Category Archives: Plant Pathogens

Plant Pathology (plant diseases)

Fungi, Plant Pathogens

Erysiphe aquilegiae DC. 1815

California Pest Rating for
Erysiphe aquilegiae DC. 1815
Pest Rating:  C
PEST RATING PROFILE
Initiating Event:  

None.

History & Status:

Background:  The fungal pathogen, Erysiphe aquilegiae, originally named, Ischnochaeta aquilegiae (DC.) Sawada 1959 is the cause of powdery mildew disease that infects several species of plant hosts, including Aquilegia sp. (columbine), mainly in the family Ranunculaceae.

The pathogen is also known by other scientific names, including, E. aquilegiae var. aquilegiae, E. aquilegiae var. ranunculi, and E. ranunculi.  According to Uwe Braun (Professor, Martin-Luther-Universitӓt, Institut für Biologie, Halle, Germany: personal communication to Cheryl Blomquist, CDFA plant pathologist, email dated October 29, 2015), as currently circumscribed, E. aquilegiae is a complex of species that have yet to be clearly distinguished genetically.

During October, 2013, CDFA plant pathologist, Cheryl Blomquist, detected the powdery mildew, Erysiphe aquilegiae on Ranunculus sp. nursery stock that was grown in fields in San Luis Obispo County.  Additionally, there is an earlier report of the asexual (anamorph) stage of Erysiphe, namely, Oidium sp. on Aquilegia sp. from southern coastal counties in California (A. M. French, 1987, California Plant Disease Host Index 2nd edition) that indicates that this powdery mildew pathogen is widely distributed within the State.

Hosts:  Erysiphe aquilegiae comprises numerous ornamental and weed hosts of several genera of the family Ranunculaceae: Aconitum, Actaea, Anemone, Aquilegia, Caltha, Clematis (=Atragene), Consolida, Coptis, Delphinium, Nigella, Ranunculus, Thalictrum, and Trollius (Farr & Rossman, 2015).

Other hosts in different families have been reported based only on morphological analysis of the pathogen.  These records have not been genetically proven and therefore, are doubtful (Braun-Blomquist: personal communication, 2015).  They include Alnus japonica and A. pendula (Betulaceae), Breea setosa and Cirsium spp. (Asteraceae), Magnolia liliiflora (Magnolioideae), Paeonia lactiflora (Paeoniaceae), Quercus crispula and M. mongolica var. grosseserrata (Fagaceae), Swertia spp. (Gentianaceae), Urena lobata and U. lobata var. tomentosa (Malvaceae), and Catharanthus roseus (Apocynaceae) (Bolay, 2005; Farr & Rossman, 2015; Liberato & Cunnington, 2006).

Symptoms:  White to grayish powdery, mildew grows in spots or patches on young plant tissue or covers entire leaves and other plant organs. Mildew growth is most common on upper side of leaves, but may also be found on the underside of leaves, young shoots and stems, buds, flowers and young fruit. Pinhead-sized spherical chasmothecia (completely closed fungal fruiting bodies containing spores), initially white to yellow brown later turning black in color, develop singly or in clusters on older mildew.

Damage Potential:  In general, powdery mildews seldom kill their hosts however they reduce photosynthesis, utilize plant nutrients, increase respiration and transpiration, impair plant growth and reduce crop yields up to 40% (Agrios, 2005).

Disease Cycle:  Erysiphe aquilegiae is an obligate parasite that produces mycelium on the surface of plant tissues without invading it.  The pathogen obtains nutrients from the plant by producing haustoria (specialized absorbing organs) that grow into the epidermal cells of the plant. On the plant surface, the mycelium produces short conidiophores which in turn produce numerous chains of conidia that appear as white powdery coating.  These conidia are easily dispersed by air currents to cause new infections of host plants.  When conditions are unfavorable, the pathogen may produce chasmothecia containing ascospores.  The disease is common in cool or warm humid regions, but can also be common in warm and dry climates since their spores only require high relative humidity and not free-standing water to be released, germinate and cause infections (Agrios, 2005).  Once a plant is infected, mycelium continues to spread on a leaf surface regardless of the level of atmospheric moisture.

Worldwide Distribution: Erysiphe aquilegiae is circumglobally distributed.  Africa: South Africa; Asia: Armenia, China, Iran, Taiwan, Japan, Korea, Israel, USSR; Africa: South Africa; Europe: Lithuania, Ukraine, Romania, Estonia, Belarus, Switzerland, Austria, Czechoslovakia, Denmark, Finland, France, Germany, Hungary, Italy, Norway, Poland, Sweden, USSR, Yugoslavia, United Kingdom, Bulgaria, the Netherlands, Montenegro;  North America: Canada,  Mexico, USA (including Alaska, California); South America: Argentina; Oceania: Australia, New Zealand (Bolay, 2005; Braun, 1987; Farr & Rossman, 2015).

Official Control: No official control has been reported specifically for Erysiphe aquilegiae.  However, the order Erysiphales and Erysiphe spp. are included in the ‘Harmful Organism Lists’ for Australia and Nauru (Erysiphales) and Dominica, Grenada and Saint Lucia (Erysiphe spp., specifically for Mangifera spp. which is not a reported host for E. aquilegiae) (USDA-PCIT, 2015).  In California, the current rating for E. aquilegiae is ‘Z’ (which is given to a previously unrated organism of known economic and or environmental detriment but generally distributed within the state).

California Distribution:  Southern coastal counties: San Benito, Monterey, San Luis Obispo, Santa Barbara, Ventura, Los Angeles, Orange, and San Diego Counties.

California Interceptions: None reported.

The risk Erysiphe aquilegiae would pose to California is evaluated below:

Consequences of Introduction: 

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

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

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

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

Risk is Medium (2): Powdery mildew disease is common in cool or warm humid regions, but can also be common in warm and dry climates since the fungal spores only require high relative humidity and not free-standing water to be released, germinate and cause infections.  Once a plant is infected, mycelium continues to spread on a leaf surface regardless of the level of atmospheric moisture.

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

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

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is High (3):  Hosts comprise ornamental and weed plants.  Most hosts of Erysiphe aquilegiae are in Ranunculaceae. Other doubtful hosts have also been reported in at least six other plant families.

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 powdery mildew pathogen has high reproduction and, under conducive environmental conditions of high relative humidity and wind currents, has high dispersal potential.

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 grown ornamental plants infected with the powdery mildew pathogen Erysiphe aquilegiae could result in lowered crop production and loss in sales.

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): Powdery mildew infection may significantly impact home/urban and ornamental plantings.  Endangered plant species are not affected.  Although five species of the thistle plant Cirsium spp. (Crystal Springs fountain thistle, San Luis Obispo thistle, Ashland thistle, Suisun thistle, and Surf thistle) and four species of larkspur Delphinium spp. (Baker’s larkspur, Cuyamaca larkspur, Golden larkspur, and San Clemente Island larkspur) are listed as endangered plants in California, these species are not reported hosts of E. aquilegiae.

Consequences of Introduction to California for Erysiphe aquilegiae:

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 = 12 (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 (-3): Erysiphe aquilegiae has been detected in several southern coastal counties extending from San Benito to San Diego.  Given its high reproduction capability and suitable environmental conditions for its spread and infection, it is possible that the distribution of this powdery mildew extends further than currently reported.

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 Erysiphe aquilegiae is C.

References:

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

Bolay, A.  2005.  Les Oïdiums de Suisse (Erysiphacées).  Cryptogamica Helvetica, 20:38-40.

Braun U.  1987.  A monograph of the Erysiphales (powdery mildews).  Beihefte zur Nova Hedwigia, Heft 89, J. Cramer Berlin-Stuttgart 1987. Pgs 208-209.

