Tag Archives: plant pathogens

Phytophthora hedraiandra de Cock & Man in’t Veld

April 9, 2015 Admin

California Pest Rating for

Phytophthora hedraiandra de Cock & Man in’t Veld

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

Recently, Suzanne Latham, CDFA plant pathologist, detected Phytophthora hedraiaindra in Arctostaphylos pumila samples that were collected from a nursery in Monterey County during an inspection related to an earlier detection of P. tentaculata. In December 2014, the pathogen had also been detected in Arctostaphylos plants propagated in a nursery in Alameda County. This nursery had requested the CDFA Plant Pathology Laboratory to test some Arctostaphylos plants for Phytophthora spp. before they were to be released for planting. The nursery baited the water flow-through the potted plants with Rhododendron and Oregano tissue that were provided by the CDFA Lab and returned the same for analysis. Suzanne Latham, CDFA plant pathologist, confirmed the detection of Phytophthora hedraiandra in culture from Rhododendron leaf baits. The collection of official samples and trace forward investigations are currently in process related to this detection. Phytophthora hedraiandra was initially detected in San Francisco, California 2013 on Arctopstaphylos plants. Arctopstaphylos native plants extracted from a natural site in San Francisco were propagated at three different nurseries in San Francisco, Berkley, and Santa Cruz. Similar to the 2014 incident, the water flow-through of potted Arctopstaphylos plants was baited with plant tissue which was then sent to the CDFA Lab for testing. Cheryl Blomquist, CDFA plant pathologist, identified P. hedraiandra in the samples. The detection was confirmed by the USDA Lab in Beltsville, Maryland. All potted plants were eventually destroyed. Phytophthora hedraiandra currently has a Q rating that is herein reassessed for the proposal of a permanent rating.

History & Status:

Background: Since the discovery of Phytophthora ramorum, causal organism for the Sudden Oak Disease, there has been an increase of surveys throughout the world, for Phytophthora spp. which resulted in the identification of several new species, including P. hedraiandra. Phytophthora hedraiandra was first discovered in 2001 on leaf spots of Viburnum sp. in the Netherlands (de Cock & Lévesque, 2004).

Hosts: The full host range of Phytophthora hedraiandra is yet not known. Presently, only certain species of Rhododendron (azalea) and Viburnum are reported as susceptible hosts (CABI, 2014; EPPO, 2014). Fagus sylvatica (common beech) is also listed as a host (CABI, 2014; Hejna, et al., 2014). According to CDFA Plant Pathology Detection Records (2014-2015), Arctostaphylos spp. appears to be a new host for this pathogen.

Symptoms: Plant symptoms caused by Phytophthora hedraiandra infections may vary with the infected host. Symptoms in Viburnum include wilting, leaf spots, stem cankers and root and collar rots, while symptoms in Rhododendron include leaf lesions and shoot dieback (Henricot & Waghorn, 2014; Schwingle, et al., 2006, 2007). Symptoms in Fagus sylvatica include root rot, leaf chlorosis and wilting (Hejna et al., 2014).

Damage Potential: Currently, there are no reports on quantitative economic losses in plant production caused by Phytophthora hedraiandra. However, infestations may result in significant damage and loss in production and stands of host plants by causing root and collar rots of infected plants. Nursery ornamentals and plants grown in natural ecosystems are particularly affected. In general for Phytophthora spp., young seedlings of trees and annual plants may be killed within a few day, weeks or months (Agrios, 2005).

Disease Cycle: Generally, species of Phytophthora that cause root and stem rots survive cold winters or hot and dry summers as thick-walled, resting spores (oospores and chlamydospores) or mycelium in infected roots, stems or soil. During spring, the oospores and chlamydospores germinate to produce motile spores (zoospores) that swim around in soil water and roots of susceptible hosts. The pathogen infects the host at the soil line causing water soaking and darkening of the trunk bark. This infected area enlarges and may encircle the entire stem of small plants which wilt and eventually die. On large plants and trees, the infected, necrotic area may be on one side of the stem and become a depressed canker below the level of the healthy bark. Collar rot canker may spread down the root system. Roots are invaded at the crown area or at ground level. Mycelium and zoospores grow in abundance in cool, wet weather causing damage where the soil is too wet for normal growth of susceptible plants and low temperatures (15-23°C) prevail (Agrios, 2005).

Transmission: Infected soils, plants, nursery and planting stock, seedlings, run-off and splash irrigation and rain water, cultivation equipment and tools that may spread contaminated soil and plant materials to non-infected sites (Yang et al., 2012).

Worldwide Distribution: Europe: Italy, Netherlands, Slovenia, Spain, United Kingdom; North America: USA; Oceania: Australia.

In the USA, Phytophthora hedraiandra has been found in California, Minnesota, and Virginia (CABI, 2014; EPPO, 2014).

Official Control: None reported.

California Distribution: Alameda, Monterey and San Francisco Counties (see ‘Initiating Event’).

California Interceptions: The pathogen has not been intercepted in quarantine shipments of plants.

The risk Phytophthora hedraiandra 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 High (3) – Phytophthora hedraiandra has already been detected in few nurseries in California. Within California, it is likely to establish in cool, wet climates in susceptible hosts.

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 full host range of Phytophthora hedraiandra is yet not known. Presently, only certain species of Rhododendron (azalea) and Viburnum, and Fagus sylvatica (common beech) are reported as susceptible hosts.

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) – Phytophthora hedraiandra is primarily spread artificially via infested soils, plants, nursery and planting stock, seedlings, run-off and splash irrigation water, cultivation equipment and tools that may spread contaminated soil and plant materials to non-infected sites.

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) – Although quantitative economic losses in plant production have not reported, the potential for infected plants to result in root and collar rot, canker, leaf lesions and shoot dieback could decrease stands on non-infected plants, increase production costs and cause loss of market of infected nursery stocks. The capability of the pathogen to survive and spread in infected soils and irrigation water could require changes in normal cultivation practices of 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 Medium (2) – Currently, the host range and geographic distribution of P. hedraiandra are not fully known. The few known host plants (see ‘Hosts’ above) can be found in natural ecological habitats as well as in nursery environments. Subsequently, under favorable climate conditions, natural plant communities and ecosystems, as well as home/urban gardening and ornamentals may be negatively impacted.

Consequences of Introduction to California for Phytophthora hedraiandra:

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 Phytophthora niederhauserii 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)

-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). To date, Phytophthora hedraiandra has been detected in three California coastal counties (Alameda, Monterey and San Francisco Counties) on the same host (Arctostaphylos spp.) under similar climate (coastal nurseries).

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.

Uncertainty:

The full host range and in-state distribution of Phytophthora hedraiandra is not currently known. To date, in California, the pathogen has only been detected from Arctostaphylos plants propagated in nurseries. Continued statewide surveys for Phytophthora spp. occurring in nurseries and natural ecosystems (e.g. restoration sites) will contribute to the present knowledge of this pathogen group as well as that of P. hedraiandra. Consequently, the current proposed rating of P. hedraiandra may be affected.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Phytophthora hedraiandra is B.

References:

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

CABI. 2014. Phytophthora hedraiandra datasheet (basic) report. Crop Protection Compendium. www.cabi.org/cpc/

de Cock A. W. A. M. and C. A. Lévesque. 2004. New species of Pythium and Phytophthora. Studies in Mycology 50: 481-487.

EPPO. 2014. Phytophthora hedraiandra (PHYTHD). European and Mediterranean Plant Protection Organization PQR database. http://www.eppo.int/DATABASES/pqr/pqr.htm.

Farr, D.F., & Rossman, A.Y. 2014. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved November 10, 2014, from http://nt.ars-grin.gov/fungaldatabases/ .

Henricot, B. and I. Waghorn. 2014. First report of collar and root rot caused by Phytophthora hedraiandra on Viburnum in the UK. New Disease Reports 29:8. http://dx.doi.org/10.5197/j.2044-0588.2014.029.008.

Hejna M., K. Cerny, L. Havrdova, and M. Mrazkova. 2014. First report of Phytophthora hedraiandra causing Rhododendron dieback and root rot of Common Beech in the Czech Republic. Plant Disease 98:1,434.2. http://dx.doi.org/10.1094/PDIS-04-14-0339-PDN

NAPPO. 2006. Phytophthora hedraiandra de Cock & Man in’t Veld First detection of Phytophthora hedraiandra in the United States and North America. North American Plant Protection Organization’s (NAPPO Phytosanitary Alert System): http://www.pestalert.org/viewNewsAlert.cfm?naid=4

Schwingle, B. W., J. A. Smith and R. A. Blanchette, S. Gould, and B. L. Blanchette. 2006. First report of dieback and leaf lesions on Rhododendrons sp. caused by Phytophthora hedraiandra in the United States. Plant Disease 90:109. http://dx.doi.org/10.1094/PD-90-0109A.

Schwingle, B. W., J. A. Smith and R. A. Blanchette. 2007. Phytophthora species associated with diseased woody ornamentals in Minnesota nurseries. Plant Disease 91:97-102.

Yang, X. P. A. Richardson, S. R. Ghimire, P. Kong, and C. X. Hong. 2012. Phytophthora hedraiandra detected from irrigation water at a perennial ornamental plant nursery in Virginia. Plant Disease 96:915.3. http://dx.doi.org/10.1094/PDIS-07-11-0614-PDN.

Responsible Party:

Dr. 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

Bacteria, Plant Pathogens

Rhodococcus fascians

April 9, 2015 Admin

California Pest Rating for

Rhodococcus fascians

Pest Rating: C

PEST RATING PROFILE

Initiating Event:

On April 10, 2014, Dr. Jennifer Randall, Associate Research Professor, New Mexico State University, notified Nick Condos, Director, Plant Health and Pest Prevention Services, California Department of Food and Agriculture (CDFA), of her confirmed identification of the plant pathogen, Rhodococcus fascians associated with abnormal pistachio UCB-1 rootstocks from several orchards in California, as well as from a California nursery in Stanislaus County where the rootstocks had originated. Subsequent communications between CDFA and Craig Kallsen, Citrus and Pistachio Farm Advisor for Kern County, indicated that thousands of pistachio rootstocks obtained from the same nursery and planted in the southern San Joaquin Valley since 2011-2014, were performing poorly and exhibiting similar symptoms to those observed and tested positive for R. fascians by Dr. Randall. The Nursery rootstocks were obtained from the University of California Foundation Plant Services. Currently, R. fascians is a C rated pathogen by CDFA. The pest rating for the bacterial pathogen is herein reanalyzed under CDFA’s new pest risk analysis process to reaffirm its permanent rating.

History & Status:

Background: Rhodococcus fascians is a yellow-orange gram positive, aerobic, non-spore forming, non-motile bacteria with cell walls containing mycolic acid. They may have mycelial growth with fragmentation into rods or coccoid forms. The species was previously known as Corynebacterium fascians, but based on cell wall composition and DNA base composition the species was allocated to the genus Rhodococcus as R. fascians (Goodfellow 1984) in the order Actinomycetales and family Norcardiaceae.

