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

The infection process of take-all causing fungus Gaeumannomyces graminis (S acc.) Arx & Oliver var tritici J. Walker on the seminal roots of wheat (Tri ticum aestivum L. emend Fiori and Paol.) and oat (Avena sativa L.), culture d at 15+/-1 degrees C under 12 hr intervals of light and dark, was shown by microscopic observations to consist of 4 stages, viz pre-infection, invasi on of epidermis, invasion of cortex and invasion of stele stages. In the pr e-infection stage, fungus spreads mainly as runner hyphae on the root and r oot hair surface, Sister hyphae matted and brown kidney- or fork-shaped hyp hopodia formed on wheat and oat roots were observed, respectively. After 48 hr (wheat) and 120 hr (oat) of inoculation, the runner hyphae producing hy aline infection hyphae penetrated into the epidermal cells of roots through intercellular spaces. However, the invasion of infection hyphae on oat roo ts was hindered. After 60 hr (wheat) and 132 hr(oat) of inoculation, the ta ke-all fungus penetrated epidermal cells into the cortical cells and spread radially in the cortex. Some infection hyphae in the cortex of oat roots w ere dissolved. After 120 hr (wheat) and 240 hr (oat) of inoculation, G. gra minis var tritici reached stele tissue resulting in the blockage of the vas cular cells and making the transport system abnormal.