Forest tree associated bacteria for potential biological control of Fusarium solani and of Fusarium kuroshium, causal agent of Fusarium dieback

Although the use of crop-associated bacteria as biological control agents of fungal diseases has gained increasing interest, the biotechnological potential of forest tree-associated microbes and their natural products has scarcely been investigated. The objective of this study was to identify bacteria or bacterial products with antagonistic activity against Fusarium solani and Fusarium kuroshium, causal agent of Fusarium dieback, by screening the rhizosphere and phyllosphere of three Lauraceae species. From 195 bacterial isolates, we identified 32 isolates that significantly reduced the growth of F. solani in vitro, which mostly belonged to bacterial taxa Bacillus, Pseudomonas and Actinobacteria. The antifungal activity of their volatile organic compounds (VOCs) was also evaluated. Bacterial strain Bacillus sp. CCeRi1-002, recovered from the rhizosphere of Aiouea effusa, showed the highest percentage of direct inhibition (62.5 %) of F. solani and produced diffusible compounds that significantly reduced its mycelial growth. HPLC-MS analyses on this strain allowed to tentatively identify bioactive compounds from three lipopeptide groups (iturin, surfactin and fengycin). Bacillus sp. CCeRi1-002 and another strain identified as Pseudomonas sp. significantly inhibited F. solani mycelial growth through the emission of VOCs. Chemical analysis of their volatile profiles indicated the likely presence of 2-nonanone, 2-undecanone, disulfide dimethyl and 1-butanol 3-methyl-, which had been previously reported with antifungal activity. In antagonism assays against F. kuroshium, Bacillus sp. CCeRi1-002 and its diffusible compounds exhibited significant antifungal activity and induced hyphal deformations. Our findings highlight the importance of considering bacteria associated with forest species and the need to include bacterial products in the search for potential antagonists of Fusarium dieback.