Abstract
Effect of heat treatment on the establishment of infection and colony development of powdery mildew of barley was studied by use of an isogenic line. Percentages of spores elongating secondary hyphae, the length of secondary hyphae, colony development, and sporulation all indicated that there were three phases in the plant response to the pathogen during the treatment with increasing doses of heat. The primary phase was an induced susceptibility found at around 45C-45min. The second stage is an inhibition of once-induced susceptibility found at around 50-53C. The third phase is another induced susceptibility detected at around 50C-60sec, and is differentiated from other phases by the visible colony development. The kinetic analysis of the inhibition phase indicated that the rate of inactivation of induced susceptibility follows that of a pseudo first-order reaction. The acceptance or rejection by the host cell of the pathogen, therefore, must be an all-or-none event.
