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.