Colletotrichum cymbidiicola | Pest Rating Proposals and Final Ratings

California Pest Rating for

Colletotrichum cymbidiicola Damm, P. F. Cannon, Crous, P. R. Johnst. & B. Weir, 2012

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

In April 2014, during an inspection of a nursery in San Diego County, California, Pat Nolan, plant pathologist, San Diego County, observed black spots on leaves of greenhouse-grown cymbidium orchids and submitted symptomatic foliar samples to the CDFA Plant Pathology Laboratory for pathogen diagnosis. Suzanne Latham, plant pathologist, CDFA analyzed the samples and detected Colletotrichum cymbidiicola in cultures of the symptomatic leaves. The identity of the associated pathogen was later confirmed by the USDA APHIS National Identification Services. This detection marked a first record of C. cymbidiicola in the USA (Bethke, 2014). Follow-up samples collected in June and August from the same nursery, also tested positive for C. cymbidiicola. Subsequently, the nursery destroyed symptomatic plants and administered sanitary and fungicidal treatment measures to protect remaining plants from future infections. Trace-back investigations revealed that the San Diego orchids originated in a nursery in Humboldt County. However, C. cymbidiicola was not detected in orchid samples collected from the Humboldt nursery greenhouse. A few months later, in June 2014, C. cymbidiicola was detected again in cymbidium orchids in a small, residential nursery in Santa Clara County, however, no trace-back information was available. Recently, on May 7, 2015, more C. cymbidiicola was detected in orchids from the original nursery in San Diego County. Therefore, there is a need to reevaluate the current temporary pest rating of C. cymbidiicola for the proposal of a permanent rating.

History & Status:

Background: Colletotrichum cymbidiicola is a fungus species belonging to the complex species group C. boninense which was originally described in 2003 as a segregate of the vastly morphological and physiological variable C. gloeosporioides complex (CABI, 2014; Morikwaki et al., 2003). In the past, isolates of C. boninense were often identified as C. gloeosporioides. However, after segregation from C. gloeosporioides, researchers found that C. boninense actually comprised of a complex of several species and by 2012, through molecular phylogenetic analyses of 86 strains of C. boninense, Damm et al. (2012) were able to recognize 18 species within the C. boninense complex including C. cymbidiicola based on DNA sequence data and morphology. Colletotrichum cymbidiicola is associated with orchids and is specific at plant genus level.

Hosts: Cymbidium spp. (orchids) (Damm et al., 2012).

Symptoms: Anthracnose symptoms are expressed as dark spots or lesions in infected orchid leaves, petioles and blossoms. Initial symptoms include brown discolorations which are irregularly shaped sunken lesions that turn to dark brown with concentric brownish black fruiting bodies (acervuli). Leaf wilting may occur often resulting in dieback and reduction in plant quality. As in orchids infected with Colletotrichum gloeosporioides, symptoms may be most common on orchid leaves when stressed plants are damaged by cold and hot temperatures, sun, wind, chemicals and mechanical damage.

Damage Potential: Anthracnose disease caused by Colletotrichum cymbidiicola can result in reduced plant quality and growth. Estimates of yield/crop loss due to this pathogen have not been reported although severe outbreaks of orchid anthracnose have been reported in India (Chowdappa, et al., 2014). 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 cymbidiicola 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 result in fruiting bodies (acervuli) that 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. Condia 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: Australia, India, Japan, New Zealand, USA (California) (Chowdappa et al., 2014; Damm, et al., 2012; Farr & Rossman, 2015).

Official Control: Colletotrichum cymbidiicola is considered a new record in North America and reportable to the USDA.

California Distribution: San Diego and Santa Clara Counties (see ‘Initiating Event’).

During the 1980s, CDFA plant pathologists identified C. gloeosporioides in Cymbidium sp. (Alex French, California Plant Disease Host Index 2^nd edition). The site of detection generally includes the southern coastal counties. Details of that specific record are not currently available. At that time specific molecular diagnostic tests were not available to enable the distinction of C. cymbidiicola. It is, therefore, possible that this detection may have included C. cymbidiicola. No eliminative action would have been taken against C. gloeosporioides as the species is known to be widespread in California. However, since that detection and until the 2014-2015 detections noted above in ‘Initiating Events’ there have been no reports of Colletotrichum sp. on cymbidium orchids in California.

California Interceptions: Colletotrichum cymbidiicola has not been intercepted in quarantine plant shipments imported to California.

The risk Colletotrichum cymbidiicola 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. cymbidiicola 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. On the other hand, the pathogen could establish in limited regions with conducive climates within California. Of particular importance is the ability for C. cymbidiicola to effectively infect and spread to host plants grown under conducive climate conditions in nurseries.

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 cymbidiicola is limited to orchids, Cymbidium sp.

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) – Under suitable climates, the pathogen could lower plant growth 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, home or ornamental plantings of orchids.

Consequences of Introduction to California for Colletotrichum cymbidiicola:

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 cymbidiicola to California = (11).

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

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

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

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

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

Evaluation is Low (-1). Colletotrichum cymbidiicola has been found in nursery greenhouses in two coastal counties: San Diego and Santa Clara.

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 detection and distribution of Colletotrichum cymbidiicola in other orchid-growing California counties is not known. Subsequent results from those detections may alter the proposed rating for the pathogen.

Conclusion and Rating Justification:

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

References:

Bethke, J. A. 2014. First detection of Colletotrichum cymbidiicola in California and water supply update. UCNFA News, University of California, Division of Agriculture and Natural Resources. http://ucanr.edu/sites/UCNFAnews/Regional_Report_San_Diego_and_Riverside_Counties/Summer_2014__First_detection_of_Colletotrichum_cymbidiicola_in_California/# .

Chowdappa, P., C. S. Chethana, R. P. Pant and P. D. Bridge. 2014. Multilocus gene phylogeny reveals occurrence of Colletotrichum cymbidiicola and C. cliviae on orchids in North East India. Journal of Plant Pathology, 96:327-334.

Damm, U., P. F. Cannon, J. H. C. Wouldenberg, P. R. Johnston, B. S. Weir, Y. P. Tan, R. G. Shivas and P. W. Crous. 2012. The Colletotrichum boninense species complex. Studies in Mycology 73:1-36; www.studiesinmycology.org .

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/ .

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.

Moriwaki, J., T. Sato and T. Tsukiboshi. 2003. Morphological and molecular characterization of Colletotrichum boninense sp. nov. from Japan. Mycoscience 44:47-53.

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.