Biocontrol potential of volatile organic compounds (VOCs) produced by cotton endophytic rhizobacteria against Macrophomina phaseolina

Rhizospheric bacteria are soil bacteria inhabiting the near-root zone, with multifarious activities including the promotion of plant growth, nutrient mobilization, and biological control of pests and diseases. Rhizobacteria produce microbial volatile organic compounds (mVOCs) that can be utilized as biocontrol components against phytopathogenic fungi. Here, we analyzed the mVOCs produced from cotton rhizobacteria and their role in biological control of the fungus Macrophomina phaseolina . Twelve endospore-forming rhizobacterial strains were isolated from the cotton rhizosphere and screened for their biocontrol potential. Three rhizobacterial strains , Bacillus cereus CICR-D3, Bacillus aryabhattai CICR-D5 and Bacillus tequilensis CICR-H3 were evaluated for mVOCs using gas chromatography-mass spectrometry (GC-MS). Major antifungal mVOCs i.e. Benzene, 1, 3-diethyl- and Benzene, 1, 4-diethyl followed by naphthalene, m-ethylacetophenone and ethanone, 1-(4-ethylphenyl) were produced by these strains. The relative abundance of mVOCs released was highest from CICR-D3 followed by CICR-D5 and CICR-H3. Bi-compartmental Petri plate assay against M. phaseolina showed that the CICR-D3 strain was the most effective in inhibiting the mycelial growth (86.70 ± 0.50%), followed by the CICR-D5 (69.27 ± 0.17%) and CICR-H3 (62.84 ± 0.50%) strains. Furthermore, in vivo co-inoculation in a polyhouse revealed that severity of root rot caused by M. phaseolina was reduced by 72.74% in potted cotton plants inoculated with CICR-D3 strain, followed by strains CICR-D5 (69.04%) and CICR-H3 (66.60%). To the best of our knowledge, the specific volatiles are being reported for the first time from native cotton rhizobacterial strains, which provides new insight into cotton rhizobacteria and their antifungal mVOCs as an eco-compatible strategy for cotton root rot management.