Morphological and physiological basis of salt resistance in different rice genotypes

Salt stress is one of the major abiotic stresses limiting profitable crop production. This study was conducted to evaluate the morphological and physiological basis of salinity tolerance in rice genotypes. Six rice genotypes (IR74099-3R-5-1-K3, FL 478, GAORI, DONGJINBYEO, RYKUU 15 and CHING-YUEH 1) were sown in germination trays filled with artificial rice soil formulated and then transferred to iron containers after germination. Salinity (100mM NaCl) was imposed in equal increments of 25mM per day. Salt stress caused substantial decrease in shoot length, leaf area and leaf fresh weight, specific leaf area (SLA) and seedling fresh and dry weights of all rice genotypes; although the genotypes varied in their response. However, root length of tested rice genotypes increased with salt stress except genotype DONGJINBYEO. A substantial decrease in K⁺/Na⁺ ratio was observed in all genotypes under salt stress due to substantial increase in Na⁺ contents, but genotypes behaved differently. Salt stress also enhanced polyphenols in genotypes IR74099-3R-5-1-K3, FL 478 and GAORI while flavonoids increased in all genotypes except RYKUU15. Rice genotypes IR74099-3R-5-1-K3 and FL 478 had minimum decrease in seedling fresh and dry weights, and higher leaf area and SLA under salt stress. Genotypes IR74099-3R-5-1-K3 and FL 478 also had 6.33 and 13.73% higher anti-oxidant activity. In conclusion, although salinity decreased the growth of all tested rice genotypes; genotypes IR74099-3R-5-1-K3 and FL 478 were more resistant to salt stress, than other genotypes, owing to higher buildup of polyphenols and flavonoids, and decrease in Na⁺ uptake and better K⁺/Na⁺ ratio, which helped to maintain higher leaf area, SLA and growth. Physiological traits like polyphenols and flavonoids, and K⁺/Na⁺ ratio may be used for mass screening of rice genotypes for salt tolerance.