Articles
PATHOGENICITY AND EPIDEMIOLOGY OF CORYNESPORA CASSIICOLA IN THE REPUBLIC OF THE SEYCHELLES
Although this fungus causes a leaf spot disease of papaya in other areas, leaf disease of papaya attributable to C. cassiicola was not observed in the Seychelles; isolates of C. cassiicola which were pathogenic on papaya were not found.
Isolates from cucumbers and tomatoes, and from papaya leaf debris on the soil, were pathogenic on cucumber and tomato leaves.
The isolate from papaya leaf debris caused leaf lesions on watermelon.
Lesions on tomato leaves inoculated with isolates from cucumber leaf lesions or from papaya leaf debris were smaller (1.8 mm) than lesions (6 mm) resulting from tomato isolates.
Corynespora cassiicola developed rapidly as a saprobe from lesions on dead tomato leaves.
An average of 32,000 and 217,000 conidia per g (dry weight) was obtained from dry vine debris in the field 14 and 28 days, respectively, after the vines had been uprooted.
An average of 116,000 conidia per g was obtained from rain-moistened vine debris in the field 14 days after the vines had been uprooted.
New generations (crops) of conidia were produced regularly on vine debris; the number of conidia increased with an increase in duration of wetting of the debris.
Germination of conidia from leaf debris in moist chambers was 82%, compared with 12% for conidia taken directly from dry leaf debris in the field 14 days after harvest. Corynespora cassiicola rapidly colonized dead papaya leaves and produced ca. 9,000 conidia per g (dry weight) of leaf tissue on the plant.
An average of 44,500 conidia per g of leaf tissue was produced on leaf debris from the soil beneath papaya plants.
Corynespora cassiicola is an aggressive, facultative parasite which sporulates abundantly on plant debris.
Sanitation as a control measure for C. cassiicola would therefore appear to be justified.