Association mapping of morphological and physiological traits of flag leaf related to drought tolerance in barley

Association mapping (AM) has proven to be a powerful approach for dissecting the genetic basis of complex traits. In this study, Quantitative Trait Loci (QTLs) controlling flag leaf characteristics under drought stress were detected in a set of 148 modem spring barley cultivars using AM analysis. Flag leaf length (FLL), flag leaf width (FLW), relative water content (RWC), chlorophyll content, and maximum quantum efficiency of PSII (Fv/Fm) which are important in photosynthetic rate, were evaluated under normal irrigation and drought stress conditions at grain filling stage. Population structure was estimated using Structure(2.3) and linkage disequilibrium (LD) was estimated by the 'Full Matrix LD' using Tassel(5.0). Significant marker/trait associations were investigated based on K-Q matrix using Tasse1(3.0). The analysis of population structure divided the cultivars into two sub-groups. Significant LD values (P < 0.01) between polymorphic sites with regions of high and low LD were observed. A total of 84 significant putative genomic regions were identified, which delineated into 37 QTLs under two water treatments. Two stable QTLs on 2H and 3H were detected for FLL in drought stress treatment. A QTL for FLL were detected on 2H in normal treatment, which alone explained around 11% of phenotypic variance of FLL. This QTL was also associated with the expression of FLW and explained around 7.5% of phenotypic variance. The results suggest that major loci are located on chromosomes 2H, 3H, 4H and 5H involved in the development of flag leaf characteristics and could be used as selection criteria in barley breeding for drought tolerance.