Introduction

Heat stress, intensified by global warming, has emerged as a major constraint on crop productivity and food security worldwide. In cereal crops, the flowering stage is particularly vulnerable to elevated temperatures, leading to substantial reductions in grain yield through diminished fertility and lower seed-setting rates. Hull-less barley genotypes grown in semi-arid regions are especially exposed to heat stress during critical growth phases. Therefore, this study aimed to evaluate grain-yield stability traits and to identify superior hull-less barley genotypes under both non-stress and heat-stress conditions.

Materials and methods

To assess terminal heat-stress tolerance, a field trial was established using 17 elite hull-less barley genotypes and three standard checks. The experiment followed a randomized complete block design with three replications at the Agricultural and Natural Resources Research Station in Darab over the 2022–2024 cropping seasons. All genotypes were cultivated under normal (6 December) and late (9 January) sown conditions. Eleven stress-tolerance indices were computed for each season: yield under non-stress (Yp) and stress (Ys) conditions, tolerance index (TOL), stress susceptibility index (SSI), mean productivity (MP), geometric mean productivity (GMP), stress tolerance index (STI), harmonic mean (HM), yield index (YI), yield stability index (YSI), and relative stress index (RSI). Phenological and agronomic traits recorded included days to heading (DHE), days to maturity (DMA), plant height (PLH), grain filling rate (GFR), thousand-grain weight (TGW), grain yield (GY) and number of grains per spike (NGS). The multi-trait stability index (MTSI) was applied to select genotypes combining high grain yield, enhanced TGW, and early maturity. Principal component analysis (PCA) was used to explore relationships among stress indices and genotype variation, while factor analysis identified the traits contributing most to stability.

Results and Discussion

Likelihood ratio tests revealed that both genotype and genotype × environment interaction effects were significant for all evaluated traits. Variance partitioning indicated that DHE, NGS, DMA, PLH, and TGW were predominantly governed by genotypic differences, whereas GFR and GY were more strongly influenced by environmental variation. MTSI analysis identified G16, G10 and G11 as the most stable genotypes across traits. Selection differentials were positive for all traits except NGS, with the largest gains observed in GY (25.3%), GFR (20.2%), and TGW (3.54%). Based on a two-year average, principal component analysis explained 99.8% of the total variability, grouping stress-tolerance indices into three clusters and genotypes into four clusters. The second PCA cluster comprised GMP, HM, STI, YI, Yp and Ys. Genotypes G5, G10, and G11 co-localized within this cluster and were thus classified as heat-stress tolerant.

Conclusion

Overall, MTSI selected genotypes combined high grain yield with a rapid grain filling rate, increased thousand-grain weight, and greater plant height. Specifically, G16, G10, and G11 ranked highest for stability across all measured traits. Concurrently, stress tolerance score (STS) identified G10, G5, and G16 (first year) and G11, G10, and G9 (second year) as heat-tolerant genotypes, each outperforming the population mean yield under both heat-stress and non-stress conditions. Consequently, G10 and G11 out-yielded the control cultivars in terms of agronomic performance and heat resilience. These lines represent promising candidates for direct cultivar release or as parental material in breeding programs aimed at enhancing hull-less barley’s yield and heat tolerance under warming climates. Given the current scarcity of commercial hull-less barley cultivars adapted to Iran’s warm regions, the deployment of these genotypes could markedly advance barley production in the face of ongoing climatic change.