Systemic resistance to strawberry anthracnose induced by <i>Paenibacillus polymyxa</i> TP3 requires the fusaricidin synthetase gene fusA

Anthracnose, caused by Colletotrichum spp., is an important fungal disease prevalent in strawberry nurseries and fruit production. Paenibacillus polymyxa, a plant growth-promoting rhizobacterium, effectively inhibits various fungal pathogens and their associated diseases. In this study, a fusaricidin synthetase gene (fusA)-disrupted mutant generated from a strawberry strain TP3 of Paenibacillus polymyxa was used to demonstrate the requirement of fusA for disease suppression directed by this beneficial bacterium. In contrast to the wild-type strain TP3, this fusA-disrupted mutant was unable to produce fusaricidins, but increased biofilm biomass; however, it reduced the inhibition of fungal growth and decreased the suppression of anthracnose symptom development in strawberry. Nevertheless, this fusA-disrupted mutant showed enhanced colonization on strawberry leaves and roots compared to the wild-type strain TP3 did. A callose deposition assay indicated that P. polymyxa TP3-directed strawberry anthracnose suppression by root-drenching required fusaricidins to enhance plant immunity. This research validates the role of fusaricidins in P. polymyxa TP3-directed induction of disease resistance and facilitates the application of P. polymyxa as a health enhancer for sustainable crop production, especially for strawberries.