Responses of cotton seed germination characteristics and storage substance metabolism to saline‒alkali stress

Abstract Background The inhibition of cottonseed germination by soil salinization is a key obstacle affecting cotton production in Xinjiang. The most economical and effective measures to alleviate soil salinization damage are to explore the mechanism of cotton salt tolerance and to cultivate and popularize salt-tolerant varieties. Four cotton varieties were used in this study: the highly saline-alkali-resistant varieties Xinluzhong 82 and Xinluzhong 68 and the saline-alkali-sensitive varieties Xinluzhong 42 and Xinshi H12. These varieties were exposed to three different mixed saline-alkali concentrations: 0 mmol·L −1 (control, CK), 219 mmol·L −1 , and 365 mmol·L −1 . Results The germination characteristics, root traits, and changes in the storage material contents (crude fat, total protein, and total sugar) during cotton seed germination were analyzed. The results revealed that with increasing mixed saline-alkali concentrations, the relative water absorption, water absorption rate, germination rate, root length, diameter, area, and volume, and total sugar content of cotton decreased by 22.7%–90.1% on average, whereas the crude fat and protein concentrations increased by 7.6% on average. Under saline-alkali stress, cotton seeds undergo metabolic reallocation characterized by a decrease in carbohydrate content and the accumulation of lipids/proteins, potentially mitigating energy deficits and structural damage. Conclusions Under saline-alkali stress, highly resistant cotton varieties presented increased growth and adaptation during early root emergence. This was achieved by increasing water uptake and adjusting the root diameter. Under 365 mmol·L −1 saline-alkali stress, damages in these resistant varieties were correlated with their crude fat, protein, and storage substance contents. Changes in stored nutrients likely support cotton growth under stress. These findings reveal the physiological mechanisms underlying saline-alkali resistance in cotton and provide a scientific basis for the breeding of tolerant varieties. This study identified the key factors affecting cottonseed germination and offered a new direction for breeding programs.