Abstract
Conidial germination, growth, and conidial production were evaluated in vitro for six isolates of Mycosphaerella fijiensis var difformis. Germination was measured at 20-35°C, and the optimum temperature was estimated to be 26.8°C. Fungal growth increased as temperature increased up to 30°C, with an estimated optimum at 27. 7°C. No growth was observed at 35°C. Spore production decreased as temperature increased, with an optimum at 20°C. Infection and disease development were evaluated on young banana plants under controlled conditions for six isolates of M. J. var. difformis. Infection of banana leaf by M. f. var. difformis and disease development were influenced by leaf wetness duration following inoculation with a conidial suspension. Symptoms of black Sigatoka disease were observed first on leaves subjected to 18 h of leaf wetness after inoculation, and were delayed at shorter periods of leaf wetness. Disease severity increased with increasing leaf wetness duration. The wild-type isolate (SB) required extended periods of leaf wetness. The other isolates showed certain adaptation to drier environments. Significant differences in aggressiveness were found among the isolates. Such differences may be associated with increased infection efficiency and (or) lesion expansion. Older leaves were more conducive to disease development.
