Drought tolerance is not often considered an independent trait by plant breeders because the collective result of many traits of a plant with positive or negative interactions may be fairly general and polygenic in nature. The objective of this study was to evaluate six drought tolerance indices, namely the stress susceptibility index (SSI), yield stability index (YSI), tolerance index (TOL), mean productivity (MP), geometric mean productivity (GMP), and stress tolerance index (STI), to be used in screening safflower (Carthamus tinctorius L.) genotypes. For this purpose, 64 genotypes were grown during two growing seasons (2011)(2012) under both normal and drought-stress field conditions at the Research Farm of Isfahan University of Technology located at Lavark, Najaf-Abad, Iran. The drought tolerance indices were calculated based on seed yield under drought stress and nonstress conditions. Results of combined analysis of variance showed the significant influences of drought stress on seed yield as well as significant differences among genotypes for seed yield and the indices. Results of calculated correlation coefficients and multivariate analyses showed that GMP and STI indices were able to discriminate between drought-sensitive and -tolerant safflower genotypes. Cluster analysis using the drought-tolerance indices divided the 64 genotypes into tolerant and susceptible groups. Based on multivariate analyses using the indices singly or in combinations, it was possible to identify the most yield-stable genotypes across the environments. Overall, we concluded that GMP and STI indices can be efficiently exploited not only to screen drought tolerance but also to identify superior genotypes for both stress and nonstress field conditions in safflower.

Terminal heat stress is one of the major constraints of cereal production. A two-year field investigation was performed to assess the response of Hordeum vulgare ssp. spontaneum genotypes to terminal heat stress using gas-exchange parameters, photosystem efficiency, proline accumulation, cell membrane leakage, and grain yield traits. Results of analysis of variance revealed the significant effects of heat stress (E), genotype (G), and G × E on the studied traits. The results of linear regression analysis showed that yield loss was inversely correlated with the maximum quantum yield of PSII photochemistry (Fv/Fm) and chlorophyll content. Path-coefficient analysis revealed that high Chl contents were either directly related to the grain yield or indirectly through the higher net photosynthetic rate and higher Fv/Fm values under high temperatures at the reproductive growth stage. Overall, the adapted wild genotypes exhibited physiological mechanisms capable of sustainable maintaining their yield capacity and plasticity flow, which could be exploited by crossing with cultivated barley to introgress heat tolerance.

Thermal stress at the reproductive stage poses a substantial constraint on cereal production worldwide. A two-year field study was conducted to assess tolerance to terminal heat stress in cultivated (Hordeum vulgare ssp. vulgare L.) and wild (H. vulgare ssp. spontaneum L.) barley genotypes using phenological and agronomic traits as well as selection indices based on grain yield. A new heat-tolerance index was tested while a simultaneous study was also carried out of both phenological and grain yield-related variables as well as previously defined indices. Results of analysis of variance showed the significant genotypic and high-temperature stress (environment) effects on all the traits studied. In contrast to the cultivated genotypes, the wild ones were found less affected by high-temperature stress. Moreover, both cultivated and wild genotypes were observed to use the life cycle shortening as a mechanism to evade heat stress. In addition, supplementary tolerance mechanisms were also found likely to contribute to heatstress evasion in the wild germplasm. Grain yield showed a strong relationship with both stress tolerance index (STI) and heat tolerance index (HTI) among the wild genotypes. However, multivariate analysis highlighted the feasibility of HTI to screen high-temperature tolerant wild genotypes under harsh environments with the most high-temperature tolerant wild genotypes identified originating from warm climates.

High‐temperature 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, four cultivars (H. vulgare ssp. vulgare), 98 F3 and 79 BC1F2 families derived from hybridization of a high‐temperature tolerant wild genotype and a susceptible cultivar ‘Mona’. Results of analysis of variance showed significant genotypic and high‐temperature stress effects on all the traits studied. Approximately one quarter of the wild genotypes originating from a warmer climate were slightly affected by high‐temperature stress. Grain yield strongly correlated (p < .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. Grain number and weight were the most effective yield components to screen high‐temperature tolerant F3 and BC1F2 families. In conclusion, strategies like escape/avoidance are being used primarily to cope with heat stress by cultivars, whereas adaptive strategies such as tolerance are being implemented by wild barley.

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