Physio-morphological and molecular characterization of ethyl methanesulfonate-derived mutant population of Gossypium herbaceum L. cv. (Wagad) for drought tolerance

This study investigates the response of ethyl methanesulfonate-derived twenty mutant lines of Gossypium herbaceum, along with the parent type Wagad cultivar, to drought stress. Physiological parameters, such as relative water content (RWC), net photosynthesis (A), stomatal conductance (g(s)), transpiration rate (E), and water use efficiency (WUE), were examined. The mutant line mut_3219 exhibited superior drought tolerance, maintaining high RWC and water retention capacity, with minimal reductions in A, g(s), and E, leading to higher WUE than parent type and other mutant lines. Chlorophyll pigments declined in all the mutants under drought. However, mut_3219 retained higher levels than mut_4785. Anthocyanin accumulation indicated a protective response. Chlorophyll fluorescence showed mut_3219 is less sensitive to drought-induced PSII damage than mut_4785, with better membrane stability and higher proline accumulation, among all other mutant lines and parent type. The morphological parameters were less affected in mut_3219 compared to mut_4785 and parent type. Molecular analyses under control and drought conditions revealed significant variations in the expression of seven drought-related genes (GhbHLH, GhMYB5, GhWRKY33, GhRAF4, GhRAF19, GhNAC2, and GhCAMTA). The relative expression of GhbHLH, GhNAC2, GhRAF4, GhRAF19, and GhCAMTA increased under drought conditions, with notable changes in mut_3219 compared to parent type and all other mutant lines, indicating its enhanced drought tolerance. These findings provide valuable insights into the molecular and physiological mechanisms underlying drought tolerance in cotton.