Plant growth promoting bacteria confer salt tolerance in Vigna radiata by up-regulating antioxidant defense and biological soil fertility

Salinity, a frequently occurring abiotic stress, is a major constraint for crop productivity worldwide. The present study was conducted to evaluate the ability of plant growth promoting rhizobacteria (PGPR) Bacillus cereus Pb25, isolated from soil irrigated with saline water, to promote Vigna radiate (mungbean) growth in the absence and presence of salt stress (9 dS m(-1)). Results demonstrated that B. cereus promoted V. radiate plant growth significantly even in the presence of salt. Inoculations with PGPR improved the plant growth, and increased the root, shoot fresh and dry biomass and yield as compared to plants with no bacterial treatment (control). Results showed that both chlorophyll content and plant growth were inhibited by saline stress and the salt-induced oxidative damage (measured by MDA, H2O2) was alleviated by PGPR inoculation. Furthermore, PGPR inoculation significantly increased the antioxidant enzymes (POD, SOD and CAT) activities and enhanced the accumulation of proline, potassium, nitrogen and phosphorus as well as decreased sodium accumulation in saline stressed plants. Regarding the soil biological activity, inoculated PGPR enhanced the activity of dehydrogenase, alkaline phosphatase, microbial biomass carbon, available phosphorus and total organic carbon under saline stress as compared to saline treatment alone. These results suggest that B. cereus can be used in salinized agricultural lands as bio-inoculant to increase crop productivity.