Research On The Host Specificity Of Phytophthora Infestans

Investigation of mating types, resistance to metalaxyl, colony characteristics, sporulation capcitities, parasite fitness and allozyme genotype were performed on 77 isolates of Phytophthora infestans.Among thwm, 58 isolates were isolated and purified from tomato and 19 isolates from potato in different area of China. The results showed that: (1) all isolates of Phytophthora infestans isolates from tomato were identified as Al mating type ,but no A2 mating type was found in the isolates tested. (2) Isolates of Phytophthora infestans from tomato which are resistant to metalaxyl have been found in China ,the frequency is 8.7%.(3)Different isolates have distinct difference on colony diameter and sporulation capacity after 11 days cultured in the dark at 18癈, but the difference had no relationship to their host plants; (4) Phytophthora infestans isolates from tomato have higher parasite fitness on tomato than on potato, and isolates from potato have higher parasite fitness on potato than on tomato,but some isolates from tomato and potato can infect both tomato and potato. (5) Isolates from single lesion and its single-zoospores isolate have the same allozyme genotype. (6) 60.5%, 34.9%, and 4.7% of isolates from tomato have the allozyme genotypes 11100/111, 00100/111, and 00111/001, respectively. Nevertheless, isolates from potato have only one different kind of allozyme genotype, 00100/001. The results indicated different genetic characteristics of Phthophthora infestans from tomato and potato.