Study of stress indices for selecting tolerant wheat genotypes in rain-fed conditions and moderate and severe salinity stress in Golestan province

Background and objectives: The region of the experiment is located in Golestan Province, Iran, with agriculture subject to various farming conditions (rain-fed and irrigation) and different levels of salinity (more than 38% of Golestan’s total land area is salt-affected). The purpose of this study has been to evaluate the stress indices in the selection of tolerant wheat genotypes, not only for rain-fed conditions but also for different levels of salinity in the region in question.
Materials and methods: The experiments were conducted in 2011-2012 with nine genotypes of wheat in three environments of no salinity, severe salinity (19 ds/m) and moderate salinity (9 ds/m) and with eight genotypes of wheat in two environments (irrigated and rain-fed) in a randomized complete block design with three replications. For all the experiments, sowing was done from 18 to 20 December and the seedling density was 300 seeds/m2. The plots consisted of six metre-long rows spaced 20 cm apart. The grain yields were measured by harvesting 4 m2 of the central part of each plot at crop maturity. After harvest, yield were measured and selection indices, including stress susceptible index (SSI), tolerance (Tol) index, mean productivity (MP), geometric mean productivity (GMP) and stress tolerant index (STI) were calculated. In order to better evaluate the genotypes’ relationships, principal component analysis was done and a biplot based on PC1 vs. PC2 (principal components one and two, respectively) was provided.
Results:
The results showed that the correlation between yield of genotypes under non stressed condition with severe salinity (stress index= 0.76) was not significant, but in two other conditions, i.e., non salinity vs. moderate salinity (stress index= 0.51) and rain-fed vs. Irrigated (stress index= 0.12), the correlation was positive and significant. In severe salinity, PC1 separated high-yielding genotypes under non-stressed conditions whereas PC2 differentiated them under stressed conditions. For both moderate salinity and rain-fed conditions, PC1 separated high-yielding genotypes under stressed and non-stressed conditions, and PC2 differentiated genotypes with high sensitivity to drought conditions. Among the indices studied, STI and GMP with Yp and Ys and SSI with Yp had positive and significant correlation. SSI was also negatively correlated with Ys. MP had higher correlation with Yp and was closer to Yp than STI, GMP and SSI.
Conclusion: In severe salinity based on SSI, Bam had the least SSI and it was a better genotype while biplot showed that Bam only had the highest value of PC2 and it was a good genotype under stressed condition. Under severe salinity, there was not any better genotype for both stressed and non stressed conditions. Some of cultivars that were tolerant in other regions of Iran, i.e. Bam and Arg in severe salinity had the highest yield and the lowest SSI suggesting that they are tolerant to high salinity. In moderate salinity and rainfed condition n-87-20 and Karim were the best genotypes, respectively. The biplot clearly simultaneously revealed the relationships needed for selecting genotypes under stressed and non stressed conditions.