Preparation of the infection court by Erysiphe graminis f. sp. hordei: cutinase is a component of the conidial exudate

Abstract

Conidia of Erysiphe graminis f. sp. hordei release a liquid upon contact with a substratum, either the surface of a barley leaf or cellophane. The liquid had been shown to contain esterase activity which partially erodes the surface of the cuticle of barley leaves. The present investigation demonstrates that the liquid exudate contains cutinase activity. The presence of cutinase in the conidial exudate was confirmed by enzyme assays using 3H-cutin as the substrate. Like other fungal cutinases, the enzyme from E. graminis was inhibited by the serine esterase inhibitor diisopropyl fluorophosphate. The results are significant since they demonstrate for the first time the production of cutinase by a powdery mildew parasite. It is possible that the cutinase is involved in the erosion of the leaf cuticle which begins prior to the development of appressoria. Such erosion may be necessary either for recognition of the host surface by the appressorium or for adhesion and more efficient penetration of the leaf.