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 a linkage map was constructed using 143 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 3 and F 4 families were phenotyped in the field and in a controlled environment growth chamber, respectively. The 15 linkage group map covered 1241 cM and was largely collinear with the previously published consensus map. QTL analysis was performed and three PM resistance QTL located on LG1, 7 and 9 were identified consistently using phenotypic data from both field and growth chamber assays. These QTL explained 97% of the phenotypic variation exhibiting a mainly dominant gene action. This work represents a first step towards understanding the genetics of PM resistance in flax and map-based cloning of candidate genes underlying the QTL. The second part of the study was conducted to assess the genetic and phenotypic variability and drought tolerance in the F 3 families derived from a cross between KO37 (Iranian cultivar) and SP1066 (Canadian genotype). The presence of high genetic and continuous variability for the studied agronomical traits and IWUE in the F 3 families under both drought stress and non stress conditions indicated that the F 3 population or its advanced generations can be used in selection programs, fine mapping, identification of QTL related to agronomically important traits and improvement of drought tolerance in flax. The results of biplot analysis based on the first two PCs and also triplot analysis based on the STI index and seed yield in stress and non stress conditions introduced five families as the most optimistic families to be used in breeding programs of flax to improve drought tolerance.
