INHERITANCE OF PATHOGENICITY AND SENSITIVITY TO METALAXYL IN PHYTOPHTHORA CACTORUM

The inheritance of pathogenicity to apple fruits and sensitivity to metalaxyl of isolate Ap14 of P. cactorum, which was isolated from diseased apple fruit in Heilongjiang province, in asexual and sexual progenies were studied. The pathogenicity was evaluated by the radiuses of lesions on the wounded apple fruits by culture block inoculation. The results showed that the pathogenicity of P. cactorum to apple fruits was steadily inherited in two successive zoospore progenies but manifested obvious variation in first single-oospore generation. The sensitivity to metalaxyl was evaluated by the ratio of the growth rates on limabean agar medium amended with 0.05μg/ml metalaxyl to the growth rates on the same medium without metalaxyl. The sensitivity of P. cactorum to metalaxyl also steadily inherited in two successive zoospore progenies but showed obvious variation in first single-oospore generation. The above results indicated the both characters tested of P. cactorum were controlled by nuclear heterozygous genes.