Physiological response of tomato plant to chitosan-immobilized aggregated Methylobacterium oryzae CBMB20 inoculation under salinity stress

The use of plant growth promoting bacteria as bioinoculant to alleviate salt stress is a sustainable and eco-friendly approach in agriculture. However, the maintenance of the bacterial population in the soil for longer period is a major concern. In the present study, chitosan-immobilized aggregated Methylobacterium oryzae CBMB20 was used as a bioinoculant to improve tomato plant (Solanum lycopersicum Mill.) growth under salt stress. The chitosan-immobilized aggregated M. oryzae CBMB20 was able to enhance plant dry weight, nutrient uptake (N, P, K and Mg2+), photosynthetic efficiency and decrease electrolyte leakage under salt stress conditions. The oxidative stress exerted by elevated levels of salt stress was also alleviated by the formulated bioinoculant, as it up-regulated the antioxidant enzyme activities and enhanced the accumulation of proline which acts as an osmolyte. The chitosan-immobilized aggregated M. oryzae CBMB20 was able to decrease the excess Na+ influx into the plant cells and subsequently decreasing the Na+/K+ ratio to improve tomato plant growth under salt stress conditions. Therefore, it is proposed that the chitosan-immobilized aggregated M. oryzae CBMB20 could be used as a bioinoculant to promote the plant growth under salt stress conditions.