Tag Archives: plant pathogen

Fungi, Plant Pathogens

Phytophthora quercina T. Jung 1999

California Pest Rating for
Phytophthora quercina T. Jung 1999
Pest Rating: B 
PEST RATING PROFILE
Initiating Event: 

On April 25, 2016, two soil samples with roots of valley oak (Quercus lobata) trees that showed symptoms of stunting in a restoration site in Santa Clara County, were collected by Santa Clara County Agricultural officials and sent to the CDFA Plant Pathology Laboratory, for diagnosis.  DNA was extracted from soil baits and determined to be 100% similar to the pathogen, Phytophthora quercina, by Suzanne Rooney-Latham, CDFA plant pathologist.   DNA samples were sent by CDFA to the USDA APHIS PPQ CPHST Laboratory in Beltsville, Maryland, and on June 10, 2016, USDA confirmed the identity of P. quercina.  This detection marked the first confirmed presence and new record of the pathogen in the United States (USDA APHIS PPQ, 2016).  Currently, P. quercina has a temporary ‘Q’ rating in California.  The risk of introduction and establishment of this pathogen in California is assessed and a permanent rating is proposed herein.

History & Status:

Background: Oak decline is a serious and frequently recurring disease in Europe since the beginning of the twentieth century (Jung et al., 1999).  During the early 1990s, several Phytophthora spp. including a newly described P. quercina were found to be associated with oak decline and root rot in central and southern Europe.  In pathogenicity tests on oak, Quercus robur, P. quercina was found to be most pathogenic in comparison to the other associated Phytophthora species (Jung et al., 1999).  Subsequent reports associated P. quercina with oak decline from Turkey, Austria, and Italy (Balcý & Halmschlager, 2002a, 2002b; Vettraino et al., 2002).  Phytophthora quercina is an oomycete, and Cooke et al, (1999) provided molecular evidence that verified P. quercina as a distinct species.

Phytophthora quercina was recently detected in soil samples obtained from the root zone area of diseased valley oak trees grown at a California restoration site.  The USDA marked this detection as the first known confirmation of the pathogen in the United States.  Details are given above in “Initiating Event”.   The species was reported in 2007 on being detected in a soil bait around a declining oak tree in Central Missouri (Schwingle et al., 2007), however, the identification was not confirmed by USDA APHIS and there have not been any further publications on the species in the USA (USDA APHIS PPQ, 2016).

Hosts: Quercus spp. (oak): Q. cerris, Q. hartwissiana, Q. frainetto, Q. ilex, Q. robur, Q. petraea, Q. pubescens, Q. suber, and Q. vulcanica (Balcý & Halmschlager, 2002a, 2002b; EPPO, 2016; Farr & Rossman, 2016; NPRG, 2010).

Symptoms:  Phytophthora quercina, along with several other Phytophthora species, occur in oak decline stands in Europe (Balcý & Halmschlager, 2002; Jung et al., 2008).  Above ground symptoms of oak decline include dieback of branches and parts of the crown, formation of epicormic shoots, high transparency of the crown, yellowing and wilting of leaves and tarry exudates from the bark.  These symptoms are indicative of water stress and poor nutrition (Jung et al., 2008).  Below ground symptoms in declining European oak species resulted in deterioration of oak fine roots, including a progressive destruction of the fine root system, dieback of long roots, and necrotic lesions on suberized and non-suberized roots.  Although these symptoms occur in both healthy and declining oaks, the damage is generally more severe in declining oaks (Jung, et al., 2008).  The pathogen also causes abnormal root branching, and produces elicitins, viz. toxic substances that induce wilting and yellowing and leaf necrosis in declining oaks (NPRG, 2010).   In pathogenicity test, P. quercina-infected Quercus robur (oak) seedlings with severe root rot showed wilting and necrosis of leaves, root necrosis and dieback of the shoot. Under natural conditions, mature Q. robur trees showed reductions in fine root length (Jung et al., 1999).

Damage Potential:  The extent of damage caused by Phytophthora quercina has not been reported.  Several Phytophthora species including P. quercina are associated with oak decline disease.  However, P. quercina has been shown to be pathogenic to some European Quercus species, such as Q. robur (Jung et al., 1999), and to be one of the most aggressive and most common species found in reported surveys in Europe (Jung et al., 1999, 2008; Balcý and Halmschlager 2002a, 2002b).  In Italy, P. quercina was the only species significantly associated with declining oak trees (Vettraino et al., 2002).

Disease Cycle: Although present in roots and rhizosphere soil of oaks exhibiting symptoms of oak decline, the precise role of Phytophthora quercina in this disease is not known and very little is known about its biology.  Jung et al. (2008), reported that at least two different complex diseases are referred to as ‘oak decline’.  On sites with a mean soil pH 3.5 or greater and sandy-loam to clayey soil texture, Phytophthora species were commonly isolated from rhizosphere soil, and highly significant correlations existed between crown transparency and various root parameters.  However, in sites with a mean soil pH less than 3.9 and sandy to sandy-loam soils, Phytophthora species were not found. Biotic and abiotic stress factors such as drought and frost, may often act synergistically and accelerate Phytophthora-mediated decline of oaks.

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, 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). Phytophthora quercina is homothallic.  Optimum growth in culture is at 20°C and 25°C, however, it is able to grow at temperatures as high as 27.5°C (Jung et al., 1999; Barzanti et al., 2001).

Transmission: Like most Phytophthora species, P. quercina is soil-borne and water-borne and may be spread to non-infected sites through infected plants, nursery and planting stock, and seedlings, soil, run-off and splash irrigation and rain water, and contaminated cultivation equipment, tools, and boots.

Worldwide Distribution: Asia: Turkey; Europe: Austria, Belgium, France, Germany, Hungary, Italy, Luxemberg, Montenegro, Serbia, Spain, Sweden, Scotland, United Kingdom: North America: USA (California) (Balcý & Halmschlager, 2002a, 2002b; EPPO, 2016; Farr & Rossman, 2016; Jung et al., 1999; NPRG, 2010).

Official Control: Phytophthora quercina is listed as an exotic forest pathogen in USDA APHIS PPQ Federal New Pest Response Guidelines for Phytophthora species (NPRG, 2010).  The species has been on the North American Plant Protection Organization (NAPPO) alert list since 2002.  Currently, P. quercina has a temporary ‘Q’ rating in California.

California Distribution: Phytophthora quercina has been detected in a California native plant restoration site in a Santa Clara County.

California Interceptions: None.

The risk that Phytophthora quercina would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Evaluate and score the pest for suitability of 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) – Although Phytophthora quercina has been reported to be associated primarily with European oak species in Europe, its recent detection in valley oak rhizosphere soil extends the capability of this pathogen to be associated with California native oaks.  Valley oak is endemic to California and present throughout the State.  Thereby, making it likely for the pathogen to establish a widespread distribution in California.  It is not yet known, but probable that other California native oaks may be affected by P. quercina.

2) Pest Host Range: Evaluate and score the pest as it pertains to host range.  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) – Phytophthora quercina has a host range limited to Quercus spp. that includes Q. cerris, Q. hartwissiana, Q. frainetto, Q. ilex, Q. robur, Q. petraea, Q. pubescens, Q. suber, and Q. vulcanica.  In California, it was found to be associated with Q. lobata.

3) Pest Dispersal Potential: Evaluate and score the pest for dispersal potential using these criteria.  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 quercina is soil-borne and water-borne and therefore, primarily spread artificially via infested soils, plants, nursery and planting stock, seedlings, run-off and splash irrigation water, cultivation equipment and tools, and boots 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 Medium (2) – The extent of damage caused by Phytophthora quercina has not been reported.  Several Phytophthora species including P. quercina are associated with oak decline disease. In Europe, P. quercina was most commonly associated with the disease than were other Phytophthora species.  The pathogen could impact nursery-produced oaks thereby triggering possible loss of markets and requiring changes in normal cultural practices to avoid spread of the soil and water-borne pathogen.  

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

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 could significantly impact cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact:

– 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) – Phytophthora quercina is listed as an exotic forest pathogen in USDA APHIS PPQ Federal New Pest Response Guidelines for Phytophthora species (NPRG, 2010).  The species has been on the North American Plant Protection Organization (NAPPO) alert list since 2002.  Although the extent of damage potentially caused by this pathogen is not yet known, its spread within California could cause serious impact on native oaks, disrupt critical habitats by killing critical species necessary for species diversity and soil stability, necessitate official or private treatment programs to preserve critical, rare, or endangered species, and significantly impact cultural practices, home/urban and/or ornamental plantings.

Consequences of Introduction to California for Phytophthora quercina:

Add up the total score and include it here

Low = 5-8 points

Medium = 9-12 points

High = 13-17 points

Total points obtained on evaluation of consequences of introduction of Phytophthora quercina 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).

Final Score

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.

Uncertainties:

The extent of economic damage caused by Phytophthora quercina is not known. Also not known is the exact role of the pathogen in oak decline disease, and details of the biology of the pathogen species.

Conclusion and Rating Justification:

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

References:

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

Balcý, Y. and E. Halmschlager.  2002a. First confirmation of Phytophthora quercina on oaks in Asia.  Plant Disease 86:442. http://dx.doi.org/10.1094/PDIS.2002.86.4.442C

Balcý, Y. and E. Halmschlager.  2002b. First report of Phytophthora quercina in Austria.  New Disease Reports volume 6, August 2002-January 2003. http://www.bspp.org.uk/ndr/jan2003/2002-28.htm

Barzanti, G. P., P. Capretti, and A. Ragazzi. 2001. Characteristics of some Phytophthora

species isolated from oak forest soils in central and northern Italy.

Phytopathologia Mediterranea 40(2): 149-156.

Cooke, D.E.L., T. Jung, N. A. Williams, R. Schubert, G. Bahnweg, W. Oswald, and J. M. Duncan.  1999.  Molecular evidence supports Phytophthora quercina as a distinct species. Mycological Research, 103:799-804.

EPPO.  2016.  Phytophthora quercina (PHYTQU).  New PQR database.  Paris, France:  European and Mediterranean Plant Protection Organization.  http://newpqr.eppo.int

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

Jung, T., D. E. L. Cooke, H. Blaschke, J. M. Duncan, and W. Oswald. 1999.  Phytophthora quercina sp. nov., causing root rot of European oaks. Mycol. Res. 103: 785-798.

Jung, T., H. Blaschke and W. Oßwald.  2008.  Involvement of soilborne Phytophthora species in Central European oak decline and the effect of site factors on the disease.  Plant Pathology, 49:706-718. DOI: 10.1046/j.1365-3059.2000.00521.x

Schwingle, B. W., J. Juzqik, J. Eggers, and B. Moltzan.  2007.  Phytophthora species in soils associated with declining and nondeclining oaks in Missouri Forests.  Plant Disease 91:633. http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-91-5-0633A

NPRG.  2010.  New Pest Response Guidelines: Phytophthora species in the Environment and Nursery Settings. USDA MRP APHIS PPQ Cooperating State Departments of Agriculture, July 09 2010. 229 pages.

USDA APHIS PPQ.  2016.  Email from J. H. Bowers, National Survey Coordinator National Policy Manager, Cooperative Agricultural Pest Survey, USDA, APHIS, PPQ, PHP, to Nick Condos, Director, CDFA, sent Friday, June 10, 2016, 11:56 am.

Vetrraino, A. M., G. P. Barzanti, M. C. Bianco, A. Ragazzi, P. Capretti, E. Paoletti, N. Luisi, N. Anselmi, and A. Vannini.  2002.  Occurrence of Phytophthora species in oak stands in Italy and their association with declining oak trees.  Forest Pathology, 32:19-28.  DOI: 10.1046/j.1439-0329.2002.00264.x

Responsible Party:

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

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Pest Rating: B 

Posted by ls

Fungi, Plant Pathogens

Puccinia kuehnii (W. Krűger) E. J. Butler 1914

California Pest Rating for
Puccinia rusts. Photo credit: Cesar Calderon, USDA APHIS PPQ. Bugwood.org
Puccinia rusts. Photo credit: Cesar Calderon, USDA APHIS PPQ. Bugwood.org
Puccinia kuehnii (W. Krűger) E. J. Butler 1914
Pest Rating:  C
PEST RATING PROFILE
Initiating Event:

On February 9, 2016, USDA’s Animal and Plant Health Inspection Service (APHIS) notified the CDFA that the rust pathogen, Puccinia kuehnii was added on February 2, 2016, to their ‘List of Pests no Longer Regulated at U.S. Ports of Entry’ under the Federally Recognized State Managed Phytosanitary (FRSMP) program (USDA APHIS 2016).  Consequently, USDA APHIS will no longer take regulatory action against this pathogen at ports of entry.  Therefore, and at the request of Stephen Brown, Assistant Director, CDFA, the risk of infestation for P. kuehnii is assessed here and a permanent rating is proposed.

History & Status:

Background:  Puccinia kuehnii is one of two major rust fungi on sugarcane and causes orange rust.  The other rust fungi known as P. melanocephala, causes brown rust and is relatively common.  The orange rust of sugarcane pathogen, P kuehnii, most likely originated in Asia-Oceania regions where Saccharum spp. are native.  In other countries where the pathogen occurs, such as Indonesia and the South Pacific, sugarcane has existed for several centuries and it is assumed that P. kuehnii was likewise introduced and also existed in those countries for the same period of time.  The pathogen is now wide spread in Asia and Australia and was recently discovered in West Africa and the Western Hemisphere and from sugarcane-growing regions in the southeastern United States, Central and South America, and the Caribbean Basin (Dixon & Castlebury, 2016). It is likely that the pathogen was introduced to Australia along with sugarcane that was introduced about 150 years ago as there are no known native hosts present in that region (CABI, 2016).  In the USA, P. kuehnii was first reported from Florida having been detected in infected, brown rust-resistant, sugarcane cultivars. The disease appears to be distributed widely in the South Florida sugarcane-growing region (Comstock et al., 2008).  In 2013, orange rust was also reported from the southern region of Louisiana’s sugarcane production area (Grisham, et al., 2013).  Puccinia kuehnii has not been reported from California nor is sugarcane a major production crop of the State.

Disease cycle:  Puccinia kuehnii completes its life cycle on the same host and has an incomplete lifecycle. Spermagonia and aecia spore states are unknown.    Urediniospores are produced abundantly under natural conditions, but the production of teliospores and basidiospores are comparatively less common.    Under favorable conditions of humidity and temperature, urediniospores present on host germinate to penetrate the tissue.  As the fungus grows, uredinia (fruiting structures) are formed and urediniospores are produced in abundance.   Urediniospores are produced between 10°C and 34°C and optimally at 15-25°C for urediniospores and 26°C for teliospores.  Relative humidity above 97% favors urediniospore germination (Hsieh & Fang, 1983; CABI, 2016).

