Antagonistic activity of secondary metabolites from rhizofunctional bacteria extracts against <i>Fusarium</i>species

Abstract

Background: Fusarium species remain important fugal pathogens that produce several mycotoxins with adverse effects on both plant and animals. This work aimed to identify biocontrol agent from rhizofunctional bacteria and assess its antagonistic activity against Fusarium sp. using dual culture technique.
 Methodology: Briefly a circular disc of the Fusarium sp. was inoculated at the center of Potato Dextrose Agar (PDA) plate and incubated for three days. The bacterial isolates were then inoculated about 2cm from the Fusarium hyphal tips and incubated for three days, and zone of inhibition was examined. Isolates that showed antagonistic activities against the fungi were subculture in nutrient broth for three days and the metabolites were extracted using ethyl acetate. The metabolic extracts were tested against the fungi using the agar disc diffusion method.
 Results: Of the 20 rhizofunctional bacterial isolates screened for antagonistic activities against Fusarium sp., 5 showed active antagonism against the fungi with observed clear zone of inhibition in the dual culture, and microscopic examination of the fungal hyphae showed excessive and diffused hyphal branching with hyphal swelling. Ethyl acetate extracts from nutrient broth cultures did not show any zone of inhibition in dual culture against the Fusarium sp. All the 5 bacterial isolates were Gram positive strains but only 2 isolates (2a and 3K) were lipase positive, which may indicate that the mechanisms of antagonism could be due to the production of enzymes that have the ability to hydrolyze the cell wall and membrane lipids of the fungi.
 Conclusion: The rhizoplane and rhizosphere of plants could be great sources of biocontrol agents and that bacterial isolates 2a and 3K have the potential to be used as antifungal agents against Fusarium sp. Molecular identification of 2a and 3K bacterial isolates to the species level is recommended.