Novel loci for flag leaf thickness with breeding potential: genetic dissection and candidate genes prediction

As a key morphological trait of flag leaves, flag leaf thickness (FLT) directly modulates light energy capture efficiency and per-unit-area photosynthetic capacity, and is thus identified as a critical regulator of wheat grain yield formation. Dissecting the genetic basis underlying FLT is of great significance for accelerating the molecular breeding of high-yield wheat varieties. In this study, two recombinant inbred line (RIL) populations were employed to map quantitative trait locus (QTL) for FLT across five independent environments. A total of 19 QTLs controlling FLT were identified in the two RIL populations. Among them, QFLT.suas-2CN-4B.2, QFLT.suas-2CN-6A, QFLT.suas-2SY-3B.2, and QFLT.suas-2SY-6A exhibited stable expression across multiple environments, and comparative analysis with previously reported QTLs indicated that all four loci are likely novel. Notably, QFLT.suas-2CN-6A and QFLT.suas-2SY-6A were co-localized within the same physical interval, suggesting they are likely the same locus. Candidate gene analysis for the co-localized locus QFLT.suas-2CN-6A and QFLT.suas-2SY-6A identified seven putative candidate genes highly expressed in wheat leaves, all of which encode chlorophyll a-b binding proteins that may participate in the regulation of FLT development. Furthermore, significant positive correlations between FLT and spikelet number per spike (SNS) were detected in both RIL populations. The favorable alleles of QFLT.suas-2CN-6A and QFLT.suas-2SY-6A significantly increased SNS by 3.21% and 3.31%, respectively. Collectively, these results deepen our understanding of the genetic basis underlying wheat FLT, and provide stable, valuable QTL resources and candidate gene targets for molecular marker-assisted breeding of high-yield wheat.