A novel QTL in durum wheat for resistance to the wheat stem sawfly associated with early expression of stem solidness

Authors: VARELLA, ANDREA - MONTANA STATE UNIVERSITY; ZHANG, HONGTAO - MONTANA STATE UNIVERSITY; WEAVER, DAVID - MONTANA STATE UNIVERSITY; COOK, JASON - MONTANA STATE UNIVERSITY; HOFLAND, MEGAN - MONTANA STATE UNIVERSITY; LAMB, PEGGY - MONTANA STATE UNIVERSITY; CHAO, SHIAOMAN; MARTIN, JOHN - MONTANA STATE UNIVERSITY; BLAKE, NANCY - MONTANA STATE UNIVERSITY; TALBERT, LUTHER - MONTANA STATE UNIVERSITY

Submitted to: G3, Genes/Genomes/Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2019
Publication Date: 6/5/2019
Citation: Varella, A.C., Zhang, H., Weaver, D.K., Cook, J.P., Hofland, M.L., Lamb, P., Chao, S., Martin, J.M., Blake, N.K., Talbert, L.E. 2019. A novel QTL in durum wheat for resistance to the wheat stem sawfly associated with early expression of stem solidness. G3, Genes/Genomes/Genetics. 9(6):1999-2006. https://doi.org/10.1534/g3.119.400240.
DOI: https://doi.org/10.1534/g3.119.400240

Interpretive Summary: An insect known as wheat stem sawfly is an important pest of wheat. Adult female sawflies posit their eggs into the stems of wheat plants, and when larvae hatch they cut the stem causing the plant to fall to the ground making it unharvestable. Wheat plants with solid stems are resistant to sawfly because larvae are unable to survive inside the stem. However, many durum wheat lines that do not have a solid stem are still resistant to sawfly. In this research, genetic analysis was conducted to identify genes associated with sawfly resistance in durum wheat without a solid stem. Analysis revealed a gene on durum wheat chromosome 3A that was associated with sawfly resistance. Additional studies revealed that resistance was due to the expression of stem solidness early in plant development, at a time critical for oviposition and larval development, and the stem solidness disappeared later in plant development. This work provides further understanding of the mechanisms governing resistance to sawfly, which will aid breeders in the development of sawfly-resistant varieties.

Technical Abstract: The wheat stem sawfly (WSS) (Cephus cinctus Norton) is a major yield-reducing pest of wheat (Triticum aestivum L.). Varieties with pith-filled, or solid, stems provide a measure of resistance by inhibiting larval survival inside the stem. Durum wheat (Triticum turgidum L.) has resistance to the wheat stem sawfly even in the absence of known genes for stem solidness. To determine the genetic basis of resistance in durum wheat, a susceptible durum wheat, PI 41353, was identified from among 1,211 landrace accessions from around the world screened in WSS-infested sites. A recombinant inbred line (RIL) population of 105 individuals was developed from a cross of PI 41353 with a typically resistant variety, Pierce. The RIL were screened in a total of three WSS-infested locations in Montana over a two year period. A genetic map was constructed with 2,867 SNP-based markers. A quantitative trait locus (QTL) analysis identified six QTL associated with resistance. An allele from resistant cultivar Pierce at a QTL on chromosome 3A, Qss.msub-3AL, caused a 25% reduction in stem cutting. Assessment of near-isogenic lines that varied for alleles at Qss.msub-3AL showed that the Pierce allele was also associated with higher stem solidness as measured early in stem development, which is a critical stage for WSS oviposition and larval development. Stem solidness of Pierce and other resistant durum wheat lines largely disappeared later in plant development. Results suggest a genetic mechanism for WSS resistance observed in durum wheat, and provide an additional source of WSS resistance for hexaploid bread wheat.