A novel tolerance index to identify heat tolerance in cultivated and wild barley genotypes

Thermal stress at the reproductive stage poses a substantial constraint on cereal production worldwide. This study was conducted to assess tolerance to terminal high-temperature stress in 45 wild (Hordeum vulgare ssp. spontaneum) genotypes, 4 cultivars (H. vulgare ssp. vulgare), 98 F3 and 79 BC1F2 families derived from hybridization of the most tolerant wild genotype and a susceptible cultivar Mona. Results of analysis of variance showed the significant genotypic and high-temperature stress effects on all the traits studied. In contrast to the cultivated genotypes, the wild ones were found less affected by high-temperature stress. The multivariate analysis highlighted the additional high-temperature tolerance components in the tolerant families and wild genotypes. Grain yield strongly correlated (p < 0.01) with stress tolerance, yield stability, and heat tolerance indices. The reduction in the reproduction period caused by high-temperature was much higher in cultivated genotypes than in wild ones. In conclusion, the ingenuous-focused strategies like escape/avoidance are being used primarily to cope with heat stress by cultivars, while adaptive-focused coping strategies such as tolerance are being implemented by wild barley.