Evaluation of wheat genotype tolerance to late-session heat stress

Background and objectives: Rising temperatures are a severe warning to humans, and heat stress is one of the principal environmental stresses that reduce the yield of crops, including wheat, worldwide. The increase in carbon dioxide in the atmosphere has caused global warming, affecting agriculture in the future. More than 50 countries experience heat stress during the wheat growing season. Therefore, the development of heat-tolerant cultivars is one of the main goals of wheat breeding programs. This study aimed to evaluate the drought tolerance indices and determine the relationships among them and their application in wheat screening programs.
Materials and Methods: This experiment was performed using alpha-lattice design with two replications in normal and delayed cultivation conditions using 132 wheat genotypes (included 62 Iranian and foreign cultivars and 70 advanced lines). The seeds were obtained from the National Rainfed Agricultural Research Institute and the Seedling and Seed Breeding Institute. Two local control cultivars named Gonbad (Abi cultivar) and Kuhdasht (rainfed cultivar) were selected among the selected genotypes. Based on the yield under non-stress (YP) and stress (YS) conditions, tolerance indices such as stress tolerance index (STI), tolerance index (TOL), Geometric mean production (GMP), mean production index (MP), Harmonic Index (HM), Yield Index (YI), Relative Drought Index (RDI) and yield Stability Index (YSI) were calculated.
Results: The results showed that tolerance indices such as STI, GMP, HM, and MP had a positive and significant correlation with yield under non-stress and stress conditions, and the genotypes with large numerical values for these indices had high yield under stress and non-stress conditions (Fernandez’ A group), which were included genotypes 51, 12, 24, 85, 6, 120, 47, 94 (Bahar), 72, 114, 91, 131, 16, and 127. Tolerance indices were divided into two components that explained 90.79% of the total variance, using principal component analysis. The first component, which explained 60.64% of the total variance, had a correlation of 0.75 and 0.86 with performance under stress and non-stress conditions, respectively. The second component, which explained 30.14% of the total variance, showed a correlation of 0.66 and -0.5% with performance under stress and non-stress conditions, respectively. Based on the two-dimensional plot resulting from principal component analysis, considerable genetic diversity was observed among the studied genotypes.
Conclusion: According to the results, genotypes that perform well under non-stress conditions will not necessarily perform well under stress conditions. Therefore, to select high-yield genotypes under stress conditions, the cultivar selection had to be made in the same stressful environment. In conclusion, it can be said that the identified genotypes using HM, GMP, and MP indices are recommended for cultivation in areas with no stress, but heat stress is likely to occur in some years. In addition, identified genotypes using YSI and RDI indices are recommended for cultivation in areas with severe heat stress at the end of the season. Accordingly, stress-resistant genotypes in F or A group C can be used as germplasm sources with heat-tolerant genes in breeding programs. Also, to locate heat stress tolerance genes, it is possible to use the intersection of genotypes located in group B of Fernandez with genotypes located in group A or C of Fernandez.