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

Microscopic studies of the interaction between the yeast-like fungus S porothrix flocculosa and the wheat powdery mildew pathogen, Erysiphe g raminis 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 d etached leaf segments infected with Egt, application of a spore suspen sion of Sp. flocculosa resulted in a rapid degeneration of Egt myceliu m and conidia. Scanning electron microscope observations revealed that the antagonist colonized and developed profusely on Egt within 12 h a nd induced a general collapse of conidial chains within 24 h. Under tr ansmission electron microscopy, first consistent reactions were observ ed 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 an tagonistic process appeared to be antibiosis-dependent since no eviden ce of cell wall erosion or penetration was observed while death of the pathogen occurred rapidly. This study presents the first report of th e potential of Sp. flocculosa as a biocontrol agent of Egt.