Metabolic regulation of host-specific toxin production in Alternaria alternata pathogen. 1. Suppression of toxin production from germinating spores under high temperature stress.

Abstract

The effect of thermal treatment on the pathogenicity of spores of Alternaria alternata Japanese pear pathotype was examined. When the virulent spores were subjected to a thermal treatment (e.g., at 50C for 10sec in water), they were not significantly inhibited their abilities of spore germination, elongation of germ tube and appressorium formation. However, they remarkably lost their pathogenicity to Japanese pear leaves susceptible to the black spot disease as well as productivity of host-specific AK-toxin during spore germination. Such an acquired effect on the pathogenicity and the toxin productivity was lost within about 24hr after the treatment. When the air-dried viable spores were continuosly exposed to hot summer temperatures for 13 days in field, the spores lost their pathogenicity and AK-toxin productivity without any visible damages on their germination ability. The above data suggest that certain thermal treatment of the spores of A. alternata Japanese pear pathotype causes to reduce their pathogenicity through the loss of AK-toxin productivity.