Biological control of plant pathogens: from soil bacteria to bio-pesticide

In recent years, there is increasing awareness regarding the potential detrimental environmental and public health effects of pesticides. Biological control, a potential alternative to chemical pesticides, applies microorganisms to inhibit plant pathogens by either direct antagonism through antimicrobial activity, or ecological exclusion or through stimulation of plant resistance. Although this approach is a safer and more environmentally sustainable method of plant protection, the efficacy of applying these microorganisms is often very low, and therefore, it is generally not a realistic alternative to chemical pesticides.

Within the framework of this project, we are applying an interdisciplinary approach aimed at developing new and effective biocontrol agents that antagonize soil borne fungal pathogens. The novelty of this project is that it integrates state-of-the-art chemical analyses with whole genome sequencing. Specifically, active metabolites from selected biocontrol agents that antagonize soil-borne pathogens are isolated, purified and characterized; and concomitantly, the expression of secondary metabolite-encoding genes are monitored to determine optimal conditions for production of antagonistic metabolites in selected bacteria. Our efforts specifically focus on Rhizoctonia solani (Basidiomycetes), Pythium aphanidermatum (Oomycetes) and Fusarium oxysporum (Ascomycetes). To date, approximately 500 bacteria were isolated from various soil niches. We conducted in-vitro assays against the three pathogens, and selected approximately 100 antagonistic bacteria for in-planta tests. In tandem, we extracted secondary metabolites from 22 bacteria that displayed significant antagonistic activity. Crude extracellular bacterial extracts and specific fractions, separated by polarity, were tested in-vitro for antagonistic effects. We are currently purifying the most active fractions using a sephadex LH-20 column, and will subsequently characterize active purified molecules using NMR. Future work will focus on in-planta experiments using both purified metabolites and combinations of antagonistic bacteria. We hope that this project will inevitably lead to the development of commercial biological products for treatment of soil-borne plant pathogens.