Evaluating the effect of Bacillus and Rhizobium. bi-inoculant on nodulation and nematode control in Phaseolus vulgaris L

Abstract

The study was undertaken to evaluate the effect of inoculating beans (Phaseolus vulgaris L.) with a bio-inoculant containing Bacillus spp. and Rhizobium spp. isolates on root damage by root-knot nematodes, nodulation and their interactions. Twenty Bacillus isolates from a previous experiment were selected based on their ability to reduce root-knot nematode populations and damage on beans. These isolates were screened to determine their compatibility with Rhizobium strains CIAT 899 and USDA 2674 in vitro. Seven Bacillus isolates were found to be compatible with the rhizobia strains. A greenhouse experiment to assess the effect of the dual inoculation of Bacillus and Rhizobium spp. on root damage by root-knot nematodes using sterile Leonard jar assembly revealed significant differences between the various treatment combinations. Damage by root-knot nematodes was generally lower in plants that were inoculated with both Bacillus and Rhizobium inoculation as compared to those that received rhizobia alone. Nodulation was significantly (P ⩽ 0.05) enhanced on bean plants even those that were treated with Bacillus alone. The seven isolates were then screened in a soil experiment in a glasshouse. Two Bacillus isolates caused an increase in nodulation, while the rest suppressed nodulation. Two isolates (K194 and K89) were found to have health promoting effects while the rest had growth promoting effects