Dispersal and spread: The main risk for natural dispersal of spores over long distances (over 2000 km) is by wind and wind-blown rain.  Other potential means for spread are the movement of infected leaves and spore-contaminated clothing (CABI, 2016).

Hosts:  Saccharum officinarum (sugarcane) is the main host.  Other hosts include few weeds and ornamental grasses belonging to Saccharum spp. within Poaceae: Saccharum arundinaceum, S. barberi, S. bengalense, S. edule, S. munja, S. narenga, S. rufipilum, S. sinense, S. spontaneum; S. ravennae (syn. Erianthus ravennae); Sclerostachya fusca (Afshan & Khalid, 2013; CABI, 2016; Dixon & Castlebury, 2013; EPPO, 2016; Farr & Rossman, 2016 )

Symptoms:  Orange rust disease is characterized by the development of lesion that initiate as small (0.5 mm diameter) spots on leaves and enlarge into elongated brown lesions (2-8 mm x 0.5-2 mm wide).  As the lesions enlarge, fungal mycelium protrudes through the leaf surface, usually on its underside, producing abundant urediniospores. These pustules usually occur in patches or groups, but cover entire leaf surfaces in severe infections. Severely infected leaf tissue becomes necrotic leading to early senescence. Affected crops appear brown with very little green tissue remaining at all. Symptom development may take 3-4 weeks from infection, depending on weather conditions (CABI, 2016).

Disease Potential:  Orange rust of sugarcane is considered a disease of low economic impact that has rarely caused significant economic losses.  The only severe economic loss was reported in Australia in 2000 on the introduced, highly susceptible Q124 sugarcane variety that was subsequently replaced (CABI, 2016).  The potential for establishment and spread of the pathogen in California is reasonably low as sugarcane, the main host, is grown in limited acreage in dry climates of the Imperial Valley.

Worldwide Distribution: Africa: Cameroon, Cote d’Ivore; Asia: China, India, Indonesia, Japan, Malaysia, Myanmar, Nepal, Pakistan, Philippines, Singapore, Sri Lanka, Taiwan, Thailand, Vietnam; Central America and Caribbean:  Costa Rica, Cuba, Dominican Republic, Guatemala, Jamaica, Nicaragua, Panama; North America: USA, Mexico; South America: Brazil, Colombia, Ecuador; Oceania: American Samoa, Australia, Cook Islands, Fiji, French Polynesia, Guam, Micronesia, New Caledonia, Papua New Guinea, Samoa, Solomon Islands (CABI, 2015; Dixon & Castlebury, 2013; EPPO, 2016; Farr & Rossman).

In the USA it has been reported from Florida and Louisiana (Comstock et al., 2008; Grisham et al., 2013).

Official Control: Puccinia kuehnii is on the “Harmful Organisms Lists” for Brazil, Costa Rica, Egypt, Honduras, and Morocco (PCIT, 2016). Currently, the pathogen has not been rated for California.

California Distribution:  Puccinia kuehnii is not established in California.

California Interceptions: None reported.

The risk Orange Rust of Sugarcane would pose to California is evaluated below.

Consequences of Introduction: 

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

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

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

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

Risk is Low (1):   The potential for establishment and spread of the orange rust pathogen in California is likely to be low as sugarcane, the main host, is grown in limited acreage under dry climates of the Imperial Valley.  Spore germination and plant infection are not expected to be favored under climates of low relative humidity common to that region.

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):  Sugarcane is the main host of P. kuehnii.  The pathogen is largely limited to Saccharum spp. and the related species Sclerostachya fusca.    

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): Puccinia kuehnii has high reproduction and dispersal potential via its windblown spores that are primarily transmitted by strong winds over distances of several hundred kilometers.  Also, they may be spread over long distances via infected plant leaves and spore-contaminated human clothing. 

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

A. The pest could lower crop yield.

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

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

D. The pest could negatively change normal cultural practices.

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

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

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

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

– Medium (2) causes 2 of these impacts.

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

Risk is Low (1): The economic impact of Puccinia kuehnii to California is considered low as the potential for establishment and spread of the pathogen is reasonably minimal within a state where sugarcane is not a majorly cultivated crop and requires high relative humidity for pathogen infection.  Potential incidents of the disease occurring under conducive climates could lower crop yield.  

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):  Puccinia kuehnii infections could affect production of ornamental grasses belonging to Saccharum spp. and grown in private and/or public commercial environments.    

Consequences of Introduction to California for Myrtle Rust:

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

-Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

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

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

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

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

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

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

Evaluation is Not Established (0).  Puccinia kuehnii is not established in California.

Final Score:

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

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

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Puccinia kuehnii is C.

References:

Afshan, N.S., and A. N. Khalid.  2013.  Checklist of the rust fungi on Poaceae in Pakistan. Mycotaxon 125: 1-17.

Comstock, J. C., S. G. Sood, N.C. Glynn, J. M. Shine Jr., J. M. McKemy, and L. A. Castlebury.  2008.  First report of Puccinia kuehnii, causal agent of orange rust of sugarcane, in the United States and Western Hemisphere. Plant Disease, 92(1):175. http://www.apsnet.org.

Dixon, L. and L. Castlebury.  2016.  Systematic Mycology and Microbiology Laboratory, ARS, USDA. . Invasive Fungi. Orange rust of sugarcane – Puccinia kuehnii. Retrieved March 10, 2016, from /sbmlweb/fungi/index.cfm.

EPPO.   2016.  Puccinia kuehnii (PUCCKU).  PQR database.  Paris, France: European and Mediterranean Plant Protection Organization.  http://www.newpqr.eppo.int.

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

Grisham, M. P., J. W. Hoy, J. S. Haudenshield, and G. L. Hartman.  2013.  First report of orange rust caused by Puccinia kuehnii in sugarcane in Louisiana. Plant Disease, 97(3):426-427. http://apsjournals.apsnet.org/loi/pdis.

Hsieh, W. H., and F. G. Fang.  1983.  The uredospore production of Puccinia melanocephala and Puccinia kuehnii in sugarcanes. Plant Protection Bulletin, Taiwan, 25(4):239-244.

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

Responsible Party:

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

Comment Format:

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

Example Comment: 

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

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

♦  Comments may not be posted if they:

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

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

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

Violates agency regulations prohibiting workplace violence, including threats.

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

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

Pest Rating:  C

Posted by ls

Plant Pathogens, Viruses and viroids

Squash Vein Yellowing Virus (SqVYV)

California Pest Rating for
Squash Vein Yellowing Virus (SqVYV)
Pest Rating:  B
PEST RATING PROFILE
Initiating Event:

None.  The risk of introduction of Squash vein yellowing virus to California is assessed and a permanent rating for SqVYV is herein proposed.

History & Status:

Background:    In 2003 in Hillsborough County, Florida, an unknown virus was detected in squash plants (Cucurbita pepo) exhibiting vein yellowing symptoms and soon after in 2005, this virus was found to cause watermelon vine decline in watermelon plants in Florida (Webb et al., 2003; Adkins et al., 2007).  In 2006, the virus was identified and characterized as a new species, Squash vein yellowing virus.  SqVYV is a whitefly-transmitted member of the genus Ipomovirus in the family Potyviridae which induces necrosis of watermelon stems and petioles resulting in rapid wilt and death of plants at or near harvest. In the field, SqVYV is often detected in watermelon in mixed infections with other viruses (Adkins et al., 2013).

Squash vein yellowing virus was reported from California in 2015 following the fall of 2014 detection of diseased pumpkin plants grown from seed at the University of California Desert Research Extension Center in Holtville, California. Molecular analysis of pathogens associated with the diseased plants revealed mixed infections with the crinivirus Cucurbit yellow stunting disorder virus, the begomovirus Squash leaf curl virus and SqVYV. Symptoms of infection and association of a divergent strain of SqVYV were confirmed through pathogenicity trials and molecular diagnostic tests of infected pumpkin and squash plants.  SqVYV-infected melon plants were also detected in commercial fields in the Imperial Valley (Batuman et al., 2015).   Subsequently, during December 2014, official melon and pumpkin samples from the infected sites were collected by Imperial County Agricultural Commissioner’s staff and sent to CDFA Plant Pathology Laboratory for diagnosis.  Tongyan Tian, CDFA plant pathologist, detected SqVYV from the samples using a RT-PCR protocol and sequence analysis.  The detection of SqVYV in Imperial County marked the first report of an Ipomovirus in California (Batuman et al., 2015).

Hosts: The host range is limited to species in Cucurbitaceae with more dramatic symptoms produced in squash (inc. pumpkin) and watermelon.  Plant hosts include two varieties of cucurbit weeds, namely, Momordica charantia (Balsam-apple) and Melothria pendula (creeping cucumber) (Adkins et al., 2008). The weeds may serve as reservoir hosts for SqVYV.

Symptoms: Initial symptoms consist of a slight yellowing of leaves. This is followed by browning and collapse of entire vines within weeks of the first symptoms.  These symptoms appear as the fruit develops to a harvestable size.  Infected fruit internally often exhibit discolored and necrotic blotches in the rind, discolored flesh (too red) and an off-taste (Baker et al., 2008).  SqVYV-infected cucurbit weed hosts are asymptomatic (Adkins et al., 2008).   In Puerto Rico, symptoms of watermelon vine decline on field-grown watermelon included leaf curling, mosaic, and internode necrosis. During the early stage of plant growth reduced vigor and general stunting occurred, and at the flowering stage, symptoms progressed to necrosis and wilting of vines (Acevedo, et al., 2013).  Adkins et al. (2013) reported that symptoms of vine decline in watermelon appeared 12-16 days after inoculation regardless of plant age at time of inoculation and greenhouse or field location. However, younger watermelon plants exhibited more severe symptoms than older ones.

Damage Potential:  In Florida, watermelon plants suffering from vine decline and fruit rot disease caused by SqVYV has resulted in severe losses in spring and fall plantings.   During this period the disease may rapidly increase in incidence from 10 to >80% within a week (Adkins et al., 2007). The disease can result in total crop loss with collapsed vines and unmarketable fruit with discolored and necrotic rinds.

Transmission:  SqVYV is transmitted by the whitefly Bemisia tabaci.  The pathogen is not transmitted by aphids unlike other common cucurbit-infecting species of the family Potyviridae (Adkins et al., 2003). Experimentally, Adkins and others determined that whiteflies required 1-2 days to feed and acquire the virus from infected plants followed by 2 hours or 2 days to inoculate or transmit the virus to non-infected squash and watermelon plants.  Transmission occurs in a semi-persistent mode by the whitefly which remains infective for 4-6 hours after acquiring the virus.  Adkins et al. (2008) experimentally demonstrated that the whitefly vector was able to acquire SqVYV from inoculated cucurbit weed host Momordica charantia and subsequently transmit it to squash and watermelon to produce typical symptoms.  While the virus has been artificially inoculated to plants under greenhouse conditions, the main mode of natural field transmission is through its whitefly vector.

Worldwide Distribution: North America: USA (California, Florida, Georgia, Indiana, South Carolina, Puerto Rico (Acevedo et al., 2013; Egel & Adkins, 2007; Adkins et al., 2013).

Official Control: Squash vein yellowing virus currently holds a temporary Q rating by the CDFA.  No other official control for SqVYV has been reported.

California Distribution: Currently, Squash vein yellowing virus has only been detected in Imperial County.

California Interceptions:  There are no official records of interceptions of Squash vein yellowing virus in California.

The risk Squash vein yellowing 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:

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

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

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

Risk is Medium (2) – SqVYV has already been able to establish in Imperial County, southern California  Its further spread to non-infected sites cultivated to cucurbits 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 low (1) – The natural host range is limited to plant species in the family Cucurbitaceae (which are grown extensively in the lower Sacramento Valley and in limited production in San Joaquin and Imperial Valleys). 

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 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) – SqVYV 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.

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) – Infestations of  SqVYV could significantly impact home/urban gardening of 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 Squash vein yellowing 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 SqVYV to California = (11).

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

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

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

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

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

Evaluation is Low (-1). 

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:

While SqVYV 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 Squash vein yellowing virus is B.

References:

Acevedo, V., J. C. V.  Rodrigues, C. E. de Jensen, C. G. Webster, S. Adkins and L. Wessel-Beaver.  2013.  First report of Squash vein yellowing virus affecting watermelon and bitter gourd in Puerto Rico.  Plant Disease 97:1516.

Adkins S., T. G. McCollum, J. P. Albano, C. S. Kousik, C. A. Baker, C. G. Webster, P. D. Roberts, S. E. Webb and W. W. Turechek.  2013.  Physiological effects of Squash vein yellowing virus infection on watermelon.  Plant Disease 97:1137-1148.

Adkins, S., S.E. Webb, D. Achor, P. Roberts, and C.A. Baker. 2007. Identification and characterization of a novel whitefly-transmitted member of the family Potyviridae isolated from cucurbits in Florida.  Phytopathology 97: 145-154.

Adkins, S.T., S. Webb, C. Baker, and C.S. Kousik. 2008. Squash vein yellowing virus detection using nested polymerase reaction demonstrates the cucurbit weed Momordica charantia is a reservoir host. Plant Disease 92: 1119-1123.

Baker, C., S. Webb and S. Adkins.  2008.  Squash vein yellowing virus, causal agent of watermelon vine decline in Florida. Plant Pathology Circular No. 407, Florida Department of Agriculture and Consumer Services, Division of Plant Industry.

Egel, D. S. and S. Adkins. 2007.  Squash vein yellowing virus identified in watermelon (Citrullus lanatus) in Indiana.  Plant Disease, 91:1056.2.

Batuman, O., E. T. Natwick, W. M. Wintermantel, T. Tian, J. D. McCreight, L. L. Hladky, and R. L. Gilbertson.  2015.  First report of an Ipomovirus infecting cucurbits in the Imperial Valley of California.  Plant Disease 99:1042.  http://dx.doi.org/10.1094/PDIS-12-14-1248-PDN.

Webb, S. E., E. Hiebert and T. A. Kucharek.  2003.  Identity and distribution of viruses infecting cucurbits in Florida.  Phytopathology 93:S89.

Responsible Party:

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

Comment Format:

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

Example Comment: 

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

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

♦  Comments may not be posted if they:

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

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

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

Violates agency regulations prohibiting workplace violence, including threats.

