Exploring biocontrol and growth-promoting potential of multifaceted PGPR isolated from natural suppressive soil against the causal agent of chickpea wilt

Chickpea is an important nutritive food crop both for humans and animals. Chickpea wilt caused by Fusarium oxysporum f.sp. ciceris (Foc) results in huge yield losses every year. Chickpea being a food crop requires the development of an eco-friendly bio-pesticide to effectively control the chickpea wilt disease. In this study, more than 50 bacterial stains isolated from the rhizosphere of healthy plants growing in wilt sick soil were examined for their Foc antagonist activities. Out of these, 17 strains showing > 90% growth inhibition of Foc were then characterized for their plant growth-promoting (PGP) and biocontrol traits. The biocontrol and PGP traits identified include amylase, hydrogen cyanide, protease, cellulase, chitinase activities, p-solubilization, nitrogen-fixing, and indole-3-acetic acid production. Two bacterial strains, IR-27 and IR-57, exhibiting the highest Foc proliferation inhibition and the PGP potential along with a consortium of four different strains (Serratia sp. IN-1, Serratia sp. IS-1, Enterobacter sp. IN-2, Enterobacter sp. IN-6) were used for controlling the chickpea wilt disease and growth promotion of the chickpea plants. Confocal laser scanning microscopy revealed their root colonization ability with partial or complete elimination of broken Foc mycelia and hyphae from roots. The bacterial inoculations particularly the consortium significantly suppressed the disease and improved the overall root morphology traits (root length, root surface area, root volume, forks, tips, and crossings), resulting in enhanced growth of the chickpea plants. Significant changes in growth (107% increase in root length, 23% increase in shoot length, and 54% increase in branches) in Foc-challenged plants were observed when inoculated with the consortium. Further investigations revealed that the chickpea plants inoculated with bacterial strains induced the expression of a number of key defence enzymes, including the phenylalanine ammonia lyase, peroxidase, polyphenol peroxidase, β-1,3 glucanase, which might have helped the plants to thwart the pathogen attack. These findings indicate the potential of our identified bacterial strains to be used as a natural biopesticide for controlling the chickpea wilt disease.