Farr, D. F., and A. Y. Rossman.  2015.  Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved October 22, 2015, from http://nt.ars-grin.gov/fungaldatabases/

Liberato, J. R., and J. H. Cunnington.  2006.  First record of Erysiphe aquilegiae on a host outside the Ranunculaceae.  Australasian Plant Pathology, 35:291-292.

USDA-PCIT.  2015.  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.

Pest Rating:  C

Posted by ls

Fungi, Plant Pathogens

Colletotrichum theobromicola Declr. 1905

California Pest Rating for
Colletotrichum theobromicola Declr. 1905
Pest Rating:  B
PEST RATING PROFILE
Initiating Event:  

On September 8, 2015 diseased Coleonema sp. (breath of heaven) seedlings exhibiting blight symptoms were collected from a nursery in Sacramento by Sacramento County Agricultural officials, and sent to the CDFA Plant Diagnostics Branch for diagnosis.  Suzanne Latham, CDFA plant pathologist identified the fungal fruit spot and anthracnose pathogen, Colletotrichum theobromicola as the cause for the disease. Subsequently, on September 14 and October 8, 2015, C. theobromicola was detected from Annona squamosa (sugar apple) fruit intercepted in shipments destined to private citizens and intercepted at the United States Postal Service by County officials in San Joaquin and Santa Clara Counties respectively.  Both shipments originated in Florida.  Consequently, all infected plant material was destroyed.  The risk of infestation of C. theobromicola in California is evaluated and a permanent rating is proposed.

History & Status:

Background:  Colletotrichum theobromicola is a distinct fungus species belonging to the vastly morphological and physiological variable C. gloeosporioides complex and is generally identified from other species of the complex only with DNA sequences. The species: C. fragariae, C. gloeosporioides f. stylosanthis, C. gloeosporioides f. stylosanthis “f. sp. stylosanthis”, and C. gloeosporioides f. stylosanthis “f. sp. guianensis’ are genetically similar to, and synonyms of C. theobromicola (Weir et al, 2012).

Colletotrichum fragariae (synonym of C. theobromicola) has been previously reported from strawberry plants in California (Gunnell & Gubler, 1992), however, that report was based only on morphological analysis of the species.  So, while there is the possibility that C. theobromicola may have been present in California prior to the CDFA detections mentioned above, its presence cannot be assumed or confirmed without genetic analysis. The recent detections of the C. theobromicola by CDFA constitute its first official State record in California.

Hosts: Colletotrichum theobromicola has been reported on different hosts from different countries:  Acca sellowiana (pineapple guava), Annona diversifolia (Ilama fruit), Annona squamosa (sugar/custard apple), Buxus microphylla var. japonica (Japanese boxwood), Cassia obtusifolia (sicklepod), coffea arabica (Arabian coffee), Coffea sp., Coleonema sp. (breath of heaven)( CDFA detection), Cyclamens persicum (Persian cyclamen), Fragaria ananassa (strawberry), Fragaria sp., F. chiloensis (coastal strawberry), F. vesca (wild strawberry), F. virginiana (woodland strawberry), Limonium sp. (statice), Olea europaea (olive), Potentilla canadensis (dwarf cinquefoil), Punica granatum (pomegranate),  Quercus sp. (oak), Stylosanthes guianensis (stylo, Brazilian lucerne), S. viscosa (poorman’s friend), Theobroma cacao (cacao, cocoa tree) (Farr & Rossman, 2015; Weir et al., 2012).

Symptoms:  Colletotrichum theobromicola 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.  The pathogen causes anthracnose disease of strawberry with symptoms that include crown rot, fruit rot and stolon lesions (Gunnell & Gubler, 1992).

Damage Potential:  Anthracnose disease caused by Colletotrichum theobromicola 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 theobromicola 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:  Colletototrichum theobromicola is widely distributed in tropical and subtropical region worldwide.  Africa: Nigeria; Asia: India, Israel, Japan; North America: Mexico, USA (California, Florida, Indiana, Louisiana, Michigan, Mississippi, New York, North Carolina, South Carolina, Virginia), Cuba, Panama; South America: Brazil, Uruguay; Australia; New Zealand (CABI, 2015; Farr & Rossman, 2015; Gunnell & Gubler, 1992; Weir et al., 2012).

Official Control:  In California C. theobromicola is an actionable, Q-rated pathogen, and infected plant material is subject to destruction or rejection.

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

California Interceptions: Two interceptions of Colletotrichum theobromicola-infected sugar apple fruit (see ‘Initiating event’).

The risk Colletotrichum theobromicola 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. theobromicola requires humid, wet, rainy weather for conidia to infect host plants. This environmental requirement may limit the ability of the pathogen to fully establish and spread under dry field conditions in California.

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

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

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Moderate (2) – Colletotrichum theobromicola has a moderate range of diverse hosts generally common in tropical and sub tropical regions. Of those hosts,strawberry, certain ornamentals, olive and oak are among the economically important hosts in California.

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

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

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

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

Risk is High (3) – The 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 High (3) – Productions of strawberry fruit and nursery grown ornamental plants, in particular, can be limited by their susceptibility to anthracnose under wet conditions. Therefore, under suitable climates, the pathogen could lower plant growth, fruit production and 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 Medium (2) – The pathogen could significantly impact cultural practices or home garden plantings.

Consequences of Introduction to California for Colletotrichum theobromicola:

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 theobromicola 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 not established (0).  Colletotrichum theobromicola 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 = 12.

Uncertainty:

None.

Conclusion and Rating Justification:

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

References:

CABI.  2015.  Colletotrichum fragariae (anthracnose of strawberry) full datasheet report.  Crop Protection Compendium.  www.cabi.org/cpc/

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/

Gunnell, P. S., and W. D. Gubler.  1992.  Taxonomy and morphology of Colletotrichum species pathogenic to strawberry.  Mycologia 84:157-165.

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

Colletotrichum queenslandicum B. Weir & P. R. Johnst. 2012

California Pest Rating for
Colletotrichum queenslandicum B. Weir & P. R. Johnst. 2012
 Pest Rating:  B
PEST RATING PROFILE
Initiating Event:  

On October 29, 2015 California Dog Teams intercepted Persea americana (avocado) fruit at parcel distribution facilities in Los Angeles and Santa Clara Counties.  The shipments had originated in Florida and Puerto Rico and were destined to private citizens in Los Angeles and Santa Clara Counties accordingly.  Diseased avocado fruit with necrotic spots were collected by County Agricultural officials, and sent to the CDFA Plant Diagnostics Branch for diagnosis.  Suzanne Latham, CDFA plant pathologist identified the fungal fruit spot and anthracnose pathogen, Colletotrichum queenslandicum as the cause for the disease. The identity of the associated pathogen was later confirmed by USDA National Identification Services at Beltsville, Maryland, and marked the first detection of C. queenslandicum in continental USA.  [According to USDA APHIS, the first US domestic detection of C. queenslandicum was reported from Hawaii on October 19, 2015.]  Consequent to the California detection, all infected plant materials were destroyed. The risk of infestation of C. queenslandicum in California is evaluated and a permanent rating is proposed.

History & Status:

Background:  Colletotrichum queenslandicum 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).  The species was originally described in 1965 as C. gloeosporioides var. minus Simmonds from Carica papaya (papaya) in Queensland, Australia.  The new name, C. queenslandicum was proposed by Weir and Johnston in 2012.

Hosts: Colletotrichum queenslandicum is known from few different hosts in different countries: Carica papaya, Carica sp. Persea americana, and Passiflora edulis (Australia); Coffea sp. (Fiji) (Farr & Rossman, 2015; James et al., 2014; Vieira et al., 2014; Simmonds, 1965).