Rhodococcus fascians is a plant pathogen that primarily lives on the exterior surfaces of plants but to a lesser degree, can also be found within plant cells. However, it is not considered to be systemic in plants. There are reports of several bacterial isolates identified as R. fascians that were found in various non-plant habitats – including ice and polar seawater, however, none of those isolates have been examined for phytopathogenicity (Putman & Miller, 2007). To cause plant disease, isolates of R. fascians must contain a plasmid with virulence genes for phytopathogenicity. Once R. fascians enters a plant, it can produce cytokinin and auxin and alter the normal ratio between the two hormones. This hormone production can block production of abscisic acid and gibberillic acid in plants.

Hosts: Rhodococcus fascians has a host range that includes 87 genera belonging to 40 plant families (CABI, 2014), however, this is considered a underestimated number. Putnam and Miller (2007) reported that the number of hosts should be expanded to at least 122 taxa. They considered several reported hosts as either unconfirmed, without published reports, of uncertain identity, or not naturally infected. Nevertheless, susceptible hosts include monocots and dicots, woody and herbaceous plants: mostly herbaceous perennial ornamentals, few woody plants, few vegetable crops and strawberry.

In California, detection of Rhodococcus fascians on ornamental plants has been reported (A. M. French: California plant disease host index 2^nd edition, updated January 11, 2014). However recently, Stamler et al., (2014) first reported the association of R. fascians on pistachio rootstocks.

Symptoms: Disease symptoms caused by R. fascians have often been overlooked and attributed to the crown gall bacterium Agrobacterium tumefaciens, viral infection, phytoplasmas, viroids, insect injury, nematodes, genetic causes, chemical substances produced by mixed bacterial populations, hormonal disturbance or crowding of plants in small plants (Putnam & Miller, 2007).

Symptoms caused by R. fascians range from witches’ broom and over-fasciation to leafy gall (Faivre-Amiot, 1967), similar to those caused by growth hormone imbalances. The level of symptom expression is dependent on the host plant genus, species and cultivar, age of the plant at time of infection (young growing tissue is more sensitive than older maturing tissue), bacterial strain (avirulent or virulent), and on plant growth conditions and the mode of infection. Symptoms in naturally infected plants include, proliferation of buds in leaf axils or at the base of stems; bunches of fleshy thick stems with misshapen and aborted leaves that develop at or below the crown of the host plant; proliferation of partially expanded buds called leafy galls; misshapen thickened leaves or shoots, expanded stems in ribbon-like growth or fasciation (formed when several hypertrophied shoots collapse); adventitious, amorphous growth from veins, petioles, or leaf edges; stunting; abnormal scales on bulbs; infrequent inhibition of root growth (Putnam & Miller, 2007). Generally, the root system is not affected, although severe infection can result in the main root becoming thickened with the inhibition of secondary roots (CABI, 2014).

In California, pistachio rootstocks associated with R. fascians exhibited symptoms that included shortened internodes, stunted growth, swollen lateral buds, bushy/bunchy growth pattern, twisted roots with virtually no lateral branching, and stem galls (Stamler et al., 2014).

Wounding of a plant host is not necessary for R. fascians infection and the pathogen does not preferentially enter the plant through natural opening. Symptoms can be produced when the bacteria are on the plant surface (CABI, 2014). However, R. fascians may have a prolonged epiphytic phase prior to symptom expression. As mentioned earlier, the presence of a plasmid with virulence genes is essential for phytopathogenicity (Putnam & Miller, 2007; Stamler et al., 2014). Symptoms are more severe and develop more rapidly when wounding occurs.

In nature, plant diseases caused by R. fascians requires moist conditions and moderate temperatures commonly occurring during late fall, mild winters and early spring, and can occur in acidic to slightly alkaline soils (Faivre-Amiot, 1967).

Transmission: The primary means of introduction of the bacterial pathogen to new, uninfested areas – fields or greenhouses, is most likely through contaminated planting material (Putnam & Miller, 2007; CABI, 2014). Putnam and Miller (2007) isolated pathogenic R. fascians from symptomatic in vitro plant tissue cultures. The pathogen is also known to be externally seed borne in some hosts including pea, nasturtium, greenhouse geranium, Marguerite daisy and carnation. Also, the pathogen is spread by irrigation water, water splash or rain and contaminated soil. The role of insects in natural disease transmission is not known, however under artificial conditions, transmission of R. fascians by aphids (Myzus persicae, M. ascalonicus) leading to disease has been reported (CABI, 2014).

Survival: It is not known if R. fascians truly resides in soil as do other members of the genus. However, it has been reported to survive in soils for 3 months or for longer periods of 4-5 years. Putnam & Miller (2007), hold that R. fascians survives in soil only as long as host tissue remains. Long term survival in natural environments is due to the ability of the pathogen to tolerate prolonged nutrient starvation. The detection of R. fascians in ice and polar seawater indicates that it can survive for very long periods at low temperatures, which further indicates that periods of chilling temperatures that are often required for certain plants will not kill the pathogen. The pathogen is also able to survive on rotation crops (CABI, 2014).

Worldwide Distribution: Rhodococcus facians is distributed in 22 countries in Europe, Asia (India, Iran, Israel), Africa (Egypt), Guatemala, Canada (British Columbia, Manitoba, Ontario, Saskatchewan), Mexico, Australia (New South Wales), New Zealand, and the USA (19 states, including California).

Official Control: R. fascians is a quarantine pest in Japan, Argentina and Peru (CABI, 2014).

California Distribution: While there has not been a statewide survey for R. fascians, early CDFA detection records of 1950-1983 document the pathogen being widespread in northern and southern, coastal counties, and northern mountain and foothill counties of California. The 2014 detection of the pathogen on pistachio includes fields and nursery in the Southern San Joaquin Valley (Kern, Tulare and Stanislaus Counties).

California Interceptions: CDFA records indicate detections of R. fascians in herbaceous ornamental plants grown in nurseries. It is quite likely that disease symptoms induced by R. fascians were either overlooked or attributed to other pathogens, chemical, hormonal or cultural factors and therefore, never recorded or recorded to a lesser extent than the actual impact caused by the pathogen.

The risk Rhodococcus fascians 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:

Risk is High (3) – Given the already widespread distribution of R. fascians in 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 High (3) – R. fascians has a very broad host range of monocots and dicots, woody and herbaceous plants: mostly herbaceous perennial ornamentals, few woody plants, few vegetable crops and strawberry.

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

Risk is High (3) – As a bacterial pathogen, under optimal growth conditions of high moisture and moderate temperature, R. fascians primarily resides epiphytically on plants, has a high reproduction rate and readily spread through contaminated planting propagative material, seed, soil, and water.

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

– 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) – Serious recurring economic losses due to R. fascians can be incurred by the nursery industry. R. fascians infestations could lower crop yield and crop values thereby increasing production costs; infestation of nursery herbaceous plants and field crops could result in great loss in markets and alter normal cultural practices to insure pathogen-free propagative plant material.

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

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) – R. fascians may significantly impact ornamental cultivation and home/urban gardening and cultivation practices.

**Consequences of Introduction to California for Rhodococcus fascians:**

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 R. fascians to California = (14).

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)

Evaluation is (-3). R. fascians is ubiquitous and already established in diverse climate areas throughout 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

Uncertainty:

While there currently remains much unknown regarding the biology of R. fascians (Putnam & Miller, 2007), as well its pathogenic relationship with several hosts including pistachio (Stamler et al., 2014), it is not likely that additional information will qualify the pathogen for a higher rating. Indeed, revelation of further plant hosts, plasmid-borne virulent strains, and detection localities will only strengthen the C-rating of this already widespread pathogen, nevertheless, emphasizing its importance as a bacterial plant pathogen causing serious economic losses to plant production.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Rhodococcus fascians is C.

References:

CABI. 2014. Rhodococcus fascians datasheet. http://www.cabi.org/cpc/datasheet/15332

Faivre-Amiot A, 1967. Quelques observations sur la presence de Corynebacterium fascians (Tilford) Dowson dans les cultures maraicheres et florales en France. Phytiatrie-Phytopharmacie, 16:165-176.

Goodfellow M, 1992. The family Nocardiaceae. In: Balows A, Trnper HG, Dworkin M, Harder W, Schleifer KH, eds. The Prokaryotes. Berlin, Germany: Springer-Verlag, 1188-1213.

Kallsen, C. 2014. Rhodococcus fascians associated with some UCB-1 rootstocks. Kern Pistachio News, University of California Cooperative Extension, April, 2014.

Kallsen, Craig, University of California Cooperative Extension Bakersfield: email to Duane Schnabel, California Department of Food and Agriculture, April 22, 2014.

Randall, Jennifer, New Mexico State University: email to Nick Condos, California Department of Food and Agriculture, April 10, 2014.

Putnam, M. 2014. Demystifying Rhodococcus fascians. Digger, February, 2014: 33-37.

Putnam, M. L. and M. L. Miller. 2007. Rhodococcus fascians in herbaceous perennials. Plant Disease, 91 (9): 1064-1076.

Stamler, R. A., J. Kilcrease, R. J. Heerama, C. E. Kallsen, and J. J. Randall. 2014. Rhodococcus sp. associated with Pistachio Bushy Top Syndrome in California and Arizona. Plant Disease (submitted).

Responsible Party:

Pest Rating: C

Posted by ls

Plant Pathogens, Viruses and viroids

Pea Seed-borne Mosaic Virus (PSbMV)

April 9, 2015 Admin

California Pest Rating for

Pea Seed-borne Mosaic Virus (PSbMV)

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

There is no initiating event. The risk of infestation of Pea seed-borne mosaic virus in California is evaluated and a permanent rating is proposed.

History & Status:

Background: In 1966 a virus disease of pea was first reported in Europe. The same virus was also described in Japan as Pea seed-borne mosaic virus. During the early 1980s the virus was also discovered in New Zealand and England and is now known to be widespread throughout the globe due to the movement of infected pea seeds through high international trade. In California, the pathogen was first discovered in 2004 on pea cultivated in a field in Monterey County.

Pea seed-borne mosaic virus belongs to the genus Potyvirus in the family Potyviridae and RNA viruses group. The nucleic acid consists of a positive-sense single stranded RNA. The virus consists of several strains or pathovars that are serologically closely related. Three strains of PSbMV (P1, P2 and P4) have been identified and the most common strains include P-1 and P-4 from pea and the L-1 from lentil. Usually, differential hosts have been used to identify specific strains (Larsen, 2001).

Hosts: The host range for PSbMV includes at least 47 plant species belonging to 12 families. However, only three hosts are considered to be economically important, namely, Pisum sativum (pea), Lens culinaris subsp. culinaris (lentil), and Vicia faba (bean). Chickpea is also a susceptible host however, there is no evidence that it transmitted through contaminated seed. Other hosts include a wide range of experimental hosts.

Symptoms: Symptoms on peas are affected by age of plant at the time of infection, temperature, virus strain or pathotype and plant genotype. Symptoms may develop in as few as 3 days after infection. Certain pea cultivars never express symptoms (Khetarpal & Maury, 1987). Symptoms may be more severe on plants germinating from infected seed. Symptoms include general stunting, leaf mild chlorosis, shortening and downward rolling of leaflets, vein clearing and swelling, rosetting (due to reduction of internodal growth), mosaic, distorted flower or seed pods and failure to set pods. However, symptoms disappear soon after infection. Seed coats of PSbMV-infected seed may become cracked, split or banded and often serve as indicators of possible PSbMV infection although these symptoms may also be caused by physiological or environmental factors. Contrarily, healthy appearing seeds with normal seed coats may also bear the virus pathogen (CABI, 2014; Larson, 2001).

