Recognition the Principle Agent of Common Crown and Root Rot of Wheat in North Khorasan Province

The common root rot of wheat is appeared as important disease in the recent years in northern Khorasan province, Iran. For this purpose several sampling was performed from diseased fields during 1386-1387. The investigated fields were localized in Shirvan, Farooj, Bojnoord, Esfaraen, Maneh and Samlaghan located in northern Khorasan provice, Iran. The samplings were done in seedling, tillage and flowering stages of wheat. The infected parts of plants were cultured on different culture media. Four species Bipolaris sorokiniana, Periconia circinat, Coniothyrium cerealis and Phoma sp. were isolated, purified and determined. Pathogenecity of isolates on wheat and their effects on wet and dry weight of plant root system was evaluated in pots containing autoclaved field soil or Perlite infested by inoculum of each isolate. This experiment was realized in greenhouse condition and under water stress treatments. The results showed high similarity between the symptoms appeared on the root of plants inoculated artificially and those of infected naturally in field. There was also significant difference (P=95%) between the mean of dry and the wet weight of plant root system inoculated by different isolates. The minimum and maximum decrease, compared with control, were noted for plants inoculated by B. sorokiniana (85.06%) and C. cerealis (20.85%), respectively. Such decrease was noted 84.59 and 57.03 % for plants inoculated with Phoma sp. and P. criminate, respectively. They showed an intermediate cases.