Soil salinization has emerged as one of the prime environmental constraints endangering soil quality and agricultural productivity. Anthropogenic activities coupled with rapid pace of climate change are the key drivers of soil salinity resulting in degradation of agricultural lands. Increasing levels of salt not only impair structure of soil and its microbial activity but also restrict plant growth by causing harmful imbalance and metabolic disorders. Potential of secondary metabolites synthesized by halotolerant plant growth promoting rhizobacteria (HT-PGPR) in the management of salinity stress in crops is gaining importance. A wide array of secondary metabolites such as osmoprotectants/compatible solutes, exopolysaccharides (EPS) and volatile organic compounds (VOCs) from HT-PGPR have been reported to play crucial roles in ameliorating salinity stress in plants and their symbiotic partners. In addition, HT-PGPR and their metabolites also help in prompt buffering of the salt stress and act as biological engineers enhancing the quality and productivity of saline soils. The review documents prominent secondary metabolites from HT-PGPR and their role in modulating responses of plants to salinity stress. The review also highlights the mechanisms involved in the production of secondary metabolites by HT-PGPR in saline conditions. Utilizing the HT-PGPR and their secondary metabolites for the development of novel bioinoculants for the management of saline agro-ecosystems can be an important strategy in the future.

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In the present study, phosphate solubilizing rhizobacterial isolate STJP from the rhizosphere of Stevia rebaudiana was identified as a Bacillus sp. on the basis of phenotypic, biochemical, and 16S rRNA gene sequencing. In addition to phosphate solubilization ability, isolate Bacillus sp. STJP produced a significant quantity of siderophore (16.06 µg/ml) and indole 3-acetic acid (30.59 µg/ml). In the greenhouse experiment, treatment with STJP along with tricalcium phosphate (TCP 200) showed significant increase in the plant growth parameters, oil yield and P uptake in M. arvensis as compared to the control plants. Amongst all the treatments, highest oil yield and menthol content were observed when treated with Bacillus sp. STJP + TCP 200. Hence, an integrated approach of using Bacillus sp. STJP along with TCP can be used to increase the production of menthol and oil yield of M. arvensis. This approach of using fertilizer along with phosphate solubilizing Bacillus sp. worked very well and was more effective in comparison with individual treatment of fertilizer or plant growth promoting rhizobacteria. A combined use of efficient phosphate solubilising bacteria loaded with plant growth promoting characters along with TCP can thus be far effective way for enhancing the yield of crops in a sustainable manner.

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