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

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

Pest Rating:  B

Posted by ls

Fungi, Plant Pathogens

Phytophthora tentaculata Kröber & Marwitz 1993

California Pest Rating Proposal for
Phytophthora tentaculata Kröber & Marwitz 1993
Pest Rating: B
PEST RATING PROFILE
Initiating Event: 

During January 2016, samples of two diseased Diplacus hybrids (monkey flower hybrid varieties) and one of diseased Artemisia palmeri (Palmer sagewort) were collected by Kathleen Kosta, CDFA, from a nursery in Santa Clara County.  The samples were processed and analyzed at the CDFA Plant Pathology Laboratory and Phytophthora tentaculata was tentatively identified as the associated pathogen by Suzanne Rooney-Latham, CDFA plant pathologist.  The identity of the pathogen was later confirmed by the USDA APHIS PPQ CPHST Laboratory in Beltsville, Maryland.  The three afore mentioned plant varieties are new hosts records for P. tentaculata.  Several detections of this pathogen have been made in California during the past few years.  Therefore, the current rating for P. tentaculata is reassessed here.

History & Status:

Background: In 1993, Phytophthora tentaculata was first isolated from roots and stems of greenhouse-grown Argyranthemum frutescens (syn. Chrysanthemum frutescens), Leucanthemum vulgare  (syn. C. leucanthemum), Delphinium ajacis, and Verbena sp. in nurseries in the Netherlands and Germany in 1993 (Kröber & Marwitz, 1993).  Later, the pathogen was also reported from Spain (Moralejo et al., 2004; Álvarez et al., 2006), Italy (Cristinzio et al., 2006; Martini et al., 2009) and China (Meng & Wang, 2006; Wang and Zhao, 2014) after detection in nursery-potted and field-grown plants.  In 2012, P. tentaculata was first detected in North America, in sticky monkey flower, Diplacus aurantiacus (syn. Mimulus aurantiacus) growing in a native plant nursery in Monterey County, California.  Plant samples collected by Monterey County and CDFA staff were submitted to CDFA for analysis and the pathogen P. tentaculata was identified by Suzanne Rooney-Latham and Cheryl Blomquist, CDFA plant pathologists (Rooney-Latham & Blomquist, 2014), and later confirmed by the USDA APHIS National Identification Services. The source of the Diplacus (Mimulus) plants was traced back to plants that were grown from seed and cuttings from a historical site in Monterey County.  No Diplacus (Mimulus) plants had been shipped from the native plant nursery prior to the initial detection.  Consequently, all positive Diplacus (Mimulus) plants and materials were destroyed.  The California detection marked the first detection on a native host, albeit in a native plant restoration nursery and a host that has a wide geographical native range in California.  Since its initial Monterey County find, P. tentaculata has also been detected in native plant nurseries in Placer, Butte, Santa Cruz, San Mateo, Orange, and Santa Clara Counties, and in out-planted nursery stock in habitat restoration sites in Alameda, Monterey, and Santa Clara Counties. The pathogen was detected and reported from several new hosts that are listed below (see ‘Hosts’) and include Artemisia douglasiana, A. californica, A. dranunculus, A. palmeri, Diplacus x “Apricot”, Diplacus x “Red brick”, Monardella villosa, and Salvia sp.  Several of these detections were made during a 2014-2015 survey of California native plant nurseries and restoration sites conducted by the collaborative efforts of CDFA, USDA and a private research company.  The survey resulted in the detection of P. tentaculata in 8 out of 16 counties.  The origin of P. tentaculata is unknown.  Presently in California, Phytophthora tentaculata has only been detected in nursery-grown plants that were out-planted in the environment.  The pathogen has persisted on those plants in the field for at least 4.5 years. Therefore, it is likely that in California, the pathway of pathogen spread is from infected nurseries to restoration field sites, and that the pathogen has been spread between and within nurseries by the use of infested pots and plants (Rooney-Latham, et al., 2015).

Hosts: The currently known hosts are included in the plant families Asteraceae, Lamiaceae, Phrymaceae,  Ranunculaceae, Rhamnaceae, Rosaceae, and Verbenaceae.  The host range includes the following plants, diseases and geographical locations:

Apium graveolens (celery); stem and root rot; China (Wang & Zhao, 2014).

Argyranthemum frutescens (syn. Chrysanthemum frutescens) (marguerite daisy); root and stem base rot; Germany & the Netherlands; Root, collar & stalk rot (Kröber & Marwitz 1993).

Artemisia douglasiana (California mugwort); root rot; California, USA (Rooney-Latham, et al., 2015).

Artemisia dracunculus (tarragon); root rot; California, USA (Rooney-Latham et al., 2015). Artemisia californica (California sagebrush); root rot; California, USA (Rooney-Latham et al., 2015).

Artemesia palmeri (Palmer sagewort); root rot; California, USA (see “Initiating Event”).

Aucklandia lappa (rhizomatous medicinal herb); China; stalk rot & wilt (Meng & Wang 2008).

Calendula arvensis (field marigold) (Li et al., 2011).

Ceanothus cuneatus (buckbrush); root rot; California, USA (Rooney-Latham et al., 2015).

Cichorium intybus (chicory, endive); Italy; collar and root rot (Garibaldi et al. 2006).

Delphinium ajacis (nursery stock); Germany & the Netherlands; root, collar & stalk rot (Kröber & Marwitz 1993).

Diplacus aurantiacus (syn Mimulus aurantiacus) (sticky monkey-flower); California, USA.  root and collar rot (Rooney-Latham & Blomquist, 2014).

Diplacus x “Apricot” (Diplacus hybrid variety); root and collar rot; California, USA (see “Initiating Event”).

Diplacus x “Red brick” (Diplacus hybrid variety); root and collar rot; California, USA (see “Initiating Event”).

Frangula californica (syn. Rhamnus californica) (coffeeberry); California; root and collar rot (Frankel et al., 2015; NPAG, 2014).

Gerbera jamesonii (African daisy); Italy; Crown & stem rot (Cristinzio et al. 2006).

Heteromeles arbutifolia (toyon) California, USA (Frankel et al., 2015; NPAG, 2014).

Leucanthemum vulgare (syn. Chrysanthemum leucanthemum) Germany & the Netherlands; Root, collar & stalk rot (Kröber & Marwitz 1993).

Monardella villosa (coyote mint); California, USA (Rooney-Latham et al., 2015).

Origanum vulgare (oregano); Italy.  Leaf russeting & chlorosis, wilt, defoliation, twig dieback,basal stem rot, root rot, entire plant collapse (Martini et al. 2009).

Salvia spp. (sage) California, USA (Frankel et al., 2015; NPAG, 2014).

Santolina chamaecyparissus (lavender cotton); Spain; Root rot (Alvarez et al. 2004).

Verbena sp. (nursery stock); Germany, Netherlands; nursery potted plant in Spain; root, collar & stalk rot (Moralejo et al. 2004).

Symptoms:  Depending on the host species, Phytophthora tentaculata causes moderate to severe root and crown rot, and death in highly infected plants. The symptoms are not unique to P. tentaculata by similar to infections caused by other Phytophthora species, root and stem pathogens and drought.   According to Rooney-Latham et al (2015) symptoms can vary in field-planted nursery stock.  Infected sticky monkey flower plants are stunted, with dull yellowish leaves that turn red as the disease progresses.  Roots and stem collars have necrotic, sunken lesions with few feeder roots and discolored leaves. In some cases, plants may exhibit poor growth and eventually collapse within their first season, while some plants may grow for a year or more before exhibiting severe dieback during hot summers. Transplanted infected Artemisia douglasiana plants did not show dieback, but exhibited stunting and chlorosis more that 4.5 years after being out-planted (Rooney-Latham et al., 2015; Frankel et al., 2015; Kröber & Marwitz 1993).

Damage Potential:  Phytophthora tentaculata causes moderate to severe root and crown rot on woody and semi-woody hosts.  Introduction of P. tentaculata-infected native plants to restoration sites could negatively impact native plants in their natural environment.

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, 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). Little information is known about the life cycle or biology of Phytophthora tentaculata other than what was provided by the original species description by Kröber and Marwitz. The temperature range of the pathogen is 7°C to 32°C, the optimum temperature being 15°C to 25°C.

Transmission: Like most Phytophthora species, P. tentaculata is soil-borne and water-borne and may be spread to non-infected sites through infected plants, nursery and planting stock, seedlings, soil, run-off and splash irrigation and rain water, and contaminated cultivation equipment and tools.

Worldwide Distribution: Asia: China; Europe: Italy, Germany, the Netherlands, Spain; North America: USA (California).

Official Control: USDA lists Phytophthora tentaculata in the top 5 Phytophthora species of concern and threat to nurseries and forests in Federal New Pest Response Guidelines (USDA APHIS, 2010).  USDA APHIS New Pest Advisory Group determined that P. tentatculata is “actionable and reportable.

California Distribution: Phytophthora tentaculata has been detected in native plant nurseries in Monterey, Placer, Butte, Santa Cruz, San Mateo, Orange, and Santa Clara Counties, and in out-planted nursery stock in habitat restoration sites in Alameda, Monterey, and Santa Clara Counties.

California Interceptions: None.

The risk that Phytophthora tentaculata would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Evaluate and score the pest for suitability of 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) – To date, Phytophthora tentaculata has been detected in native plant nurseries in eight counties and in habitat restoration sites (in out-planted nursery stock) in three of those eight counties.  Several native plant hosts are widespread in California.  Since the pathogen is known to attack many plants in the nursery trade, it is possible that the pathogen could appear and survive wherever nurseries, including native plant nurseries, are present in California.  Therefore, there is the potential for this pathogen to establish a widespread distribution in California.

2) Pest Host Range: Evaluate and score the pest as it pertains to host range.  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) – Presently, 23 plant hosts belonging to 7 families have been reported.  Of these, almost half the number of hosts have been reported from California, and are native to the State.  While several new hosts have been reported after the initial detection of the pathogen in Monterey County, based on the present known host range, the risk of the pathogen is evaluated as medium.

3)   Pest Dispersal Potential: Evaluate and score the pest for dispersal potential using these criteria.  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 tentaculata is soil-borne and water-borne and therefore, 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) – The presence of Phytophthora tentaculata could cause severe economic impacts in nursery trade, impacting a number of nursery-produced native and ornamental plants that are commonly used in California landscapes as well as some of which play a significant role in the State’s florist trade.  In addition to lowered crop yields and lowered crop values due to increased need for protective treatments, the management of infestations of a soil- and water-borne pathogen such as Phytophthora spp. in a commercial nursery may be a laborious and expensive problem that would involve alterations in the normal cultural practices such as choice of sites to grow susceptible hosts, and water and growth medium management practices to ensure pathogen propagule-free irrigation water and growth media.

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

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 could significantly impact cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact:

– 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) – The USDA APHIS lists Phytophthora tentaculata in the top 5 Phytophthora species of concern and threat to nurseries and forests in Federal New Pest Response Guidelines (USDA APHIS, 2010).  The presence of P. tentaculata could cause serious impact on native plants, threatened or endangered species, disrupt critical habitats by killing critical species necessary for species diversity and soil stability, necessitate official or private treatment programs to preserve critical, rare, or endangered species, and significantly impact cultural practices, home/urban and/or ornamental plantings.

Consequences of Introduction to California for Phytophthora tentaculata:

Add up the total score and include it here

– Low = 5-8 points

– Medium = 9-12 points

– High = 13-17 points

Total points obtained on evaluation of consequences of introduction of Phytophthora tentaculata 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)

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

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

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

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

Evaluation is Medium (-2). To date, Phytophthora tentaculata has been detected in native plant nurseries in Monterey, Placer, Butte, Santa Cruz, San Mateo, Orange, and Santa Clara Counties, and in out-planted nursery stock in habitat restoration sites in Alameda, Monterey, and Santa Clara Counties 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 = 12.

Uncertainties:

While more is known about the presence of Phythophthora tentaculata in California since its original detection in Monterey County, more researched information is needed on the distribution, behavior and threat of Phytophthora tentaculata in California’s natural soils and plant communities under diverse climatic environments.  

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Phytophthora tentaculata remains B.

References:

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

Álvarez, L. A., A. Pérez-Sierra, M. León, J. Armengol, and J. García-Jiménez.  2006.  Lavender cotton root rot: a new host of Phytophthora tentaculata found in Spain. Plant Disease 90:523. http://dx.doi.org/10.1094/pd-90-0523A

Cristinzio, G., I. Camele and C. Marcone.  2006.  Phytophthora tentaculata su gerbera in Italia.  First report of Phytophthora tentaculata on gerbera in Italy.  Informatore Fitopatologico 56:23-25. http://www.cabdirect.org/abstracts/20063066005.html;jsessionid=C23F9F14D93FF641EEE94948EFEB99D5.

Frankel, S., S. Rooney-Latham, C. L. Blomquist, and E. Bernhardt.  2015.  Pest Alert: Phytophthora tentaculata.  Technical Report, February 2015, United States Department of Agriculture. http://www.suddenoakdeath.org/wp-content/uploads/2015/02/P.tentaculata.

Garibaldi A., G. Gilardi, M. L. Gullino.  2010. First report of collar and root rot caused by Phytophthora tentaculata on witloof chicory (Cichorium intybus) in Italy. Plant Disease 94:1504.

Kröber, H., and R. Marwitz.  1993.  Phytophthora tentaculata sp. nov. und Phytophthora cinnamomi var. parvispora var. nov., zwei neue Pilze von Zierpflanzen in Deutschland. Zeitschrift fur Pflanzenkrankheiten und Pflanzenschutz 100, 250-258. [Original Description]

Martini, P., A. Pane, F. Raudino, A. Chimento, S. Scibetta, and S. O. Cacciola.  2009.  First report of Phytophthora tentaculata causing root and stem rot of oregano in Italy. 93:843. http://dx.doi.org/10.1094/PDIS-93-8-0843B.

Meng, J., and Y. C. Wang.  2008.  First Report of Stalk Rot Caused by Phytophthora tentaculata on Aucklandia lappa in China. Plant Disease 92 (9): 1365.

doi:10.1094/PDIS-92-9-1365B. http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-92-9-1365B.

Moralejo, E., M. Puig, and W. A. Man in’t Veld.  2004.  First report of Phytophthora tentaculata on Verbena sp. in Spain. The British Society for Plant Pathology.

http://www.bspp.org.uk/publications/new-disease-reports/ndr.php?id=009038. May 31, 2009.

USDA APHIS.  2010.  New Pest Response Guidelines: Phytophthora species in the Environment and Nursery Settings. 229 pages.

