Abstract
Fusarium oxysporum is the causal agent for wilt diseases of many major ornamental and horticultural crops. In this study, we plated a local cut flower grower’s soil, with a persistent history of Fusarium wilt of scented stock, Matthiola incana but not the lettuce rotational crop. This yielded culture plates with characteristic pink to carmine red fungi, together with a mixed bacterial population, a percentage of which was visibly antagonistic to the Fusarium. Using molecular analyses via Polymerase Chain Reaction (PCR) assays, we identified that Fusarium oxysporum, Fusarium culmorum, Fusarium equiseti and Fusarium venenatum were prevalent in the soil. The co-habiting bacterial colonies that exhibited strong antagonistic activity (zone of clearance) towards the soil fungi corresponded to Bacillus subtilis, Bacillus amyloliquefaciens and Paenibacillus polymyxa species. Our results arising from an in vitro study involving Kirby-Bauer disc-diffusion agar assays, coupled with bio-imaging software techniques demonstrated that the three native soil bacteria were effective inhibitors of all Fusarium species tested, while Bacillus subtilis exhibited the highest antagonism towards the Fusarium oxysporum. Bioassay tests of micro-biocides Prestop (Gliocadium catenulatum), Serenade Max (Bacillus subtilis QST713) and commercial seaweed extract, AlgiVyt suppressed in vitro growth of Fusarium oxysporum infecting the scented stock flower to a greater extent, whilst fresh aqueous extracts of garlic (Allium sativum) and meadowsweet (Filipendula ulmaria) flowers were ineffective towards soil pathogen suppression. This scoping study offers cut flower growers additional options of tapping into populations of antagonistic bacteria found in soil persistently infected with the opportunistic soil phytopathogen Fusarium oxysporum, affecting cut flower crops, such as M. incana.
Highlights
Commercial floriculture worldwide is characterized by high investment and stringent quality demands which often imply high pesticide usage
The bacteria were carefully isolated, purified on several rounds of plating and individual pure colonies were identified using molecular analyses involving Polymerase Chain Reaction (PCR) of the DNA and gene sequencing followed by bioinformatic query (Blastn) for its taxonomic tree similarity and identity of the bacterial genomes held in the databases (GenBank)
The results indicated that there were three specific bacteria viz., Bacillus subtilis, Bacillus amyloliquefaciens and Paenibacillus polymyxa exhibiting antagonism in the same PDA plate carrying presumptive Fusarium spp
Summary
Commercial floriculture worldwide is characterized by high investment and stringent quality demands which often imply high pesticide usage. Chemical fungicides are increasingly proving either inadequate or ineffective to cope with the severity of Fusarium wilt disease losses frequently encountered by many flower growers. This hiatus has led the greenhouse industry and the allied researchers to seek sustainable biological alternatives [4] such as microbial and (medicinal) plant resources as either soil drenches or root dips amongst other conservative crop rotational strategies against Fusarium wilt of ornamental crops. Options involving manipulation of specific antagonists/antibiotics isolated from Fusarium suppressive soils for disease management are a widely practised classical methodology for soil-borne fungal infection containment. Together with the natural biota, commercial microbiocides and aqueous extracts of garlic and meadowsweet flowers were evaluated for their efficacy against soil-borne Fusarium species, isolated from the same soil
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