Zinc and phosphate solubilizing Rhizobium radiobacter (LB2) for enhancing quality and yield of loose leaf lettuce in saline soil

Abstract

In the present study, rhizobial isolate LB2 was procured from the root nodules of Leucaena leucocephala wildly growing in saline soil. On the basis of morphology, biochemical analysis and nucleotide sequence homology LB2 was identified as Agrobacterium tumefaciens syn. Rhizobium radiobacter (Accession no. KY392996). Rhizobium radiobacter LB2 showed various plant growth promoting (PGP) activities such as mineral (zinc and phosphate) solubilisation, nitrogen fixation, production of indole acetic acid (IAA), exopolysaccharides (EPS) and siderophore. LB2 also showed salt tolerance activity up to 4% NaCl concentration. In this study, four types of fertilizers, including chemical (NPK), vermicompost (VC), farmyard manure (FYM) and bacterial inoculant (R. radiobacter LB2) were applied on lettuce crop to check their impact on growth, nutritional content and yield in the field conditions. Among all the treatments, bacterial inoculant R. radiobacter was observed as best for lettuce cultivation. Rhizobium radiobacter (LB2) caused highest increment in all the plant growth parameters with improved nutritional content in comparison to control and other treatments. Rhizobium radiobacter treatment was found to be effective even in saline soil. Rhizobium radiobacter (LB2) can thus be used for the enhanced lettuce cultivation along with combating soil salinity in sustainable manner without the input of harmful chemicals.