Corynespora cassiicola (Berk. & M. A. Curtis) C. T. Wei 1950

California Pest Rating for

Corynespora cassiicola (Berk. & M. A. Curtis) C. T. Wei 1950

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

On September 27, 2017, a shipment of desert rose (Adenium obesum) plants showing symptoms of leaf spot disease was intercepted by San Diego Agricultural County inspectors. The shipment had originated in Florida and was destined to a private company in San Diego County. A sample of symptomatic plant leaves was collected by the San Diego Agriculture County and sent to the CDFA Plant Pathology Laboratory in Sacramento. On October 18, 2017, the fungus, Corynespora cassiicola, was identified by CDFA plant pathologist, Suzanne Latham, to be associated with the leaf spot symptoms. A temporary ‘Q’ rating was assigned to the pathogen and consequently, the shipment was destroyed. Corynespora cassiicola was previously detected on May 7, 2008, in an intercepted shipment of Mandevilla plants that originated in Florida and was destined to a nursery in San Diego County. This detection marked the first report of the pathogen in California and resulted in the destruction of the shipment. The current rating and consequences of introduction of C. cassiicola in California are assessed here and a permanent rating is proposed.

History & Status:

Background: Corynespora cassiicola is a fungal plant pathogen that attacks a wide range of plants from tropical and subtropical countries causing leaf spot disease in several economically important crops under different common names such as Corynespora leaf spot of cucumber and several other hosts, blotch disease of cucurbits, stem and fruit spot of eggplant, papaya and target spot of tomato and cotton. The fungus has been found in plant leaves, stems, fruit, roots, nematode cysts, and human skin and comprises many isolates. Majority of isolates reported have been obtained from lesions or from fulfilled Koch postulate trials and are known to be plant pathogens. However, isolates have also been reported from dead organic matter and non-symptomatic plant tissue and some can be both depending on the host substrate (Dixon et al., 2009). Isolates may vary in virulence in host specificity. Some isolates that specifically parasitize weed hosts without affecting agricultural crops may serve as potential bioherbicides agents (Smith & Schlub, 2005). In South-east Asia, C. cassiicola causes leaf fall disease of rubber, which is one of the most serious leaf diseases of rubber in that region.

The pathogen was first described as Helminthosporium cassiicola by Berkeley and Curtis in 1868, and subsequently underwent several taxonomic changes to now be known as Corynespora cassiicola (Farr & Rossman, 2018). This pathogen is ubiquitous and has been reported to cause major economic losses in more than 70 countries (Dixon et al., 2009).

Disease cycle: The pathogen survives in infested plant materials for more than two years. High humidity, warm temperature (25-32°C) and long days are necessary for conidia production, infection and disease development. Fluctuating day and night temperatures favor disease development (Williams, 1996). The disease develops in tomatoes at favorable temperatures of 20-28°C and infection can occur at 16-32°C. Extended periods of 16 to 44 hours of high moisture are necessary for optimum disease development (Pernezney et al., 2014).

Dispersal and spread: Infested planting stock, plant material, plant debris. Conidia (spores) are airborne and seedborne (Daughtrey et al., 1995).

Hosts: More than 530 plant species from 380 genera including monocots, dicots, ferns, and one cycad have been reported to support growth of C. cassiicola (Dixon et al., 2009). Economically important host crops for California include Cucumis sativus (cucumber), Cucurbita moschata (pumpkin), C. moschata (pumpkin), C. pepo (marrow), cucurbits, Gossypium sp. (cotton), Solanum lycopersicum (tomato), S. melongena (eggplant) and ornamentals (CABI, 2018; Farr & Rossman, 2018). Ornamental hosts include Aeschyanthus pulcher (lipstick vine), Aphelandra squarrosa (zebra plant), Catharnathus roseus (Madagascar periwinkle), Begonia, Hydrangea macrophylla (bigleaf hydrangea), Euphorbia pulcherrima (poinsettia), Saintpaulia ionantha (African violet) and Salvia splendens (scarlet sage) (Daughtrey et al., 1995)

Symptoms: The initial symptoms of target spot in tomato are pinpoint-size, water-soaked lesions on the upper surfaces of leaves. These lesions increase in size, turn circular and pale brown with individual yellow halos. Over time lesions coalesce and tissue may collapse while the leaflet remains attached to the petiole. Similar lesions may develop on petioles and stems resulting in rapid collapse of affected leaflets. Lesions can develop on young fruit and resemble those caused by abiotic factors. These lesions are initially dark, sunken, pinpoint and brown and may later develop into craters. On ripe fruit, large, circular lesions develop with pale brown centers that crack and over time create avenues for secondary invading pathogens (Pernezny et al., 2014). In infected cucurbits, initial lesions are angular yellow spots with light brown centers and dark brown borders. As these lesion age, they drop out. Young and green fruit are not susceptible however, early infection of the blossom end of fruit may result in shriveling and darkening of the infected area with dark sporulation (Williams, 1996). On ornamental plants such as poinsettia, lesions may be irregular, large and brown on bracts and primarily at the tips and margins of leaves; on hydrangea lesions may be small, reddish purple, circular with tan centers and reddish-purple margins; on African violets lesions are irregular and brown (Daughtrey et al., 1995).

Damage Potential: In the USA, reports of losses from target spot of field tomatoes are restricted to the Southeast which is frequented with high humidity and warm temperature climate (Pernezny et al., 2014). In California, if left uncontrolled, Corynespora disease development is likely to occur in greenhouses under favorable temperature and high humidity conditions. Impact of disease caused by this pathogen may be mitigated through proper sanitation, use of resistant varieties and regular applications of fungicidal treatments.

