Colletotrichum siamense Prihastuti, L. Cai & K. D. Hyde, 2009

California Pest Rating Proposal for
Colletotrichum siamense Prihastuti, L. Cai & K. D. Hyde, 2009
Pest Rating: B


Initiating Event:  

On June 26, 2015, a California Dog Team intercepted Cacao seed pods with necrotic spots at a parcel distribution facility in Mariposa County and sent a sample to the CDFA Plant Diagnostics Branch for disease diagnosis.  The shipment had originated in Mircao, Puerto Rico and was destined to a private citizen in Mariposa County, California.  Suzanne Latham, CDFA plant pathologist identified the fungal anthracnose and fruit rot pathogen, Colletotrichum siamense as the cause for the disease and marked the first detection of C. siamense in California.  Several detections of this fungal pathogen followed the initial find: on October 8, 2015, in fruit of star fruit and Jew plum originating in Florida and destined for San Diego and Santa Clara Counties; on October 13, 2015, in avocado fruit from Puerto Rico and destined for Contra Costa County; on November 9, 2015, in fruit of two unknown hosts that originated from Florida.  In all these cases the fruit were intercepted by California Dog Teams and destined to private citizens in California. Consequent to these California detections, all infected plant materials were destroyed. The risk of infestation of C. siamense in California is evaluated and a permanent rating is proposed.

History & Status:

BackgroundColletotrichum siamense 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.  However, C. jasmine-sambac and C. hymenocallidis are synonyms of C. siamense (Weir et al, 2012).  The species was originally described in 2009 from infected coffee berries (Coffea arabica) in Thailand.  Since then, it has been found on a wide range of hosts from several tropical and subtropical global regions.

Hosts:    Jackfruit (Artocarpus heterophyllus), bamboo orchid (Arundina graminifolia), neem (Azadirachta indica), capsicum (Capsicum annuum); papaya (Carica papaya), mandarin orange (Citrus reticulata), coffee (Coffea sp., C. arabica, C. canephora), dayflowers (Commelina sp.), Guinea yam (Dioscorea rotunda), loquat (Eriobotrya japonica), edible fig (Ficus carica), strawberry (Fragaria ananassa), spider lily (Hymenocallis sp., H. americana), jasmine (Jasminum sambac), apple (Malus domestica), mint (Mentha sp.), avocado (Persea Americana), black pepper (Piper nigrum), pistachio (Pistacia vera), king protea (Protea cynaroides), rosemary (Rosmarinus officinalis), cacao (Theobroma cacao), grape (Vitis vinifera) (Farr & Rossman, 2015).  Onion (Allium cepa) (Chowpadda et al., 2015), chili pepper (Capsicum sp.) (Sharma & Shenoy, 2014), bauhinia (Bauhinia forficate subsp. pruinosa) (Larran et al., 2015).  The recent California detections mentioned above include C. siamense in star fruit (Averrhoa carambola) and Jew plum (Spondias dulcis).

SymptomsColletotrichum siamense causes leaf and fruit spots and leaf drop.  In mandarin orange, initial symptoms appeared on young leaves as reddish-brown lesions 2-5 mm in diameter. Several weeks later 20-70% of leaves had dropped and 10-50% exhibited brown spots 5-40 mm in diameter (Cheng, et al., 2013).  Circular or irregular light brown necrotic lesions surrounded by dark brown borders were present in bauhinia leaves in Argentina (Larran et al., 2015).  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 siamense can result in reduced plant quality and growth, fruit production and marketability.  In China, about 15% yield losses was observed on different aged trees of mandarin orange, Citrus reticulata cv. Shiyue .  In California, nursery productions of fruit and ornamental 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 siamense 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 DistributionColletotrichum siamense is distributed in Asia: China, India, Thailand, Vietnam; Africa: Kenya, Malawi, Nigeria, South Africa, Zimbabwe; North America: USA (Alabama, Florida, North Carolina); South America: Argentina, Brazil, Colombia; Australia (Farr & Rossman, 2015; Larran et al., 2015).

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

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

California Interceptions: There have been seven interceptions of Colletotrichum siamense-infected fruit of avocado, star fruit, Jew plum, cacao seed pods, and two unknown hosts (see ‘Initiating event’).

The risk Colletotrichum siamense 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 siamense 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 High (3) – Colletotrichum siamense has a wide and diverse range of host plants grown in subtropical and tropical regions.  Several of these are grown in California and include grape, strawberry, apple, avocado, fig, and 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) –Anthracnose-infected 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 fruit and ornamental plants wherever grown in California.

Consequences of Introduction to California for Colletotrichum siamense:

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 siamense 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 siamense 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.



Conclusion and Rating Justification:

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


Cheng, B. P., Y. H. Huang, X. B. Song, A. T. Peng, J. F. Ling, and X. Chen.  2013.  First report of Colletotrichum siamense causing leaf drop and fruit spot of Citrus reticulata Blanco cv. Shiyue Ju in China.  Plant Disease 97:1508.

Chowpadda, P., C. S. Chethana, and K. V. Pavani.  2015.  Colletotrichum siamense and C. truncatum are responsible for severe outbreaks of anthracnose on onion in southwest India.  Journal of Plant Pathology 97, No. 1: (abstract). doi: 10.4454/JPP.V97I1.015. Farr, D. F., & A. Y. Rossman.  Fungal databases, systematic mycology and microbiology laboratory, ARS, USDA. Retrieved April 7, 2015, from

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.

Larran, S., J. V. Bahima, G. D. Bello, E. Franco, and P. Balatti.  2015.  Colletotrichum siamense causing anthracnose in Bauhinia forficate subsp. pruinosa in Argentina.  Australasian Plant Disease Notes 10:7.

Prihastuti, H., L. Cai, H. Chen, E. H. C. McKenzie, and K. D. Hyde.  2009. Characterization of Colletotrichum species associated with coffee berries in northern Thailand. Fungal Diversity 39: 89-109.

Sharma, G., and B. D. Shenoy.  2014.  Colletotrichum fructicola and C. siamense are involved in chili anthracnose in India.  Archives of Phytopathology and Plant Protection 47:1179-1194.

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,[@]

Comment Period:  CLOSED

The 45-day comment period opened on Friday, December 18, 2015 and closed on February 1, 2016.

Comment Format:

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

Example Comment: 

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

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

♦  Comments may not be posted if they:

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

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

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

Violates agency regulations prohibiting workplace violence, including threats.

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

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

Pest Rating: B

Posted by ls