Accumulation of compatible solutes in rice (Oryza sativa L.) cultivars by inoculation of endophytic plant growth promoting bacteria to alleviate salt stress

Salinization of agricultural lands, particularly rice paddies, results in the drastic decline of crop yields. Soil salinization impacts the plant physiology by inducing salt stress which may leads to osmotic stress, ionic stress and water-related nutrient imbalance. These imbalances necessitate the need for plants to produce osmolytes including proline and glycine betaine. This study aimed to elucidate the dynamic changes in proline and glycine betaine accumulation modulated by the inoculation of Brevibacterium linens RS16 in salt-sensitive and moderately salt-tolerant rice plants under salt stress conditions. This study showed the interaction of four major factors including rice genotypes with differing tolerance to salt stress, length of exposure to salt stress, level of salt stress and effects of inoculation. Salt stress resulted in significant reduction in plant growth parameters with the salt-sensitive rice genotype (IR29) having a more significant growth reduction. Both the salt-sensitive and salt-tolerant rice genotypes increased in total proline and glycine betaine accumulation at 3 days and 10 days after subjecting under 50 mM and 150 mM salt stress conditions. A significant increase in proline and glycine betaine was observed in the salt-sensitive genotype after 10 days under 50 mM and 150 mM salt stress conditions. Inoculation of the rice genotypes with B. linens RS16 resulted in the improvement of plant growth parameters in both rice genotypes, and total proline and glycine betaine accumulation, especially in IR29. This study showed that proline and glycine betaine are compatible osmolytes of rice under salt stress, and that inoculation of rice genotypes with B. linens RS16 mediated salt tolerance through improvement of plant growth parameters and proline and glycine betaine accumulation in rice plants.