Evaluation of drought tolerance indices in various cotton cultivars (Gossypium hirsutum .L) under irrigation deficit

Drought stress poses a significant challenge to crop production globally, including in Iran. Selecting drought-tolerant cultivars is crucial to mitigate adverse environmental conditions. This study aimed to evaluate the drought tolerance of various cotton cultivars using drought tolerance indices to identify the best cultivar adapted to low irrigation stress conditions. In order to investigate and determine the response of 10 cotton varieties to drought stress, an experiment in the form of a statistical design of randomised complete blocks under medium stress conditions and without stress with three replicates was conducted in 2021 and 2022 at the Teaching and Research Farm of Gonbad Kavos University. To evaluate the tolerance and sensitivity of the studied cotton cultivars to drought stress, TOL (tolerance index), MP (mean productivity index), SSI (stress sensitivity index), STI (stress tolerance index), GMP (geometric mean productivity index), YI (yield index), YSI (yield stability index), SDI (drought sensitivity index), K1STI (adjusted stress tolerance index under non-stressed conditions), K2STI (adjusted stress tolerance index under stressed conditions), SSPI (percentage sensitivity index to stress), SNPI (performance index of stress and non-stress conditions) were used. After the analysis of variance and comparison of means, correlation coefficients, principal component analysis and cluster analysis were performed to identify and introduce indicators of drought tolerance. The results of the composite Based on the analysis of variance and the significance of the simple effect and the interaction effects of year, variety and low irrigation, the comparison of the average data in two years was carried out separately, with the highest yield of Vash in the two years 2021 and 2022 under non-stressed (YP) and stressed conditions. Under low irrigation (YS), the Sajdi and Golestan varieties were the highest yielding. The varieties Mai, Shayan, Lodos, Armaghan and Latif achieved above-average yields under both non-stressed and low irrigation conditions. The analysis of the two-year correlation coefficients between the drought stress indices and rice yield under non-stress (YP) and low irrigation (YS) conditions showed the superiority of the STI, MP, GMP and K1STI indices. The results of the analysis by principal components showed that the first two components explained 99.51 and 96.50 per cent of the changes in the first and second year, respectively. The MP, GMP, STI and K2STI indices were the most suitable indices for selecting varieties tolerant under low irrigation stress, as they showed a high correlation with wash yield and more principal components under both conditions. The superior values and cluster analysis of Golestan and Sajdi cultivars were identified as the most tolerant and Sahel and Sepid cultivars as the most sensitive cultivars to low irrigation stress. It seems that production and presentation of varieties with high yield and tolerance to water stress is one of the effective solutions to reduce the harmful effects of water stress.