Damage Potential: The loss of market due to infected seed is a significant factor in the estimated economic loss caused by the virus. As much as 36% reduction in pea seed yields are estimated to be due to PSbMV infection (Khetarpal & Maury, 1987). Seed infections greater than 30% have been reported (CABI, 2014).

Transmission: The most common means of long-distance transmission of PSbMV is through infected seed. The virus infects seed internally and all parts of inflorescences from infected plants contain the virus. Infected seed is an important means of introducing the virus into new, non-infected areas. Spread from plant to plant is brought about mainly by aphid vectors and mechanical transmission. The virus can be transmitted in a non-persistent manner by 21 aphid species. The pea aphid (Acyrthosiphon pisum), green peach aphid (Myzus persicae), and cotton aphid (Aphis gossypii) are the most common vectors. Natural aphid vectors are the pea aphid, cowpea aphid (Aphis craccivora), black bean aphid (Aphis fabae), Dactynotus escalanti, mint aphid (Ovatus crataegarius), and bird cherry-oat aphid (Rhopalosiphum padi). If aphid populations are high and uncontrolled during a growing season, then only a few PSbMV-infected seeds can result in spreading the disease over a large percentage of a field. Typically, the aphid vector can acquire the virus in 5 min and transmit it after a single probe of one minute or less (Larsen, 2001). Hampton and Mink (1975) reported that aphids acquire PSbMV and inoculate it in 10-90 sec feeding periods without requiring a latent period. High aphid populations are favored by cool growing seasons thereby enabling effective spread of PSbMV.

Worldwide Distribution: PSbMV is distributed worldwide largely due to the distribution of pea germplasm infected with the seed-transmitted virus (Larsen, 2001; Hampton et al., 1993). It is distributed in Asia: India, Iran, Israel, Japan, Jordan, Lebanon, Nepal, Pakistan, Syria, Taiwan, Turkey, Yemen; Africa: Algeria, Egypt, Ethiopia, Libya, Morocco, South Africa, Sudan, Tanzania, Tunisia, Zambia, Zimbabwe; North America: Canada, USA; South America: Brazil; Europe: Belgium, Bulgaria, Czech Republic, former Czechoslovakia, Denmark, Finland, France, Germany, Netherland, Poland, Romania, Russian Federation, Serbia, Slovakia, Sweden, Switzerland, United Kingdom, Yugoslavia; Oceania: Australia, New Zealand.

In the USA is it has been found in California, Idaho, Maryland, Minnesota, New York, Oregon, Vermont, Washington, and Wisconsin (CABI, 2014; EPPO, 2014).

Official Control: Since 1995, PSbMV has been listed by Argentina and Brazil as an A1 quarantine pathogen (EPPO, 2014). The pathogen is on the ‘Harmful Organism List’ for nine countries: Australia, Costa Rica, Georgia, Japan, Nambia, Nauru, South Africa, Taiwan and Uruguay (PCIT, 2014).

California Distribution: Monterey County, California.

California Interceptions: There are no official records of PSbMV detected in incoming plant shipments to California.

The risk Pea seed-borne mosaic virus 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:

Risk is Medium (2) – The establishment of PSbMV within CA is closely related to the establishment of its major hosts and associated aphid vector. Cultivation of pea and bean plants requires cool and humid climate – such as is found mainly along the California’s coastal regions. Already PSbMV is established in Monterey County, 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 Medium (2) – PSbMV has a moderate host range of 47 plant species belonging to 12 families. However, the main hosts of economic importance are pea, bean and lentil. The former two crops are in limited commercial production in California.

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

Risk is High (3) – The spread of PSbMV is through infected seed and several (21) Aphid species. The combination of both agents, plus the high rate of multiplication of the virus within an infected host render the pathogen a high risk potential for spread to non-infected sites.

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

– 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) –Incidence and spread of PSbMV could adversely affect pea and bean production in California by lowering crop yield, value, increasing production costs, affecting local and international markets, negatively change normal cultivation practices to prevent incidence of further occurrence and spread of the virus and its whitefly vector.

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

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) – Several weeds may be hosts of PSbMV and serve as sources of inoculum acquired by aphids against economically important hosts. However, several weed hosts may be asymptomatic and it is not known how well the whitefly vector will acquire the virus from such infected hosts that may comprise natural environments. The effect on these hosts in nature is not known. Nevertheless, PSbMV infections may impact home/urban gardening and cultivation of ornamentals.

Consequences of Introduction to California for Peas seed-borne mosaic virus

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 PSbMV to California = (12).

Evaluation is (-1).

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

Uncertainty:

Current field data is always needed on the probable establishment and spread of PSbMV beyond the known infested regions of Monterey County. Such information would be obtained through periodic surveys. Also not known is the distribution of the virus in natural environments and the potential that infected natural hosts may play in its possible spread to legume fields.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Pea seed-borne mosaic virus is B.

References:

CABI 2014. Pea seed-borne mosaic virus full datasheet. Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/1695

EPPO, 2014. Pea seed-borne mosaic virus (PSBMV0). New PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://newpqr.eppo.int

Hampton, R. O and G. I. Mink. 1975. Pea seed-borne mosaic virus. CMI/AAB Descriptions of Plant Viruses. No. 146, 4pp. Wellesbourne, UK: Association of Applied Biologists. http://www.dpvweb.net/dpv/showdpv.php?dpvno=146.

Hampton, R. O, J. M. Kraft, F. J. Muehlbauer. 1993. Minimizing the threat of seedborne pathogens in crop germ plasm: elimination of pea seedborne mosaic virus from the USDA-ARS germ plasm collection of Pisum sativum. Plant Disease, 77(3):220-224

Khetarpal R. K. and Y. Maury. 1987. Pea seed-borne mosaic virus: a review. Agronomie, 7(4):215-224

Larsen, R. C. 2001. Pea Seedborne mosaic virus. In: Compendium of Pea Diseases and Pests Second Edition. St.Paul, USA: APS Press, 37-38.

PCIT. 2014. USDA Phytosanitary Certificate Issuance & Tracking System. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Responsible Party:

Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Kweilingia divina (Syd.) Buriticá 1998

April 7, 2015 Admin

California Pest Rating for

Kweilingia divina (Syd.) Buriticá 1998

Pest Rating: A

PEST RATING PROFILE

Initiating Event:

In December 2014, Kweilingia divina was detected in a quarantine interception of bamboo leaves showing symptoms of rust, imported from Florida to California. The detection was made by Contra Costa Agricultural Commissioner’s office inspector and the associated pathogen was identified by Suzanne Latham, CDFA plant pathologist. This rust fungus had also been intercepted in 2006 by Los Angeles County in a similar shipment of bamboo from Hawaii. All infected plants were destroyed. The risk of introduction and establishment of Kweilingia divina in California is evaluated here and a permanent rating is proposed.

History & Status:

Background: The bamboo rust fungal pathogen, Kweilingia divina was originally ascribed as the type species of the genus Dasturella (D. divina) which was detected in infected bamboo leaves (Bambusa sp.) in 1943 (Mundkur & Kheswalla, 1943). However, in 1998, Dasterulla divina was renamed Kweilingia divina.

Kweilingia divina requires two different kinds of hosts to complete its life cycle (heteroecious), producing two types of specialized spores on each host, namely urediniospores and teliospores on bamboo and spermatia (pycniospores) and aeciospores on its alternate host, Catunaregam spinosa (mountain pomegranata). The pycnial and aecial state are not known in the New World (Farr & Rossman, 2015).

Hosts: Several species of bamboo including, Bambusa balcooa, B. bambos, B. domestica, B. multiplex, B. mutabilis, B. oldhami, B. polymorpha, B. tulda, B. shimadai, B. tuldoides, B. vulgaris, Dendrocalamus brandisii, D. hamiltonii, D. latiflorus, D. longispathus, D. strictus, Ischurochloa stenostachya, Ochlandra scriptoria, O. travancorica, Oxtenanthera sp.,O. abyssinica, O. nigrociliata, Phyllostachys bambusoides,Pleioblastus sp., Pseudoxytenanthera ritcheyi, Pseudosasa japonica var. usawai, P. usawai, Shibataea kumasaca, Thyrsostachys oliveri, T. sianensis, and the alternate, non-bamboo host Catunaregam spinosa (Blomquist et al., 2009; Cummins, 1971; Nelson & Goo, 2011; Farr & Rossman, 2015).

Symptoms: On bamboo, initial symptoms of infection are the presence of water-soaked, pinhead-sized flecks on the lower surface of leaves. Soon yellowish-orange to brown, elongate, interveinal, linearly aligned fruiting structures (uredinia) develop and produce urediniospores. On the corresponding side of the upper leaf surface, grayish-brown to dark brown lesions with yellowish halos for along the parallel veins. Numerous lesions may develop on a leaf surface or coalesce to form larger areas of tan-colored necrotic blight. Over time, brownish black linear structures (telia) develop within the lesions on the lower leaf, either inside old, degenerating uredinia or separately. Severely infected leaves defoliate prematurely (Nelson & Goo, 2011). The alternate host, Catunaregam spinosa is not present in California but is native to tropical Southeast Asia and tropical Africa.

Damage Potential: Bamboo is not a main cultivated crop in California. However, bamboo plants are grown and sold mainly as nursery ornamentals and commercial plantings in private residences, public parks, amusement parks, and other environments. The bamboo rust disease is a threat to these limited yet economically important regions where bamboo is grown in California. Rusted bamboo leaves are not only aesthetically unsightly but also negatively impact plant growth. Severe infestations of bamboo rust can result in defoliation and reduction in plant growth, vigor and stand. Once established in California, containment and management of the rust pathogen will be difficult as infected leaves produce masses of air-borne spores enabling long-range spread and infection.

Transmission: The pathogen is spread from plant to plant mainly by windblown spores. Urediniospores can be transported over several hundred kilometers by strong winds and washed down by rain to available hosts. Insects, animals, humans, and rain may also aid in spreading spores to non-infected plants. Infected nursery plants also aid in introducing and spreading the pathogen.

Worldwide Distribution: Asia: India, China, Hong Kong, Japan, Pakistan, Taiwan, Malaysia; Africa: Cote d’Ivoire, Ghana, Nigeria, North America: Mexico, USA; Oceania: Australia, New Calendonia, Samoa; Caribbean Islands: Cuba, Dominican Republic, Jamaica, Puerto Rico, Trinidad and Tobago, West Indies, Virgin Islands; Central America: Costa Rica; South America: Brazil, Guyana, Colombia, French Guiana (Farr & Rossman, 2015).

In the USA it has been reported from the Hawaiian Islands (Oahu, Hawaii, Kauai, and Maui). The detections in California resulted in the eradication of the disease (Blomquist et al., 2009; Nelson & Goo, 2011).

Official Control: None reported.

California Distribution: Bamboo rust pathogen, Kweilingia divina, is not established in California. All 2006 and 2014 intercepted shipments of infected bamboo plants were destroyed (see ‘Initiating Event’).

California Interceptions: Kweilingia divina was intercepted in Los Angeles in 2006 and in Contra Costa County in 2014.

