New Genes for Resistance to the Wheat Stem Sawfly from Geographically Targeted Landrace Selections of Wheat

Plant landraces have long been recognized as potential gene pools for biotic and abiotic stress-related genes. Our research used wheat landrace accessions to identify new genes for resistance to the wheat stem sawfly (WSS), an important insect pest of wheat in the northern Great Plans of North America. Two steps were taken to increase the likelihood of identifying novel genes for resistance. First, landrace accessions targeted geographical areas of the world where WSS is endemic or where a high frequency of landrace accessions possess the resistance characteristic of solid stems. Second, resistant accessions were crossed to a local susceptible cultivar to generate recombinant inbred lines (RIL) with phenological characteristics compatible with WSS infestation in the local environment. More than one thousand spring wheat landrace accessions were screened in fields naturally infested by WSS for antixenosis and antibiosis types of resistance between 2012 and 2015. Resistance to the WSS was identified in approximately 30% of the accessions. A series of resistant accessions were used as parents in the development of RIL populations for genetic mapping and QTL analysis. Two RIL populations were evaluated for resistance in field trials in 2016. Halley-Knott regression and interval-mapping analysis allowed the detection of previously identified QTLs for reduced stem cutting and increased stem solidness. Novel resistance QTLs were also identified on chromosomes 1D, 2A, 2B, 4A, 4D, 5A, 7A and 7D. Preliminary results presented here highlight the considerable potential of improving WSS resistance in wheat by mining new genes for resistance in landrace accessions.