Critical osmotic, ionic and physiological indicators of salinity tolerance in cotton (Gossypium hirsutum L.) for cultivar selection

Salinity affects the germination, growth and ultimately the yield of cotton (Gossypium hirsutum L.) which demands reliable traits for the evaluation and selection of salt tolerant cultivars. Here, ten major osmotic, ionic and physiological parameters have been studied to distinguish the effect of salinity in two different cultivars of cotton. Plants were grown in hydroponic system and exposed to different salinity levels of NaCl followed by its recovery under non saline conditions. Data was recorded at three different stages i.e., before stress, after stress and after recovery for comparative study. Recovery assay proved to be very helpful in extracting reliable results. Both cultivars showed significantly different response to Na⁺ and K⁺ accumulation and phenotypically salt tolerant cultivar (Coker 312) accumulated less Na⁺ and more K⁺ in comparison with susceptible (Simian 3). Decrease in leaf area, seed germination and seedling growth were also conclusive to differentiate these cultivars. We also found other physiological parameters like relative leaf water content (RLWC), plant fresh-weight (PFW), plant dry-weight (PDW), relative growth rate (RGR) and stomatal behavior as good indicators of salinity but could not find their significant role to differentiate two closely relevant cultivars regarding salinity tolerance. Our studies revealed that proline accumulation and chlorophyll concentration are not significant to be used as accurate indicators to characterize the sensitivity of cotton cultivars to salinity. We found post-recovery analysis to be very useful in understanding the role and behavior of different indicators of salinity.