Colletotrichum aracearum

California Pest Rating for

Colletotrichum aracearum L. W. Hou & L. Cai 2016

PEST RATING: B

PEST RATING PROFILE

Initiating Event:

On July 28, 2017, diseased Cymbidium sp. plants exhibiting leaf spots, were detected by the CDFA Dog Team, in a shipment of plants that had originated in and was destined to a private resident in San Diego County. Symptomatic leaves were sent to the CDFA Plant Pest Diagnostics Branch for diagnosis. On August 21, 2017, Suzanne Latham, CDFA plant pathologist, detected the fungal pathogen, Colletotrichum aracearum, in culture from the leaf spots. The identity of the pathogen was also confirmed by the USDA APHIS National Identification Services at Beltsville, Maryland (Kennedy, 2017). Currently, C. aracearum has a temporary ‘Q’ rating. The risk of introduction and establishment of C. aracearum in California is assessed and a permanent rating is proposed herein.

History & Status:

Background: Colletotrichum aracearum causes anthracnose disease in its host plants. The recently described species (Hou et al., 2016) has only been reported from China, until its detection in California, USA. In California, prior to the July 28, 2017 detection of Colletotrichum aracearum (see ‘Initiating Event’), there had been several detections of the pathogen which was then identified as Colletotrichum cf. cliviae (‘cf’ in biological terminology means ‘a significant resemblance to’). However, those detections were recently shown to be C. aracearum (Kennedy, 2017; Latham, 2017). The first detection of C. aracearum (then identified as Colletotrichum cf. cliviae) was made on April 28, 2015, from diseased Dieffenbachia sp. plants exhibiting leaf spots and detected in a nursery in San Diego County during regulatory nursery inspections by the San Diego County Agricultural officials. This marked a probable new U.S. record by the USDA National Identification Services at Beltsville, Maryland. Several detections followed from different nurseries within San Diego County. On June 11, 2015 and August 19, 2015, the same pathogen was detected in Chinese evergreen (Aglaonema sp.) leaves from cuttings that were shipped from Guatemala and intercepted by San Diego County, and from diseased Aglaonema sp. plants detected during regulatory nursery inspections. On December 3, 2015 and April 20, 2016, infected Aglaonema sp. were intercepted in plant shipments from Costa Rica, and on April 29, 2016, during regulatory nursery inspections, the pathogen was detected in Cymbidium sp. orchid plants showing leaf spots. In all these cases, subsequent to the detection of the pathogen, infected plant shipments/nursery stock were either destroyed or rejected from entering California. The presence and status of anthracnose disease caused by C. aracearum in Guatemala and Costa Rica have not been reported.

Hosts: Aglaonema sp. (Chinese evergreen), Cymbidium sp. (orchid), Dieffenbachia sp. (CDFA detection records 2015-2017), Monstera deliciosa (Swiss cheese plant/tarovine/windowleaf), Philodendron selloum (cut-leaf philodendron) (Farr & Rossman, 2016; Hou et al., 2016).

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

Damage Potential: Anthracnose disease caused by Colletotrichum aracearum 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. However, in California, nursery and greenhouse production of orchids, Chinese evergreen, dieffenbachia, and other host plants are particularly at risk as nursery conditions are often conducive to infection by Colletotrichum species. In California’s 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 aracearum 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: Asia: China; North America: USA (Farr & Rossman, 2017; Hou et al., 2016). Currently, in the USA, C. aracearum has only been reported from California.

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

California Distribution: San Diego County (see “Background”).

California Interceptions: During 2015-17, four shipments of Colletotrichum aracearum-infected Aglaonema sp. (Chinese evergreen) cuttings and one of Cymbidium sp. were intercepted in California. The shipments had originated Guatemala, Costa Rica, and China (see ‘Background’ and ‘Initiating Event’.).

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

Consequences of Introduction:

1) Climate/Host Interaction: Similar to other species of Colletotrichum, aracearum 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

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– 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.

2) Known Pest Host Range: Presently, the host range of Colletotrichum aracearum is limited to few nursery ornamental plant species belonging to the family Araceae.

Evaluate the host range of the pest.

Score: 1

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

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: 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.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– 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.

4) Economic Impact: Under suitable, wet climates, the pathogen could lower plant growth, fruit production and value and trigger the loss of markets. Nursery-grown orchids and other ornamental host plants could be negatively affected.

Evaluate the economic impact of the pest to California using the criteria below.

Score: A, B, C

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.

Economic Impact Score: 3

– 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.

5) Environmental Impact: The pathogen could significantly impact cultural practices or home garden plantings.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E

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.

Environmental Impact Score: 2

– 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.

**Consequences of Introduction to California for Colletotrichum aracearum: Medium (11)**

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 aracearum 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 aracearum was detected in a nursery in San Diego County.

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 host range of Colletotrichum aracearum is presently limited to few plants in Araceae. Further host range studies are needed. Also, results of detection surveys for C. aracearum in nursery, commercial, and natural environments within California may alter its proposed rating.

Conclusion and Rating Justification:

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

References:

Farr, D. F., & A. Y. Rossman. 2016. Fungal databases, systematic mycology and microbiology laboratory, ARS, USDA. Retrieved April 3, 2016, from

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

Hou, L.W., F. Liu, W. J. Duan, and L. Cai. 2016. Colletotrichum aracearum and C. camelliae-japonicae, two holomorphic new species from China and Japan. Mycosphere 7(8): 1111-1123.

Kennedy, A. 2017. Email from A. H. Kennedy, Molecular Biologist, National Identification Services, USDA APHIS PPQ PM to John Chitambar, CDFA, sent: August 29, 2017, 12:54 pm.

Latham, S. 2017. Email from A. H. Kennedy, Molecular Biologist, National Identification Services, USDA APHIS PPQ PM to Suzanne Latham, CDFA, sent: August 18, 2017, 12:11 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.

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