Identifying root-lesion nematode (Pratylenchus spp.) resistance and functional mechanisms in wheat

Root-lesion nematodes (RLN) Pratylenchus thornei Sher and Allen, 1953 and P. neglectus (Rensch, 1924) Filipjev Schuurmans and Stekhoven are soil-borne pathogens of wheat that invade and feed on root host cells. In the Pacific Northwest (PNW) these species of nematode were found in 95% of sampled fields and were estimated to cause 37% - 50% yield loss in spring wheat. Resistance to P. thornei had previously been found in 78 Iranian landrace accessions. The accessions were tested for resistance to P. neglectus and 21 accessions were found to be resistant to both species. The dual-resistant landrace accession, AUS28451 (PI623470), was used to generate a recombinant inbred line (RIL) population by crossing it to the susceptible PNW cultivar, Louise. One-hundred and fifty F2:F6 derived RILs were genotyped using SSR and SNP based molecular markers. The RILs were then phenotyped using inoculated field soil greenhouse assays where nematodes counted at the end of a 12 week period. A new root rating method to determine nematode resistance was also developed and tested in the greenhouse assays. Resistance associated quantitative trait loci (QTL) were identified on chromosomes 1A, 2B, 4A, 5A, 5B, 6B and 7A using both phenotyping methods for P. thornei and P. neglectus. Canopy temperature and photosynthesis yield (phiPSII) were used to develop a prediction model for nematode population densities on resistant and susceptible cultivars planted in infested fields. The RIL population was used to verify the accuracy of the prediction model. Predicted nematode resistance associated QTL were identified on chromosomes 4A, 5A, 6A, 6B, and 6D. Root morphology observations suggested AUS28451 (PI623470) had increased root lignin content compared to Louise. Root lignin content was examined in the RIL population and associated QTL were identified on chromosomes 2D and 5B. With this research, three new methods for indirect Pratylenchus resistance screening have been developed. These methods include molecular markers associated with resistance, root ratings, and field stress measurements. With these methods breeders will be able to incorporate nematode resistance breeding into their programs using a variety of tools.