The risk Kweilingia divina 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 High (3) – Kweilingia divina is able to establish a widespread distribution in California wherever bamboo is grown.

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 of Kweilingia divina is mainly limited to several species of bamboo. The alternate host does not exist in California.

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) – The infective spores of Kweilingia divina namely, urediniospores, are produced in abundance and are spread to healthy plants mainly by wind. Insects, animals, humans, rain, and infected nursery plants also aid in its 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 High (3) – Severe infestations of the bamboo rust pathogen could result in defoliation and reduction of plant growth, vigor and stand, and loss of markets. Nursery plantings are at risk being significantly impacted by the introduction of this pathogen. Without eradicative action subsequent to detection of bamboo rust-infected plants within greenhouse environments, there is the risk of spread to the outside environment. The spread of the rust pathogen would be difficult to manage due to its effective means of windblown transmission.

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

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) – Outbreaks of the disease could have significant impact on established bamboo ecosystems. Commercial bamboo plantings in public parks, resorts and plantings in private residences may be impacted by the bamboo rust pathogen subsequently triggering additional treatment programs.

Consequences of Introduction to California for Kweilingia divina

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 Kweilingia divina to California = (13).

-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: Kweilingia divina is not established in California (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 = 13

Uncertainty:

Future detection surveys for Kweilingia divina in nurseries and established bamboo groves are needed to gain further information of the probable introduction, establishment and distribution of this pathogen in California. This information could alter the proposed rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Kweilingia divina is A.

References:

Blomquist, C. L., J. M. McKemy, M. C. Aime, R. W. Orsburn and S. A. Kinnee. 2009. First report of bamboo rust caused by Kweilingia divina on Bambusa domestica in Los Angeles County, California. Plant Disease 93: 201. http://dx.doi.org/10.1094/PDIS-93-2-0201A

Cummins, G. B. 1971. The rust fungi of cereals, grasses and bamboos. Springer-Verlag New York Inc. 570 p.

Farr, D. R., and A. Y. Rossman. 2015. Fungal databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved March 18, 2015, from http://nt.ars-grin.gov/fungaldatabases/

Johnson, G. I. 1985. Rust (Dasturella divina) of Bambusa spp. in Australia. Australasian Plant Pathology 14:54-55.

Mundkur, B.B., and K. F. Kheswalla. 1943. Dasturella: A New Genus of Uredinales. Mycologia 35:201–206.

Nelson, S., and M. Goo. 2011. Kweilingia rust of bamboo in Hawaii. College of Tropical Agriculture and Human Resources, University of Hawaii at Mānoa. Plant Disease PD-74.

Responsible Party:

Pest Rating: A

Posted by ls

Plant Pathogens, Viruses and viroids

Pepino Mosaic Virus (PepMV)

April 7, 2015 Admin

California Pest Rating for

Pepino Mosaic Virus (PepMV)

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

In January 2015, Tongyan Tian, CDFA Plant Pathologist, detected Pepino mosaic virus(PepMV) in two official tomato samples collected from plants grown in a greenhouse in San Diego County. The virus has been previously reported by researchers who collected non-official samples also from greenhouse tomatoes in Camarillo, Ventura County, California (Ling et al., 2008). The current regulatory status of PepMV and its potential risk of infestation in California are reassessed here for the proposal of a permanent rating.

History & Status:

Background: Pepino mosaic virus was first described in 1980 when it was isolated from pepino (Solanum muricatum) plants that were collected in 1974 from the coastal region of Peru (Jones et al., 1980). Following its original detection, it was not until 1999 that this pathogen was discovered infecting tomato plants grown in many greenhouses in the Netherlands, and later in the early 2000 in the UK, France and Germany. Since then, it initially spread to several countries in Europe but was subsequently eradicated from Croatia, Czech Republic, Norway, and Slovakia (EPPO, 2014a). Soon it was reported worldwide as a significant disease of greenhouse tomatoes in North America, South America, Asia and Africa. In North America, PepMV was first reported in 2001 (French et al., 2001). In their study of a US isolate of PepMV, Maroon-Lango and other scientists first reported the detection of the virus in tomato samples obtained from California (Maroon-Lango et al., 2003).

Pepino mosaic virus belongs to the genus Potexvirus in the family Alphaflexiviridae and RNA viruses group. Two strains of the virus are currently recognized: the pepino strain and the tomato strain (CABI, 2014). Ling (2007) reported that almost all North America PepMV isolates belonged to the European tomato strain. This was confirmed by Ling et al. (2008) in their study of genetic diversity and distribution of PepMV genotypes in North America. These scientists found four major genotypes of PepMV in the North America and only the European (EU) genotype in California.

Hosts: Pepino mosaic virus was originally described on pepino (Solanum muricatum). The natural and experimental host range is limited primarily to Solanceous plants. In addition to pepino, major and main hosts of PepMV are Solanum lycopersicum (tomato), S. melongena (eggplant) and S. tuberosum (potato). Natural infections have not been observed in potato and eggplant crops (EPPO, 2014b). During surveys in Peru the pathogen was found to be naturally present in several wild Lycopersicum species (L. chilense, L. chmielewskii, L. parviflorum, L. peruvianum) (EPPO, 2014b). Ocimum basilicum (basil) is a minor host. A number of wild and weed plants are hosts including, Amaranthus graecizans (tumbleweed/pigweed), A. retroflexus (red-root amaranth), A. viridis (green amaranth), Calendula arvensis, Chenopodium murale, Chrysanthemum segetum, Convolvulus arvensis, C. humilis, Datura stramonium (jimsonweed), Lycopersicon pimpinellifolium (currant tomato), Malva neglecta, M. nicaeensis, M. parviflora, M. sylvestris, Nicotiana glauca (tree tobacco), N. rustica (wild tobacco), Plantago lagopus, P. major, Solanum nigrum (black nightshade), Sonchus asper, S. oleraceus (common sowthistle) and S. tenerrimus (CABI, 2014; EPPO, 2014a, 2014b).

Symptoms: Symptoms may depend on climate conditions and become more distinct under low light conditions. Because of the variable influence of climate, leaf symptoms may be weak and difficult to observe thereby enabling PepMV-infected plants to escape unnoticed. Initial symptoms on tomato plants include small yellow leaf spots. However later, older, mature leaves may exhibit mottling, while top leaves may show slight curling. Fruit may show orange mottling which may differ between trusses (cluster of small stems bearing flowers and fruit) in a single plant. In Peru, young leaves of infected pepino exhibited yellow mosaic, while in the Netherlands affected tomato plants showed yellow spots, mild interveinal chlorosis and sometimes minor malformation (enation) of leaves. In UK, affected plants showed leaf distortion, chlorosis and bubbling of leaf surfaces, stunted and distorted plants (EPPO, 2014b; Mumford & Jones, 2005).

Damage Potential: Tomato plants infected with PepMV do not always result in significant economic damage since fruit symptoms may be absent. On the other hand, fruit setting may be delayed and yield affected. The virus can cause significant crop losses if early infections are not eliminated (EPPO, 2014b). Greenhouse-grown plants are particularly affected by the virus.

Transmission: Pepino mosaic virus is a very contagious pathogen that is transmitted mainly through mechanical means including contaminated tools, hands, clothing, direct plant to plant contact, grafting, cuttings, and seeds. High concentrations of the virus can be present in plant materials, leaves, fruits and roots of infected plants. The virus can be present in the seed coat of immature and mature tomato seeds, but not within the seed (embryo) (Ling, 2008). Damage or death of roots may release the virus in soil and drainage/irrigation water. Experimentally the virus has been shown to be spread by contact with bumble bees (Bombus terrestris, Bombus spp.) used as pollinators of tomato plants (EPPO, 2014b; CABI, 2014).

Worldwide Distribution: Asia: Syria, Turkey; Africa: South Africa; Europe: Austria, Belgium, Bulgaria, Cyprus, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, Lithuania, Netherlands, Poland, Spain, Switzerland, United Kingdom; North America: Canada, Mexico, USA; South America: Chile, Ecuador, Peru (EPPO, 2014a, CABI, 2014).

The recorded absence of Pepino mosaic virus from China, Taiwan, Madagascar, Morocco and Guatemala is considered unreliable (EPPO, 2014a; CABI, 2014).

In the USA it is present in Alabama, Arizona, California, Colorado, Florida, Maryland, Minnesota, Oklahoma, and Texas.

Official Control: Currently, Pepino mosaic virus is on the ‘Harmful Organism List’ for 45 countries: Albania, Austria, Belgium, Brazil, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Greece, Guatemala, Holy See (Vatican City State), Honduras, Hungary, India, Ireland, Italy, Japan, Republic of Korea, Latvia, Lithuania, Luxembourg, Malta, Monaco, Montenegro, Netherlands, New Zealand, Poland, Portugal, Romania, San Marino, Serbia, Slovakia, Slovenia, SPaid, Sweden, Switzerland, Taiwan, Turkey and United Kingdom (PCIT, 2014).

In California, PepMV is currently a Q-rated, quarantine pathogen.

California Distribution: Greenhouse environments within San Diego and Ventura Counties.

California Interceptions: There are no official records of PSbMV detected in incoming plant shipments to California.

The risk Pepino mosaic virus 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:

Risk is High (3) – PepMV is likely to establish wherever its hosts are cultivated or grow naturally in California. Tomato, the primary host, is a major crop that is widely cultivated in 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 Low (1) – The host range is limited primarily to Solanaceous plants of which tomato is the primary host that is cultivated over significant acreage throughout California. Eggplant and potato are also affected, although natural infection of both crops has not been reported.

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) – Pepino mosaic virus is a very contagious pathogen that is artificially spread mainly through mechanical means including contaminated tools, hands, clothing, direct plant to plant contact, grafting, cuttings, and seeds. It is externally seed-borne, and is also spread through infected planting materials. Experimentally, it has been transmitted by contact with bumble bees. Since symptoms are not always readily recognized, there is the potential for this virus to spread rapidly and unnoticed within nursery greenhouse environments as well as to outdoor field environments.

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) – PepMV could lower tomato yield, value and marketability particularly when infected fruit are symptomatic. Due to its contagious nature soil and irrigation water may become contaminated when infected roots and plant residue in soil are damaged or break down, thereby causing changes in normal cultivation practices.

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

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) – Several Solanaceous weeds have been experimentally shown to be hosts of PepMV. Natural infestations of such hosts could serve as reservoirs for the pathogen – although this would need to be confirmed through further research. The virus could negatively affect home/urban gardening and cultivation of tomato and eggplant in particular.

Consequences of Introduction to California for Peas seed-borne mosaic virus

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 PepMV to California = (11).

-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).

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:

The presence and distribution of PepMV in California agricultural field production and environmental sites is not known. Such information would be obtained through periodic surveys and may affect the current proposed rating. Due to the nature of its transmission, it is possible for the virus to escape detection and spread to non-infected sites.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Pepino mosaic virus is B.

References:

CABI 2014. Pepino mosaic virus full datasheet. Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/1695

EPPO, 2014a. Pepino mosaic virus (PEPMV0). New PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://newpqr.eppo.int

EPPO. 2014b. Pepino mosaic virus. European and Mediterranean Plant Protection Organization. http://www.eppo.int/QUARANTINE/Alert_List/viruses/PEPMV0.htm (Panel review date 2014-03).

