QTL mapping of flag leaf traits in common wheat using an integrated high-density SSR and SNP genetic linkage map

Photosynthesis of carbohydrates is the primary source of grain yield in wheat. Photosynthetic organs, especially flag leaves and awns play important roles in wheat growth and development. Genetic analysis of flag leaf posture, size and shape and presence/absence of awns was conducted using a set of 269 recombinant inbred lines (RILs) derived from Yanda1817 x Beinong6. Six agronomic traits comprising flag leaf angle (FLAN), flag leaf width (FLW), flag leaf length (FLL), the ratio of length/width of flag leaf (FLR), flag leaf area (FLA) and presence/absence of awns were evaluated in Shijiazhuang (2011, 2012 and 2013) and Beijing (2012). Using the available high-density single nucleotide polymorphism and simple sequence repeats (SSR) genetic linkage map, a total of 61 putative quantitative trait loci (QTL) for FLAN, FLW, FLL, FLR and FLA were detected on 16 of the 21 wheat chromosomes excluding 1D, 4B, 5D, 6A and 7A, with single QTL in different environments explaining 2.49-42.41 % of the phenotypic variation. Among the identified QTL, 17 were for FLAN, 11 for FLW, seven for FLL, 13 for FLR and 13 for FLA. Twenty-five (41 %) QTL were detected in at least two environments, while four QTL for FLW were detected in all environments. Thirty QTL were associated with higher number of flag leaf traits originated from Yanda1817 alleles, whereas the remaining 31 QTL were derived from Beinong6. In addition, pleiotropic effects were detected for QTL on chromosomes 2D, 3B, 4A, 4D, 5A, 5B, 6B, 6D and 7D that could serve as target regions for fine mapping and marker-assisted selection in wheat breeding programs. Genetic analysis revealed that the presence/absence of awns in the RIL population is controlled by the awn-inhibitor gene B1 linked to SSR marker Xgwm291 on the long arm of chromosome 5A. Our results also suggest that physiological traits FLL, FLW and FLA were significantly and positively correlated to spike length (SL), grain weight per spike and grain number per spike. FLR was significantly and positively related to SL but negatively related to grain width and grain thickness (GT). In addition, the awn trait was strongly and positively correlated to thousand grain weight, grain length and GT.