Development of Salt and Drought Tolerance Classification in the Kazakhstan Cotton Collection Using Optimal Phenotypic Traits

In arid and semi-arid regions, salinity and drought limit cotton productivity. As the northernmost cotton-growing country, Kazakhstan often deals with these issues. The objective of this study was to classify salt- and drought-tolerant groups within the Kazakhstan cotton collection based on key phenotypic traits. Fifty-six Gossypium hirsutum genotypes were evaluated under controlled conditions using NaCl and PEG-6000. Six morphophysiological traits, including germination rate, plant height, fresh weight, root dry weight, and relative water content, were analyzed. Increasing NaCl and PEG levels reduced vegetative growth, while germination remained relatively stable under moderate stress. Regression analysis identified 200 mM NaCl as the optimal salinity level for salt tolerance and 20–30% PEG as the optimal level for drought tolerance. Cluster analysis using membership function values grouped the genotypes into five tolerance categories. Eight lines including M-4016-6, M-4031-8, M-4014-6, M-4029-9, M-4016-7, M-4016-8, M-4020-2, and M-4016-4 exhibited high tolerance to both stresses. Additional lines exhibited combined tolerance, indicating strong breeding potential. Principal component analysis revealed an inverse relationship between salt and drought tolerance, suggesting stress-specific adaptation. This study is the first to report on the development of a classification system for salt and drought tolerance in the Kazakhstan Cotton Collection. The results demonstrate substantial genetic variability and highlight the potential for developing cotton cultivars adapted environments prone to stress.