Ferguson, G. 2001. Management of Pepino mosaic virus in greenhouse tomatoes – factsheet. Modified November 13, 2013. Ontario Ministry of Agriculture, Food and Rural Affairs. http://www.omafra.gov.on.ca/english/crops/facts/01-017.htm .

French, C. J., M. Bouthillier, M. Bernardy, G. Fergusen, M. Sabourin, R. C. Johnson, C. Masters, S. Godkins and R. Mumford. 2001. First report of Pepino mosaic virus in Canada and the United States. Plant Disease 85:1121.

Jones, R. A. C., R. Koenig, D. E. Lesemann. 1980. Pepino mosaic virus, a new potexvirus from pepino (Solanum muricatum). Annals of Applied Biology, 94(1):61-68

Mumford, R. A., and R. A. C. Jones. 2005. Description of Plant Viruses: Pepino mosaic virus. Association of Applied Biologists 411 (DPV 350 revised version). http://www.dpvweb.net/dpv/showdpv.php?dpvno=411 .

Ling, K. S., 2007. The population genetics of Pepino mosaic virus in North America greenhouse tomatoes. Phytopathology 97:S65.

Ling, K. S., 2008. Pepino mosaic virus on tomato seed: virus location and mechanical transmission. Plant Disease, 92:1701-1705.

PCIT. 2014. USDA Phytosanitary Certificate Issuance & Tracking System. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp .

Responsible Party:

Pest Rating: B

Posted by ls

Plant Pathogens, Viruses and viroids

Potato Spindle Tuber Viroid

March 16, 2015 Admin

California Plant Pest Rating for

Potato Spindle Tuber Viroid

Pest Rating: A

PEST RATING PROFILE

Initiating Event:

On December 16, 2013, CDFA was notified by USDA APHIS of the detection of potato spindle tuber viroid (PSTVd) in three Cestrum samples that were shipped under federal permit from California to Illinois. The detection was made by Ball Horticultural Company Plant Pathologist, and communicated to USDA APHIS as per federal permit requirement that APHIS is notified within 10 days on receipt of permitted materials if the permitee detects a pathogen that is not widely prevalent in the State from which the infected material was obtained.” The Cestrum plant samples came from plants raised in a Nursery greenhouse in San Diego County, CA. Subsequently, there is a need to reevaluate the current status and pest rating of PSTVd as a necessary step toward dealing with the current and future detections of this pathogen in California.

History & Status:

Background: Potato spindle tuber viroid is the first recognized viroid that was discovered in 1971 as the causal agent of the potato spindle tuber disease. The disease itself was first discovered in potato fields in New Jersey, USA (Martin, 1922). The 1971 study led to discovery of viroids which are small naked single-stranded, covalently closed, circular molecule of infectious RNAs that multiply autonomously in plant cells and lack a coat protein as they are too small to coat for a single protein. They infect plant cells and are replicated within the plant nucleus. PSTVd consists of 359 nucleotides and is the type species of the genus Pospiviroid.

Hosts: Potato is considered the main host of PSTVd large due to the presence of serious symptoms and large scale outbreaks. Other symptomatic hosts include tomato and pepper. Symptomless infections have been reported on Persea americana (avocado) and mainly solanaceous ornamentals: Brugmansia spp., Chrysanthemum sp., Calibrachoa sp., Cestrum spp., Dahlia sp., Datura sp., Lycianthes rantonnei, Petunia sp., Physalis peruviana, Solanum pserdocapsicum, Streptosolen jamesonii, Solanum jasminoides, Solanum muricatum, Ipomoea batatas (sweet potato) and wild Solanum spp.

Symptoms: In potato, symptom expression is influenced by potato cultivar, viroid strain, environmental conditions and method of inoculation (Pfannenstiel and Slack, 1980; Diener, 1987; Owens and Verhoeven, 2009). Symptoms include severe or barely distinct growth reduction, smaller vines, plants appear more erect and with smaller leaves than healthy, non-infected ones. Also, leaflets are darker green, sometimes with rolling and twisting. Tubers may be small, elongated (spindle-shaped), misshapen and cracked. Tuber eyes are pronounced and sometime borne on knob-like protuberances.
Infected tomatoes show growth reduction which may develop into permanent stunting with occasional death or recovery. Top grow is chlorotic sometimes turning to reddening and/or purpling causing leaves to become brittle. Flowers and fruit fail to develop as stunting begins. Very mild symptoms are produced on infected peppers in the form of slight distortion or ‘waviness’ of the leaf margins near the top of infected plants (Lebas et al., 2005). Infected solanaceous ornamentals do not exhibit any symptoms.

Damage Potential: PSTVd attacks all potato varieties causing severe losses. Up to 24% reduction in tuber yields are reported with mild strains of PSTVd and 64% with a severe strain (Singh et al., 1971). According to Pfannenstiel and Slack (1980) reduction of tuber weight depended on the potato cultivar and length of time they were infected with PSTVd. Plant age at the time of infection and the number of infected plants are factors that determine the amount of yield loss in tomatoes, reportedly from a few to 10% of plants (CABI International, 2013).

Transmission: PSTVd can infect all or most parts of susceptible plants. The viroid is mechanically transmitted and spread mainly through knives used for cutting infected and healthy tubers. Other means by which infected sap of diseased plants is transmitted to healthy plants include normal cultivation equipment and practices. Also, it is readily transmitted by infected plant material, namely cuttings, tubers, and micro-plants. Symptomless ornamental plants may serve as a source of inoculum. It is also transmitted by pollen, seed – especially for crops propagated by botanical seed, and by contaminated mouth parts of several insect vectors including aphids (Agrios, 2005, CABI International, 2013).

Worldwide Distribution: PSTVd is present in several countries in Europe, although in few occurrences for certain countries. Erratic outbreaks have been reported in tomato and substantial infections of ornamental plants have been reported. Effective measures have reduced the incidence of PSTVd in those crops but it has not been eradicated. However, the viroid was eradicated from Finland and France (CABI International, 2013). It has also been reported in Asia: China, Turkey, India, Iran, Israel, Japan, Afghanistan, Azerbaijan, Bangladesh, and the Republic of Georgia; Africa: Egypt, Nigeria, (absent from Kenya & South Africa – unreliable record according to CABI International 2013); Costa Rica; South America: Peru, Venezuela, Brazil, and Uruguay (it was eradicated from Argentina); Oceania: New Zealand, (it was eradicated from Australia); North America: Mexico, USA. It was successfully eradicated in seed potato production in the USA and Canada.

Official Control: Countries that require phytosanitary certification of PSTVd-free plant commodities imported from the USA include: Israel (tomato and petunia seeds), Austria (solanaceous seeds), Bosnia and Herzegovina (potato tubers), Chile (sweet potato and potato seeds and in vitro plantlets), Columbia (potato plantlets and seeds), India (tomato seeds), Macedonia (potato tubers), Mexico (tomato seedlings and potato in vitro plantlets), Morocco (potato tubers for propagation and consumption), New Caledonia (potato tubers for propagation) and Yemen (pepper and tomato seeds). At least 78 countries worldwide consider PSTVd an actionable pathogen but do not require phytosanitary certification. It is quite probable that these countries may require official certification in the event that PSTVd becomes further established within the USA.

California Distribution: There are no reports of PSTVd being established in field or natural environments within California – that would indicate an established distribution. However, PSTVd was reported for the first time in 2010 in tomatoes grown in commercial greenhouses in Ventura County (Ling, et al., 2010). The 2013 detection of PSTVd was made from infected Cestrum spp. nursery stock (C. fasciculatum Newellii, C. elegans Smithii, and C. elegans) also grown in greenhouses. It is likely that the 2010 PSTVd infected plants were destroyed and appropriate sanitary measures led to the eradication of the pathogen in the affected greenhouses. Similar eradicative measures will most likely be taken against the recent 2013 detection.

California Interceptions: There are no state reports of PSTVd detections in plant materials intercepted within or at points of entry in California.

The risk Potato spindle tuber viroid 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 high (3) as shown by the 2010 and 2013 detections of PSTVd in California greenhouses. Suitable climates for potato, tomato and other host plants would also favor the establishment of PSTVd.

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). Potato and tomato are grown in significant acreages throughout the State. Ornamental plants appreciably increase the host range of this pathogen.

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): PSTVd multiply autonomously in infected plant material and are easily transmitted through various means.

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): PSTVd infected potato tubers could lower crop yield, crop value, trigger loss of market through the imposition of quarantine regulations by other countries and states, can influence normal cultural practices and is vectored by insects.

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

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): Incidence of PSTVd could require additional official and private treatments, impact cultural and horticultural practices, at the very least.

Consequences of Introduction to California for potato spindle tuber viroid:

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 = 14 (High).

– 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: PSTVd is not established in California (0). PSTVd has only been detected in nursery plants contained in greenhouses. Those detection would have led to eradicative and greenhouse sanitary measures. They do not indicate the establishment of the pathogen 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 = 14 (High).

Uncertainty:

Information of the source of the pathogen is not known. The pathogen has not been reported from environments outside greenhouses.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Potato spindle tuber viroid is A.

References:

Agrios, G. N. 2005. Plant Pathology. Fifth edition. Elsevier Academic Press. 922 p.
CABI International. 2013. http://www.cabi.org/cpc/?compid=1&dsid=43659&loadmodule=datasheet&page=868&site=161

Diener TO, ed., 1987. The Viroids. New York, USA: Plenum Press.

Martin WH, 1922. “Spindle tuber”, a new potato trouble. Hints to Potato Growers, New Jersey State Potato Association, 3:8.

Lebas BSM, Clover GRG, Ochoa-Corona FM, Elliott DR, Tang Z, Alexander BJR, 2005. Distribution of potato spindle tuber viroid in New Zealand glasshouse crops of Capsicum and tomato. Australasian Plant Pathology, 34(2):129-133.

Ling, K. S. and D. Sfetcu. 2010. First report of natural infection of greenhouse tomatoes by Potato spindle tuber viroid in the United States. Plant Disease, 94:1376.

Owens RA, Cress DE, 1980. Molecular cloning and characterization of potato spindle tuber viroid cDNA sequences. Proceedings of the National Academy of Sciences USA, 77:5302-5306.

Owens RA, Verhoeven JTJ, 2009. Potato spindle tuber. External factsheets. Minnesota, USA: APSnet, unpaginated. http://dx.doi.org/10.1094/PHI-I-2009-0804-01.

Pfannenstiel MA, Slack SA, 1980. Response of potato cultivars to infection by the potato spindle tuber viroid. Phytopathology, 70(9):922-926.

Singh RP, Finnie RE, Bagnall RH, 1971. Losses due to the potato spindle tuber virus. American Potato Journal, 48:262-267.

Responsible Party:

Pest Rating: A

Posted by ls

Plant Pathogens, Viruses and viroids

Cucurbit Yellow Stunting Disorder Virus (CYSDV)

March 16, 2015 Admin

California Plant Pest Rating for

Cucurbit Yellow Stunting Disorder Virus (CYSDV)

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

The risk of infestation of Cucurbit yellow stunting disorder virus in California is evaluated and a permanent rating is herein proposed.

