Effect of the "in vitro" subculture in conidial production and aggressiveness of Mycosphaerella fijiensis Morelet

The effect of in vitro subculturing on the production of conidia and the aggressiveness of Mycosphaerella fijiensis Morelet isolates that were inoculated on the Musa cultivar "Grande Naine " was determined. The in vitro capacity of production of conidia and the behavior after artificial inoculation on "Grande Naine" were compared for isolates with a different number of in vitro subcultures. It was possible to obtain M. fijiensis conidia in vitro in all of the isolates. A great decrease in conidia production was observed when the number of subcultures increased, after eight subcultures this number of conidia was reduced in 80%. All the isolates occasioned symptoms in the plant inoculated leaves. Nevertheless, differences among M. fijiensis isolates were found regarding their aggressiveness. These results demonstrated that the aggressiveness and the capacity to produce spores of Mycosphaerella fijiensis isolate decreases after serial vegetative transfers on artificial substrates.