The activity of esterase secreted by conidia of wheat powdery mildew fungus, Blumeria graminis f. sp. tritici, was assayed using indoxyl acetate hydrolysis, which generates indigo blue crystals. Mature, ungerminated, and germinating conidia secrete esterase(s) on artificial media and on plant leaf surfaces. The activity of these esterases was inhibited by diisopropyl fluorophosphate, which is s...