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Invasive Species

Research in Pacific and Caribbean Basins
on Corynespora cassiicola

The plant pathogenic fungus Corynespora cassiicola, which causes the vegetable disease Target Leaf Spot, has been reported on at least 145 genera (group of similar species) in 53 plant families and in at least 15 different tropical or subtropical countries. Crops that suffer the greatest yield loss due to the fungus include cowpea, cucumber, papaya, pepper, rubber, soybean and tomato. In Florida alone, tomato losses caused by C. cassiicola are over $3,000/acre, and the pathogen is responsible for major crop losses around the world.

Though the species has a wide range of host plants, individual isolated strands vary greatly in virulence and host specificity. For the past three years, C. cassiicola has been isolated from various hosts by researchers at the University of Guam (UG) as part of a NIFA Pacific Tropical and Subtropical Agriculture Research (T-STAR) grant: “The Impact of Invasive Weeds on the Occurrence of the Target Leaf Spot Pathogen.” As a result, dozens of new hosts have been identified, including several ornamentals and native plants.

A second related project began in October 2005, also funded by a T-STAR grant: “Characterization of the Species Corynespora cassiicola and its Impact on Quarantine Regulations.” It is a collaborative effort between the UG and the University of Florida.

Over the next 3 years, isolates of C. cassiicola collected from American Samoa, Guam, Hawaii, Palau, Saipan, and Yap in the Pacific basin and from Florida, the Virgin Islands, and Puerto Rico in the Caribbean basin, will be thoroughly characterized based on genetic data, host range, and form and structure.

As a final project activity, researchers are seeking C. cassiicola found on different hosts around the world to compare with the Pacific and Caribbean isolates. Isolates will be examined according to sequence data, ability to cause disease on six index hosts, form and structure, and location. This information will be used to clarify the occurrence of various subspecies groupings; provide a better understanding of the diversity within the species; enable virulent races of C. cassiicola to be tracked within the region; and, provide a means to evaluate isolates for quarantine, plant breeding, and bioherbicide considerations.

If you possess C. cassiicola isolates and are interested in participating in the study, contact Linley Smith at the University of Florida or Robert Schlub at the University of Guam.


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