Symptoms:  Colletotrichum queenslandicum 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:  Anthracnose disease caused by Colletotrichum queenslandicum 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 papaya and avocado 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 queenslandicum 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 queenslandicum is distributed in Australia and Fiji (Farr & Rossman, 2015; James et al., 2014; Vieira et al., 2014; Simmonds, 1965).

Official Control:  In California C. queenslandicum is an actionable, Q-rated pathogen, and infected plant material is subject to destruction or rejection.

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

California Interceptions: There have been two reported interceptions of Colletotrichum queenslandicum-infected avocado fruit. (see ‘Initiating event’).

The risk Colletotrichum queenslandicum 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 queenslandicum requires humid, wet, rainy weather for conidia to infect host plants. This environmental requirement and narrow host range may limit the ability of the pathogen to fully establish and spread under dry field conditions in mainly in southern California.

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

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

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1) – Colletotrichum queenslandicum has a limited host range comprising mainly of avocado, papaya, coffee and purple Granadilla (Passiflora edulis).  The Latter two hosts are not grown in California and avocado and papaya have limited productions mainly in the southern regions of the State.

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 papaya and avocado fruit may result in lower crop value and market loss.  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 backyard productions of papaya and avocado wherever grown in California.

Consequences of Introduction to California for Colletotrichum queenslandicum:

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 queenslandicum 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 not established (0).  Colletotrichum queenslandicum 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 = 10.

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the anthracnose pathogen, Colletotrichum queenslandicum 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/

James, R.S., J.  Ray, Y. P. Tan and R. G. Shivas.  2014.  Colletotrichum siamense, C. theobromicola, and C. queenslandicum from several plant species and the identification of C. asianum in the Northern Territory, Australia. Australasian Plant Disease Notes : 1-6.

Simmonds, J. H.  1965.  A study of the species of Colletotrichum causing ripe fruit rots in Queensland.  Queensland Journal of Agricultural and Animal Sciences 22: 437-459.

Vieira, W.A.S., S. J. Michereff, M. A. de Morais, Jr., K. D. Hyde and M. P. S. Camara.  2014. Endophytic species of Colletotrichum associated with mango in northeastern Brazil. Fung. Diversity 67: 181-202.

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

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

Geosmithia pallida (G. Sm.) M. Kolarík, Kubátová & Paotová

California Pest Rating for
Geosmithia pallida (G. Sm.) M. Kolarík, Kubátová & Paotová
 Pest Rating:  C
PEST RATING PROFILE
Initiating Event:

During August 2014, The CDFA Pathology Laboratory received official samples of diseased oak trees exhibiting symptoms of foaming cankers, collected from residential and commercial landscape sites in Marin and Napa counties.  The fungal pathogen Geosmithia pallida, causing foamy bark canker disease, was identified by Suzanne Latham, CDFA Plant Pathologist.  Within a few weeks of this detection, G. pallida was also detected in official oak samples collected in Santa Clara and El Dorado counties.  Prior to these official reports, the foamy bark canker disease has been known to exist throughout southern California extending to Monterey County.   The pathogen has not been previously rated and therefore, the need for a definite rating is necessitated and proposed.

History & Status:

Background:  Researchers at the Department of Plant Pathology, University of California, Riverside, have observed since 2012 decline of coast live oak (Quercus agrifolia) throughout urban landscapes in southern California (Lynch, et al., 2014). The fungus Geosmithia pallida was determined to be the cause of the observed symptoms which were successfully reproduced in pathogenicity tests on detached coast live oak shoots and in 2014, Lynch et al. provided the first report of G. pallida causing foamy bark canker on coast live oak in California and the USA.  They recovered the fungal species from symptomatic plant tissues associated with the western oak bark beetle Pseudopityophthorus pubipennis.  The western oak bark beetle is native to California and common as a secondary agent that readily attacks stressed plants.  It has not been previously associated with disease; however, cryptic species may be common among bark and ambrosia beetles (Lynch et al., 2014). The beetle burrows through the tree bark forming shallow tunnels below the bark and across the grain of the wood.  Eggs are laid within the tunnels and on hatching, the developing larvae form tunnels at right angles to their main tunnel and mostly within the inner bark or phloem close to the surface.  The fungus is dry-spored and occurs in the tunnels or galleries built by the beetles. Once insect larvae develop, they carry fungal spores and fly to other uninfected trees thereby spreading the fungus.

The fungal pathogen was originally placed in the genus Penicillium as the species, P. palladium which was later considered a synonym of Geosmithia putterillii (Pitt, 1979).  The latter species is a complex group of species comprising three genetically isolated cryptic species with worldwide distribution (Kolařík et al., 2004). Several isolates have been acquired from wood or subcorticolous insects.  In 2004, based on molecular and morphological analyses, Kolařík and others separated G. pallida from the G. putterillii species complex.

Hosts: Quercus agrifolia (coast live oak), Q. rubra (northern red oak), Q. wislizenii (interior live oak).

Symptoms:  Symptoms of G. pallida infection occur on the trunk and primary branches of trees and include wet discoloration seeping through entry holes caused by the western oak bark beetle.  Necrotic phloem and xylem tissue is apparent beneath the outer bark.  Multiple beetle entry holes may also be apparent on a single tree.  As the disease advances, a cream to reddish sap may ooze from the entry hole, followed by a prolific foamy liquid which may run down the trunk for about 2 feet.  The symptoms may be confused with those caused by Fusarium dieback/Polyphagous Shot Hole Borer; however, the size of the entry hole associated with foamy canker is smaller than those made by the Polyphagous Shot Hole Borer (Lynch et al., 2014).  In Europe, in laboratory plant growth culture tests using garden cress plants, G. pallida inhibited root growth by 25% whereas stem growth was almost unimpaired (Čižková et al., 2005).

Damage Potential:  Symptom associated with foamy bark canker disease on coast live oak result in branch dieback and tree death.

Transmission:  The fungal pathogen is associated with the western oak bark beetle and transmitted from infected to non-infected trees during movement and feeding by the beetle.  The fungus is also spread to uninfected sites through the movement of infected wood, such as firewood, and contaminated pruning and cutting equipment.

Worldwide Distribution:  Geosmithia pallida has a worldwide distribution (Kolařík et al., 2004).

Official Control:  There are no reports of official control of the fungal pathogen.

California Distribution: Los Angeles, Orange, Riverside, Santa Barbara, Ventura and Monterey counties (Lynch et al., 2014).  CDFA official samples collected from El Dorado, Napa, Marin and Santa Clara counties were positive for Geosmithia pallida (see ‘Initiating Event’).

California Interceptions:  Geosmithia pallida has not been intercepted in imported official shipments to California.

The risk Geosmithia pallida 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). Geosmithia pallida is already established in ten 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).   Presently the pathogen has been observed causing decline and death of coast live oak in association with the western oak bark beetle.  In California, coast live oak occurs in the coastal ranges from north central to southern counties. So, even though Geosmithia pallida has been found affecting one host, the latter as well as other host species of oak are relatively wide spread throughout the State.

 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 fungal pathogen is artificially spread by movement of its associated insect vector and infected wood. The western oak bark beetle vector is native to California and is capable of moving and finding habitation throughout the State.

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).  Foamy bark canker disease caused by Geosmithia pallida could result in tree decline and death of coast live oak trees.  Currently, there are no known control measures against this pathogen. Early detection is noted as being crucial and could lead to pruning back infected branches, and other cultural treatments.  Regulations against movement of oak firewood could be necessary and this could directly trigger loss of markets. Plus the pathogen is easily vectored by the native western oak bark beetle.   

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 decline of infected oak trees could have significant environmental impact by disrupting natural communities, critical habitats or changing the ecosystem process. The potential loss of coast live oak could seriously threaten the conservation of the host plant thereby negatively impacting the 2001 California Oak Woodlands Conservation Act approved by California State Legislature.

