Phytobeneficial Properties of Bacteria Isolated from the Rhizosphere of Maize in Southwestern Nigerian Soils

Abstract

Biocontrol agents isolated outside Africa have performed inconsistently under field conditions in Africa. The development of indigenous phytobeneficial microbial strains that suit local environments may help enhance competitiveness with in situ microorganisms and effectiveness at suppressing local pathogen strains. We isolated bacteria from the rhizosphere of maize growing in southwestern Nigeria and assessed them for growth-promoting characteristics. The best isolates were characterized using 16S rRNA genes and were further evaluated in the greenhouse on maize seedlings. Four isolates (EBS8, IGBR11, EPR2, and ADS14) were outstanding in in vitro assays of antagonistic activity against a local strain of Fusarium verticillioides, phosphate solubilization efficiency, chitinase enzyme activity, and indole-3-acetic acid production. Inoculation of maize seeds with these isolates resulted in ≥95% maize seed germination and significantly enhanced radicle and plumule length. In the greenhouse, maize seedling height, stem girth, number of leaves, leaf area, shoot mass (dry matter), and nutrient contents were significantly enhanced. The bioprotectant and phytobeneficial effects were strongest and most consistent for isolate EBS8, which was identified as a Bacillus strain by 16S rRNA gene analysis. As a bacterial strain that exhibits multiple growth-promoting characteristics and is adapted to local conditions, EBS8 should be considered for the development of indigenous biological fertilizer treatments.

FIG 1

Phylogenetic relationship of EBS8, EPR2, ADS14, and IGBR11, based on 16S rRNA genes and inferred using the neighbor-joining method. Type strains used for comparison are given. Numbers above each node are bootstrap confidence levels (expressed as percentages) generated from 500 bootstrap trees.

FIG 2

Disease expression (expressed as a percentage) of maize seedlings inoculated with different bacterial isolates and planted in unsterilized soil. Mean values for five replicates are shown. Error bars, standard deviations. Different letters above the bars indicate significant differences according to the Student-Newman-Keuls multiple-range test (α = 0.05).