Rooney-Latham, S., and C. L. Blomquist.  2014. First report of root and stem rot caused by Phytophthora tentaculata on Mimulus aurantiacus in North America. Plant Disease 98(7):996.

Rooney-Latham, S., C. L. Blomquist, T. Swiecki, and E. Bernhardt.  2015.  Phytophthora tentaculata.  Forest Phytophthoras 5(1):  doi:10.5399/osu/fp.5.1.3727.

Schwartzburg, K., H. Hartzog, C. Landry, J. Rogers, and B. Randall-Schadel.  2009. Prioritization of Phytophthora of Concern to the United States. USDA APHIS PPQ CPHST PERAL (Plant Epidemiology and Risk Analysis Laboratory), Raleigh, NC. 61 pages.

Wang, T. and W. Zhao.  2014.  First report of Phytophthora tentaculata causing stem and root rot on celery in China. http://dx.doi.org/10.1094/PDIS-06-13-0592-PDN.

Responsible Party:

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

Comment Format:

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

Example Comment: 

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

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♦  Comments may not be posted if they:

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Pest Rating: B

Posted by ls

Plant Pathogens, Viruses and viroids

Freesia Sneak Virus (FreSV)

California Pest Rating forFreesia Sneak Virus
Freesia Sneak Virus
Pest Rating: B
PEST RATING PROFILE
Initiating Event:

None.     

History & Status:

Background:  Freesia sneak virus (FreSV) is associated with freesia leaf necrosis disease. The disease has been reported in Europe since the 1970s.  Although FreSV has been most closely correlated with freesia leaf necrosis symptoms in freesia plants, other species within the same genus may also be correlated (e.g., Freesia mosaic virus FreMV) and, therefore, the causal agent(s) is/are still being determined (Bouwen, 1994; Meekes & Verbeek, 2011).

Freesia sneak virus is a plant virus belonging to the genus Ophiovirus in the family Ophioviridae.  Freesia sneak virus is soil-borne and vectored by the soil-borne fungus, Olpidium brassicae. Initially, the virus was provisionally called Freesia Ophiovirus, but is now known as Freesia sneak virus (Vaira et al., 2006).

In the USA, Freesia sneak virus was first reported from infected Freesia spp. in Virginia in 2009 (Vaira et al., 2009).  The pathogen was detected in California, in symptomatic freesia plant samples collected during April 2014, from a nursery in San Luis Obispo County. The pathogen was identified by Tongyan Tian, CDFA plant pathologist.  Subsequently, all infected plant material was destroyed.

Hosts: Freesia spp. (Iradaceae) and Lachenalia spp. (Hyacinthaceae) (Jeong, et al., 2014; Meekes & Verbeek, 2011; Vaira et al., 2007, 2009).  Both hosts are monocots native to South Africa.

Symptoms: Symptoms may be affected by environmental conditions (Vaira et al., 2006).

Freesia leaf necrosis disease mainly affects the leaves exhibiting chlorotic spots and stripes that start at the leaf tip and usually spread over the entire leaf.  Later these chlorotic spots turn grey-brown and become necrotic.  Mildly infected plants show light chlorotic symptoms only on the lower leaves.  Flowers and corms do not seem to be affected by the disease (Van Dorst, 1973; Bouwen, 1994; Meekes & Verbeek, 2011).

Damage Potential: In detection surveys conducted in Korea, Freesia sneak virus was detected from 71.7% of 138 plants tested (Jeong et al., 2014).  Infection rates of 10-25% percent of plants shipped to the USA have been reported (Hansen, 2008; Vaira et al., 2009).  In California, nursery and private productions of freesia and lachenalia plants, in particular, may be impacted if infected with Freesia sneak virus.

Transmission: in nature, Freesia sneak virus is vectored by the soil-borne fungus, Olpidium brassicae, and not by mechanical transmission.  Resting spores of O. brassicae are very persistent and can survive for more than twenty years in soil without losing the capacity to transmit the disease (Meekes & Verbeek, 2011).   Therefore, spread of FreSV is also through movement of contaminated soils and plants.

Worldwide Distribution:  Asia: Korea; Africa: South Africa; Europe: Northern Europe including the Netherlands, Italy; North America: USA (Virginia) (Jeong et al., 2014; Meekes & Verbeek, 2011; Vaira, et al., 2007, 2009).

Official Control: None reported.

California Distribution: San Luis Obispo (nursery).

California Interceptions: There have not been any interceptions of Freesia sneak virus-infected plants entering California.

The risk Freesia sneak 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:

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

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

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

Risk is Medium (2) – Freesia sneak virus is likely to establish wherever freesia and lachenalia plants are grown in limited areas of California. Freesia has limited production in state and is naturalized mostly in the north coast region, as well as cultivated in nursery and private production sites – including home gardens.    Lachenalia is grown mainly in nurseries and in private productions as a hobbyist’s plant.   

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

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

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1) – Freesia sneak virus is limited to Freesia spp. (Iradaceae) and Lachnenalia spp. (Hyacinthaceae).

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

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

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

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

Risk is Medium (2) – Freesia sneak virus has high reproductive potential.  In nature, its spread to non-infected plants is dependent on the presence of the soil-borne fungus vector, Olpidium brassicae.  Resting spores of O. brassicae are very persistent and can survive for more than twenty years in soil without losing their viability. Therefore, FreSV is also spread through movement of contaminated soils and plants.  The pathogen is not mechanically transmitted.

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) – Incidents of Freesia sneak virus infections could lower plant value resulting in loss in market sales of nursery-grown freesia and lachenalia plants.  The pathogen is vectored by the soil fungus, Olpidium brassicae.    

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

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

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

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

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

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

Score the pest for Environmental Impact. Score:

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

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

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

Risk is Low (1) – Plant infections caused by Freesia sneak virus are likely to have a minimal impact on the overall environment but may significantly impact home gardening and ornamental plantings.

Consequences of Introduction to California for Freesia sneak 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 Freesia sneak virus to California = 9.

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

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

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

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

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

Evaluation is not established.  Freesia sneak virus-infected freesia plants have only been detected in a contained nursery environment in California.  Those plants were subsequently destroyed and therefore, the pathogen is not considered established in the State.

Final Score:

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

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

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Freesia sneak virus is B.

References:

Bouwen, I.  1994.  Freesia leaf necrosis: some of its mysteries revealed.  Virus Diseases of Ornamental Plants VIII, Acta Horticulturae 377: 311-318.

Hansen, M. A.   2008.  Freesia sneak virus – a new find for the United States.  Virginia Cooperative Extension, Virginia Tech Plant Disease Clinic: https://www.cals.ncsu.edu/plantpath/activities/societies/ornamental/2008_talks/freesia_sneak_virus_4.pdf.

Jeong, M. I., Y. J. Choi, J. H. Joa, K. S. Choi, and B. N. Chung.  2014.  First report of Freesia sneak virus in commercial Freesia hybrida cultivars in Korea.  Plant Disease 95:162. http://dx.doi.org/10.1094/PDIS-05-13-0484-PDN.

Meekes, E. T. M., and M. Verbeek.  2011.  New insights in Freesia leaf necrosis disease.  Proceedings XIIth IS on Virus Diseases of Ornamental Plants; Editors A. F. L. M. Derks et al.  Acta Horticulturae  901, ISHA 2011.

Vaira, A. M., V. Lisa, A. Costantini, V. Masenga, S. Rapetti, and R. G. Milne.  2006.  Ophioviruses infecting ornamentals and a probable new species associated with a severe disease in Freesia.  Proceeding XIth IS on Virus Diseases in Ornamentals, Ed. C. A. Chang.  Acta Horticulturae 722, ISHA 2006.

Vaira, A. M., R. Kleynhans, and J. Hammond.  2007.  First report of Freesia sneak virus infecting Lachenalia cultivars in South Africa.  Plant Disease 91:770.  http://dx.doi.org/10.1094/PDIS-91-6-0770A.

Vaira, A. M. , M. A. Hansen, C. Murphy, M. D. Reinsel, and J. Hammond.  2009.  First report of Freesia sneak virus in Freesia sp. in Virginia.  Plant disease, 93:965. http://dx.doi.org/10.1094/PDIS-93-9-0965B.

Van Dorst, H. J. M.  1973. Two new disorders in freesias.  Netherland Journal of Plant Pathology 79:130-137.

Responsible Party:

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

Comment Format:

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

Example Comment: 

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

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

♦  Comments may not be posted if they:

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

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

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

Violates agency regulations prohibiting workplace violence, including threats.

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

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

Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Greeneria uvicola (Berk. & M. A. Curtis) Punith. 1974

California Pest Rating Proposal for
Greeneria uvicola (Berk. & M. A. Curtis) Punith. 1974
Pest Rating: B
PEST RATING PROFILE
Initiating Event:  

On December 16, 2015, a shipment of grape leaves from Texas, destined to a retail store in California, was intercepted by the Los Angeles County officials.  The leaves had symptoms of leaf spots and a sample was collected and sent to the CDFA Plant Pathology Laboratory for disease diagnosis.  The fungal pathogen, Greeneria uvicola, was identified as the cause for the leaf spots, by Suzanne Rooney Latham, CDFA plant pathologist.  The pathogen was given a Q rating and subsequently the shipment of grape leaves was destroyed.  The risk of infestation of Greeneria uvicola in California is evaluated and a permanent rating is herein proposed. 

History & Status:

Background:  Greeneria uvicola is the cause of ‘Bitter Rot’ of grapes. The disease is cosmopolitan and common in the southern eastern United States, while being an occasional problem in the northern region as far as Long Island and New England states.  Greeneria uvicola is an asexually reproducing fungus with no known sexual state. Taxonomically, the pathogen is also known by several synonyms (including, Greenaria fuliginea, Melanconium fuligineum, and Phoma uvicola) and based on molecular data was placed in Ascomycetes, Diaporthales (Farr et al., 2001; Sutton, 2015).

Hosts: Grapevine (Vitis spp.).

Symptoms:  The pathogen infects all above ground vegetative plant parts including stem, leaves, tendrils and fruits.  Leaf symptoms, which are more common on muscadine grapes than on bunch grapes, appear as tiny, sunken, reddish-brown flecks with yellow halos.  Stem and petiole infects result in round to elliptical, reddish brown to black lesions which may be slightly raised or sunken.  Flecking of sepals and blighting of flower buds may also occur.  The fungus initially invades the berry from the berry stem (pedicel) at the onset of ripening. Infected light-skinned berries turn brown and form multiple, prominent fungal asexual fruiting bodies (acervuli) once the berries reach their full size.  As the rot progresses through the infected berries, the acervuli form in concentric rings, but are more uniformly distributed once the fruit is completely rotted.  These symptoms are less visible on dark-skinned berries which rough-skinned and iridescent.  Eventually, infected berries soften, shrivel, may be completely covered with acervuli, and may abscise or become mummified and remain attached (Sutton, 2015).

Damage Potential:  Infected fruit becomes rotted and as rotted fruit begins to soften they have a distinct bitter taste which is carried through the winemaking process resulting in a finished wine with an unpleasant, burnt or bitter taste.  Therefore, the marketability of diseased fruit for table or wine use is reduced.

Disease Cycle: The pathogen overwinters as a saprophyte on fallen fruit, cold-damaged shoot tips, and necrotic bark of the trunk and cordons.  In spring, gelatinous masses of spores (conidia) are produced from acervuli and washed by rain to green vegetative parts including the pedicels.  Disease development requires long and warm rains in spring, followed by warm, humid summers.  Infections occur during wet periods at 12-30°C, and optimally at 22.4-24.6°C, with 6-12 hrs wetness.  The fungus invades the pedicel and remains latent until fruit mature.  At that time the pathogen actively grows from the infected pedicel into the maturing fruit resulting in berry rot.  Conidia are produced in infected berries and rain splashed onto other ripening fruit causing secondary infections.  Infections usually occur in fruit wounded by insects, birds, hail, heavy rainstorms, or mechanically.  Berries are most susceptible at the onset of ripening however they may be infected by conidia anytime between bloom and harvest (Sutton, 2015).

Transmission:   The pathogen is spread through infected above ground vegetative plant materials and dead plant debris (leaves, stems, tendrils, and mummied fruits), rain/water splash.

Worldwide Distribution: Greeneria uvicola is distributed worldwide and reported from Asia: India, China, Taiwan, Thailand; Africa: South Africa; Europe: Bulgaria, Poland, Ukraine; North America: USA, Mexico; South America: Brazil, Costa Rica; Uruguay; Australia (Farr & Rossman, 2016; Samuelian, et al., 2013; ChaoYu et al., 2015).  Greece, Japan, and New Zealand have also been reported (Sutton, 2015).

In the USA, Greeneria uvicola has been reported mainly from the south eastern states.  Its distribution includes Florida, Georgia, Missouri, Mississippi, Ohio, Oklahoma, North Carolina, South Carolina, and West Virginia (Farr & Rossman, 2016).

Official Control:  Greeneria uvicola is on the ‘Harmful Organism List’ for China (PCIT, 2015).  Presently, G. uvicola has a temporary (Q) rating as a quarantine, actionable pathogen by the CDFA.

California Distribution:  Greeneria uvicola is not reported from California.

California Interceptions: There has been only one interception of Greeneria uvicola-infected grape leaves in California (see ‘Initiating Event”).

The risk Greeneria uvicola would pose to California is evaluated below.

Consequences of Introduction: 

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

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

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

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

Risk is Low (1) – The requirements for a suitable climate of long periods of warm rains in spring, followed by warm, humid summers would not likely favor or greatly limit the establishment of Greenaria uvicola in California where grape is usually cultivated under warm and dry conditions.

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) – Grape (Vitis spp.) is the only host.  Although the host range is very limited, in California grape is a major crop that is cultivated over significant acreage.

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

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

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

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

Risk is Medium (2) – Greeneria uvicola is highly reproductive, producing gelatinous masses of conidia for primary and secondary infections.  Dispersal of conidia is dependent on rain splash for delivery to, and infection of non-infected above ground parts of the grapevine.

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) – Bitter rot diseased fruit is rotted and has a bitter taste that results in finished wine with an unpleasant bitter or burnt flavor.  Therefore, Greeneria uvicola-infected fruit could lower crop yield of healthy fruit bunches, lower crop value, and trigger loss of markets of table and wine grapes.   

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) – Home gardens cultivated with table and/or wine grapes could be significantly impacted if infected with the bitter rot pathogen.

Consequences of Introduction to California for Greeneria uvicola:

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 Greeneria uvicola to California = 9

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

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

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

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

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

Evaluation is not established 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 = 9.

