Pakish, Bradley, authorHaley, Scott D., advisorMuñoz-Amatriaín, Maria, committee memberPeairs, Frank B., committee member2021-01-112021-01-112020https://hdl.handle.net/10217/219553The 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.born digitalmasters thesesengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.Text