Consequences of Introduction to California for Geosmithia pallida:

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 Geosmithia pallida to California = (13).

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

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

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

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

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

Evaluation is High (-3). The pathogen has been reported in more than two contiguous or non-contiguous counties with suitable host and climate.

Final Score:

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

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

Uncertainty:

The pathogen is capable of spreading throughout California wherever suitable host and climate are present.  Since its detection in the southern counties it has spread to the central coastal region.  With the widespread distribution of the host plant and the associated western oak bark beetle vector, there is the possibility for the foamy bark canker disease to continue to spread statewide.  Further statewide survey and reports would be necessary to confirm this probability.  With further spread of the pathogen, the numeric score assessed here is not expected to change by much, thereby, strengthening its proposed ‘C’ rating.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the Foamy Bark Canker Disease pathogen, Geosmithia pallida is C.

References:

Čížková, D., P. Šrůtka, M. Kolařík, A. Kubátová and S. Pažoutová.  2005.  Assessing the pathogenic effect of Fusarium, Geosmithia and Ophiostoma fungi from broad-leaved trees.  Folia Microbiologica, 50:59-62.

Kolařík, M., A. Kubátová, S. Pažoutová and Petr Šrůtka.  2004.  Morphological and molecular characterization of Geosmithia putterillii, G. pallida comb. nov. and G. flava sp. nov., associated with subcorticolous insects.  Mycological Research 108: 1053-1069.

Lynch, S. C., D. H. Wang, J. S. Mayorquin, P. Rugman-Jones, R. Southamer and A. Eskalen.  2004.  First report of Geosmithia pallida causing foamy bark canker, a new disease on coast live oak (Quercus agrifolia) in association with Pseudopityophthorus pubipenis (western oak bark beetle, Coleoptera: Curculionidae: Scolytinae) in California.  Plant Disease “First Look” paper posted 05/21/2014: http://dx.doi.org/10.1094/PDIS-03-14-0273-PDN.

Lynch, S. P., R. Rugman-Jones, R. Southamer and A. Eskalen.  (Not dated).  Pest Alert:  Geosmithia pallida and Western Oak Bark Beetle (Pseudopityophthorus pubipenis) causing foamy bark canker disease on coast live oak (Quercus agrifolia) in California.  University of California, Riverside.

Pitt, J. I. (1979) Geosmithia gen. nov. for Penicillium lavendulum and related species. Canadian Journal of Botany 57: 2021–2030.

Responsible Party:

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

 Pest Rating:  C

Posted by ls

Fungi, Plant Pathogens

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

Plant Pathogens, Viruses and viroids

Tomato Mottle Mosaic Virus (ToMMV)

California Pest Rating for
Tomato Mottle Mosaic Virus (ToMMV)
Pest Rating: B
PEST RATING PROFILE
Initiating Event: 

On September 17, 2015, the CDFA was notified by a seed company of the detection of Tomato mottle mosaic virus (ToMMV) in tomatoes grown at the company’s farm in San Joaquin County.  Subsequently, the CDFA will collect official samples of ToMMV-infected tomato plants for pathogen diagnosis and the seed company disposed of infected plants and fruit and administered sanitization measures to prevent the possible spread of this pathogen to the environment.  The risk of infestation of Tomato mottle mosaic virus (ToMMV) in California is evaluated and a permanent rating is proposed.

History & Status:

Background:  Tomato mottle mosaic virus is a relatively new plant virus that was first reported in 2013 from Tamazula, Jalisco in Mexico, after being isolated from symptomatic tomatoes which were discovered in a greenhouse in 2009 (Li et al., 2013).   In the USA, ToMMV was first reported from Florida in 2014, following a 2010 and 2012 discovery of symptomatic tomato plants grown in a commercial tomato field and greenhouse respectively (Webster et al., 2014).

Tomato mottle mosaic virus belongs to the genus Tobamovirus in the family Virgaviridae.  Other tobamoviruses that naturally infect tomato include tomato mosaic virus and tobacco mosaic virus – both which are known to be widely distributed within California.  Complete genomic sequences were determined for the Mexico and USA isolates and reported to be 99% identical (Fillmer et al., 2015; Li et al., 2013; Webster et al., 2014). Tomato mottle mosaic virus is closely related to, but distinct from tomato mosaic virus.  In fact, Webster et al., (2014) compared gene sequences of tomato mosaic virus, deposited in GenBank, from pepper and tomato and determined that those were closely identical (98-100% nucleotide and deduced amino acid identity) to ToMMV, suggesting that in prior reports, ToMMV may have been misidentified as tomato mosaic virus and therefore, may be more wide spread than currently reported.

Hosts: Presently, natural hosts include tomato (Lycopersicon esculentum) and pepper (Capsicum annuum)

Symptoms: Foliar mosaic of light and dark green symptoms, chlorosis, and leaf deformation in mature tomato (Webster et al., 2014), whereas a rapid tissue necrosis occurred on the upper leaves inoculated tomato seedlings (Li et al., 2013).  Foliar mottle, shrinking, and necrosis occur in pepper plants (Li, et al., 2014).

Damage Potential:  Presently, there are no reports of quantitative crop yield losses specifically caused by ToMMV, nevertheless, losses similar to those caused by the closely-related tomato mosaic virus can be expected. Tomato mosaic virus can cause yield losses up to 25% in infected non-resistant greenhouse or field-grown susceptible tomato crops (CABI, 2015).  ToMMV has the potential of damaging tomato and pepper production mainly through the destruction of foliar growth.

Transmission: As a member of the genus Tobamovirus – tomato mottle mosaic virus is most likely transmitted in similar manner as tomato mosaic virus, and therefore, is contagious and transmitted through plant to plant contact as well as mechanically via contaminated hands, clothing, and tools; insects, contaminated irrigation water, contaminated soils, infected plants, plant debris, and seed. No particular insect vector species has been reported for ToMMV. Healthy seedlings can be infected in contaminated soils through minor wounds caused by natural damage to roots without involvement of vectors (CABI, 2015).

Worldwide Distribution:  Asia:  China, Iran; North America: USA (Florida), Mexico; South America: Brazil (Li et al., 2013; Li et al., 2014; Webster et al., 2014).

Official Control: None reported.

California Distribution: Tomato mottle mosaic virus is not known to be established within California.  However, ToMMV was detected by a seed company in their farm site in Acampo, San Joaquin County.  Consequently, infected plants were removed and sanitization measures were administered (see “Initiating Event”).

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

The risk Tomato mottle 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 High (3) – It is likely that Tomato mottle mosaic virus can establish a widespread distribution in California wherever tomato and pepper plants are cultivated, similar to its closely related species, Tomato mosaic virus.

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

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

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1) – Presently, the host range for Tomato mottle mosaic virus is limited to tomato and pepper plants.

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

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

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

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

Risk is High (3) – As a tobamovirus,Tomato mottle mosaic virus is easily transmitted through plant to plant contact as well as mechanically via contaminated hands, clothing, tools, and insects;contaminated irrigation water, contaminated soils, infected plants, plant debris, and seed. No particular insect vector species has been reported for ToMMV. Healthy seedlings can be infected in contaminated soils through minor wounds caused by natural damage to roots without involvement of vectors. 

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) – Tomato mottle mosaic virus is expected to cause economic impact similar to its closely related species, tomato mosaic virus.  Therefore, this pathogen could lower crop yield and market value, alter normal cultural production and irrigation practices to prevent spread to non-infected regions, and be vectored by contaminated insects to non-infected plants. 

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

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

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

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

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

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

Score the pest for Environmental Impact. Score:

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

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

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

Risk is Medium (2) – The host range is limited to tomato and pepper – cultivated crops, therefore no significant detrimental impact to the environment is expected.  However, home/urban gardening of host plants may be impacted if infected by ToMMV.

