Effects of antifungal compounds on conidial germination and on the induction of appressorium formation of Magnaporthe grisea

Appressorium formation in germinating conidia of Magnaporthe grisea was ind uced on a hydrophilic (noninductive) surface by antifungal compounds. Respi ratory inhibitors or uncoupling agents such as strobilurins, antimycin A, m yxothiazol, rotenone, pterulone A, and oligomycin A were particularly effec tive whereas sodium cyanide had no effect. Cyclosporin A was effective only at high concentrations. These differentiation-inducing effects were only o bserved at subfungicidal concentrations at which more than 50% of the germi nating conidia formed appressoria. Cycloheximide, nystatin, amphotericin B, and papulacandin A did not induce appressoria. Different strains of M. gri sea displayed the same overall response to the inhibitors, varying merely i n the percentage of appressoria formed. A combination of the respiratory in hibitors with 2-phenyl-4H-1-benzopyran-4-one (flavone), diphenyleneiodonium (DPI), or salicplhydroxamic acid (SHAM), compounds which interfere with th e cyanide-resistant respiration, resulted in a higher sensitivity of the st rains towards the respiratory inhibitors, but had no effect on appressorium formation.