnidia (asexual fruiting structures) and ascospores (sexual spores) in perithecia (sexual fruiting structures) in infected plant leaf debris. Conidia and ascospores are only released when the fruiting structures become thoroughly wet.  Conidia are exuded from pycnidia in mucoid mass and are washed down or splashed away by rain or overhead irrigation water.  Ascospores are shot out forcibly from perithecia and carried by air currents.  On landing on host leaf surfaces, conidia or ascospores are germinate and infect plant tissue of young leaves.  Pycnidia are produced within lesions and provide conidia for secondary infections of plants (Agrios, 2005).

Dispersal and spread: rain/water splash, air currents, infected plant material and debris.

Hosts:  Yucca sp., Y. aloifolia, Y. elephantipes, Y. filamentosa (Farr & Rossman, 2016).

Symptoms:  Phyllosticta yuccae infections result in production of leaf spots in Yucca plants.  Initial symptoms include dark brown, elliptical, and scattered lesions which later become grey at the center with a reddish brown margin, irregular and coalesced (Silva et al., 2013).

Disease Potential:  Symptomatic Yucca plants infected with Phyllosticta yuccae may be more of a serious problem for nursery greenhouse productions where favorable wet requirements for disease development and spread are more likely to occur under controlled environments than in open field environments in California.  The disease could negatively impact value and marketability of nursery-grown Yucca plants.

Worldwide Distribution: Asia: Iran; Caribbean: Dominican Republic; North America: Canada, USA (Florida), Guatemala; South America: Brazil; Oceania: New Zealand (Farr & Rossman, 2016; Silva et al., 2013).

Official Control:  Currently, Phyllosticta yuccae has a temporary Q rating in California.

California Distribution:  Phyllosticta yuccae is not established in California.

California Interceptions: Phyllosticta yuccae was detected once in a shipment of Yucca elephantipes plants from Florida and destined to a San Diego nursery.

The risk Phyllosticta yuccae would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2): Yucca plants. grow naturally under dry conditions in southern California.  Under those natural conditions, Phyllosticta yuccae may not receive adequate wet conditions for infection and spread.  However, certain species of the host plant may be grown as residential and commercial landscape ornamentals in coastal regions of southern and central California under favorable environments for disease development.     

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1):  The host range is limited to Yucca spp.   

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

Risk is Medium (2): Phyllosticta yuccae has high reproductive potential, however, the dispersal of spores from fruiting structures is dependent on wet conditions.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Low (1): Nursery grown Yucca plants infected with Phyllosticta yuccae and exhibiting leaf blotch/spot symptoms could lower crop value and marketability.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

 Risk is Medium (2):  Under favorable conditions for disease development, Phyllosticta yuccae may significantly impact ornamental plantings of commercially and home grown Yucca plants.     

Consequences of Introduction to California for Phyllosticta yuccae:

Add up the total score and include it here. (Score)

–Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 8 (Low).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

–Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Not Established (0).  Phyllosticta yuccae is not established in California.   

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 8 (Low).

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Phyllosticta yuccae is C.

References:

Agrios, G. N.  2005.  Plant Pathology (Fifth Edition).  Elsevier Academic Press, USA.  922 p.

Farr, D. F. and A. Y. Rossman.  2016.   Fungal databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved August 24, 2016 from http://nt.ars-grin.gov/fungaldatabases/.

Ingram, S.  2008.  Cacti, Agaves and Yuccas of California and Nevada.  Pacific Horticulture, 69 (3): http://www.pacifichorticulture.org/articles/cacti-agaves-and-yuccas-of-california-and-nevada/

Silva, A.D.A., Pinho, D.B., Jr., Hora, B.T., and Pereira, O.L. 2013. First Report of Leaf Spot Caused by Phyllosticta yuccae on Yucca filamentosa in Brazil. Plant Disease 97: 1257.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

PEST RATING:  C

Posted by ls