Worldwide Distribution: Asia: Bangladesh, Brunei Darussalam, Cambodia, China, India, Indonesia, Japan, Republic of Korea, Laos, Malaysia, Maldives, Myanmar, Nepal, Pakistan, Philippines, Singapore, Sri Lanka, Taiwan, Thailand, Vietnam, Yemen; Africa: Benin, Cameroon, Congo, Democratic Republic of Congo, Côte d’Ivoire, Egypt, Ethiopia, Gabon, Ghana, Guinea, Liberia, Mauritius, Nigeria, Seychelles, Sierra Leone, South Africa, Sudan, Tanzania, Togo, Uganda, Zambia; Central America and Caribbean: Antigua and Barbuda, Barbados, Belize, British Virgin Islands, Costa Rica, Cuba, Dominica, El Salvador, Guadeloupe, Guatemala, Haiti, Honduras, Jamaica, Nicaragua, Puerto Rico, Trinidad and Tobago, United States Virgin Islands; Europe: Austria, Bulgaria, Denmark, France, Germany, Hungary, Italy, Netherlands, Norway, Romania, Russian Federation, United Kingdom, Ukraine; North America: Canada, Mexico, USA; Oceania: American Samoa, Australia, Fiji, Guam, Micronesia, New Zealand, northern Mariana Islands, Palau, Papua New Guinea, Samoa, Solomon Islands, Vanuatu; South America: Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Venezuela (CABI, 2018).

In the United States, C. cassiicola has been reported from Alabama, Florida, Hawaii, Illinois, Iowa, Louisiana, Minnesota, Mississippi, Nebraska, New York, North Carolina, North Dakota, South Carolina, Tennessee, Virginia, and Wisconsin (CABI, 2018).

Official Control: Corynespora cassiicola is on the ‘Harmful Organism Lists” for Israel, Namibia, South Africa and Vietnam (USDA PCIT, 2018).

California Distribution: Corynespora cassiicola has not been reported from California. The pathogen is not known to be established in California.

California Interceptions: There have been two interceptions of plants infected with Corynespora cassiicola (see: ‘Initiating Event’).

The risk Corynespora cassiicola would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Corynespora cassiicola requires prolonged periods of high humidity (16-44 hours) and warm temperature (25-32°C) for disease development. These climatic conditions would limit the ability of the pathogen to establish and spread within California.

Evaluate if the pest would have suitable hosts and climate to establish in California. Score: 1

– 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: The pathogen has a very wide and diverse host range that comprises more than 530 plant species from 380 genera including monocots, dicots, ferns, and one cycad. Economically important host crops for California include cucurbits, cotton, tomato, eggplant and ornamentals.

Evaluate the host range of the pest.

Score: 3

– 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: Conidia are produced in abundance and are dispersed by air currents, infected seeds, host plant material and debris. Therefore, a high score is given to this category.

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: Plant damage caused by cassiicola is more likely under prolonged periods of high humidity and warm temperatures found in greenhouse cultivation than in open field environments of the state. If left uncontrolled, infections by the pathogen could result in lower crop yield and value resulting in the loss of markets. However, the administration of proper control measures may mitigate impact of damage caused by this pathogen. Therefore, a medium score is given to this category.

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

Economic Impact: A, B

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: 2

– 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: No significant impact to the environment is likely as the requirements of prolonged, high humidity and warm temperatures would considerably limit the ability of cassiicola to establish within the state.

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

Environment Impact: None

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: 1

– 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 Corynespora cassiicola:**

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 = 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.

Evaluation is ‘Not established’ in California and has only been detected in intercepted plant shipments to the State.

Score: (0)

–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.

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 Corynespora cassiicola is B.

References:

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

Daughtrey, M. L., Wick, R. L., and Peterson, J. L. 1995.Corynespora leaf spot of Catharanthus, Hydrangea, Poinsettia, and Saintpaulia. In, Compendium of Flowering Potted Plant Diseases. APS Press, The American Phytopathological Society 90p.

Dixon, L. J., Schlub, R. L., Pernezny, K., and Datnoff, L. E. 2009. Host specialization and phylogenetic diversity of Corynespora cassiicola. Phytopathology 99: 1015-1027.

Farr, D.F., and Rossman, A. Y. 2016. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved August 1, 2016, from http://nt.ars-grin.gov/fungaldatabases/

Pernezny, K. L., Blazquez, C. H., Smith, L. J., and Schlub, R. L. 2014). Target spot. In, Compendium of Tomato Disease and Pests Second Edition, Edited by J. B. Jones, T. A. Zitter, T. M. Momol, and S. A. Miller. 44-46p.

Smith, L. J., and Schlub, R. L. 2005. Foliar fungi on weeds of Guam and the potential for Corynespora cassiicola as a bioherbicide for Stachytarpheta jamaicensis. (Abstr.) Phytopathology 95: S93.

USDA PCIT. 2017. USDA Phytosanitary Certificate Issuance & Tracking System. Retrieved May 23, 2018. 11:53:45 am CDT. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Williams, P. H. 1996. Target leaf spot. In, Compendium of Cucurbit Diseases, Ed. T. A. Zitter, D. L. Hopkins, and C. E. Thomas. APS Press, The American Phytopathological Society p 31-32.

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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