Genetic basis of flag leaf thickness and its contribution to yield in wheat (Triticum aestivum L.)

Previous studies on leaf morphological traits are predominantly focused on flag leaf length (FLL), width (FLW), and area (FLA), which are known to affect light interception. However, limited research has addressed on flag leaf thickness (FLT) and its intricate relationship with various yield components. Recent studies have highlighted the importance of FLT in determining photosynthetic capacity and yield potential in wheat. Understanding the genetic regulation of FLT and its interactions with other morphological traits is essential for developing wheat varieties with higher yield potential. Due to the technical difficulties of directly measuring FLT, earlier studies have typically relied on indirect methods.

In contrast, this study directly measured FLT across 194 doubled haploid lines, aiming to identify quantitative trait loci (QTL) associated with these traits and yield components, and to clarify their relationships. The results showed that flag leaf traits were positively correlated with spike length (SL), grain number per spike (GNS), thousand-grain weight (TGW), grain length (GL), grain width (GW), grain thickness (GT), and average seed area (ASA). The major QTL for FLT (Qflt-5 A) was located in the similar regions to those for FLL (Qfll-5 A), GW (Qgw-5 A), and GT (Qgt-5 A). FLT had a larger contribution to GW and GT than other flag leaf traits. Neixiang 5 alleles Qflt3D.1 and Qflt5A, associated with thicker flag leaf led to higher yield potential. Six genes within the major QTL intervals were identified as candidate genes for flag leaf traits.

Targeted pyramiding of genetic loci governing FLT represents a promising breeding strategy. Its potential to boost wheat productivity would be mediated through optimized photosynthetic capacity, though the functional significance of this relationship awaits direct physiological validation.