Characterization and quantitative trait loci (QTL) analysis for wheat stem sawfly (Hymenoptera: Cephidae) resistance in winter wheat

2020 Fall.Includes bibliographical references.The wheat stem sawfly (Cephus cinctus) (WSS) has quickly become a major pest of Colorado wheat production over the past ten years. Prior resistant cultivars have relied on the expression of a solid-stemmed trait (Qss.msub-3BL) to decrease damage from sawfly infestations, however environmental factors (sun, rain, etc.) may result in inconsistent pith expression. The limitations of solid-stemmed varieties have aided in the recent identification of novel quantitative trait loci (QTL) for reducing WSS infestation and stem cutting by host-plant preference. In this light, crosses between 'Denali'/'Hatcher' and 'Avery'/'CO11D1397' were completed in the greenhouse during Fall 2014 and Spring 2015 to create two doubled haploid (DH) populations for discovery of QTL associated with non solid-stemmed resistance. Each population was grown under naturally occurring sawfly pressure at two different northeastern Colorado locations during the 2018-19 field season, however only the Avery/CO11D1397 population was selected for planting in the 2019-20 field season due to resource limitations. Entries were evaluated for plant height, heading date, physiological maturity, cutting score, and kernel weight. Next generation sequencing data were generated through genotyping-by-sequencing and resulted in 776 single-nucleotide polymorphisms (SNP) markers in the final genetic map for Avery/CO11D1397. Quantitative trait loci analysis identified a total of 11 QTL, seven major-effect and four minor-effect, in the Avery/CO11D1397 DH population for reduced WSS cutting in multiple environments. Two QTL were associated on the same chromosomal arms as photoperiod genes Ppd-D1 (Qwss.csu-2DS) and Ppd-B1 (Qwss.csu-2BS). The Qwss.csu-1BL was also associated on the long arm of chromosome 1B with the earliness per se gene Eps-B1. Qwss.csu-7DS and Qwss.csu-5BS were the only two major-effect QTL identified that were not associated with major developmental genes, and thus could be associated with antixenosis. Results from this study suggest that a relationship between lower cutting score and a later flowering date exists for genotypes within the Avery/CO11D1397 DH population. Introgression of Qwss.csu-7DS and Qwss.csu-5BS into cultivars with stem-solidness may help in developing new wheat varieties with durable WSS resistance