Effect of predisposition temperature on subsequent hyphal growth and colony development of Erysiphe graminis hordei on barley leaves.

Abstract

Hyphal growth and colony development of Erysiphe graminis hordei on leaves which are otherwise immune but had been predisposed by heating at 55C-75sec were compared with those on leaves that had been heated at 45C-20min to characterize qualitative differences between predisposition effects incited at these two temperatures. The duration of predisposition incited at 55C-75sec was 48-60hr in contrast with the earlier recovery (24hr) observed of leaves that had been heated at 45C-20min Hyphal growth, colony development and sporulation were much more rapid and extensive on leaves that had been heated at 55C than those observed on leaves treated at 45C. The duration of predisposition effect alone did not account for the differences in these rates of hyphal and colony growth and the leaf responses against the established fungus. Leaves that had been heated at 45C responded mainly with yellowing followed by chlorosis, while those treated at 55C responded with browning and subsequent necrotic degeneration, against infection-established fungus. These responses were considered to be different types of manifestation of resistance and most likely to be the consequence of recognition by host cell of the fungus that succeeded in establishing the primary pseudosymbiotic association with cells predisposed to susceptibility by heating.