Rhizobium radiobacter : A unique maize endophyte with high level of stress tolerance and multiple plant growth promoting properties

Abstract

A unique naturally occurring bacterial endophyte BHU-4 was isolated from surface sterilized roots of the maize (Zea mays L.) plants north eastern part of India that exhibit a number of plant growth promoting properties. This isolate was identified as Rhizobium radiobacter (deposited in NCBI with accession number JN033549) showing 99.7% similarity when the phylogenetic analysis of the nucleotide sequence of 16S rRNA was done. It forms white mucilaginous colonies on yeast extract mannitol plates and the cells were rod shape with gram negative reaction. It grows in wide range of pH (4-10), temperature (4-45°C) and salt concentration (0.1-10%) that provide an opportunity to survive in highly adverse conditions. High level of tolerance to nalidixic acid and ciprofloxacin, the inhibitors of DNA gyrase provides an addition attribute to this strain for survival under extreme temperature stress. Capability of producing high amount of phytohormone IAA (8.04μg ml-1) and solubilising zinc (0.3mm h-1) helps this strain to support the plant growth as plant growth promoting rhizobacteria. It was tested as bioinoculant for its effect on the growth of three cultivars of maize both under laboratory and glass house conditions. Plants grown under laboratory conditions exhibited significant increase in plant height (23.02 to 44.09%) and plant dry weight (15 to 25.73%) of inoculated plants over uninoculated (control) plants. Variability within the cultivars of maize in response to bacterial inoculation of BHU-4 was more visible when the same experiment was conducted in glass house. It was therefore concluded that due to presence of multiple plant growth promoting properties and high level of a number of abiotic stresses tolerance, this strain will be highly useful as bioinoculant sustainable cultivation of maize (Zea mays L.). © 2020 Plant Archives. All rights reserved.