Isolation of a multi-trait plant growth promoting Brevundimonas sp. and its effect on the growth of Bt-cotton

Arid regions pose a serious problem for crop production by suppressing plant growth. The use of plant growth promoting rhizobacteria (PGPR) as bioinoculant may be promising to enhance the crop yield in arid conditions. In the present investigation, four strains of cultivable bacteria associated with the rhizosphere of Saccharum L. grown in arid region were isolated using N-free media. Assessment of their nitrogen-fixing ability through amplification of nifH gene showed the presence of nifH gene (390 bp) in only one (MDB4) of the four isolates. The nitrogen-fixing potential of this isolate was confirmed by the presence of nitrogenase activity determined using acetylene reduction assay. The diazotrophic MDB4 isolate also exhibited other PGPR traits, such as the production of indole-3-acetic acid (IAA) and ammonia. In pot experiments, inoculation of Bt-cotton seeds with MDB4 enhanced the growth of plants as shown by significant increase in plant height (68.41 %), shoot dry weight (58.44 %) and root dry weight (64.81 %) over untreated control. The MDB4 strain was Gram negative and identified as Brevundimonas sp. on the basis of phenotypic, biochemical, phylogenetic and 16S rRNA gene sequencing data. It is concluded that the MDB4 bacterial strain having different plant growth promoting activities can be considered as a beneficial microbe for sustainable agriculture in arid regions.