Infection process of take-all causing fungus (Gaeumannomyces graminis var tritici) on wheat (Triticum aestivum) and oat (Avena sativa) roots

Abstract

The infection process of take-all causing fungus Gaeumannomyces graminis (Sacc.) Arx & Oliver var tritici J. Walker
on the seminal roots of wheat (Triticum aestivum L. emend Fiori and Paol.) and oat (Avena sativa L.), cultured at 15+1oC
under 12 hr intervals of light and dark, was shown by microscopic observations to consist of 4- stages, viz
pre-infection, invasion of epidermis, invasion of cortex and invasion of stele stages. In the pre-infection stage, fungus
spreads mainly as runner hyphae on the root and root hair surface. Sister hyphae matted and brown kidney- or forkshaped
hypha podia formed on when and oat roots were observed, respectively. After 48 hr (wheat) and 120 hr (oat) of
inoculation, the runner hyphae producing hyaline infection hyphae penetrated into the epidermal cells of roots through
intercellular spaces. However, the invasion of infection hyphae on oat roots was hindered. Alter 60 hr (wheat) and 132
hr (oat) of inoculation, the take-all fungus penetrated epidermal cells into the cortical eells and spread radially in the cortex. Some infection hyphne in the cortex of oat roots were dissolved. After 120 hr (wheat) and 240 hr (oat) of inoculation, G. graminis var trifici reached stele tissue resulting in the blockage of the vascular cells and making the transport system abnormal.