Evaluation of salt tolerance in cotton (Gossypium hirsutum L.) under NaCl treatment based on chlorophyll and SPAD parameters

Increasing soil salinisation, exacerbated by global warming, poses a major threat to sustainable agriculture, as salinity severely impairs plant growth and development. Salinity is one of the most severe abiotic stresses affecting plant growth and development. In this study, the salt tolerance of 28 cotton (Gossypium hirsutum L.) cultivars was evaluated under controlled phytotron conditions through the measurement of chlorophyll a, b, total chlorophyll (a+b), carotenoids and SPAD index under NaCl treatments (0, 50 and 100 mM). The experiment was conducted in triplicate and measurements were taken 21 days after salt application. The obtained data revealed significant variability among the cultivars. At 100 mM NaCl, a reduction in chlorophyll a exceeding 20 % compared to the control was observed in 12 cultivars, whereas others (e.g., Baraka, Gulbahor-2, C-4727) maintained relatively high levels of total chlorophyll. A strong correlation was found between SPAD readings and laboratory-determined total chlorophyll content (r = 0.82; p < 0.001), confirming the suitability of SPAD as a rapid screening tool for identifying salt-tolerant genotypes. The findings highlight promising donor cultivars (Porloq-1, Afsona, Baraka, Kelajak, Buxoro-14) for breeding programmes and recommend an integrated approach combining chlorophyll content and SPAD measurements for early-stage selection of salt-tolerant cotton genotypes. The results may contribute to breeding for stress resistance in cotton and support the development of strategies for precision agriculture under saline conditions.