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.