Cutinase Production by Alternaria alternata Japanese Pear Pathotype and Its Role in Pathogenicity

Abstract

When grapefruit cutin was added to spore suspension of Alternaria alternata Japanese pear pathotype, significant cutinase activity was observed in the spore-germinated fluid. Cutinase activity was also detected in cutin-containing liquid medium, but not in sucrose-containing medium. Cutinase was produced not only by virulent isolates of this pathotype, but also by the avirulent mutants and saprophytic A. alternata in their spore-germinated fluids. Several organophosphorus pesticides which strongly inhibited cutinase were found to have a strong inhibitory effect on lesion formation on pear leaves by the fungus. The cutinase in culture filtrate of the fungus was precipitated by ammonium sulfate, and the precipitate was chromatographed by gel filtration, chromatofocusing and cation exchange columns. The purified fraction expressed clear cutinase activity and appeared as a single protein band with a molecular weight of 32, 000 daltons on SDS-PAGE. These data suggested that cutinase production, in addition to AK-toxin production, is essentially required for infection and disease development by this fungus.