Consequences of Introduction to California for Tomato mottle 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 ToMMV 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 not established. Tomato mottle mosaic virus is not known to be established within California.  Detection in San Joaquin led to removal of diseased plants and sanitization treatments.

Final Score:

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

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

Uncertainty:

Presently, only tomato and pepper have been reported as hosts of this relatively new plant virus.  It is probable that in due time, other members of the Solanaceae plant family may be included as hosts. Therefore, reports of  host range studies may provide additional information on other possible hosts.  Furthermore, based on gene sequence analysis of tomato mosaic virus, researchers have suggested that ToMMV may have been misidentified as tomato mosaic virus.  The latter species is widely distributed in California, but whether or not it also includes ToMMV is not known.

Conclusion and Rating Justification:

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

References:

CABI   2015.  Tomato mosaic virus full datasheet.  Crop Protection Compendium.  http://www.cabi.org/cpc/datasheet/1695.

Fillmer, K., S. Adkins, P. Pongam and T. D’Ella.  2015.  Complete genome sequence of a Tomato mottle mosaic virus isolated from the United States.  Genome Announcements, 3 (2): e00167-15. doi:10.1128/genomeA.00167-15.

Li, R., S. Gao, Z. Fel and K. Ling.  2013.  Complete genome sequence of a new Tobamovirus naturally infecting tomatoes in Mexico.  Genome Announcements, 1(5):e00794-13. doi:10.1128/genomeA.00794-13.

Li, Y. Y., C. L., Wang, D. Xiang, R. H. Li, Y. Liu and F. Li.  2014.  First report of Tomato mottle mosaic virus infection of pepper in China.  Plant Disease, 98 (10):1447. http://dx.doi.org/10.1094/PDIS-03-14-0317-PDN.

Webster, C.G., E. N. Rosskopf, L. Lucas, H. C. Mellinger and S. Adkins.  2014.  First report of Tomato mottle mosaic virus infecting tomato in the United States.  Plant Health Progress, doi:10.1094/PHP-BR-14-0023.

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

Plant Pathogens, Viruses and viroids

Tomato Chlorotic Dwarf Viroid

California Pest Rating for
Tomato Chlorotic Dwarf Viroid
Pest Rating: A
PEST RATING PROFILE
Initiating Event: 

On October 23, 2014 CDFA was notified by USDA APHIS of the detection of Tomato chlorotic dwarf viroid (TCDVd) in four experimental Petunia samples that were shipped under federal permit from California to Illinois (Kress, 2014). The detection was made by the plant pathologist of an ornamental plant breeding company, and communicated to USDA APHIS as per federal permit requirement that “APHIS is notified within 10 days on receipt of permitted materials if the permitee detects a pathogen that is not widely prevalent in the State from which the infected material was obtained.”  The Petunia plant samples came from plants raised in a greenhouse environment by a different plant breeding company in Arroyo Grande, California.   Following that detection the Company took action by discarding all infected Petunia plants and administering phytosanitary measures. Furthermore, the Company reported to San Luis Obispo County that they had the (remaining) Petunia plants in the greenhouse tested for TCDVd and the results were negative. Nevertheless, following the disposal and sanitary action taken by the Company, official samples of the remainder Petunia plants in the greenhouse were collected for diagnostic analysis conducted by the CDFA Plant Pathology Laboratory (Taylor, 2014).  The current status and pest rating of TCDVd is re-evaluated and a permanent rating is proposed.

History & Status:

Background:  Tomato chlorotic dwarf viroid (TCDVd) belongs to the genus Pospiviroid.  PSTVd has a circular single stranded RNA molecule with 360 nucleotides and lacks a coat protein.  It is closely related to the Potato spindle tuber viroid but significantly differs from it in sequence homology. Little is known about the pathogen’s host range, host-pathogen interactions, transmission and epidemiology however, the pathogenicity properties of TCDVd are expected to be similar to those of the Potato spindle tuber viroid.    As with other members of its genus, TCDVd use the infected plant cell nucleolus to multiply in numbers and accumulate. TCDVd then move from cell to cell through natural openings in the cell wall (plasmodesmata) and throughout the plant via the phloem.  In general, viroids survive in nature outside a host or in dead plant material for only brief periods of a few minutes to a few months. They overwinter and oversummer within infected perennial hosts.  TCDVd is active at high temperatures and therefore, warm climates are expected to increase its rate of transmission.

Hosts: Tomato (Solanum lycopersicum) is the major host.  Incidental hosts include Brugsmania hybrids (Angel’s trumpet), Petunia, Verbena and Vinca minor (periwinkle) (EPPO, 2014; CABI, 2014).  Several artificially inoculated, experimental, susceptible hosts belonging to the family Solanaceae have been reported (Singh, et al., 1999).

Symptoms:  Symptoms are difficult to distinguish as specific to TCDVd – as several viroids and viruses can produce similar symptoms.  Symptoms expressed by tomato plants are influenced by the TCDVd strain, tomato variety, age and vigor of the plant, and climatic conditions.  Initial symptoms, produced in tomato plants 3-6 weeks after initial infection, are exhibited as reduction in growth and chlorosis (yellowing) of young terminal leaves. Over time infected plants become stunted, distinctly chlorotic leaves that may turn bronze and/or purplish, sometimes with lesions, and turn brittle and distorted.  However, commonly observed symptoms include stunting, bunchiness, reduced leaves and fruit, leaf chlorosis, necrosis and leaf and petiole, downward bending of leaves, distorted fruit and may lead to death of the plant.

The pathogen has been detected in petunia and verbena although no symptoms were exhibited by these hosts (Sabaratnam, 2012).  Symptomless ornamental plants may serve as a source of inoculum.

Damage Potential: Estimates of crop/yield loss caused by the pathogen are not available however TCDVd can be a serious threat to tomato production in field and greenhouse environments. Extensive damage has especially been noted in greenhouse-grown tomato plants.

Transmission:  Similar to other members of the genus pospiviroid, Tomato chlorotic dwarf viroid is mechanically transmitted in infected plant sap spread through handling of contaminated plants, pruning tools, cultivation equipment, clothing, and plant to plant contact.  The pathogen is also spread through vegetative propagation and contaminated seed (Singh & Dilworth, 2009).  Natural transmission of TCDVd by insects and pollen is not known, however, Ling (2010) stated the transmission of TCDVd by bumblebee pollinators of tomato plants grown in greenhouse environments. The pathogen is transmitted less efficiently from older mature plants during the picking of fruit and old leaves (Sabaratnam, 2012).

Worldwide Distribution:  Asia:  India; America: Mexico, USA; Europe: Czech Republic, France, Slovenia.   In the USA, TCDVd is present and limited in its occurrence in Arizona and Colorado (EPPO, 2014; CABI, 2014).

Official Control:  The following countries include Tomato chlorotic dwarf viroid on their ‘Harmful Organism’ lists: Georgia, Japan, Republic of Korea, New Zealand, and Thailand (PCIT, 2014).

Tomato chlorotic dwarf viroid has been eradicated in Canada (Manitoba), Japan (Honshu), Finland and Norway, and is no longer present in Belgium.  It is considered transient, under eradication in United Kingdom (Scotland) (EPPO, 2014; CABI, 2014).

California Distribution: There are no reports of TCDVd being established in field or natural environments within California – that would indicate an established distribution.

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

The risk Tomato chlorotic dwarf viroid would pose to California is evaluated below.

Consequences of Introduction: 

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

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

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

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

Risk is High (3) – TCDVd is capable of establishing within greenhouse as well as field environments within California.  Suitable climates for tomato and other host plants would also favor establishment of TCDVd.  

