Genetic dissection of flag-leaf related traits in barley (Hordeum vulgare L.) under normal and drought stress conditions

Barley (Hordeum vulgare L.) is known as the fourth most important grain crop in the world. Drought stress is also one of the main factors that reduce the growth and yield of barley, and grain yield is directly related to the morphological characteristics of the flag leaf.. In order to identify the main and epistatic genomic regions and investigate their interaction with the environment for morphological traits related to flag leaf, including length, width, area, and flag leaf sheath length, an experiment was conducted with 136 doubled haploid lines of barley along with their parents 'Nure' and 'Tremois' using an alpha lattice design with two replications under normal and drought stress conditions at the Zabol Agricultural Research Station, Iran, in 2015-16 growing season. The genetic map of the target population comprised 543 markers (including DArT, SSR, SNP, and AFLP markers) for the QTL analysis. In this study, single-locus and two-locus QTL analyses were performed using the composite interval mapping (CIM) and mixed-model based composite interval mapping (MCIM) methods, respectively. Based on a single-locus analysis, five QTLs were identified, including three putative QTLs, Q1FLW-1H.SZ, Q1SHFLL-1H.NZ and Q2SHFLL-1H.NZ at bPb-6343-bPb-8081, bPb-1419-bPb-9180, and bPb-9108-bPb-6343 marker intervals, and two suggestive QTLs, on chromosomes 1H and 5H for the traits of flag leaf width (FLW, cm) and flag leaf sheath length (SHFLL, cm). Based on a two-locus analysis, eight additive (M-QTL) QTLs and 15 pairs of epistatic effects (E-QTL) were detected for different traits, among which two pairs of epistatic QTLs for the FLW trait showed significant QTL × environment interactions (AAEI). All detected M-QTLs for flag-leaf-related traits across two environments, without additive × environment interactions (AEI), were identified as stable QTLs, and the highest number of stable QTLs was associated with chromosome 1H. In this study, drought stress-tolerant QTLs were identified in all barley chromosomes except chromosome 2H. Most of the QTLs associated with the investigated traits in the Nure/Tremois population in the present study have not been reported previously and, therefore, are novel. The stable and putative QTLs controlling flag-leaf-related traits in this study, along with the markers linked to these QTLs, can be utilized in marker-assisted selection (MAS) and gene pyramiding breeding programs after confirmation and validation in different environmental conditions and genetic backgrounds to create high-yielding and drought-tolerant barley cultivars. Additionally, these findings will accelerate the understanding of the genetic relationships among spike-related traits at the molecular level.