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the bitter rot pathogen, Greeneria uvicola is B .  

References:

ChaoYu, Cui, Jiang JunXi, Ouyang Hui, Li Cheng, Liu DengQuan, and Huang Ting.  2015.  First report of Greeneria uvicola causing bitter rot of grape in China.  Journal of Phytopathology, 163:780-782.

http://www.eppo.int/DATABASES/pqr/pqr.htm .

Farr, D. F., and A. Y. Rossman.  2015.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved January 12, 2016, from http://nt.ars-grin.gov/fungaldatabases/

Farr. D. F., L. A. Castlebury, A. Rossman, and O. Erincik.  2001.  Greeneria uvicola, cause of bitter rot of grapes, belongs in Diaporthales.  Sydowia-Horn, 53:185-199.

PCIT.  2015.  USDA Phytosanitary Certificate Issuance & Tracking System. July 21, 2015.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp .

Samuelian, S. K., L. A. Greer, K. Cowan, M. Priest, T. B. Sutton, S. Savocchia, and C. C. Steel.  2013.  Phylogenetic relationships, pathogenicity and fungicide sensitivity of Greeneria uvicola isolates from Vitis vinifera and Muscadinia rotundifolia.  Plant Pathology, 62: 829-841.

Sutton, T. B.  2015.  Diseases caused by biotic factors, diseases caused by fungi and Oomycetes: Bitter Rot.  Compendium of Grape Disease, Second Edition.APS Press, The American Phytopathological Society, pg. 24-26.

Responsible Party:

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

Comment Format:

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

Example Comment: 

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

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

♦  Comments may not be posted if they:

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

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

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

Violates agency regulations prohibiting workplace violence, including threats.

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

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

Pest Rating: B

Posted by ls

Fungi, Plant Pathogens

Colletotrichum cordylinicola Phoulivong, L. Cai & K. D. Hyde, 2011

California Pest Rating Proposal for
Colletotrichum cordylinicola Phoulivong, L. Cai & K. D. Hyde, 2011
Pest Rating: B
PEST RATING PROFILE
Initiating Event:  

On October 6, 2015 a shipment of Green Ti plant cuttings (Cordyline glauca) showing leaf blight symptoms and destined to a nursery in San Diego County, was intercepted and sampled by San Diego County Agricultural officials.   The shipment had originated in Costa Rica.  Diseased plant samples were sent to the CDFA Plant Diagnostics Branch for diagnosis.  Suzanne Latham, CDFA plant pathologist identified the leaf spot and anthracnose pathogen, Colletotrichum sp. as the cause for the disease. The identity of the associated pathogen was later confirmed to be C. cordylinicola by USDA National Identification Services at Beltsville, Maryland, and marked the first detection of C. cordylinicola in continental USA.  The pathogen was assigned a temporary Q rating by the CDFA and consequently, all infected plant materials were destroyed. The risk of infestation of C. cordylinicola in California is evaluated and a permanent rating is proposed.

History & Status:

Background:  In 2010, Phoulivong et al. first reported the fungal species, Colletotrichum cordylinicola causing anthracnose disease in Cordyline fruticosa in Thailand and Eugenia javanica in Laos. They noted that the isolate from C. fruticosa was not pathogenic to E. javanica and vice versa, and that both strains may represent different pathotypes.  However, Weir et al. (2012), through further molecular analysis placed both isolates within the same species.  Colletotrichum cordylinicola is a distinct fungus species belonging to the vastly morphological and physiological variable C. gloeosporioides and is genetically identified from other species of the complex (Weir et al, 2012). Colletotrichum cordylinicola has not been reported from the USA.  A reported identification of C. cordylinicola detected on Cordyline fruticosa in Florida (Sharma et al., 2014) is considered inconclusive by the USDA APHIS PPQ National Identification Services.

Hosts: Cordyline (Cordyline fruticosa) in the Asparagaceae family, and wax jambu (Eugenia javanica = syn. Syzygium samarangense) in the Myrtaceae family.

Symptoms:  Colletotrichum cordylinicola causes leaf and fruit spots.  Generally, Colletotrichum-infected host plants exhibit symptoms of anthracnose which include dark brown leaf, stem and fruit spots and wilting of leaves which often result in dieback and reduction in plant quality.

Damage Potential:  In general, anthracnose disease of fruits and leaves caused by Colletotrichum spp., can result in reduction in yield quantity and quality of agricultural crops and fruit trees (Phoulivong et al., 2010).  It is, therefore, highly likely that Colletotrichum cordylinicola can result in reduced plant quality and growth, fruit production and marketability.  Estimates of yield/crop loss due to this pathogen have not been reported.  Nursery productions of ornamental cordyline and wax jambu plants are particularly at risk as nursery conditions are often conducive to infection by Colletotrichum species.  In open fields, disease development may be sporadic as it is affected by levels of pathogen inoculum and environmental conditions.

Disease Cycle:  It is likely that Colletotrichum cordylinicola has a similar life cycle to that of other Colletotrichum species and survives between crops during winter as mycelium on plant residue in soil, on infected plants, and on seeds.  During active growth, the pathogen produces masses of hyphae (stromata) which bear conidiophores, on the plant surface. Conidia (spores) are produced at the tips of the conidiophores and disseminated by wind, rain, cultivation tools, equipment, and field workers.   Conidia are transmitted to host plants.  Humid, wet, rainy weather is necessary for infection to occur.  These requirements in particular may limit the occurrence of the pathogen in California fields and subsequently, the pathogen may be more of a problem under controlled environments of greenhouses.  Conidia germinate, penetrate host tissue by means of specialized hyphae (appresoria) and invade host tissue.

Transmission:  Wind, wind-driven rain, cultivation tools, and human contact.

Worldwide Distribution:  Colletotrichum cylindricola is distributed in Thailand, Laos, and New Zealand (Farr & Rossman, 2015; Phoulivong et al., 2010; Weir et al., 2012).

Official Control:  Presently, in California C. cordylinicola is an actionable, Q-rated pathogen, and infected plant material is subject to destruction or rejection.  The pathogen is categorized as ‘reportable’ by the USDA.

California Distribution: Colletotrichum cylindricola is not established in California (see “Initiating Event”).

California Interceptions: There has been one reported interception of Colletotrichum cordylinicola-infected Cordyline glauca plant cuttings. (see ‘Initiating event’).

The risk Colletotrichum cordylinicola would pose to California is evaluated below.

Consequences of Introduction: 

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

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

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

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

Risk is Low (1) – Similar to other species of Colletotrichum cordylinicola requires humid, wet, rainy weather for conidia to infect host plants. The environmental requirements and narrow host range may limit the ability of the pathogen to fully establish and spread under outdoor dry conditions 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) – Colletotrichum cylindricola has a limited host range comprising of cordyline (Cordyline fruticosa) and wax jambu (Eugenia javanica) .  Cordyline is an indoor decorative plant that is commonly produced in nursery greenhouses in California. Outdoor cultivation of this plant is not common.  Wax Jambu (Eugenia javanica) may be grown in limited residential and commercial public regions in Southern 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 pathogen has high reproductive potential and conidia are produced successively.  They are transmitted by wind, wind-driven rain, cultivation tools, and human contact however conidial germination and plant infection require long, wet periods.

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

A.  The pest could lower crop yield.

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

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

D.  The pest could negatively change normal cultural practices.

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

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

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

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

– Medium (2) causes 2 of these impacts.

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

Risk is Medium (2) –Anthracnose-infected cordyline and wax jambu plants may result in lower crop value and market loss.  .Nursery production of these hosts is particularly at risk as nursery conditions are often conducive to infection by Colletotrichum species.  Its economic impact is evaluated as a medium risk.   

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

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

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

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

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

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

Score the pest for Environmental Impact. Score:

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

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

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

 Risk is Medium (2) – The pathogen could significantly impact home/urban gardens and ornamental plantings.

Consequences of Introduction to California for Colletotrichum cordylinicola:

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 Colletotrichum cordylinicola to California = (9).

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

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

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

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

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

Evaluation is not established (0).  Colletotrichum cordylinicola is not established in California. 

Final Score:

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

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

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the anthracnose pathogen, Colletotrichum cordylinicola is B.

References:

Farr, D. F., & A. Y. Rossman.  Fungal databases, systematic mycology and microbiology laboratory, ARS, USDA. Retrieved April 7, 2015, from

http://nt.ars-grin.gov/fungaldatabases/

Phoulivong S., L. Cai, N. Parinn, H. Chen, K. A. Abd-Elsalam, E. Chukeatirote, and K. D. Hyde.  2010.  A new species of Colletotrichum from Cordyline fruticosa and Eugenia javanica causing anthracnose disease.  Mycotaxon 114:247-257.

Sharma K., E. Goss, and Ariena H. C. van Bruggen.  2014.  Isolation and identification of the fungus Colletotrichum cordylinicola causing anthracnose disease on Cordyline fruticosa in Florida.  HortScience 49:911-916.

Weir, B. S., P. R. Johnston and U. Damm.  2012.  The Colletotrichum gloeosporioides species complex.  Studies in Mycology, 73:115-180. DOI:10.3114/sim0011.

Responsible Party:

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

Comment Format:

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

Example Comment: 

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

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

♦  Comments may not be posted if they:

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

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

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

Violates agency regulations prohibiting workplace violence, including threats.

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

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

Pest Rating: B

Posted by ls

Plant Pathogens, Viruses and viroids

Grapevine Red Blotch associated Virus (GRBaV)

California Pest Rating for
Grapevine Red Blotch associated Virus (GRBaV)
Pest Rating:  B
PEST RATING PROFILE
Initiating Event:

None.

History & Status:

Background: The origin of Grapevine red blotch does not appear to be recent.  For long the disease escaped the attention of vineyard growers because of its close resemblance to leafroll disease symptoms. Nevertheless, in 2008, an emerging grapevine disease – later termed red blotch disease, was first recognized in a Cabernet Sauvignon vineyard in Napa Valley, California. The disease was typified by leaf reddening and delayed fruit maturity in red cultivars of grapevine and initially confused with grapevine leafroll due to the late-season symptom of leaf reddening.  However, some symptomatic leafroll grapevine cultivars were found to be free of leafroll viruses and DNA sequencing analysis revealed the presence of a single stranded DNA virus that was named, Grapevine red blotch associated virus (Al Rwahnih et al., 2012, 2013).  In 2010, severe decline of grapevine cultivar ‘Cabernet franc’ was discovered in a vineyard in New York.  As in California, the disease was initially described as leafroll but following nucleic acid analysis, was found to be free of leafroll viruses, and found to have a single stranded DNA that, on sequence analysis, resembled members of the virus family Geminiviridae.  This virus was tentatively named, Grapevine cabernet franc-associated virus (GCFaV).  Subsequently, both GRBaV and GCFaV were found to be the same virus and the name, Grapevine red blotch associated virus was used for the causal organism of the associated grapevine red blotch disease to distinguish the symptoms from those caused by leafroll viruses and other graft-transmissible agents (Krenz et al., 2014).  Grapevine red blotch associated virus is a newly identified virus of grapevines and a putative member of a new genus within the family Geminiviridae (Sudarshana et al., 2015).  In 2013, in Washington State vineyards, a disease similar to grapevine red blotch was reported to be caused by Grapevine red leaf-associated virus, which was determined to be genetically identical to GRBaV (Poojari et al., 2013).

Since its initial discovery in 2008, GRBaV has been detected in several regions of California (see ‘California Distribution’).  Furthermore, through surveys, the disease was found to be widely distributed in North America.  Grapevine red blotch has not been reported outside of North America. Studies conducted in the National Clonal Germplasm Repository (NCGR) located near Winters, California, revealed that grapevine accessions originating from 33 countries and five continents outside North America tested positive for the virus.  However, it was not concluded from those studies that the virus occurs in those countries (Rwahnih et al., 2015).

Hosts: Vitis vinifera (grapevine) red cultivars: Cabernet Franc, Cabernet Sauvignon, Malbec, Merlot, Mourvèdre, Petite Sirah, Petit Verdot, Pinot Noir, and Zinfandel; white V. vinifera cultivars such as Chardonnay, Riesling, Semillon, and Viognier; also, table and raisin grapes and some root stocks.  GRBaV has been detected in grapevine collections, nursery stock and established vineyards (EPPO, 2015).

Symptoms: Symptoms have been observed in grapevines of various ages in young (first leaf) and mature (5-20 yr old vineyards. Generally, symptoms appear in late August through September as red blotches on leaf blades on basal portions of shoots either between secondary or tertiary veins or extending from the leaf margin with the veins turning partly or fully red (Sudarshana & Fuchs, 2015). Foliar symptoms in white cultivars are less conspicuous and usually involve irregular chlorotic areas that may become necrotic late in season (Sudarshana et al., 2015).  Certain white cultivars, such as Sauvignon Blanc may remain asymptomatic (EPPO, 2015).  Symptoms of red blotch are very similar to those caused by leafroll disease in that leaves, primarily at the base of shoots, turn red during early fall.  However, unlike leafroll, red blotch affected leaves have pink or red veins on the underside of leaves without the margins rolling downwards.

Damage Potential:  GRBaV reduces fruit quality and ripening of grape.  The most significant impact of red blotch disease is the reduction of sugar levels (°Brix), up to 4-5 times lower, in fruit of diseased grapes than in fruit of healthy grapes thereby, causing delayed harvests.  This is of particular concern to wine grape growers who must achieve a certain sugar level in their wine grapes before the latter are acceptable for wine production.  Also, fruit of diseased grapevines have increased acidity. The effect of red blotch disease on fruit yield or vine longevity is not known.

Transmission:  GRBaV is graft transmissible.  The primary source of spread of the pathogen is through infected planting material.  There is no evidence for seed transmission (similar to other members of Geminiviridae).  While the role of an insect vector in transmitting GRBaV in vineyards has not been confirmed, greenhouse experiments have shown that the Virginia creeper leafhopper (Erythroneura aicazc) is involved in spreading the virus from vine to vine in the greenhouse.  The role of this leafhopper in vineyards and how plant-to-plant spread of GRBaV occurs under field conditions are not yet known (Rwahnih et al., 2015; Sudarshana & Fuchs, 2015).

Worldwide Distribution: North America: USA (Arizona, Arkansas, California, Georgia, Idaho, Maryland, New Jersey, New York, North Carolina, Oregon, Pennsylvania, Texas, Virginia, and Washington) and Canada (British Columbia and Ontario) (EPPO, 2015; McFadden-Smith, 2013; Sudarshana & Fuchs, 2015).