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) – Of what is currently known, the host range of TCDVd is limited to tomato and few ornamental crops.  However, tomato is grown in significant acreages throughout the State.

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) – TCDVd multiply autonomously in infected plant material and are easily transmitted through infected seed and mechanical means.

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

A. The pest could lower crop yield.

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

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

D. The pest could negatively change normal cultural practices.

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

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

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

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

– Medium (2) causes 2 of these impacts.

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

Risk is High (3) – TCDVd can potentially lower tomato crop value, yield, trigger loss of market through the imposition of quarantine regulations by other countries and states, and can influence normal cultural practices.

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) – At the very least, incidence of TCDVd could result in requirement of additional official and private treatments, impact cultural and horticultural practices.

Consequences of Introduction to California for Tomato chlorotic dwarf viroid

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

-Low = 5-8 points

-Medium = 9-12 points

–High = 13-15 points

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

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

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

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

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

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

Evaluation is (0).  TCDVd is not established in California.  TCDVd has only been detected in nursery plants contained in greenhouses. That detection led to destruction of infected plants and implementation of phytosanitary measures (see “Initiating event”) and does not indicate the establishment of the pathogen in California. 

Final Score:

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

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 13 (High).

Uncertainty:

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

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Tomato chlorotic dwarf viroid is A.

References:

CABI   2014.  Tomato chlorotic dwarf viroid basic datasheet.  Crop Protection Compendium.  http://www.cabi.org/cpc/datasheet/1695.

EPPO, 2014.  Tomato chlorotic dwarf viroid (TCDVD0).  New PQR database.  Paris, France:  European and Mediterranean Plant Protection Organization.  http://newpqr.eppo.int.

Kress, J.  2014.  Email to John Chitambar (CDFA) and others (CDFA), subject: RE: Attention Shailaja Rabindran/Pathogen Detection, sent: Thursday 10/23/2014, 11:06 am.

Ling, K. S., J. Th. J. Verhoeven, R. P. Singh, and J. K. Brown.  2009.  First report of tomato chlorotic dwarf viroid in greenhouse tomatoes in Arizona.  Plant Disease, 93:1075.

Ling, K. S.  2010.  Genetic diversity of tomato viroids in North America.  USDA-ARS, U. S. Vegetable Laboratory Charleston, South Carolina, Power Point Presentation.

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

Sabaratnam, S.  2012.  Tomato chlorotic dwarf viroid on greenhouse tomato.  British Columbia Ministry of Agriculture, Abbotsford Agriculture Center.  http://www.agf.gov.bc.ca/cropprot/tcdvd.htm.

Singh, R. P. and A. D. Dilworth.  2009.  Tomato chlorotic dwarf viroid in the ornamental plant Vinca minor and its transmission through tomato seed.  European Journal of Plant Pathology, 123:111-116.

Singh, R. P. X. Nie, and M. Singh.  1999.  Tomato chlorotic dwarf viroid: an evolutionary link in the origin of pospiviroids.  Journal of General Virology, 80:2823-2828.

Taylor, C.  2014.  Email to Karen Lowerison (San Luis Obispo County Agricultural Commissioner’s office) and others (CDFA, SLO County), subject: Re: Tomato chlorotic dwarf viroid detection, sent: Friday 10/24/2014, 2:31 pm.

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: A

Posted by ls

Fungi, Plant Pathogens

Sarocladium oryzae (Sawada) W. Gams & D. Hawksworth

California Pest Rating for
Sarocladium oryzae (Sawada) W. Gams & D. Hawksworth
Pest Rating: A
PEST RATING PROFILE
Initiating Event:

In August 2014, during a routine Controlled Import Permit inspection, Anthony Jackson, USDA APHIS PPQ WR, sampled rice seedlings imported from Spain and grown under post quarantine permit conditions in a greenhouse in Pleasant Grove, Sutter County, California.  A fungal pathogen, Sarocladium oryzae was detected in the sampled seedlings and identified by Cheryl Blomquist, plant pathologist, CDFA.  This identification marked the first detection of S. oryzae in California.  Later, in October 2014, the same pathogen was again detected by Suzanne Latham, plant pathologist, CDFA, in rice seedlings grown in the same Pleasant Grove greenhouse.  Subsequently, all post quarantine rice seedlings held at the greenhouse were destroyed by steam sterilization at the CDFA Plant Pathology Laboratory.   The fungal pathogen was assigned a Q (temporary) rating which is reassessed herein for the proposal of a permanent rating.

History & Status:

Background:  Sarocladium oryzae is a fungal pathogen that causes the sheath rot of rice disease.  Historically, the pathogen was initially described as Acrocylindrium oryzae by Sawada in 1922 from Taiwan.  In 1956, a species which caused symptoms similar to Sarocladium oryzae, was named by Gams and Hawksworth as S. attenuatum.  However, genetic and biochemical analyses revealed no differences between S. oryzae and S. attenuatum and subsequently the latter species was declared a synonym of S. oryzae (Bridge et al., 1989).  Sarocladium oryzae belongs to the order Hypocreales in the class Sordariomycetes, Phylum Ascomycota.

Hosts: Oryza sativa (rice) is the main host. However, rice cultivars differ in their susceptibility to the pathogen.  Other naturally infected hosts include O. rufipogon (wild rice) and grasses: Hymanchne assamica, Leersia hexandra, Panicum walense.  Other hosts include monocot weeds found in rice fields which may serve as a natural source of inoculum for infection of rice: Cyperus iria (rice flat sedge), C. tenneriffae, C. difformis (small-flowered nut sedge), Echinochloa crus-galli (barnyard grass), Eleusine indica (goose grass) and Monochoria vaginalis.  Also, Echinochloa colona (jungle rice).  Other monocot agricultural crops include millets, sorghum and maize. Several weeds and wild rices are included experimental, greenhouse-tested hosts (CABI, 2014; EPPO, 2014).

Symptoms:  The pathogen mainly attacks the uppermost leaf sheaths which enclose young panicles at the booting stage.  Lesions develop, initiating as irregular spots 5-10 mm, which become dark lesions, sometimes oblong, with brown margins and light-brown centers or grayish-brown throughout. Lesions may coalesce and cover most of the leaf sheath.  Young lesions bear whitish, powdery fungal growth on the outer and inner sides of affected sheaths, while old lesions have less or no fungal growth and appear as dry, brownish lesions with the enclosed rotted panicle. When infected early, young panicles remain compressed within the sheath, do not develop and rot, or only partially emerge from the sheath.  Outside the rotted sheath, partially emerged spikelets/grains are dark brown, chaffy and partially filled.

Infected seeds are usually symptomless and germinate normally.  Sometimes, primary and secondary leaves wither prematurely due to S. oryzae infection (CABI, 2014).

Damage Potential:  In India, rice yield losses of 10-26% and 50% are reported (Chakravarty and Biswas, 1978; CABI, 2014).  In Taiwan, 3-20% incidence of sheath rot disease have been observed reaching 85% in susceptible varieties.  Losses include production of fewer spikelets per panicle, lower grain weight of diseased panicles, and increased grain chaffiness. In India, 70% disease severity with 15-35% grain chaffiness, and 100% seed sterility in severe cases has been reported (CABI, 2014).

Disease Cycle: Sarocladium oryzae survives as mycelium on and in seeds.  Fungal inoculum or spores (conidia) from several infected weed hosts are capable of infecting rice.  The pathogen invades rice through the stomata and wounds and grows intercellularly within vascular and mesophyll tissues.  Additionally, wounds created in rice plants facilitate infection and disease development.  This is particularly true of wounds caused by mites, stem borers, mealy bugs, and rice bug.  The incidence and severity of sheath rots of rice disease is favored at 20-30°C and 65-85% relative humidity.

