Antifungal activity of marine-derived Paenibacillus sp. PNM200 against Fusarium oxysporum f. sp. lycopersici, the causal agent of tomato vascular wilt

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Marine-derived bacteria are known for producing a wide range of specialized metabolites with antifungal activity against phytopathogens. Assessing the marine bacteria's ability to establish themselves in the rhizosphere and inhibit soil-borne phytopathogens under in vivo conditions could provide evidence that supports their use for biological control, widening biological control agent’s isolation sources. The current study evaluated the antifungal activity of a marine-derived bacterial collection against the tomato phytopathogen Fusarium oxysporum f. sp. lycopersici (FOL). Out of 152 isolates, 28 Firmicutes strains showed antifungal activity against ten isolates of F. oxysporum in in vitro testing. From them, Paenibacillus sp. PNM200 was identified as a potential PGPR and as a biocontrol agent against Fusarium vascular wilt. PNM200 colonized the tomato plant root system, increased plant growth, and reduced vascular wilt severity on greenhouse assays. Interestingly, plants treated with the spent supernatants of PNM200 cultures did not show a decrease in vascular wilt severity. This result indicates that the ability of PNM200 to act as a biocontrol agent against FOL does not depend on the diffusible antifungal metabolites produced during the fermentation process. Other Paenibacillus sp. PNM200 traits like chemotactic response towards tomato root exudates, biofilm, IAA, enzyme activity, and phosphate solubilization may contribute to PNM200 rhizospheric competence and biological control ability. Overall, the obtained results suggest that marine-derived bacteria could be a new source of biological control agents for integrated pest management of soil-borne diseases like Fusarium vascular wilt.