Improving barley resilience to heat and drought: genetic and physiological insights into stay-green, root-mediated gene expression, and dual-purpose quality traits

Abstract

Barley (Hordeum vulgare L.), a major cereal crop grown globally for feed, forage, and malting, is increasingly threatened by abiotic stresses such as heat and drought. These conditions reduce biomass, digestibility, starch accumulation, and grain filling, while increasing grain protein concentration by altering the timing of senescence. Such losses undermine profitability for growers, reducing forage value and compromising malting quality. This dissertation investigates the genetic and physiological basis of barley's response to heat and drought through three integrated studies. First, genome-wide association study (GWAS) was conducted in two diverse iCore populations across irrigated and dryland environments to dissect the genetic architecture of forage traits. Biomass and development traits showed high heritability, while digestibility traits were more environmentally responsive. Several QTL were identified that maintained forage quality without compromising yield. The second study assessed the performance of near-isogenic lines (NILs) harboring stay-green alleles at four QTL (QGFhd-2H, QLN-2H, QGFmt-6H, and QGF-7H) under heat stress and control conditions. Under heat stress, stay-green NILs demonstrated improved tillering and reduced grain protein compared to non-stay-green lines. Trait correlations revealed key trade-offs, particularly between vegetative growth and grain protein under stress, emphasizing the importance of optimized assimilate allocation. The third project evaluated the role of HvNAM-1, a NAC transcription factor regulating senescence and protein accumulation, in modulating root responses under both control and combined heat-drought conditions. Root transcriptomic analysis of NILs differing in alleles for HvNAM-1 revealed an allele that promoted root longevity and activated stress-protective pathways under combined heat and drought. These responses included enhanced expression of genes related to oxidative defense, and membrane stabilization in ND lines, suggesting root-based resilience complements the stay- green phenotype. The identified QTL and gene expression profiles offer promising targets for breeding cultivars with improved yield, quality, and resilience across diverse environments.