Mapping Quantitative Trait Loci for Powdery Mildew Resistance in Flax (Linum usitatissimum L.)

Powdery mildew (Oidium lini Skoric, [PM]), an obligate biotrophic ascomycete, is a common and widespread foliar disease of flax in most flax-growing areas of the world. In this study, we constructed a linkage map using 143 simple sequence repeat (SSR) markers and an F-2 population of 300 individuals generated from a cross between the susceptible cultivar NorMan and the resistant cultivar Linda. The F-2-derived F-3 families were phenotyped in the field and the F-3-derived F-4 families were phenotyped in a controlled environment growth chamber. The 15 linkage group map covered 1241 cM and was largely collinear with the previously published consensus map. Quantitative trait loci (QTL) analysis was performed and three PM resistance QTL located on LG1, 7, and 9 were identified consistently using phenotyping data from both field and growth chamber studies. These QTL explained 97% of the phenotypic variation exhibiting a mainly dominant gene action. This work represents a first step toward understanding the genetics of PM resistance in flax and map-based cloning of candidate genes underlying the QTL.