Some Characteristics of the Heat-Induced Susceptibility Demonstrated in Powdery Mildew of Barley

Abstract

Heat predisposition effects were studied of barley powdery mildew by use of some compatible and incompatible combinations. Heat treatment above 45C rendered barley leaves susceptible to incompatible races, although the pattern of dose-responses differed from one combination to the other. Treatment at 50C suggested that the once-induced susceptibility is reduced by exposing leaves for longer time. Incompatible and nonpathogenic races established infection on heat-treated leaves with much higher efficiency comparing with compatible one, but never reached the level of the compatible race in terms of ESH frequency, suggesting that these races induce rejection reaction prior to the elongation of secondary hyphae. The heat-induced susceptibility disappeared about 24hr after heat treatment at the rate of a pseudo first-order reaction. Compatible combination is also affected by heat treatment, as was illustrated in significant increase of ESH frequency by the treatment at 45C and a retreat at 50C-min.