Official Control: Grapevine red blotch associated virus is on the “2015 Alert list” of the European and Mediterranean Plant Protection Organization (EPPO, 2015).  Currently, it is a Q-rated quarantine pathogen in California.

California Distribution:  Red blotch disease has been found in Napa and Sonoma Counties, as well as in the central coast (San Luis Obispo County) and San Joaquin Valley (Fresno County) regions of the State (Al Rwahnih et al., 2013; Sudarshana & Fuchs, 2015).

California Interceptions: There are no records of detection of GRBaV in quarantine shipments of plant material intercepted in California.

The risk Grapevine red blotch associated 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:

– 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) –.Grapevine red blotch associated virus has already spread to certain grape growing counties in California’s northern, central and San Joaquin Valley regions.  If left unchecked, the pathogen is likely to establish a widespread distribution in grape producing regions of the State.

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

– Low (1) has a very limited host range.
– Medium (2) has a moderate host range.
– High (3) has a wide host range.

Risk is Low (1) – Grapevine red blotch associated virus has been identified in nine Vitis vinifera red cultivars: Cabernet Franc, Cabernet Sauvignon, Malbec, Merlot, Mourvèdre, Petite Sirah, Petit Verdot, Pinot Noir, and Zinfandel; and white cultivars V. vinifera cultivars such as Chardonnay, Riesling, Semillon, and Viognier; also, table and raisin grapes and some root stocks. Although the pathogen has a limited host range, Grape production is a major enterprise and grapevine is cultivated over significant acreage 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) – Grapevine red blotch associated virus is graft transmissible.  The primary source of spread of the pathogen to vineyards is through infected planting material. The role of an insect vector in vineyards and plant-to-plant spread of GRBaV under field conditions are not yet known.

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

A.  The pest could lower crop yield.

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

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

D.  The pest could negatively change normal cultural practices.

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

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

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

– Low (1) causes 0 or 1 of these impacts.
– Medium (2) causes 2 of these impacts.
– High (3) causes 3 or more of these impacts.

Risk is Medium (2) – The effect of red blotch disease on fruit yield or vine longevity is not known. However, Grapevine red blotch associated virus reduces fruit quality and ripening of grape resulting in lowered crop value, loss of markets and is likely to negatively change normal cultural practices including removal of diseased vines and replant of vineyards since there is no cure once the virus is present in a vineyard (UCDavis News & information, 2013).  The most significant impact of red blotch disease is the reduction of sugar levels (°Brix), up to 4-5 times lower, in fruit of diseased grapes than in fruit of healthy grapes thereby, causing delayed harvests.  This is of particular concern to wine grape growers who must achieve a certain sugar level in their wine grapes before the latter are acceptable for wine production.  Also, fruit of diseased grapevines have increased acidity. The involvement of an insect vector in spreading the virus under field conditions is not known.

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) – Grapevine red blotch associated virus could significantly impact cultural practices, home/urban plantings of disease infected grapevines and trigger official or private treatment programs.

Consequences of Introduction to California for Grapevine red blotch associated 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 GRBaV to California = Medium (11).

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

-Not established (0) Pest never detected in California, or known only from incursions.
-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
–Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Medium (-2). Presently, Grapevine red blotch associated virus has been reported from Napa and Sonoma Counties, as well as in the central coast (San Luis Obispo County) and San Joaquin Valley (Fresno County) regions 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 = 9.

Uncertainty: 

The means by which GRBaV spreads in vineyards is not known and is a current focused study of  researchers.  Virus spread is suspected via a vector but this has yet to be identified. Knowledge gained in this area may further the distribution of the virus than what is reported here.     

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Grapevine red blotch associated virus is B.

References:

Al Rwahnih, M., A. Dave, M. Anderson, J. K. Uyemoto, and M. R. Sudarshana.  2012.  Association of a circular DNA virus in grapevine affected by red blotch disease in California.  Proceedings of the 17th Congress of ICVG, Davis, California, USA. October 7-14, 2012.

Al Rwahnih, M., M. R. Sudarshana, and J. Wolpert.  2013. Red Blotch Disease.  Viticulture Information, University of California Integrated Viticulture: http://iv.ucdavis.edu/Viticultural_Information/?uid=284&ds=351.

Al Rwahnih, M., A. Dave, M. M. Anderson, A. Rowhani, J. K. Uyemoto, and M. R. Sudarshana.    2013.  Association of a DNA virus with grapevines affected by red blotch disease in California.  Phytopathology 103:1069-1076.

Al Rwahnih, A. Rowhani, D. A. Golino, C. M. Islas, J. E. Preece, and M A. Sudarshana.  2015.  Detection and genetic diversity of Grapevine red blotch-associated virus isolated in table grape accessions in the National Clonal Germplasm Repository in California.  Canadian Journal of Plant Pathology, 37:130-135. http://dx.doi.org/10.1080/07060661.2014.999705.

EPPO.  2015.  Grapevine red blotch-associated virus.  European and Mediterranean Plant Protection Organization: http://www.eppo.int/QUARANTINE/Alert_List/viruses/GRBAV0.htm.

Krenz, B., J. R. Thompson, H. L. McLane, M. Fuchs, and K. L. Perry.  2014.  Grapevine red blotch-associated virus is widespread in the United States.  Phytopathology 104:1232-1240.

McFadden-Smith, W.  2013.  Grapevine red blotch associated virus: A newly identified disease in vineyards.  Ontario Ministry of Agriculture, Food and Rural Affairs: http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2013/22hrt13a1.htm.

Poojari S, O. J. Alabi, V. Y. Fofanov, and R. A. Naidu RA. 2013. A leafhopper transmissible DNA virus with novel evolutionary lineage in the family Geminiviridae implicated in grapevine redleaf disease by next-generation sequencing. PLoS One. 8:e64194. doi:10.1371/journal.pone.0064194.

Sudarshana M., and M. Fuchs.  2015.  Grapevine Red Blotch.  In Compendium of Grape Diseases, Disorders, and Pests, Second Edition, Edited by W. F. Wilcox, W. D. Gubler, and J. K. Uyemoto. The American Phytopathological Society, St. Paul, Minnesota. 122-123 pp.

Sudarshana, M. R., K. L. Perry, and M. F. Fuchs.  2015.  Grapevine red blotch associated virus, an emerging threat to the grapevine industry.  Phytopathology, 105:1026-1032.  http://dx.doi.org/10.1094/PHYTO-12-14-0369-FI.

UCDavis News and Information.  2015.  New technology offers hope for solving grapevine red blotch disease problem.  http://news.ucdavis.edu/search/news_detail.lasso?id=10499.

Responsible Party:

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

Comment Format:

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

Example Comment: 

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

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

♦  Comments may not be posted if they:

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

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

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

Violates agency regulations prohibiting workplace violence, including threats.

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

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

Pest Rating: B

Posted by ls

Plant Pathogens, Viruses and viroids

Bamboo Mosaic Virus (BaMV)

California Pest Rating for 
Bamboo Mosaic Virus (BaMV)
Pest Rating:  B
PEST RATING PROFILE
Initiating Event: 

None.

History & Status:

Background:  Bamboo mosaic virus was originally isolated from two species of bamboo, Bambusa multiplex and B. vulgaris, in Brasilia, Brazil and reported as a new virus as well as the first virus identified infecting bamboo plants.  No evidence of spread in Brazil was observed outside the original site. (Lin et al., 1977).  Since then, the virus pathogen has also been reported from the Pacific islands, Taiwan, Australia, the Philippines, and the USA.  In the USA, Bamboo mosaic virus was first reported from San Diego, California, in Beechey bamboo plants growing in the San Diego Zoo (Lin et al., 1995).  During April 2014, BaMV was detected in bamboo growing in San Diego Botanic Garden.  This detection was made by the CDFA Plant Pathology Laboratory.   The pathogen is reported to have been tentatively diagnosed in a Bambusa sp. sample in Florida during the 1980s, although bamboo enthusiasts in Florida claim to have observed virus-like symptoms in the collections prior to the 1980s (Elliott & Zettler, 1996). The pathogen has also been reported from Hawaii in B. vulgaris (Nelson & Borth, 2011).

Bamboo mosaic virus is a plant pathogenic virus in the genus Potexvirus within the family Potexvirus.

Hosts: Bamboo is the natural host.  Ten species of bamboo are included namely, Bambusa beecheyana, B. beecheyana cv. pubescens, B. edulis, B. multiplex, B. oldhamii, B. vulgaris, B.vulgaris var. striata, Dendrocalamus latiflorus, D. latiflorus cv. ‘Mei-nung’, Phyllostachys nigra.  Experimental susceptible plants include Gomphrena globosa, Chenopodium amaranticolor, Bambusa vulgaris ‘Vittata’, and Dendrocalamus latiflorus cv. ‘Mei-nung’ (Brunt et al., 1996 onwards).

Symptoms: Bamboo mosaic virus-infected bamboo plants may exhibit chlorotic mosaic and mottling patterns running parallel to the leaf veins, necrotic streaks on shoots and culms, vascular discoloration, aborted stems and death of plants.  Symptoms may be mild or subtle in some infected plants (Brunt et al., 1996; Nelson & Borth, 2011).

Damage Potential:  Bamboo mosaic virus can affect growth and stand of infected bamboo plants.  While quantitative crop loss values have not been reported, the pathogen has the potential to cause losses in production and is considered a threat to the bamboo industry in Taiwan (Lin et al., 1993).  In California, mainly nursery, private and commercial cultivations of bamboo in public parks, landscapes, and gardens are at risk of reductions in healthy stands if infected with BaMV.  Furthermore, once established, the disease cannot be eradicated without destroying infected plants (Nelson & Borth, 2011).

Transmission: Bamboo mosaic virus is mechanically transmitted to non-infected bamboo cultivars.  Contaminated cultivation tools and infected BaMV bamboo plants are a means for spreading the virus.  Transmission does not involve an insect vector.

Worldwide Distribution:  Asia: Philippines, Taiwan; North America: USA; South America: Brazil; Australia: Queensland, Western Australia (Brunt et al., 1996 onwards; Dodman & Thomas, 1999; Elliot & Zettler, 1996; Lin et al., 1977; Lin et al., 1993, 1995)

Official Control: Bamboo mosaic virus is on the ‘Harmful Organism List’ for Costa Rica, French Polynesia, Georgia, India, Japan, and New Zealand (PCIT, 2015).  Currently, BaMV has a temporary Q rating in California.

California Distribution: San Diego, San Diego County.

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

The risk Bamboo 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:

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

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

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

Risk is Medium (2) – Bamboo mosaic virus is likely to establish within California wherever bamboo is grown in southern and northern regions of the State.

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

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

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1) – The host range is limited to bamboo – the natural host. Ten species of bamboo are included namely, Bambusa beecheyana, B. beecheyana cv. pubescens, B. edulis, B. multiplex, B. oldhamii, B. vulgaris, B.vulgaris var. striata, Dendrocalamus latiflorus, D. latiflorus cv. ‘Mei-nung’, Phyllostachys nigra.

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

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

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

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

Risk is Medium (2) – Bamboo mosaic virus increases rapidly within infected bamboo plants and can be spread to new non-infected sites through movement of infected plants.  The virus is also mechanically transmitted through infected cultivation tools such as those used in pruning.  It is not spread by an insect or other biological vector.

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) – Infections by Bamboo mosaic virus could lower crop yield and value, increase production costs due to removal and replacement of diseased plants, and trigger loss of domestic and international markets.  In particular, nurseries could be negatively affected by losses in production and sale.

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) – In California, bamboo is mainly grown in specialty nurseries, public parks, landscapes, and garden environments.  Healthy bamboo stands in such environments could be significantly impacted if infected with Bamboo mosaic virus.

Consequences of Introduction to California for Bamboo 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 BaMV to California = (10).

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

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

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

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

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

Evaluation is Low (-1).  Presently, Bamboo mosaic virus is established in San Diego, 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 = 9.

Uncertainty:

None.

Conclusion and Rating Justification:

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

References:

Brunt, A.A., K. Crabtree, M. J. Dallwitz, A. J. Gibbs, L.Watson, and E. J. Zurcher (eds.). (1996 onwards). `Plant Viruses Online: Descriptions and Lists from the VIDE Database. Version: 20th August 1996.’ URL http://biology.anu.edu.au/Groups/MES/vide/.

CABI.  2015.  Bamboo mosaic virus datasheet (basic). Crop Protection Compendium.  http://www.cabi.org/cpc/datasheet/1695.

Dodman, R.L., and J. E. Thomas. 1999. The first record of Bamboo mosaic potexvirus from Australia. Australasian Plant Pathology 28:337–337.

Elliot, M.S., and F. W. Zettler. 1996. Bamboo mosaic virus detected in ornamental bamboo species in Florida.  Proceedings of the Florida State Horticultural Society 109:24–25.

Lin, M. T., E. W. Kitajima, F. P. Cupertino, and C. L. Costa.  1977.  Partial purification and some properties of Bamboo mosaic virus.  Phytopathology 67:1439-1443.

Lin, N. -S., Y.-J. Chai, T. -Y. Chang, and Y. -H. Hsu.  1993.  Incidence of Bamboo mosaic potexvirus in Taiwan.  Plant Disease 77:448-450.

Lin, N. –S., B. –Y. Lin, T. –Y. Yeh, and Y. -H. Hsu.  1995.  First report of Bamboo mosaic virus and its associated satellite RNA on bamboo in the U. S.  Plant Disease 79 (12):1249.

Nelson, S., and W. Borth.  Bamboo Mosaic.  2011.  College of Tropical Agriculture and Human Resources University of Hawai’i at Mānoa, Plant Disease September 2011 PD-76.

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

Fazzio, D.  2015.  Bamboo.  Sonoma County Master Gardeners University of California.  http://ucanr.edu/sites/scmg/Plant_of_the_Month/Bamboo/# .

Responsible Party:

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

Pest Rating:  B

Posted by ls

Fungi, Plant Pathogens

Didymella bryoniae (Auersw.) Rehm [teleomorph] (Auersw.) Rehm

California Pest Rating for
Didymella bryoniae (Auersw.) Rehm [teleomorph] (Auersw.) Rehm
Pest Rating:  B
PEST RATING PROFILE
Initiating Event:

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

History & Status:

Background:  Didymella bryoniae is the fungal pathogen that causes gummy stem blight of cucurbits disease affecting members of the family Cucurbitaceae.  Gummy stem blight was first reported in 1891 in France, Italy and the United States and affects the leaves, stems, fruits and seeds of all cucurbits.   The disease is most common in subtropical and tropical regions globally but also found in temperate regions, especially on winter squash and pumpkin and greenhouse grown cucumber (Sitterly & Keinath, 1996).  The disease is most common in the southern United States, and in California, gummy stem blight was first reported in greenhouse-produced transplants of watermelon in the Salinas Valley (Koike, 1997).  Since 1997, there have not been any further reports of the pathogen in California.

