Exiguobacterium oxidotolerans, a halotolerant plant growth promoting rhizobacteria, improves yield and content of secondary metabolites in Bacopa monnieri (L.) Pennell under primary and secondary salt stress.

Brahmi (Bacopa monnieri), an integral component of Indian Ayurvedic medicine system, is facing a threat of extinction owing to the depletion of its natural populations. The present study investigates the prospective of exploitation of halotolerant plant growth promoting rhizobacteria (PGPR) in utilising the salt stressed soils for cultivation of B. monnieri. The effects of two salt tolerant PGPR, Bacillus pumilus (STR2) and Exiguobacterium oxidotolerans (STR36) on the growth and content of bacoside-A, an important pharmaceutical compound in B. monnieri, were investigated under primary and secondary salinity conditions. The herb yields of un-inoculated plants decreased by 48 % under secondary salinization and 60 % under primary salinization than the non salinised plants. Among the rhizobacteria treated plants, E. oxidotolerans recorded 109 and 138 %, higher herb yield than non-inoculated plants subjected to primary and secondary salinity respectively. E. oxidotolerans inoculated plants recorded 36 and 76 % higher bacoside-A content under primary and secondary salinity respectively. Higher levels of proline content and considerably lower levels of lipid peroxidation were noticed when the plants were inoculated with PGPR under all salinity regimes. From the results of this investigation, it can be concluded that, the treatments with salt tolerant PGPR can be a useful strategy in the enhancement of biomass yield and saponin contents in B. monnieri, as besides being an eco-friendly approach; it can also be instrumental in cultivation of B. monnieri in salt stressed environments.