History & Status:

Background: Cucurbit yellow stunting disorder virus CYSDV belongs to the genus Crinivirus in the family Closteroviridae. As indicated by its name, the pathogen causes cucurbit yellow stunting disorder which is primarily a disease of cucurbits such as, watermelon, melon and squash. CYSDV isolates have been reported from different countries and can be divided into two distinct groups. One group contains isolates from Spain, Lebanon, Jordan, Turkey and North America while the other group contains isolates from Saudi Arabia (EPPO, 2014; CABI, 2014).

Cucurbit yellow stunting disorder virus was originally discovered in the Middle East. In North America, the disease was first discovered in 2006 in southern California’s Imperial Valley, near Yuma, Arizona, and Sonora, Mexico infecting various types of squash including cantaloupe, honeydew, melon and watermelon. In 2007, the virus was also discovered in Florida – although it is not clear how the virus spread to California and Florida. Isolates of CYSDV from Florida and California are genetically identical (Durham, 2011).

The life cycle of the virus is dependent on its whitefly vector, Bemisia tabaci. In tests using melon plants, the vector required 18h or more to acquire the virus during feeding on CYSDV-infected plants and inoculations periods of 24 hours or more to achieve transmission rates of over 80% (CABI 2014).

Hosts: The natural hosts are restricted to Cucurbitaceae: watermelon, melon, cucumber, and ornamental gourd (Cucurbita pepo). Incidental host plants include Cucurbita maxima, Lactuca sativa and Medicago sativa. Cucurbit maxima and Lactuca sativa are also experimental hosts. Other hosts include weeds belonging to Amaranthaceae, Chenopodiaceae, Malvaceae, Solanaceae, Brassicaceae and Asteraceae. The virus is capable of infecting plants in seven plant families besides Cucurbitaceae (Durham, 2011).

Symptoms: Symptoms can take 3 to 4 weeks to develop following infection. Symptoms in CYSDV-infected cucumber and melons initiate as an inter-veinal mottle on older leaves and intensify as leaves age (Abou-Jawdeh, 2000). Infected cucumber plants show chlorotic mottling, yellowing and stunting while yellowing and severe stunting is exhibited on infected melon plants. Symptoms on Cucurbit pepo have not been reported. Several CYSDV-infected weeds and alternate plants such as alfalfa and lettuce can be symptomless.

Damage Potential: The virus can cause serious damage to cucurbit production resulting in complete loss in fruit yield and quality and plant death, especially in regions where the whitefly vector is well established during the growing season Durham (2011). Serious economic problems occur in countries that have Mediterranean climates. Melons produced from CYSDV infected plants have reduced sugar levels, even though they may appear healthy.

Transmission: CYSDV is spread by the whitefly, Bemisia tabaci as it feeds and carries the virus from plant to plant. All biotypes of B. tabaci known to exist in North America can transmit the virus, including biotypes A, B and Q. The virus is transmitted over long distances through the movement of infected plants (particularly cucurbit plants). As symptoms develop in 3 to 4 weeks following infection, it is possible for the virus to be transported in symptomless plants. Also, it is possible to spread CYSDV over long distances through virus-carrying whiteflies that may accompany transported plant materials. All stages of the whitefly vector can be carried on plants for planting. Also, virus-carrying whiteflies can move long distances with high winds. The virus is infectious within whiteflies for up to 9 days. CYSDV is not transmitted mechanically and is not seed-borne (Davis et al., 2012).

Survival: Even with a relatively narrow host range, CYSDV was able to overwinter in California and Arizona in 2006-07. While the incidence of the virus was low in spring planted melons in 2007 it was high in fall-planted melons in the Imperial and Yuma Valleys in both years (Davis et al., 2008).

Worldwide Distribution: Asia: China, Iran, Israel, Jordan, Lebanon, Saudi Arabia, Syria, Turkey, United Arab Emirates; Africa: Egypt, Morocco, Tunisia; Europe: Cyprus, Greece, Portugal, Spain; North America: Mexico, USA (Arizona, California, Florida, Texas) (CABI, 2014; EPPO, 2014).

Official Control: Presently, Georgia, Honduras, Japan and the Republic of Korea list CYSDV have included CYSDV on their ‘Harmful Organism lists’ (USDA PCIT, 2014). In 2004, CYSDV was added to the A2 action list by the European and Mediterranean Plant Protection Organization (EPPO) and member countries are encouraged to regulate it as a quarantine pest, however, there are no specific measures against the pathogen in Europe (EPPO, 2005, 2014).

California Distribution: Imperial Valley, Imperial County.

California Interceptions: There are no official records of CYSDV intercepted in incoming plant material shipments to California.

The risk Cucumber yellow stunting disorder virus 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:

Risk is Medium (2) – CYSDV is established in the Imperial Valley, southern California. Its further spread to non-infected sites is limited by the distribution of its vector, Bemisia tabaci which to date, has not been found in natural cooler climates of northern California 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) – The natural host range is restricted to Cucurbits in the family Cucurbitaceae (which are grown extensively in the lower Sacramento Valley and in limited production in San Joaquin and Imperial Valleys). Additional hosts include plants in seven families other than Cucurbitaceae that can serve as source plants for the whitefly vector which then can carry the virus back to cucurbits.

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

Risk is High (3) – The virus is able to thrive in climates that are favorable for its vector. Its potential for spread is always artificial being completely dependent on the distribution of its vector and infected plant materials. Therefore, factors that increase movement and activity of the vector and infected plants will also influence that of the virus.

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) – CYSDV infections could lower crop yield and value, increase production costs, trigger loss of market, and the virus is vectored by the whitefly, Bemisia tabaci which would require implementation of management strategies to minimize the risk of the introduction and establishment of the virus in non-infected regions within California.

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

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) – Infestations of CYSDV could significantly impact home/urban gardening of cucurbits and non-cucurbit host plants resulting in the imposition of additional official or private treatment programs in order to prevent spread of the virus and virus-carrying whitefly vector.

Consequences of Introduction to California for Cucurbit yellow stunting disorder virus:

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 CYSDV to California = (12).

Evaluation is Low (-1). CYSDV is established in one suitable climate/host region (Imperial Valley) 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

Uncertainty:

While CYSDV is established in the Imperial Valley and there have been no further reports of its spread to other intrastate regions, targeted surveys for the pathogen have not been conducted in other cucurbit production sites. The distribution and establishment of the virus is largely dependent on the distribution and established infestations of virus-carrying Bemisia tabaci. Subsequently, detections outside the Imperial Valley may alter the proposed rating for this virus pathogen.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Cucurbit yellow stunting disorder virus is B.

References:

CABI. 2014. Cucurbit yellow stunting disorder virus datasheet. Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/17070 .

Davis, R. M., T. A. Turini, B. J. Aegerter and J. J. Stapleton. 2008. Cucurbit yellow stunting disorder. University of California Agriculture & Natural Resources, UCIPM Online, Statewide Integrated Pest Management Program.
http://www.ipm.ucdavis.edu/PMG/r116100211.html .

Durham, S. 2011. Combating Cucurbit yellow stunting disorder virus. http://www.ars.usda.gov/is/pr/2011/110309.htm .

EPPO. 2005. Cucurbit yellow stunting disorder crinivirus – European and Mediterranean Plant Protection Organization data sheet on quarantine pests. OEPP/EPPO bulletin 35:442-444.

EPPO. 2014. Cucurbit yellow stunting disorder virus (CYSDV0). European and Mediterranean Plant Protection Organization PQR database. http://www.eppo.int/DATABASES/pqr/pqr.htm .

USDA PCIT. 2014. United States Department of Agriculture, Phytosanitary Certificate Issuance & Tracking System (PCIT). https://pcit.aphis.usda.gov/PExD/faces/ViewPExD.jsp .

Responsible Party:

Pest Rating: B

Posted by ls

Bacteria, Plant Pathogens

Acidovorax citrulli (Schaad et al., 1978) Schaad et al., 2008

March 16, 2015 Admin

California Plant Pest Rating for

Acidovorax citrulli (Schaad et al., 1978) Schaad et al., 2008

Pest Rating: A

PEST RATING PROFILE

Initiating Event:

In July 2013, the bacterial fruit blotch pathogen (BFB), Acidovorax citrulli, was detected in a melon field (Cucumis melo) in Yolo County. This detection marked the first official record of the bacterial fruit blotch disease in California. Three contiguous fields planted to cucumber (2 fields) and watermelon (1 field), were also tested, however only melon was found infected with BFB. Subsequent trace back investigations revealed that the source seed for the Yolo County melon site was grown in a seed lot in Sutter County in 2012 and later, was found positive for BFB (and Cucumber green mottle mosaic virus – which is not evaluated in this proposal). The 2013 trace back also revealed that in 2012, two sites in Sutter County produced a total of 6 melon and watermelon seed lots that were positive for BFB. Those two sites are currently planted to non-hosts, and volunteer plants of 2013 tested negative for BFB. Two foreign sources of melon and cucumber seed lots planted in the two Sutter County sites were identified as Chile and Romania. However, no (melon) seed remained for testing from the Chilean source, and the source cucumber seed from Romania was not tested for BFB as the progeny seed tested negative for the pathogen. As for the 2013 Yolo County BFB positive site, County and State approved abatement measures were implemented. Wheat, a non-host, was grown at the site and in 2014, volunteer melon plants tested negative for BFB. To date, additional monitoring and testing of volunteer plants continues and those in the field are treated with herbicide and biodegraded. Furthermore, in 2013, approximately 120 trace forward seed lots were evaluated for risk of potential infection with BFB. Pathways identified as possible risk links for potential BFB infection were source seed, shared irrigation, proximity to a positive detection, mechanical transmission (equipment and workers), and seed processing operational steps. Trace forward investigations revealed that 2012 Sutter County melon seeds had been sent to San Benito County and tested positive for BFB. Also, BFB infested watermelon seed had been sent to San Benito County as well as shipped overseas to Lebanon, Italy and Africa. To date, 34 trace forward and trace back seed lots were sampled and tested for BFB, of which 6 were positive for the pathogen. Any remaining seeds from positive seed lots are currently on hold in Sutter and San Benito Counties pending destruction or CDFA approved treatment and proven freedom from the bacterium. Given this current detection and subsequent actions taken, A. citrulli is presently considered a quarantine, actionable pathogen that is temporary, transitional and under eradication, and therefore, not established within California. A permanent pest rating for the pathogen is herein proposed.

History & Status:

Background: Acidovorax citrulli is the causal agent of bacterial fruit blotch and seedling blight of cucurbit plants. The disease is seed transmitted and is a serious pathogen particularly of watermelon and melon worldwide.

Bacterial fruit blotch of cucurbits was first reported in 1965 causing seedling blight symptoms on watermelon seedlings at the USDA regional plant introduction station in Griffin, Georgia, USA. The causal agent was determined to be seed-borne and seed transmissible with the capability of surviving up to 7.5 years in stored seed. Seedling blight was also observed in squash and melon that were artificially inoculated with the pathogen. In 1969, the disease was observed on watermelon at a research farm in Leesburg, Florida, USA, and in 1978 it was observed in Queensland, Australia. The causal agent was identified as Pseudomonas pseudoalcaligenes subsp. citrulli (Schaad et al., 1978). The first outbreak of BFB in commercial watermelon fields was observed in the Mariana Islands (Guam and Tinian). In 1989, the first outbreak of BFB in the continental USA was in major watermelon producing states including Florida, South Carolina and Indiana. Between 1990 and 1995 sporadic and devastating outbreaks occurred in watermelon production regions of the Midwest, Northeast and Southern USA. Despite the implementation of stringent BFB management guidelines developed by academic and industry professionals, BFB outbreaks were reported in cucurbits other than watermelon in 1999 (Walcott, 2005, 2008). In 2013, BFB was first detected in California and consequently treated as a state actionable pathogen (CDFA-PEA, 2013).

