Isolation and pathogenicity of fungi associated with root and crown rot of walnut trees in Kermanshah township

The aim of this research, identifying the fungi taxa associated with root and crown rot of walnut trees in Kermanshah. For this purpose, the soil around root of trees and root and crown samples of walnut trees showing disease were collected in different region in Kermanshah. The purified isolates were identified using morphological characters on the different culture media, asexual and sexual organ as well as growth rates at different temperatures. In this research, 13 isolates, belong to three species including Phytophthora cactorum, P. citricola and Pythium sp. were identified. Pythium sp. maybe is a new species, because characteristics of this species did not match completely with other recognized Pythium species. Pythium sp. (1) and Pythium sp. (2) isolated from diseased tissue and infected soil, respectively. Pathogenicity test of these species were performed on excised shoots and seedlings In vitro and In vivo, respectively. Results of In vitro indicated that the most disease extension was appeared by Phytophthora cactorum, but was placed in one statistical group with Pythium sp. (1). Phytophthora citricola and Pythium sp. (2) were placed in the following statistical group. Results of greenhouse experiment shown that, P. citricola and P. cactorum caused complete death of seedlings after 8 and 12 days, respectively. Pythium sp. (1, 2) after 14 days caused drying of stem and leaves and death of seedlings.