Groundnut (Arachis hypogaea) nodule Rhizobium and passenger endophytic bacterial cultivable diversity and their impact on plant growth promotion

Root nodules offer habitat not only for Rhizobium also for a wide variety of endophytic bacteria that have a positive impact on growth and nutrient status of the plant. To evaluate this statement, the present study was aimed to reveal the cultivable Rhizobium (R) and passenger endophytes (PE) of groundnut nodule and explored their impact on plant growth parameters. Two groundnut phenotypes, bunch (cv., VRI 2) and semi-spreading (cv., VRI 7) varieties nodule were collected for isolation of endophytes. Molecular characterization of nodule endophytic bacterial isolates were done using 16S rDNA sequencing. Isolates were screened based on their early plant growth promotion and selected efficient R and PE were co-inoculated to assess the impact on plant growth. Ninety eight nodule endophytic bacterial isolates were distributed among the Firmicutes, Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria. In bunch type groundnut (VRI 2) co-inoculation of Rhizobium phaseoli S18 and Pantoea dispersa YBB19B registered significantly higher shoot length, root length, dry weight and nodule number. Similarly, in semi-spreading groundnut (VRI 7) co-inoculation of Rhizobium mayense S19 with Kosakonia oryzae ESB1 recorded maximum shoot length, root length, dry weight and nodule number. R and PE in nodules are visualized in SEM micrograph and changes in mot exudates composition as a result of endophytic bacteria inoculation was assessed through GC-MS. This study showed that the nodule endophytic bacterial diversity of groundnut is vast and co-inoculation of native R and nodule PE significantly improved the plant growth than that of Rhizobium alone.

Automated summary

This study revealed the vast diversity of nodule endophytic bacteria in groundnut, and co-inoculation of native Rhizobium and nodule endophytes significantly improved plant growth.