A survey of root lesion and cereal cyst nematodes in the dryland wheat production areas of eastern Washington and resistance of pacific Northwest wheat varieties
Root lesion nematodes (Pratylenchus neglectus and P. thornei) and cereal cyst nematode (Heterodera avenae) are important parasites of wheat worldwide. Three studies were conducted focusing on the distribution of root lesion and cereal cyst nematodes in eastern Washington and the resistance response of spring wheat varieties to the cereal cyst nematode. The first study was conducted to estimate nematode densities in soils cropped to winter and spring cereals and spring legumes. P. neglectus and P. thornei were observed in nearly 60 percent of the sampled fields. H. avenae was observed in approximately 12 percent of the sampled fields; however, it was detected from about 45 percent of sampled fields in the annual cropping zone. Multivariate regression models were developed to determine the explanatory weather variables for Pratylenchus densities in soil. The majority of the weather variables selected in the models were precipitation variables. The second study was conducted at the Cook Agronomy Farm to determine the spatial distribution of Pratylenchus spp. in relation to crop rotation, soil and terrain attributes. Pratylenchus spp. were detected in more than 85% of the sampled sites. Classification and regression trees were developed to derive the relationship between soil and terrain variables and nematode densities. An aggregated pattern was observed, and soil organic carbon was identified as one of the most important variables to explain nematode densities. Molecular identification of Pratylenchus spp. in region-wide surveys of eastern Washington and at the Cook Agronomy Farm was conducted using species-specific primers targeting P. neglectus and P. thornei through conventional PCR. P. thornei was observed more frequently than P. neglectus in both region-wide surveys and Cook Farm, but some locations showed both species. The third field experiment was conducted to evaluate the resistance of Pacific Northwest spring wheat varieties and wheat entries carrying different Cre genes to H. avenae. Spring wheat genotypes with Cre1 gene had fewer numbers of H. avenae white females than other genotypes. However, all of the tested spring wheat varieties appear to be susceptible to H. avenae
