Microscopic specification of compatible and incompatible interactions in barley leaves inoculated with Erysiphe graminis hordei.

Abstract

The details of the primary infection process of E. graminis hordei on barley leaves was observed. No difference was observed before maturation of appressoria between compatible and incompatible host-parasite combinations, but the differnce became appararent at the stages of fungal penetration as reflected on subsequent haustorium formation and colony development by succeeded conidia. Most of the parasite units in the compatible combinations developed synchronously, while those in the incompatible ones did not. More than 80% of parasite units in the latter combinations ceased growth at the stage of papilla formation. It was recognized that the more resistant the host is the more conidia failed to penetrate at the stage of papilla formation. Close examination of fungal growth on different cultivars and variance analysis of individual colonies indicated that the extent of formation of collapsed mesophyll cells (CMC) could hardly be causally related to resistance. However, the rapidity of CMC formation seemed to be correlated with the strength of resistance as assessed by the final infection type, although the correlation did not become significant until 30hr after inoculation. It was suggested that a mechanism determining the disease specificity functions in the initial phase of penetrating stage of the mildew fungus and before the appearance of mesophyll cell collapse.