Abstract
The inhibitory effects of chemical treatments on toxin production during spore germination and pathogenicity of the spores of A. alternata pathogens were examined. The spores of A. alternata Japanese pear pathotype treated with cerulenin (20ppm) or methionine (100ppm) almost completely 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, whereas the abilities of spore germination, elongation of germ tube, appressorium formation and invading hypha formation were not significantly inhibited. These chemicals caused a similar reduction in pathogenicity and toxin production of apple pathotype (AM-toxin producer) and strawberry pathotype (AF-toxin producer) of A. alternata. The treatments of the spores of A. alternata Japanese pear pathotype with NH4Cl, KH2PO4, yeast extracts and L-cysteine also exhibited similar effects at higher concentrations. The above data suggest that the chemical treatments of the spores of A. alternata pathogens cause the reduction of their pathogenicity through the suppression of host-specific toxin productivity.
