Infection and colonization of bean leaf by Phaeoisariopsis griseola

Infection and spread of Phaeoisariopsis griseola in the leaf of bean (Phase olus vulgaris) were investigated by scanning and transmission electron micr oscopy. Conidia of P. griseola germinated by releasing a germ tube either a t one end of the conidia or both ends. The germ-tube growth followed the co ntours of epidermal cells. The fungus entered the leaf through the stomata and grew mainly intercellularly between mesophyll and palisade cells. The c hloroplast envelope and plasma membrane of adjacent cells disintegrated, lo st 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 c onidiophores. Conidiophores also emerged through stomata.