Whole-Genome QTL Analysis of Stagonospora nodorum Blotch Resistance and Validation of the SnTox4–Snn4 Interaction in Hexaploid Wheat

Abstract

Necrotrophic effectors (also known as host-selective toxins) are important determinants of disease in the wheat–Stagonospora nodorum pathosystem. To date, five necrotrophic effector–host gene interactions have been identified in this system. Most of these interactions have additive effects while some are epistatic. The Snn4–SnTox4 interaction was originally identified in a recombinant-inbred population derived from a cross between the Swiss winter wheat cultivars ‘Arina’ and ‘Forno’ using the S. nodorum isolate Sn99CH 1A7a. Here, we used a recombinant-inbred population consisting of 121 lines developed from a cross between the hexaploid land race Salamouni and the hexaploid wheat ‘Katepwa’ (SK population). The SK population was used for the construction of linkage maps and quantitative trait loci (QTL) detection using the Swiss S. nodorum isolate Sn99CH 1A7a. The linkage maps developed in the SK population spanned 3,228 centimorgans (cM) and consisted of 441 simple-sequence repeats, 9 restriction fragment length polymorphisms, 29 expressed sequence tag sequence-tagged site markers, and 5 phenotypic markers. The average marker density was 6.7 cM/marker. Two QTL, designated QSnb.fcu-1A and QSnb.fcu-7A on chromosome arms 1AS and 7AS, respectively, were associated with disease caused by the S. nodorum isolate Sn99CH 1A7a. The effects of QSnb.fcu-1A were determined by the Snn4–SnTox4 interaction and accounted for 23.5% of the phenotypic variation in this population, whereas QSnb.fcu-7A accounted for 16.4% of the phenotypic variation for disease but was not associated with any known effector sensitivity locus. The effects of both QTL were largely additive and collectively accounted for 35.7% of the total phenotypic variation. The results of this research validate the effects of a compatible Snn4–SnTox4 interaction in a different genetic background, and it provides knowledge regarding genomic regions and molecular markers that can be used to improve Stagonospora nodorum blotch resistance in wheat germplasm.