Transmission:  Seed – the pathogen is externally and internally seedborne.  Sachan and Agarwal (1995) found S. oryzae within the seedcoat, endosperm and embryo of discolored seeds however the pathogen may also be detected on seeds that are not discolored. S. oryzae may also be spread through infected straw and plant parts – leaves, seeds, flowers, inflorescences, cones, and calyx.

Worldwide Distribution:  Africa:  Burundi, Cameroon, Cote d’Ivore, Gambia, Kenya, Madagascar, Niger, Nigeria, Senegal, Tanzania; North America: Mexico, USA; Central America: Cuba; South America: Argentina, Brazil, Colombia, Venezuela; Asia:  Bangladesh, Brunei Darussalam, China, India, Indonesia, Iran, Japan, Malaysia, Nepal, Pakistan, Philippines, Saudi Arabia, Sri Lanka, Taiwan, Tajikistan, Thailand, Uzbekistan, Vietnam, Oceania: Australia.  In the USA it is reported as being widespread, and specifically present in Louisiana (CABI, 2014; EPPO, 2014).

Official Control: Sarocladium oryzae is on the “Harmful Organism List’ for Honduras and Peru (PCIT, 2014). The species is currently listed as a Q rated pest for California.

California Distribution: Sarocladium oryzae is not present in California.

California Interceptions:  Prior to its current detection in Sutter County (see ‘Initiating event’) Sarocladium oryzae has not been detected in incoming plant shipments to California.

The risk Sarocladium oryzae 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) – If allowed to enter California, Sarocladium oryzae is capable of establishing a widespread distribution in the States rice cultivated acreage.

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) – Rice is the major host of the pathogen and is grown in significant acreage in California.  Other hosts include several weeds that are capable to harboring inoculum for rice infections.

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) – Long distance spread is mainly through infested seed.  Infected plant parts and rice straw also serve as significant means of spread.  Potentially, conidia may be moved over short distances via winds, and wind-blown water droplets.  

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

A. The pest could lower crop yield.

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

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

D. The pest could negatively change normal cultural practices.

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

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

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

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

– Medium (2) causes 2 of these impacts.

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

Risk is High (3) – The pathogen could significantly impact rice production in California by lowering crop yield and value which would result in the loss of markets.  Additionally, certain species of mites and stem borers have been reported to harbor large numbers of fungal spores (conidia) and spread the pathogen to non-infected plants thereby, increasing the incidence of the sheath rot of rice disease.

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) – Several species of natural grasses and wild rice are hosts of Sarocladium oryzae. If these hosts are infected they may significantly impact the ecosystem of a natural environment. 

Consequences of Introduction to California for Sarocladium oryzae:

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 Sarocladium oryzae to California = (13).

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

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

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

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

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

Evaluation is not established (0).

Final Score:

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

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 13.

Uncertainty:

Sarocladium oryzae has not been previously detected in California.  The initial detection recorded in this report was made in a greenhouse and subsequently all rice plants within the greenhouse were destroyed.  No targeted surveys of natural environments, rice fields or seed rice storage facilities have been conducted for the detection of this pathogen within California.  If detected, the proposed rating may alter.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the sheath rot of rice pathogen, Sarocladium oryzae is A.

References:

CABI.  2014.  Sarocladium oryzae full datasheet report.  Crop Protection Compendium.  www.cabi.org/cpc/.

Chakravarty, D. K, and S. I. Biswas. 1978. Estimate of yield loss in rice affected by sheath rot. Plant Disease Reporter, 62:226-227.

EPPO.  2014.  Sarocladium oryzae (SARMOR).  European and Mediterranean Plant Protection Organization PQR database.  http://www.eppo.int/DATABASES/pqr/pqr.htm.

Farr, D.F., & Rossman, A.Y. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved December 4, 2014, from http://nt.ars-grin.gov/fungaldatabases/.

Groth, D.  1992.  Sheath rot.  In, Compendium of Rice Diseases edited by R. K. Webster and P. S. Gunnell.  The American Phytopahtological Society, Minnesota, USA: 25.

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

Sachan, I. P., and V. K. Agarwal. 1995. Seed discolouration of rice: location of inoculum and influence on nutritional value. Indian Phytopathology, 48(1):14-20; 17 ref.

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: A

Posted by ls

Fungi, Plant Pathogens

Peronospora belbahrii (Downy mildew of basil)

California Pest Rating for
Peronospora belbahrii
(Downy mildew of basil)
Pest Rating: C
PEST RATING PROFILE
Initiating Event:

During June 2014, Cheryl Blomquist, CDFA Plant Pathologist, detected Peronospora belbahrii in basil plants grown in a Nursery in Alameda County.  The plants had been purchased from a different nursery in Sebastopol, Sonoma County.  In 2008, the pathogen had been detected in basil plants produced in various nurseries.  Trace-back investigation of the 2008 detections revealed that the seeds had originated in Italy.  Presently, the origin of seeds cultivated in Sonoma County is not known.  Peronospora belbahrii currently has a Q rating that is herein reassessed for the proposal of a permanent rating.

History & Status:

Background:  Peronospora belbahrii is a fungal pathogen that causes downy mildew disease of basil (Ocimum spp. of the family Lamiaceae).  Traditionally it was believed that the downy mildew disease of Lamiaceae, including the downy mildew of basil, was caused by a single species namely, P. lamii.  However, that view has been proven inaccurate by several researchers, and Belbahri et al. (2005) showed through ITS sequencing that a then newly occurring fungal species on basil was different from P. lamii.  Later, Thines et al. (2009) formally introduced this fungal species as P. belbahrii and distinguished it from a different closely related species that parasitizes sage (Salvia).  They determined that P. belbahrii isolates infected both basil and coleus (Solenostemon sp.), and while those isolates seemed closely related, Thines et al. (2009) refrained from distinguishing them as two separate species until further studies have been conducted (albeit depending on the taxonomical concept taken, downy mildew on basil and coleus may be attributed to one or two different species).  Downy mildew of basil was first reported from Africa from where it is assumed to have originated on sweet basil (Ocimum basilicum). Later, it was reported from Europe.  It continued to spread globally and is considered a relatively new disease of basil in the United States.

Disease cycle:  Peronospora belbahrii is an oomycete belonging to the family Peronosporaceae.  Generally, downy mildews overwinter as thick-walled resting spores called oospores that are produced through the fertilization of two mating types.  However, currently only one mating type of P. belbahrii has been found in the USA.  Consequently, no oospores are formed and the pathogen is unable to survive harsh cold winters (Grabowski, 2014).  It is likely that the pathogen survives as mycelium and/or condia (spores) in infected plant buds, plant debris, leaf tissue and shoots.  Peronospora belbahrii thrives in warm, humid climates.  However, it can tolerate cool weather, infect and produce conidia at temperatures as low as 59°F (Grabowski, 2012).  Generally, under favorable weather conditions, condia are carried by wind or water to wet leaves near the ground where they infect through stomata of the lower leaf surface.  A conidium germinates via a germ tube that grows through leaf stomata into intercellular spaces within the leaf tissue and eventually penetrates plant cells through special structures called haustoria.  Developing hypha that spreads intercellularly forms a cushion of mycelia just below the stomata.  From this cushion, conidophores arise and emerge through stomata.  At their tips, conidia (sporangia/spores) are produced simultaneously and are carried by wind and rain to new infection sites of the same or different plant.

Dispersal and spread:  The pathogen is seed borne and can also be spread through contaminated plant cuttings, transplants, and fresh leaves.  Also, it produces airborne conidia (spores) can disperse and be carried by moist winds.  It can also be present in soil associated with host and non-host plants and therefore, can spread by any means that aids in the movement of soil and/or water from infected plants to non-infected ones.