Taxonomically, the pathogen belongs to the family Comamonadaceae in the order Burkholderiales. As a result of further taxonomic studies in 1992, Pseudomonas pseudoalcaligenes subsp. citrulli was found to be molecularly closely related to the genus Acidovorax and was subsequently reassigned (Willems et al., 1992). In 2008, Acidovorax avenae subsp. citrulli was reclassified and elevated to species rank, namely, A. citrulli (Schaad et al., 2008).

Disease cycle: The disease cycle begins with contaminated seed. Seedborne inoculum is the most important source of primary inoculum for BFB development in cucurbit seed and fruit production fields as well as in transplant production houses. Acidovorax citrulli has been detected on the external seed surface as well as internally on the papery perisperm-endosperm layer (Kurowski, 2014). In seed and fruit production fields, other sources of inoculum include infected seedlings, the previous season’s plant debris, and volunteer watermelon seedlings or cucurbitaceous weeds. In the USA watermelon production is mostly from dry seeded plants, although transplants are increasing in popularity (CABI, 2014). Contaminated seed result in infected seedlings. Warm temperatures and high relative humidity are favorable for the development of the disease. Under such conditions, bacteria from infested seed infect emerging and developing cotyledons. Little is known about the epidemiology of BFB in seed production environments. Under cool temperatures and low moisture conditions typical BFB fruit and foliar symptoms may not develop however, even with the lack of symptoms infested seeds are produced (Walcott, 2008).

Under field conditions, high relative humidity and rainfall are critical for the spread of bacterial cells through splash dispersal by wind-driven rain or overhead irrigation to uninfected plants. Bacterial cells are also spread by contact with cultivation equipment, irrigation and human contact. Once deposited on uninfected plants, bacterial cells swim through open stomata and leaf wounds and penetrate intercellular sub-epidermal spaces where they rapidly multiply causing the production of water soaked lesions and secondary inoculum. Acidovorax citrulli does not move systemically through the plant. Under favorable conditions, a few primary infections sites can result in widespread infection of all plants by the time of harvest. Leaf lesions that develop are reservoirs of bacteria for fruit infection. At anthesis (fruit set), bacteria are splashed dispersed by wind-driven rain or irrigation onto the surfaces of immature ovaries which they penetrate through open stomata thereby initiating fruit infection (Walcott, 2008). Watermelon fruit are most vulnerable to bacterial infection 2-3 weeks after anthesis. After this brief infection window a wax layer is deposited over the surface of fruit covering stomata and preventing bacteria from penetrating (Frankle et al., 1993). Once wax is deposited, bacteria are only able to enter mature fruit through wounds. Symptoms of fruit infection do not usually develop until about 2 weeks before harvest maturity. The exact reason for this latency period is unknown but may be influenced by fruit physiology (ASTA, 2009). Debris or seed from infested and rotten fruit, cucurbitaceous weeds, and volunteer cucurbit plants may allow the pathogen to over-season and perpetuate the disease cycle in the next cropping cycle.

Typical transplant house conditions favor development of Bacterial fruit blotch. Those conditions include high watermelon seedling populations, high temperatures high relative humidity and overhead irrigation. Infected seeds serve as the source of primary inoculum and bacterial cells from a few infected seedlings can rapidly spread throughout a greenhouse by splash dispersal and production of aerosols. As in field conditions, dispersed bacterial cells are deposited on uninfected seedlings which are penetrated through open stomata to intercellular spaces eventually leading to numerous secondary infection cycles. Asymptomatic plants with epiphytic A. citrulli cells can cause disease outbreaks under field conditions. Infected seedlings produced in transplant greenhouses can result in introduction and widespread development of BFB in the field.

Hosts: Acidovorax citrulli are pathogenic to various species of the Cucurbitaceae family. The most susceptible hosts are watermelon (Citrullus lanatus) and melons (Cucumis melo) including cantaloupe and honeydew melons which develop symptoms on fruit and leaves. Other cucurbits include cucumber (Cucumis sativus), squash (Cucurbita pepo), and Cucurbita moschata which only develop symptoms on foliage and not on fruit. Wild cucurbits are also hosts, such as, wild Citron (Citrullus lanatus var. citroides) that develops symptoms on leaves and fruit with seed transmission. Host range studies using artificial inoculations of the bacteria have resulted in symptoms on several solanaceous hosts including tomato, eggplant and pepper foliage, but not on fruit. Bacteria have been isolated from tomato seeds and foliage of betel pepper (Piper betle).

Symptoms: Acidovorax citrulli can attack all stages of cucurbit plants. Initial symptoms are water-soaked areas along the edges or the midveins on the undersides of cotyledons. In time the water-soaked lesions dry and become reddish to dark brown along the length of the midrib. In severe situations lesions coalesce on cotyledons, hypocotyls and stems and cause seedling collapse. On true leaves water-soaked lesions and reddish-brown to dark brown water soaked lesions are present along the leaf veins. Leaf symptoms may become inconspicuous over time.

Symptoms on fruit may be conspicuous or inconspicuous. Symptoms on watermelon fruit characteristically appear as small, dark olive, greasy irregularly shaped, blotch-like water-soaked spots on the rind of the upper surface of infected fruit. The lesions may rapidly enlarge from a few millimeters in diameter to cover the entire upper surface of the fruit leaving only the ground spot symptomless. In advance stages, the infected site becomes necrotic, cracks develop from which sticky, amber-colored ooze may exude. Internally, the lesions may penetrate into the flesh of the fruit causing rot. On fruit with netting, such as melon, symptoms initiate as small water-soaked spots. In muskmelons, netting does not form over lesions and the lesions do not expand on the rind surface but appears a small inconspicuous pits which extend into the flesh of the fruit forming rotten cavities (Walcott, 2008). In honeydew, initial water-soaked spots over time become brown and cracked with a water-soaked margin.

Damage Potential: Bacterial fruit blotch is the most economically important bacterial disease of cucurbits worldwide (Walcott, 2008). With its outbreak in 1989 in commercial watermelon fields in the continental USA, losses of more than 90% if the total marketable fruit occurred in some affected fields. Since then, although in most years BFB has occurred in relatively few fields, it has continued to be a threat to the watermelon industry and cucurbit seed, transplant and fruit producers, resulting in marketable watermelon fruit losses of over $100,000 to individual growers. In 1992, in Georgia thousands of hectares were lost to the disease (CABI, 2014).

Under favorable environmental conditions fruit losses of 90-100% have been observed in commercial watermelon fields in the USA. In 2000 estimated losses of 40-50% to 100% occurred in melon fields. A survey of 18 melon fields resulted in the detection of 4% to 47% of the disease in all fields (EPPO, 2014).

Transmission: Infested seed is the main mode of transmission of Acidovorax citrulli. The bacteria is also spread through infested seedlings, host crop debris, cucurbitaceous weeds, volunteer cucurbit plants, overhead irrigation, wind driven rain, contaminated cultivation equipment and tools, and human contact.

In field experiments, honey bees were shown to transmit the pathogen to female watermelon blossoms resulting in infection of 25% of seedlots although no fruit symptoms were observed (Fessehaie et al., 2005). Honey bees are not used for pollination in commercial seed production.

Worldwide Distribution: The geographical origin of Acidovorax citrulli is not known, however, the disease has spread to many regions of the world mainly through the passage of contaminated seeds.

Bacterial fruit blotch is distributed in Asia (China, Japan, Republic of Korea, Taiwan, Thailand, Turkey, Iran, Israel, and Malaysia), Europe (Greece, Hungary, Italy), Oceania (Queensland: Australia, Guam, Northern Mariana Islands), South America (Brazil), Central America and Caribbean (Costa Rica, Trinidad and Tobago), and North America (Canada, USA).

Within USA it is distributed in Alabama, Arkansas, Delaware, Florida, Georgia, Iowa, Illinois, Indiana, Maryland, Mississippi, Missouri, North Carolina, Oklahoma, Oregon, South Carolina, and Texas. The disease was detected in 1989 in Delaware, Iowa and Maryland but has not been reported since then (CABI, 2014; EPPO, 2014). The detection in California is considered transient, actionable and under eradication.

Official Control: Presently, 16 countries have included A. avenae subsp. citrulli (syn. of A. citrulli) on their ‘Harmful Organism Lists’. Those countries are; Chile, China, Colombia, Costa Rica, Ecuador, Guatemala, Honduras, India, Israel, Japan, Mexico, Nicaragua, Panama, Peru, Taiwan, and Turkey. Acidovorax citrulli is a quarantine pathogen in California, USA.

California Distribution: There are no official reports of BFB being established in field or natural environments within California – that would indicate an established distribution. The 2013 field detection in Yolo County, California is considered transient, actionable and under eradication.

California Interceptions: There are no state reports of Acidovorax citrulli detections in plant materials intercepted within or at points of entry in California.

The risk Bacterial fruit blotch 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:

Risk is medium (2): Although California climate is not considered conducive for the establishment (development and increase) of A. citrulli, the presence of suitable microenvironments and macro/micro climate changes enable establishment and perpetuation of pathogenic strains within California as evidence by the 2013 field outbreak in Yolo County, 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 medium (2). The host range is mainly limited to various species of the Cucurbitaceae family. Nevertheless, Cucurbitaceous hosts, including watermelon, melon, squash and cucumber, are widely grown commercially within California to warrant of establishment and spread of this pathogen.

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

Risk is high (3): Under favorable environmental conditions BFB has a high reproductive rate and depends on artificial means for its dispersal. Infested seeds are the main means of long distance dispersal, and in fields and greenhouses, the bacterium is capable of widespread transmission through contaminated plant materials and debris, equipment, water-splash, human contact and possibly insects.

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): Incidence of the BFB pathogen could result in lowered crop yields, crop value, increased production costs, loss of markets due to the imposition of quarantine rules and regulations, alteration of cultural practices and possible interference with the delivery of irrigation water where a supply is shared between fields.

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

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): incidence of A. citrulli could result in additional official or private treatment programs as well as significantly impact cultural practices and home/urban gardening.

Consequences of Introduction to California for Acidovorax citrulli:

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 (High).

Evaluation: Acidovorax citrulli is not established in California (0). Actions taken subsequent to the detection of the pathogen in Yolo County and detailed in the “Initiating Event” section above, provide evidence of the current ‘non-established’ status of the pathogen.

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 = 13 (High).

Uncertainty:

Information of the source of the Yolo County BFB detection is not known. Infested seeds and transplant are a ready source of introduction of the pathogen to CA fields. Diligent monitoring and testing of seed/plants in greenhouses and fields must be followed to mitigate risk of further field introduction and potential establishment of the pathogen in California soils.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Acidovorax citrulli is A.