Didymella bryoniae is the sexual (teleomorph) stage of the fungus that produces ascospores, while Phoma cucurbitacearum represents the asexual stage (anamorph) that produces conidia.  Didymella bryoniae was originally described as Sphaeria bryoniae, but since then has undergone several classifications that resulted in synonymizations of many different species.

Hosts: Members of the family Cucurbitaceae including wax gourd (Benincasa hispida), watermelon (Citrullus lanatus), melon (Cucumis melo), cucumber (C. sativus), pumpkin (Cucurbita sp.), giant pumpkin (C. maxima), ornamental gourd (C. pepo), buffalo gourd (C. foetidissima), bottle gourd (Lagenaria siceraria), bitter gourd (Momordica charantia), loofah (Luffa cylindrica), white bryony (Bryonia alba), red bryony (B. dioica), chayote (Sechium edule), and burcucumber (Sicyos angulatus) Occasionally, the pathogen has been found in members of Solanaceae, Caricaceae, and Primulaceae (CABI, 2015; Farr & Rossman, 2015).

Symptoms:  Didymella bryoniae invades the leaves and stems of watermelon, cucumber, and muskmelon (cantaloupe) and gummy stem blight diseased plants may exhibit a variety of symptoms which are referred to as leaf spot, stem canker, vine wilt and black fruit rot (Ferreira & Boley, 1992).  Initial spots on leaves, petioles and stems usually become pale brown or gray. On stems, spots usually start at the joints, frequently elongate into streaks and exude an amber-colored gummy liquid.  Lesions on leaves and fruit initiate as spreading water-soaked areas which in leaves may have a chorotic halo, become light brown and irregular in outline, and necrotic.  Leaves wilt and collapse; affected plants wilt and eventually die. On fruit, faded and irregular spots first form on the surface and eventually turn dark and may have a hardened droplet of exudates in the center; cracked sunken lesions form with internal rotting – especially in storage fruit.  In certain kinds of squash, lesions are superficial and spread almost over the entire fruit surface.  When seed-transmitted, the pathogen causes damping-off thereby, killing seedlings.  In the field, initial symptoms include plant collapse with sunken girdling cankers that result in total loss of plants.  Vine cankers are common near the crown of the plant.  (Agrios, 2005; CABI, 2015; Ferreira & Boley, 1992; Koike, 1997; Sitterly & Keinath, 1996.)

The main diagnostic symptoms are the gummy exudates on stem and fruit lesions, and the presence of abundant closely spaced groups of pale-colored pycnidia (asexual fruiting body) and dark brown to black-colored perithecia (sexual fruiting body) on fruit, stem or leaves.  During rainy seasons lesions can become water-soaked and spread resulting in severe defoliation.  Gummy substances may exude from cracks, and severe infections can result in death of plants (CABI, 2015).

Damage Potential: Didymella bryoniae has the potential of damaging plant growth causing reductions in plant growth, death of infected plants, fruit rot, and seedling death resulting in significant crop losses.

Disease Cycle:   The pathogen usually overwinters in diseased plant debris as chlamydospores and possibly in or on seeds.  Subsequently, spores or infected seed result in primary infection of plants. Cucurbit plants are predisposed to infection by wounds and bruises although uninjured plants have also been shown to become infected when exogenous nutrients are present (Ferreira & Boley, 1992).  The disease thrives in cool moist climates with an optimum temperature of 20-28 C for development.  Moisture, especially extended periods of wetness, is necessary for infection (at least 1 hour) and disease development.  Leaves are penetrated directly through the cuticle or through intercellular spaces around the bases of trichomes. Stems are penetrated through wounds and fruit are penetrated through wounds or flower scars at the time of pollination.  Fruit rot initiates approximately 3 days following infection.  Following penetration and development, the fungus produces numerous pycnidia and perithecia.  Pycnidia are filled with conidia (spores) that protrude from the fruiting body in a gelatinous substance appearing as long cream to pink tendrils.  Water dissolves this gelatinous substance and the conidia are dispersed usually by wind and rain.  Perithecia are also produced along with pycnidia and filled with ascospores. Both types of spores serve as inoculum for infection.  Neither type survives long after dispersal (Agrios, 2005; Ferreira & Boley, 1992; Sitterly & Keinath, 1996).

Transmission:  Infected planting material (transplants), infected fruit, plant debris, weeds, and soil.  In addition, conidia can be transmitted by air transport and water splashing (Ferreira & Boley, 1992).  Seed transmission has only been demonstrated experimentally (Brown et al., 1970; CABI, 2015; Lee et al., 1984).  Reports of seed transmission are conflicting and there is no evidence that seed transmission occurs naturally although fruiting bodies (pycnidia and perithecia) of the pathogen have been found on naturally infected cucumber and pumpkin seeds (CABI, 2015).  The striped cucumber beetles (Diabrotica undecimpunctata howardii and Acalymma vittatum) are believed to transmit D. bryoniae in a nonpersistent manner by providing wounds in plants as avenues for fungal infections. It has also been shown experimentally that cucumber plants infested with melon aphids were susceptible to D. bryoniae and powdery mildew (Ferreira & Boley, 1992).

Worldwide Distribution:  Didymella bryoniae is distributed worldwide in several countries in Asia, Africa, North America, Central America and Caribbean, South America, Europe, and Oceania (CABI, 2015).

In the USA, it has been reported from Florida, Georgia, New York, North Carolina, and South Carolina.

Official Control:  Didymella bryoniae is included on the ‘Harmful Organism Lists’ for nine countries namely: Bangladesh, Ecuador, Egypt, Indonesia, Iran, Israel, Panama, Syrian Arab Republic and Timor-Leste (PCIT, 20115).  It is a quarantine pest in Jordan (EPPO, 2015).   Currently, it is an actionable, temporary ‘Q’-rated pathogen in California.

California Distribution: Didymella bryoniae has only been reported once in 1997 in Salinas in greenhouse watermelon transplants.  The diseased plants would have been destroyed following detection.  The pathogen has not been reported since then and is not known to be established in California.

California Interceptions:  None reported.

The risk Didymella bryoniae would pose to California is evaluated below.

Consequences of Introduction: 

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

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

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

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

Risk is Medium (2) – Didymella bryoniae requires cool and moist conditions to infect cucurbit hosts and cause gummy stem blight disease.  At least 1 hour of wetness is required for infection and extended periods for disease development.  This may limit the establishment of the disease in cucurbit productions in California and may also be why this disease has not been observed outside greenhouse production in California since the early 1990s.  Therefore, a ‘medium’ rating is given to this category.

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.

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

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

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

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

Risk is High (3) – Under favorable environmental conditions Didymella bryoniae has a high reproductive rate and depends on wind and moisture or rain for its short distance dispersal.  Infected planting material, infected fruit, plant residues, weeds, soil, and possibly seed provide the means for long distance dispersal, also in fields and greenhouses. In addition, the striped cucumber beetles are believed to transmit D. bryoniae in a nonpersistent manner by providing wounds in plants as avenues for fungal infections.  

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

A.  The pest could lower crop yield.

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

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

D.  The pest could negatively change normal cultural practices.

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

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

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

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

– Medium (2) causes 2 of these impacts.

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

Risk is High (3) –  The cucurbit gummy stem blight pathogen could lower crop value and yield, cause increases in production costs for disease management, and negatively change normal cultural practices to mitigate potential damages.  There is also the possibility for the pathogen to be vectored by pestiferous striped cucumber beetles.  Therefore, a ‘high’ rating is given to this category.   

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) – Cucurbitaceous plants grown in home/urban gardens could be negatively impacted if infected with Didymella bryoniae.

Consequences of Introduction to California for Didymella bryoniae:

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 Didymella bryoniae to California = Medium (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 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 =12 (Medium).

Uncertainty:

Infested seeds and transplants are a ready source of introduction of the pathogen to CA fields.  The future status of Didymella bryoniae, gummy stem blight of cucurbits disease, can be known through periodic surveys, diligent monitoring and testing of seed/plants in greenhouses and will be necessary in order to mitigate risk of 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 the anthracnose pathogen, Didymella bryoniae is B.  

References:

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

Brown, M. E., E. M. Howard, and B. C. Knight. 1970. Seedborne Mycosphaerella melonis on cucumber. Plant Pathology, 19:198.

CABI.  2015.  Didymella bryoniae (gummy stem blight of cucurbits) datasheet (full) report.  Crop Protection Compendium.  www.cabi.org/cpc/

EPPO.  2015.  Stagonosporopsis cucurbitacearum (DIDYBR).  European and Mediterranean Plant Protection Organization PQR database.  http://www.eppo.int/DATABASES/pqr/pqr.htm .

Farr, D. F., and A. Y. Rossman.  2015.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved July 14, 2015, from http://nt.ars-grin.gov/fungaldatabases/

Ferreira, S. A., and R. A. Boley.  1992.  Didymella bryoniae Gummy stem blight, black rot, canker (Plant Disease Pathogen).  http://www.extento.hawaii.edu/kbase/crop/Type/d_bryon.htm

Koike, S. T.  1997.  First report of gummy stem blight, caused by Didymella bryoniae, on watermelon transplants in California.  Plant Disease, 81:1331. http://dx.doi.org/10.1094/PDIS.1997.81.11.1331B.

Lee, D. H., S. B. Mathur, and P. Neergaard. 1984. Detection and location of seed-borne inoculum of Didymella bryoniae and its transmission in seedlings of cucumber and pumpkin. Phytopathologische Zeitschrift, 109(4):301-308.

PCIT.  2015.  USDA Phytosanitary Certificate Issuance & Tracking System. July 21, 2015.  https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp .

Sitterly, W. R., and A. P. Keinath.  Gummy stem blight.  1996.  In, Compendium of cucurbit diseases.  Compendium of cucurbit diseases ed. T. A. Zitter, D. L. Hopkins, and C. E.  Thomas, APS Press  pg 27-28. http://www.apsnet.org/publications/apsnetfeatures/Pages/GummyStemBlight.aspx .

Responsible Party:

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

 Pest Rating:  B

Posted by ls

Fungi, Plant Pathogens

Colletotrichum spaethianum (Allesch.) Damm, P. F. Cannon & Crous, 2009

California Pest Rating for
Colletotrichum spaethianum (Allesch.) Damm, P. F. Cannon & Crous, 2009
Pest Rating:  B
PEST RATING PROFILE
Initiating Event:  

On March 27, 2015, a mail shipment containing Iris sp. plants with leaf spots was intercepted by the CDFA Dog Team, at the United States Postal Service Center in West Sacramento, Yolo County.   The plants had been shipped by a private owner in Gowen, Oklahoma.  Samples collected were submitted to the CDFA Plant Pathology Laboratory and the fungal pathogen, Colletotrichum spaethianum, was isolated from the diseased plants and identified by Suzanne Latham, CDFA plant pathologist.  The species identity was confirmed on August 18, 2015, by the USDA PPQ National Mycology Laboratory.  This detection was considered a new US record and reportable by the USDA. Consequently, the shipment of Iris sp. plants was destroyed.  The risk of infestation of C. spaethianum in California is evaluated and a permanent rating is proposed.     

History & Status:

Background:  The fungal pathogen Colletotrichum spaethianum was originally described in 1895 under the name Vermicularia spaethiana from dead stems of Funkia univittata (synonym Hosta sieboldiana) in Berlin, Germany.  A living strain of the original material of pathogen is no longer available however, as a result of taxonomic and phylogenetic studies, Damm et al., (2009) combined V. spaethiana to the genus Colletotrichum becoming C. spaethianum and designated an epitype (representative specimen in place of the non-available original specimen) from the same host in the same city as the original fungal species.

Hosts: Hosta sieboldiana, Hemerocallis sp.(daylily), H. flava, H. fulva, H. citrine, Hymenocallis americana (northern spider lily), Lilium sp. (Lily), Peucedanum praeruptorum (Qian Hu), Allium fistulosum (Welsh onion), (Damm et al., 2009, 2012; Yang et al., 2009; Yang et al., 2014; Guo et al., 2013; Vieria et al., 2014; Farr & Rossman, 2015). The CDFA detection of Colletotrichum spaethianum in Iris sp. is a new host record.

Symptoms:  Colletotrichum spaethianum infected host plants exhibit symptoms of anthracnose which include reddish brown to dark brown leaf and stem necrotic spots and wilting of leaves which often result in dieback and reduction in plant quality.

Damage Potential:  Anthracnose disease caused by Colletotrichum spaethianum can result in reduced plant quality and growth, fruit production and marketability.  Estimates of yield/crop loss due to this pathogen have not been reported.  Nursery production of potted host plants or in greenhouses are particularly at risk as nursery conditions are often conducive to infection by Colletotrichum species.  In cultivated fields, disease development may be sporadic as it is affected by levels of pathogen inoculum and environmental conditions.

Disease Cycle:  It is likely that Colletotrichum spaethianum has a similar life cycle to that of other Colletotrichum species and survives between crops during winter as mycelium on plant residue in soil, on infected plants, and on seeds.  During active growth, the pathogen produces masses of hyphae (stromata) which bear conidiophores, on the plant surface. Conidia (spores) are produced at the tips of the conidiophores and disseminated by wind, rain, cultivation tools, equipment, and field workers.   Conidia are transmitted to host plants.  Humid, wet, rainy weather is necessary for infection to occur.  These requirements in particular may limit the occurrence of the pathogen in California fields and subsequently, the pathogen may be more of a problem under controlled environments of greenhouses.  Conidia germinate, penetrate host tissue by means of specialized hyphae (appresoria) and invade host tissue.

Transmission:  Wind, wind-driven rain, cultivation tools, and human contact.

Worldwide Distribution:  Europe: Germany; Asia:  South Korea; North America: Florida, South America: Oceania: New Zealand (Cai, et al., 2009; Damm et al., 2009; Farr & Rossman, 2015; Yang, et al., 2009; Yang et al., 2014).

Official Control:  In California C. spaethianum is an actionable, Q-rated pathogen, and infected plant material is subject to destruction or rejection.   The species is considered ‘reportable’ by the USDA.

California Distribution: Colletotrichum spaethianum is not established in California (see “Initiating Event”).

California Interceptions:  There has been one interception of Colletotrichum spaethianum –infected (Iris) plants that originated in Oklahoma (see ‘Initiating event’).

