Infection and colonization of bean leaf by Phaeoisariopsis griseola

Abstract

Infection and spread of Phaeoisariopsis griseola in the leaf of bean (Phaseolus vulgaris) were investigated by scanning and transmission electron microscopy. Conidia of P. griseola germinated by releasing a germ tube either at one end of the conidia or both ends. The germ-tube growth followed the contours of epidermal cells. The fungus entered the leaf through the stomata and grew mainly intercellularly between mesophyll and palisade cells. The chloroplast envelope and plasma membrane of adjacent cells disintegrated, lost structural integrity and dried out. Hyphae did not penetrate host cells. A stroma subsequently formed on the leaf surface. Conidiophores elongated under favourable conditions forming synnemata with conidia at the tips of conidiophores. Conidiophores also emerged through stomata.