Hosts:  Ocimum spp. (basil, including culinary and ornamental varieties), Solenostemon sp. coleus (Thines et al., 2009), Agastache sp. hyssop (Henricot et al., 2009).

Symptoms and damage potential: Infection starts on lower leaves and progresses upwards.  Initially symptoms appear as yellowing (slightly chlorotic) of affected leaves with the veins remaining green. Following this, the central portion of a chlorotic lesion may become necrotic; slight curvature of leaves occurs followed by premature leaf fall.  In some cases entire area of the leaf surface is affected.  Grey to brown, furry or downy (conidia) growth is apparent on underside of symptomatic leaves giving the leaves a dirty appearance.  These symptoms may sometimes occur on upper surfaces of leaves.

Under cool dry conditions infected transplants and leaves may not exhibit symptoms (Grabowski, 2012).   Basil plants not showing symptoms at harvest are capable of developing symptoms during transport (Roberts et al., 2009).  Chen et al. (2010) noted that in Taiwan, the pathogen caused chlorosis and leaf shrinkage on basil in the field, but did not cause any symptom on coleus.

Downy mildew is one of the most destructive diseases of sweet basil which is grown as a specialty crop in greenhouses and production fields in several regions of the United States and other countries. Once infected, basil plants are no longer marketable.  Under favorable weather conditions complete yield loss can be expected.  In Florida, almost 100% incidence of the disease occurred causing complete yield loss in the field for fresh and potted herbs markets (Roberts et al., 2009).  The frequency of disease occurrence and the percentage of infected leaf area were 80-90% and 17-20% respectively on full-grown basil leaves grown a greenhouse in Hungary (Nagy & Horvath, 2011).

Worldwide Distribution: Basil downy mildew has been reported from several countries and continents including, Argentina (greenhouse), Belgium, Benin, Cameroon, Canada, Cuba, Cyprus, France, Switzerland, Hungary, Israel, Iran, Italy, New Zealand, South Africa, Taiwan, Tanzania, Uganda, United Kingdom (Zhang et al., 2012; CABI, 2014; EPPO, 2014; Henricot et al., 2009).

In the United States, the pathogen was first discovered in Florida in 2007 (Roberts et al., 2009).  Since then, the disease has been found throughout the eastern United Sates and commercial basil production regions in the Midwest and California, namely, Alabama, California, Connecticut, Delaware, Georgia, Hawaiian Islands, Illinois, Indiana, Kansas, Kentucky, Massachusetts, Missouri, Minnesota, New Jersey, New York, North Carolina, Ohio, Oregon, Pennsylvania, South Carolina, Texas, Vermont, Virginia and Wisconsin (Zhang et al., 2012; Grabowski, 2012; PNW, 2014).

Official Control: Currently, the pathogen is not officially controlled in the United States Department of Agriculture.

California Distribution:  In California, the pathogen has been found in nursery and/or field environments of Alameda, San Diego, San Joaquin, Ventura, and Southern Valley Counties.

California Interceptions:  Recently P. belbahrii was detected in basil plants grown in a nursery in Alameda County.  The plants had originated from a different nursery in Sonoma County (see ‘Initiating Event’).

The risk Downy mildew of basil 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): As evident from current distribution records in California, Peronospora belbahrii – causing downy mildew of basil – is able to develop in warm (not hot), humid weather conditions and can tolerate cool climates as well.  Interestingly, in San Diego County, basil was drip irrigated and grown in a hot inland valley.  Under those conditions the disease still spread, possibly due to the humid microenvironment that developed in a basil field where plants were grown close together so that dew was produced when evening temperatures dropped.

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 basil, coleus and hyssop.  Although several species and varieties of basil exist, the host range is thus far limited to three plant genera.

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): Conidia are easily produced simultaneously and in abundance.  The pathogen is seed borne as well as transmitted via infected plant material; conidia are dispersed by winds, water and associated soil. 

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): Presence of the pathogen in field and/or greenhouse environments can significantly lower crop value and yield.  Infected, symptomatic plants are not marketable resulting in total loss in recovery of production costs.  Markets for crop sale are directly affected.  Normal cultivation practices, including delivery and supply of irrigation water, would need to be altered to prevent spread of the pathogen.

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/urban gardening of basil and cultivation of coleus and hyssop ornamental plants can be significantly impacted if the pathogen is present in private home garden environments.  

Consequences of Introduction to California for Downy mildew of basil:

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

-Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

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

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

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

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

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

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

Evaluation is High (-3):  To date, the pathogen has been detected in more than four non contiguous 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 = 8.

Uncertainty:  

Surveys for the detection of P. belbahrii have not been conducted to fully establish its presence in field environments within California.  Results of future survey may result in further detections of the pathogen in new locations.  This will only strengthen the current proposed C rating.  However, due to the devastating effects on crop production, direct action is necessary to mitigate risk of establishment and spread of P. belbahrii on host plants particularly grown in nursery environments.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Downy mildew of basil is C.

References:

Belbahri, L., G. Calmin, J. Pawlowski and F. Lefort.  2005.  Phylogenetic analysis and real time PCR detection of a presumbably undescribed Peronospora species on sweet basil and sage.  Mycological Research, 109:1276-1287.

Blomquist, C.L., S. Rooney-Latham and P. A. Nolan.  2009. First report of downy mildew on field-grown sweet basil caused by a Peronospora sp. in San Diego County, California. Plant Disease 93:968.

CABI.  2014.  Pernospora belbahrii data sheet report (basic).  Crop Protection Compendium.  http://www.cabi.org/cpc/datasheetreport?dsid=118352.

Chen, C. H., J. H. Huang, J. H. and T. F. Hsieh.  2010.  First report of Peronospora belbahrii causing downy mildew on basil.  Plant Pathology Bulletin, 17:177-180.

EPPO.  2014.  Peronospora belbahrii (PEROBE).  PQR database.  Paris, France: European and Mediterranean Plant Protection Organization.  http://www.newpqr.eppo.int.

Grabowski, M.  2012.  Basil Downy Mildew Peronospora belbahrii.  Regents of the University of Minnesota.  University of Minnesota Extension. http://www.extension.umn.edu/garden/yard-garden/vegetables/basil-downy-mildew/docs/basil-downy-mildew-pub.pdf.

Henricot, B., J. Denton, J. Scarce, A. V. Barnes and C. R. Lane.  2009.  Peronospora belbahrii causing downy mildew disease on Agastache in the UK: a new host and location for the pathogen.  New Disease Reports, 20:26.

Nagy, G. and A. Horvath.  2011.  Occurrence of downy mildew caused by Peronospora belbahrii on sweet basil in Hungary.  Plant Disease, 95:1034.1.

PNW.  2014.  Basil, Sweet (Ocimum basilicum) – Downy Mildew.  Pacific Northwest Plant Disease Management Handbook.  http://pnwhandbooks.org/plantdisease/basil-sweet-ocimum-basilicum-downy-mildew.

Roberts, P. D., R. N. Raid, P. F. Harmon, S. A. Jordan and A. J. Palmateer.  2009.  First report of Downy Mildew caused by a Peronospora sp. on basil in Florida and the United States.  Plant Disease 93: 199.

Thines, M., S. Telle, S. Ploch and F. Runge.  2009.  Identity of the downy mildew pathogens of basil, coleus and sage with implications for quarantine measures.  Mycological Research 113:532-540.

Wyenandt, C. A., J. E. Simon, M. T. McGrath and D. L. Ward.  2010.  Susceptibility of basil cultivars and breeding lines to downy mildew (Peronospora belbahrii).  2010.  HortScience 45:1416-1419.

Zhang, S. Z. Mersha, P. D. Roberts and R. Raid.  2012.  University of Florida, IFAS Extension Document PP271.  http://edis.ifas.ufl.edu/pdffiles/PP/PP27100.pdf.

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

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