Physiological and biochemical parameters as a basis of screening salinity tolerance at seedling stage in Rice (Oryza sativa L.)
Twelve rice genotypes were evaluated at seedling stage with response to salinity stress at 60 mM NaCl for fourteen days in hydophonics in Yashida solution at B.C.K.V., Mohanpur, Nadia, West Bengal, following 12 × 2 factorial experimental design in RCB with 2 replications. Three physiological and biochemical parameters considered for study viz., chlorophyll content (chlorophyll a, chlorophyll b and total chlorophyall), relative water content (RWC) and Na+/K+ ratio. There was reduction in chlorophyll a, chlorophyll b and total chlorophyll content, increase in Na+/K+ ratio and decrease in relative water content (RWC) in the saline condition as compared to control. Chlorophyll a ranged from 0.26 (Annada) to 1.57 (IR10206-29-2-1-1) mg/g of fresh leaf tissue, Chlorophyll b value varied from 0.08 mg g-1 fresh leaf tissue (CSR 22) to 0.58 mg/g fresh leaf tissue (IR06M143). Under saline condition, the highest and lowest RWC was obtained for the genotype IR06M143 (90.84) and Lalat (75.35) respectively whereas the genotype IR10206-29-2-1-1 recorded highest value (0.77) and genotype IR06M143 lowest value (0.24) with respect to shoot Na+/K+ ratio. Visual scoring for salt stress injury showed that six rice genotypes viz., IR10206- 29-2-1-1, PUSA NR 580-6, BRRI Dhan 53, CSR 22, Annada and Lalat fall under susceptible category and rest six genotypes viz., IR11T138, Lal Minikit (WGL20471), IR66946-3R-149-1-1, IR06M143, IRRI 147 and BRRI Dhan 47 fall under moderately tolerant category. The genotypes IR11T138, Lal Minikit (WGL20471) and IR66946-3R-149-1-1 showed lower increase in Na+/ K+ ratio as well as lesser decrease in RWC and chlorophyll content hence may be considered as tolerant to salinity whereas genotypes BRRI Dhan 53 and Lalat showed greater increase in Na+/K+ ratio and greater decrease in RWC and chlorophyll content hence may be considered as susceptible to salinity. Hence Na+/K+ ratio, RWC and chlorophyll content were found to be critical physiological parameters for evaluating rice genotypes for salinity tolerance.