The risk Colletotrichum spaethianum would pose to California is evaluated below.

Consequences of Introduction: 

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

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

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

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

Risk is Medium (2) – Similar to other species of Colletotrichum, C. spaethianum requires humid, wet, rainy weather for conidia to infect host plants. This environmental requirement may limit the ability of the pathogen to establish and spread in less conducive climates. Also confining is the limited host range comprising primarily of lily and iris ornamental plants which are cultivated in nurseries, residential and commercial community environments such as parks and gardens.  The pathogen could establish within these limited regions when grown under favorable moist conditions.

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

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

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1) – Presently, the host range of Colletotrichum spaethianum is limited to hosta, daylilies, northern spider lily, lily, iris, Qian Hu (Chinese medicinal plant), and Welsh onion.

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 pathogen has high reproductive potential and conidia are produced successively.  They are transmitted by wind, wind-driven rain, cultivation tools, and human contact however conidial germination and plant infection require long, wet periods.

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

A. The pest could lower crop yield.

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

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

D. The pest could negatively change normal cultural practices.

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

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

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

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

– Medium (2) causes 2 of these impacts.

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

Risk is Medium (2) – In particular, nursery and private productions of lily, hosta, and iris ornamental plants can be limited by their susceptibility to anthracnose under wet conditions. Therefore, under suitable climates, the pathogen could lower plant growth, value and trigger the loss of markets.

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

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

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

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

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

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

Score the pest for Environmental Impact. Score:

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

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

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

 Risk is High (3) – The pathogen could significantly impact cultural practices or home/urban garden plantings. Also, the pathogen could impact endangered lily plants in California, namely: western lily (Lilium occidentale) and Pitkin Marsh lily (Lilium pardalinum ssp. Pitkinense) (State and federally listed endangered, threatened and rare plants of California, California Natural Diversity Database, California Department of Fish and Wildlife, July 2015).

Consequences of Introduction to California for Colletotrichum spaethianum:

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 Colletotrichum spaethianum to California = (11).

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

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

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

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

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

Evaluation is not established (0).  Colletotrichum spaethianum is not established in California.  The intercepted C. spaethianum-infected iris plants were either rejected or destroyed. 

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:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the anthracnose pathogen, Colletotrichum spaethianum is B.

References:

Cai, L., Hyde, K.D., Taylor, P.W.J., Weir, B.S., Waller, J.M., Abang, M.M., Zhang, J.Z., Yang, Y.L., Phoulivong, S., Liu, Z.Y., Prihastuti, H., Shivas, R.G., McKenzie, E.H.C., and Johnston, P.R. 2009. A polyphasic approach for studying Colletotrichum. Fungal Diversity 39: 183-204.

Farr, D. F., & A. Y. Rossman.  Fungal databases, systematic mycology and microbiology laboratory, ARS, USDA. Retrieved April 7, 2015, from

http://nt.ars-grin.gov/fungaldatabases/

Guo, M., Y. M. Pan, Y. L. Dai, and Z. M. Gao.  2013.  First report of leaf spot caused by Colletotrichum spaethianum on Peucedanum praeruptorum in China.  Plant Disease, 97:1380.

Kitterly, W. R., and A. P. Keinath.  1996.  Fungal disease of aerial parts: Anthracnose. In ‘Compendium of Cucurbit Diseases’.  Edited by T. A. Zitter, D. L. Hopkins, and C. E. Thomas, APS Press The American Phytopathological Society Minnesota, USA, p. 24-25.

Santana, K. F. A., C. B. Garcia, K. S. Matos, R. E. Hanada, N. R. Sousa, G. F. and Da Silva.  2015. First report of anthracnose caused by Colletotrichum spaethianum on Allium fistulosum in Brazil.  Plant Disease (Accepted for publication) posted on line on 3Aug 2015, First Look.  http://dx.doi.org/10.1094/PDIS-07-15-0737-PDN.

Vieira, W. A. S., S. J. Michereff, A. C. Oliveira, A. Santos and M. P. S. Câmara.  2014.  First report of anthracnose caused by Colletotrichum spaethianum on Hemerocallis flava in Brazil.  Plant Disease, 98:997.  http://dx.doi.org/10.1094/PDIS-10-13-1026-PDN

Yang, Y. L., Z. Y. Liu, L. Cai, K. D. Hyde, Z. N. Yu and E. H. C. McKenzie. 2009. Colletotrichum anthracnose of Amaryllidaceae. Fungal Diversity 39: 123-146

Yang, H. C., J. S. Haudenshield and G. L. Hartman. 2014. Colletotrichum incanum sp. nov., a curved-conidial species causing soybean anthracnose in USA. Mycologia 106: 32-42.

Weir, B. S., P. R. Johnston, and U. Damm.  2012.  The Colletotrichum gloeosporioides species complex.  Studies in Mycology, 73:115-180. DOI:10.3114/sim0011.

Responsible Party:

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

 Pest Rating:  B

Posted by ls

Fungi, Plant Pathogens

Melampsoridium hiratsukanum S. Ito ex Hirats. f., (Alder Rust)

California Pest Rating
Melampsoridium hiratsukanum S. Ito ex Hirats. f.,
(Alder Rust)
Pest Rating:  C
PEST RATING PROFILE
Initiating Event:

The pest rating of Alder Rust has been raised by certain counties and related nurseries due to its increased spread within California.  Currently, Melampsoridium hiratsukanum has a temporary Q rating that is herein reconsidered for a permanent rating.

History & Status:

Background:  Three Melampsoridium species are reported as causing foliar rust on alder (Alnus spp.) namely, M. alni, M. betulinum and M. hiratsukanum. Confusion has existed on the distinct identity of the species as all three are morphologically similar.  This confusion has caused doubt about the authenticity of many older records.  However, since the late 1990s, the use of DNA analysis has confirmed the identities of the three species. Melampsoridium hiratsukanum belongs to the family Pucciniastraceae in the order Pucciniales.  The species was first described on Manchurian alder (A.hirsuta) from Hokkaido in Japan in 1927.

Disease cycle:  Melampsoridium hiratsukanum is a heteroecious rust that produces two different fruiting bodies (uredinia and telia) on the leaves of its main host alder (Alnus spp.) and two different fruiting bodies (spermagonia and aecia) on its alternate host larch (Larix sp.).  On alder, the fungal species forms uredinia which give rise to urediniospores.  These spores are produced repeatedly and form the major stage for reproduction and dispersal.  Urediniospores are the only spores that re-infect their same host plant repeatedly.  Later, the pathogen produces the sexual, overwintering fruiting body structure or telia which give rise to thick-walled teliospores.  During the following spring, teliospores germinate forming a basidium which produces haploid basidiospores.  Basidiospores may infect young needles of larch (Larix spp.) and develop to form spermogonia – which form pycniospores or spermatia and receptive hyphae.  Following fertilization of spermatia and compatible receptive hyphae, dikaryotic mycelium is produced which forms aecia that produce aeciospores. Aeciospores may infect alder but not other larch or Larix spp. On infection, aeciospores produce more dikaryotic mycelium that this time forms uredinia that produce urediniospores thereby completing the life cycle.

The fungal pathogen may also exhibit a shortcut life cycle especially where the alternate aecial host (Larix spp.) is not present.  In such situations, the life cycle of the pathogen is completed on alder alone without the need of the alternate host and is therefore, reproduces and spreads only through the production of urediniospores.  Such may be the situation with the occurrence of the disease on alder plants in California nurseries.  The pathogen has not been reported on an alternate host in California.  It is likely that the urediniospores re-infect fresh alder leaves thereby enabling their survival and perpetuating the disease through a rapid build-up of inoculum.  Such a shortcut life cycle is known for many rust fungi with alternate hosts and is assumed to occur in Austria and Hungary (NOBANIS, 2007; Szabo, 2002).

Dispersal and spread:  Alder may be infected by aeciospores, or as discussed above for California, it may be infected with urediniospores produced in other alder plants.  Also, it may survive as mycelium infecting buds or with urediniospores.  The rust fungus spreads from plant to plant mainly by windblown spores.  Urediniospores are formed repeatedly and in abundance and may be transmitted over several hundred kilometers by strong winds and then washed down by rain on to host plants that are readily infected.  Aeciospores are also capable of long distance dispersal.  Over the past 10 years, the introduction and rapid spread of the pathogen in Europe was most likely due mainly to dry airborne spores, although specific distances have not been reported (Lane et al., 2013).  Infected nursery stock or plantings also provide a means for long distance spread of the pathogen which is capable of surviving in bud scales in dormant buds.

Hosts:  Alder (Alnus spp.), Black, European or common alder (Alnus glutinosa), Manchurian alder (A. hirsuta), Grey or Speckled alder (A. incana), Red alder (A. rubra) (EPPO, 2014), white alder (A. rhombifolia) (Blomquist et al., 2014); Larch (Larix spp.), Dahurian larch (L. gmelinii), Siberian larch (L. russica) (EPPO, 2014) and White or Downy birch (Betula pubescens) (Lane et al., 2013).  Experimental hosts: European larch (L. decidua), Tamarack or American larch (L. laricina) (Lane et al., 2013).

Symptoms and damage potential:  Infected white alder leaves exhibit numerous small orange-yellow uredinia pustules on the lower leaf surfaces, with corresponding yellow to orange spots on the upper surface.  Later, leaves turn dark brown and curl inwards with the production of telia.  Infected leaves often turn yellow, die and sometimes drop prematurely. The disease causes considerable damage to alder foliage in late summer causing them to be easily distinguished from a distance.  Repeated infections can cause defoliation and crown thinning leading to tree death (Lane et al., 2013).

Worldwide Distribution: Records of the detection of M. hiratsukanum prior to 2005 may be dubious due to taxonomic difficulty that existed in distinguishing it from other closely related species, viz. M. alni and M. betulinum without using molecular analysis.  Many records prior to 2005 may have been of M. betulinum (Lane et al., 2013).  Nevertheless, it is probable that M. hiratsukanum originated in Eastern Asia and has spread to temperate regions of Europe and North America.  Reliable records of the global distribution of M. hiratsukanum (EPPO, 2014) include:

Asia: China, Japan, Nepal (Adhikari & Manandha, 1989; EPPO, 2014)

Europe: Austria, Czech Republic, Estonia, Finland, France, Germany, Hungary, Italy, Latvia, Lithuania, Norway, Poland, Romani, Russia, Slovakia, Switzerland, Turkey, Ukraine, UK.

North America: Canada, USA (California and Oregon:  Bloomquist et al., 2014; Pscheidt & Ocamb, 2013).  Most likely, it is widespread in nurseries of western US coastal states (Blomquist 2014: pers. comm.)

Official Control: Currently, there are no reports of official control imposed against Melampsoridium hiratsukanum.

California Distribution:  Melampsoridium hiratsukanum is most likely widespread on alders in California nurseries (Blomquist 2014: pers. comm.). The pathogen has been in California since 1931 and a first published report was issued in 2014 of its detection in white alder from a nursery in Santa Cruz County (Blomquist et al., 2014).  However, disease symptoms on trees caused by the pathogen have not been found in California wild lands – mainly due to the absence to high moisture conditions necessary for the perpetuation of the disease in its natural habitat.

California Interceptions:  The pathogen has been in California since in the 1931 as evident by a sample that was submitted to the Federal Herbarium in Beltsville, MD.  However, this sample had been misidentified, and later, when it was correctly identified the revised identification was never published.  The pathogen has also been found in several locations in California Central Valley.

The risk Alder Rust 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):  Melampsoridium hiratsukanum is already established and suspected to be widely distributed wherever alder is grown in California nurseries.  The pathogen has not been found in California wild lands.

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 mainly limited to alder and larch trees. Only a few records of its occurrence on birch are from Europe (U.K.).  In California, the pathogen has only been found on alder.     

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): Alder Rust has high reproduction and dispersal potential via windblown spores that are capable of being transmitted by strong winds over distances of several hundred kilometers.  Also they may be spread over long distances via infected nursery stock

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

A. The pest could lower crop yield.

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

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

D. The pest could negatively change normal cultural practices.

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

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

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

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

– Medium (2) causes 2 of these impacts.

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

Risk is Medium (2): Trees infected with Melampsoridium hiratsukanum could cause significant loss of foliage, thereby generally reducing their yield and value in nursery productions.

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): Alder rust has been in California since 1931, although the pathogen was misidentified.  Although it is difficult to find nursery alder trees that are not infected with the pathogen, according to Dr. Cheryl Blomquist (CDFA, pers. comm.), this rust pathogen has not been found in the wild lands, and no significant impact to California’s environment has been reported.  Nevertheless, it may cause significant concern for home/urban gardens or ornamental settings.

Consequences of Introduction to California for Alder Rust:

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

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

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

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

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

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

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

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

Evaluation is Medium (-2).  Melampsoridium hiratsukanum is widespread in California nurseries, but has not been detected in wild lands.

Final Score:

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

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

Uncertainty:

 While Melampsoridium hiratsukanum has been in California since 1931, it was not possible to distinguish it from M. alni and M. betulinum based on morphology alone.  The latter two species have been reported earlier from California.   It may well be those earlier detections are, in fact, M. hiratsukanum which have yet to be molecularly differentiated.  If this is determined to be so, then it will only strengthen the proposed C rating for this pathogen, as also will its detection in California’s wild land habitats.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Alder Rust is C.

References:

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

Blomquist, C. L., H. J. Scheck, J. Haynes, P. W. Woods and J. Bischoff.  2014.  First published report of rust on white alder caused by Melampsoridium hiratsukanum in the United States.

EPPO.   2014.  Melampsoridium hiratsukanum (MELDHI).  PQR database.  Paris, France: European and Mediterranean Plant Protection Organization.  http://www.newpqr.eppo.int.

Lane, C., S. Matthews Berry and H. Anderson.  2013.  Rapid pest risk analysis for Melamsoridium hiratsukanum.  The Food & Environment Research Agency, Version 3, March, 2013.

NOBANIS.  2007.  Melampsoridium hiratsukanum.  NOBANIS – Invasive Alien Species Fact Sheet.  http://www.nobanis.org/files/factsheets/Melampsoridium_hiratsukanum.pdf.

Pscheidt, J. W. and C. M. Ocamb.  2013.  Pacific Northwest Plant Disease Management Handbook.  URL: pnwhandbooks.org/plantdisease/node/2616.

Szabo, I.  2002.  First report of Melampsoridium hiratsukanum on common alder in Hungary.  Plant Pathology, 51:804.

Responsible Party:

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

 Pest Rating:  C

Posted by ls