Integrated Control of Soilborne Pathogens of Wheat

There are no resistant varieties or chemical controls for the major soilborne pathogens of wheat in the Pacific Northwest of the United States. Root and crown diseases of wheat include Rhizoctonia root rot and bare patch (caused by R. solani and R. oryzae), Fusarium crown rot (caused by F. pseudograminearum and F. culmorum), Pythium root rot (caused by numerous Pythium spp.) and take-all (caused by Gaeumannomyces graminis var. tritici). Growers rely almost completely on cultural control measures. Our research program has evaluated many of these techniques, some of which are effective against Rhizoctonia, including greenbridge (weed and crop volunteer) management, fallow (both chemical and mechanical), seed opener disturbance, precision seed row placement, crop rotation, residue and nitrogen management, and chemical seed treatment. Until recently, there was no way of accurately detecting and quantifying pathogens in soil. We have developed real-time PCR assays to quantify nine species of Pythium and seven groups of Rhizoctonia, based on ITS sequences of the rDNA. In the last 3 years, soils were extensively sampled in eastern Washington, including grower fields and breeder variety-testing sites. By developing a pathogen profile for each testing site, breeders can focus on locations with high pathogen densities to select for tolerance. This survey has shown that pathogen species composition is affected by cropping system and rotation. With accurate detection and quantification of soilborne pathogens, growers can determine risk before planting and make management decisions to mitigate the effects of soilborne fungal pathogens.