References:

ASTA. 2009. “Bacterial fruit blotch – a commercial grower’s guide” brochure. June 2009.

Burdman S. and R. Walcott. 2012. “Acidovorax citrulli: generating basic and applied knowledge to tackle a global threat to the cucurbit industry.” Molecular Plant Pathology 13(8): 805-15.

CABI. 2014. “Acidovorax citrulli.” Crop Protection Compendium. Wallingford, UK: CAB International. www.cabi.org/cpc.

CDFA-PEA. 2013. Cucumber Green Mottle Mosaic Virus and Bacterial fruit blotch detections in California. California Department of Food and Agriculture, Pest Exclusion Advisory no. 29-2013.

EPPO. 2014. “Acidovorax citrulli Bacterial fruit blotch of cucurbits.” Panel review date 2013-03. http://www.eppo.int/QUARANTINE/Alert_List/bacteria/Acidovorax_citrulli.htm.

Frankle, W. G., D. L. Hopkins and R. E. Stall. 1993. “Ingress of the watermelon fruit blotch bacterium into fruit.” Plant Disease, 77(11):1090-1092.

Kurowski, C. “CGMMV – BFB Training.” Presentation at the ‘Cucumber green mottle mosaic virus and bacterial fruit blotch disease training” California Department of Food and Agriculture, Sacramento, CA on May 1and 2, 2014. Monsanto Vegetables, Woodland, CA.

Schaad, N. W., G. Sowell Jr, R. W. Goth, R. R. Colwell and R. E. Webb. 1978. “Pseudomonas pseudoalcaligenes subsp. citrulli subsp. nov.” International Journal of Systematic Bacteriology, 28(1):117-125.

Schaad, N. W., E. Postnikova, A. Sechler, L. E Claflin, A. K. Vidaver, J. B. Jones, I. Agarkova, A. Ignatov, E. Dickstein and B. A. Ramundo. 2008. “Reclassification of subspecies of Acidovorax avenae as A. avenae (Manns 1905) emend., A. cattleyae (Pavarino, 1911) comb. nov., A. citrulli Schaad et al., 1978) comb. nov., and proposal of A. oryzae sp. nov.” Systematics and Applied Microbiology 31: 434–446.

Walcott, R. R. 2005. “Bacterial fruit blotch of cucurbits.” The Plant Health Instructor. DOI: 10.1094/PHI-I-2005-1025-02.

Walcott, Ron R. 2008. “Integrated pest management of bacterial fruit blotch of cucurbits.” In Integrated Management of Diseases caused by fungi, phytoplasma and bacteria, Eds. A. Ciancio & K. G. Mukerji. 187-205 p.

Willems A., M. Goor, S. Thielemans, M. Gillis, K. Kersters K and Jde Ley. 1992. “Transfer of several phytopathogenic Pseudomonas species to Acidovorax as Acidovorax avenae subsp. avenae subsp. nov., comb. nov., Acidovorax avenae subsp. citrulli, Acidovorax avenae subsp. cattleyae, and Acidovorax konjaci.” International Journal of Systematic Bacteriology, 42(1):107-119.

Zhao, T., J. Feng, A. Sechler, P. Randhawa, J. Li and N. W. Schaad. 2009. “An imporved assay for detection of Acidovorax citrulli in watermelon and melon seed.” Seed Science & Technology, 37: 337-349.

Responsible Party:

Pest Rating: A

Posted by ls

Phytoplasmas, Plant Pathogens

Texas Phoenix Palm Decline Phytoplasma

March 16, 2015 Admin

California Pest Rating for

Texas Phoenix Palm Decline Phytoplasma

Pest Rating: A

PEST RATING PROFILE

Initiating Event:

During the month of February 2014, CDFA Plant Pathologist Dr. Cheryl Blomquist was notified by Dr. N. Harrison, Plant Pathologist, University of Florida, Fort Lauderdale of palm stem tissue samples he had received from a California private palm grower whose date palms had been dying for the past several years. Dr. Harrison analyzed the samples to be positive for the Texas Phoenix Palm Decline disease (TPPD). Dr. Blomquist followed through by contacting the private grower in Desert Hot Springs, Riverside County, CA to assess the palm disease situation at her site and with a request for CDFA to collect samples to send to the USDA diagnostic laboratory for testing. The grower obliged and further mentioned two other sites in Riverside County (one in Palm Desert: a mobile home community with a golf course; one date farm in Sky Valley) where she had noticed symptoms of palm decline similar to those observed in palm trees at her site (Blomquist, 2014). CDFA Plant Pathologist Magally Luque-Williams collected official samples from the locations at Desert Hot Springs (1date palm tree) and Palm Desert (2 queen palm trees). Those samples were submitted for analysis to the USDA CPHST Beltsville Laboratory, however, due to delayed shipping and poor quality of the received samples, the results were negative for TPPD. Subsequently, re-samples taken from the same locations (2 trees at each location) and resubmitted to the Beltsville Laboratory were also declared negative for TPPD. Palm trees at the date farm in Sky Valley were not officially sampled due to objection raised by the property owner. An assessment of the risk presented by TPPD in California is herein conducted to propose an official rating.

History & Status:

Background: Texas Phoenix Palm Decline disease is caused by a phytoplasma which has been classified as a member of 16S rDNA RFLP group 16SrIV, subgroup D (16SrIV-D). The TPPD phytoplasma is related to, but genetically distinct from the phytoplasma that causes lethal yellowing in palms. It was originally identified in 2001 on Phoenix canariensis (Canary Island date palm) grown in the southern coastal region of Texas, hence the name of the disease. Texas Phoenix Palm Decline has only been reported from the USA, specifically from Texas, Florida and most recently from Louisiana (LSU AgCenter, 2014).

Hosts: Currently, susceptible hosts for the TPPD phytoplasma are Phoenix dactylifera (date palm), P. canariensis (Canary Island date palm), P. sylvestris (silver or Sylvester date palm), P. reclinata (Senegal/wild date palm), Sabal palmetto (cabbage/sabal palm), and Syagrus romanzoffiano (queen palm).

Symptoms: TPPD chronologically progresses through a series of symptoms so that no single symptom is diagnostic of the disease. The first obvious symptom on mature palms is premature drop of most or all fruits over a period of a few days and not over a prolonged period of time. Inflorescence necrosis follows fruit drop. However, fruit drop and inflorescence necrosis only occurs if the palm is mature enough to produce fruit, it is the season for flowering and fruiting, and the flowers or fruits have not been trimmed from the plants. The next symptom is the discoloration of foliage beginning with the oldest leaves and beginning at leaf tips. Instead of turning yellow or only turning yellow for a brief period, the leaves turn varying shades of reddish-brown to dark brown or gray. Unless monitored carefully, leaf discoloration may often be confused with natural senescence or senescence caused by nutritional deficiency, Lethal yellowing (phytoplasma disease) or Gandoderma butt rot (fungal disease causing dry rot within trunks of palms). However, with TPPD, there are a greater number of dead older leaves than normal for natural senescence. This symptom may easily be overlooked if dying or dead leaves are regularly removed from diseased trees. The death of the spear leaf is the next symptom. This may occur in Phoenix species when less than one-third or one-quarter of the oldest leaves have discolored and turned necrotic, and in cabbage palms when about two-thirds of the oldest leaves have discolored. Death of the spear leaf means death of the apical meristem. Once that happens, no new leaves will develop and the remaining leaves from the oldest to the youngest will continue to discolor and die. Death of the spear leaf is not always obvious and unless it is dead, hanging from the canopy, or on the ground, it will require close examination to determine if it is healthy or not. Sometimes, by the time spear leaf dies, mature palm roots at or near the soil surface are soft in texture and easily broken. The rooting root system enables such plants to be easily rocked back and forth in the ground (Harrison & Elliott, 2009).

The TPPD phytoplasma is usually not detectable in palms that are not showing symptoms and may not be detectable until the spear leaf dies (Harrison & Elliott, 2009)

Texas Phoenix Palm Decline is a fatal disease. The phytoplasma colonizes the phloem (vascular) tissue so that it spread systemically and quickly kills palms.

Transmission: The TPPD phytoplasma is spread naturally by piercing-sucking, insects, feeding on phloem sap. The species of the insect vector is not known, however, plant hoppers, psyllids or treehoppers are the most-likely groups of insects to transmit the TPPD phytoplasma. The phytolasma is spread from plant to plant through the feeding activities of these insects and does not survive outside their plant or insect host. Also, TPPD is spread through human activity which causes the movement of vector and infected hosts.

Worldwide Distribution: Texas Phoenix Palm Decline disease has only been reported from the USA. Within the USA, it has been reported from Texas, Florida and Louisiana.

Official Control: Texas established quarantine regions and imposed the “Texas Date Palm Lethal Decline Quarantine” requiring phytosanitary certification of imported palms from the state of Florida. (Under the Texas Lethal Yellowing quarantine date palm- another existing quarantine for palm trees – Phoenix dactylifera; Canary Island date palm, Phoenix canariensis; and silver date palm, Phoenix sylvestris are prohibited entry from Florida, the Commonwealth of Puerto Rico and Territory of Guam.)

California Distribution: Texas Phoenix Palm Decline Phytoplasma was not detected in official samples collected in Riverside County (see ‘Initiating event’) and therefore, there is no official record of the presence of TPPD within California. Nevertheless, as also detailed above in ‘Initiating event”, the detection of TPPD in a non-official sample initially analyzed by Dr. Harrison (University of Florida), suggests the presence of TPPD in diseased date palms cultivated by a private owner. Further investigation of several trees will be necessary to establish this as fact.

California Interceptions: There have been no interceptions of TPPD in California.

The risk Texas Phoenix Palm Decline phytoplasma 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:

Risk is High (3) – TPPD is likely to establish wherever date palms are grown in 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 Medium (2) – Thus far, susceptible hosts of TPPD include date, cabbage and queen palms – although these hosts are widely grown mainly in Southern California.

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

Risk is High (3) – Although the exact species of the vector is not known, the group of leafhoppers, treehoppers or psyllids as possible vectors of the TPPD phytoplasma render the TPPD phytoplasma a relatively high potential for increase and dispersal to non-infected sites.

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) – TPPD phytoplasma kills palms thereby, causing losses in date fruit yields, increases in crop production, loss of date fruit and ornamental palm markets, impositions of necessary quarantines, plus the phytoplasma is vectored by sap-sucking insects.

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

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) – Palms infected by the TPPD phytoplasma could trigger additional official and private treatment programs, impact cultural practices, home/urban gardening and ornamental plantings and disrupt natural communities of palm growth in California.

Consequences of Introduction to California for Texas Phoenix Palm Decline:

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 Texas Phoenix Palm Decline phytoplasma to California = (14).

– 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 (-0). TPPD phytoplasma has never been officially detected 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 = 14.

Uncertainty:

Texas Phoenix Palm Decline Phytoplasma has not been officially detected in California. Only a few trees were sampled from the suggested sites (see ‘Initiating event’). To fully establish the possible presence and distribution of the pathogen, more complete and timely surveys of several symptomatic palm trees from those and possibly other sites would be necessary. Also not known is the specific identity of the insect vector involved. Leafhoppers are considered the most likely vector, however, their distribution, host preferences and other aspects of biology would directly impact the current knowledge of the TPPD phyoplasma.