Evaluation of tolerance to drought stress in bread wheat (Triticum aestivum L.) cultivars and Landraces using tolerance indices

Introduction: Drought is one of the most destructive stresses affecting the growth and development of plants. The increase in global population, wheat demand, and also drought, has increased the importance of breeding for drought tolerance in wheat. The use of selection indices for drought tolerance is an effective strategy for screening drought-tolerant wheat genotypes in breeding programs for this crop.

Materials and methods: This study was conducted at the Dryland Agricultural Research Institute in Maragheh-Iran in two consecutive years 2018-2019 and 2019-2020, under normal irrigation and drought stress conditions to examine the effect of drought stress on grain yield in 300 genotypes of wheat, including 210 landraces and 90 cultivars (15 dryland and 75 irrigated cultivars; 64 spring, 15 winter, and 11 facultative cultivars), evaluated in a simple alpha lattice design. Drought-tolerant genotypes were identified using various indices such as Tolerance index (TOL), Mean productivity (MP), Sensitivity index to stress (SSI), Fernandez Drought index (STI), Geometric mean productivity (GMP), Harmonic mean (HM), Drought tolerance index (DI), Non-biological stress index (ATI), and modified tolerance index (MSTI). The performance of all genotypes was assessed under normal and stress conditions to calculate these indices. The analysis of variance was done using Agricolae package, heatmap clustering of bread wheat genotypes was performed using heatmap3, RColorBrewer, dendextend, gplots and colorspace packages and bi-plot diagrams was created using factoextra package and correlation diagram between traits and indices was drawn using corrplot package in R4.2.2 software. Additionally, a Selection Index for Drought Tolerance (SIIG) was calculated based on the integration of 12 variables to improve the efficiency of selecting and screening drought-tolerant genotypes.

Research findings: The results of analysis of variance for grain yield showed that the environment, genotype, and genotype×environment interaction effect were significant at 0.001 probability level, indicating significant differences among genotypes, demonstrating desirable diversity among genotypes, and the significant interaction effect between genotype and environment showing different responses of genotypes to changes in environmental conditions. Cluster analysis results categorized genotypes into three clusters for both years and an average of two years. Principal Component Analysis (PCA) showed that, in the first year, cultivars Shanghai, Naz, Falat, Bam, and landraces 626358, 623109, and 621908 were drought-tolerant, according to second-year data, cultivars Shanghai, Koohdasht, Karim, Pishgam, and landraces 628189, 627460, and 627616 were drought-tolerant, and based on the average data of two years, cultivars Koohdasht, Karim, Pishgam, Adl, Naz, and landraces 628189, 627460, 624944, and 627299 were drought-tolerant genotypes. Correlation analysis results showed a negative correlation between grain yield and SSI and TOL indices, while positive correlations were found with other indices, especially MP, GMP, HM, STI, and K2STI.

Conclusion: According to the results of drought tolerance indices and the SIIG index, the spring and irrigated cultivars Adl, Naz, and Shanghai, which are old cultivars, the spring and dryland cultivars Karim and Koohdasht, which are new wheat cultivars in the country, and landraces 626358 (originating from Isfahan province) and 621908 (originating from Arak) showed drought tolerance and high performance under two different environmental conditions. The results of this study provide valuable information for selecting drought-tolerant genotypes that can be utilized in breeding programs and the production of new high-yielding cultivars, as well as for their use as parents for genetic analysis, gene mapping, and improving drought tolerance in wheat.