شناسایی دو گونه بیمارگر‌ Phytophthora، عامل پوسیدگی ریشه و طوقه با تشکیل زئوسپور در مزارع گوجه فرنگی بجنورد

Tomato is one of the most summer cultivated crops that develops in Northern khorasan. Among soil borne pathogens, different species of Phytophthora are potential pathogens in highly moisture and soil waterlogged conditions of Bojnourd fields can damage the tomato crop. They affect symptoms such as seedling damping off, blighting and fruit rot, stem, crown and root rot when they infect the tomato and cause the plants to die mostly. This pathogen produces the special spores that swim in the irrigation water and transmit the infection that named zoospore. The infected plants and roots surrounding the soils in Bojnourd tomato fields were sampled in summer 2013. After transferring the plants to the laboratory, crown and root parts were washed with tap water. Then cut the infection parts of the root, crown and fruit, then the small pieces were disinfected and cultured on the selective medium, CMA+ PARP. So baiting with cucumber cuttings conducted in waterlogged soils within petri plates. In order to identify Phytophthora species the identification key of Stamps et al. (1990) was used. 84% isolates were identified as Phytophthora capsici and 16% isolates were P.nicotianae. Optimum mycelia growth diameter measured in temperature 280C for P.capsici and 300C for P.nicotianae. Both species produced aerial hyphae in agar medium plus pear shape sporangium and papila. Many numbers of sporangium formed in distilled water after 24 hours and a few Chlamydospores formed after a week in solid medium in P.capsici. So sporangium formed at solid medium rapidly in this species. Both species hyphae had pathogenicity in a two-week old seedling of tomato. P.capsici species showed the most pathogenicity test and injure the plants in waterlogged soils. Root, crown rot and plant wilt were observed in both species. But buckeye rot was in fruits affected by P.capsici. These types of symptoms were wavy light and dark brown in shape. The Number of zoospore produced in these species were affected by light and temperature conditions. Sporulation of zoospores followed by heamositometer. Most zoospore number observed in one of isolates of P.capsici at 200C and dark conditions was number of 1/7 × 106 zoospores in one cm3 of distilled water. But in P.nicotianae most zoospores were produced at 250C and their number in light conditions were 1/3 × 106 zoospores in one cm3 of distilled water. Inoculation of zoospore cell suspensions on tomato fruits resulted in white molds on fruits surface. Providing slides from white molds showed the mycelium and a lot of sporangium mass. In soil conditions and moisture a great number of zoospores can be produced and result in the extreme pathogenicity and disease epidemic.