ANTAGONISM OF THE YEAST-LIKE PHYLLOPLANE FUNGUS SPOROTHRIX FLOCCULOSA AGAINST ERYSIPHE-GRAMINIS VAR TRITICI

Microscopic studies of the interaction between the yeast-like fungus Sporothrix flocculosa and the wheat powdery mildew pathogen, Erysiphe graminis var. tritici (Egt) were undertaken in an attempt to determine the potential antagonistic activity of Sp. flocculosa against Egt and to gain a better insight into events underlying this interaction. On detached leaf segments infected with Egt, application of a spore suspension of Sp. flocculosa resulted in a rapid degeneration of Egt mycelium and conidia. Scanning electron microscope observations revealed that the antagonist colonized and developed profusely on Egt within 12 h and induced a general collapse of conidial chains within 24 h. Under transmission electron microscopy, first consistent reactions were observed 12 h following application of the antagonist. These reactions were characterized by a sequence of ultrastructrural changes beginning with retraction of the plasmalemma followed by complete disintegration of the cytoplasm and death of host cells after 24 h. The basis of this antagonistic process appeared to be antibiosis-dependent since no evidence of cell wall erosion or penetration was observed while death of the pathogen occurred rapidly. This study presents the first report of the potential of Sp. flocculosa as a biocontrol agent of Egt.