EFFECT OF TEMPERATURE ON GROWTH AND CONIDIAL PRODUCTION IN-VITRO, ANDCOMPARISON OF INFECTION AND AGGRESSIVENESS IN-VIVO AMONG ISOLATES OF MYCOSPHAERELLA-FIJIENSIS VAR DIFFORMIS

Conidial germination, growth, and conidial production were evaluated i n vitro for six isolates of Mycosphaerella fijiensis var difformis. Ge rmination was measured at 20-35-degrees-C, and the optimum temperature was estimated to be 26.8-degrees-C. Fungal growth increased as temper ature increased up to 30-degrees-C, with an estimated optimum at 27.7- degrees-C. No growth was observed at 35-degrees-C. Spore production de creased as temperature increased, with an optimum at 20-degrees-C. Inf ection and disease development were evaluated on young banana plants u nder controlled conditions for six isolates of M. f. var. difformis. I nfection of banana leaf by M. f. var. difformis and disease developmen t were influenced by leaf wetness duration following inoculation with a conidial suspension. Symptoms of black Sigatoka disease were observe d 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 isolat e (SB) required extended periods of leaf wetness. The other isolates s howed certain adaptation to drier environments. Significant difference s in aggressiveness were found among the isolates. Such differences ma y be associated with increased infection efficiency and (or) lesion ex pansion. Older leaves were more conducive to disease development.