Fusaricidin Produced by Paenibacillus polymyxa WLY78 Induces Systemic Resistance against Fusarium Wilt of Cucumber

Cucumber is an important vegetable crop in China. Fusarium wilt is a soil-borne disease that can significantly reduce cucumber yields. <i>Paenibacillus polymyxa</i> WLY78 can strongly inhibit <i>Fusarium oxysporum</i> f. sp. <i>Cucumerium</i>, which causes Fusarium wilt disease. In this study, we screened the genome of WLY78 and found eight potential antibiotic biosynthesis gene clusters. Mutation analysis showed that among the eight clusters, the fusaricidin synthesis (<i>fus</i>) gene cluster is involved in inhibiting the <i>Fusarium</i> genus, <i>Verticillium albo-atrum</i>, <i>Monilia persoon</i>, <i>Alternaria mali</i>, <i>Botrytis cinereal</i>, and <i>Aspergillus niger</i>. Further mutation analysis revealed that with the exception of <i>fusTE</i>, the seven genes <i>fusG</i>, <i>fusF</i>, <i>fusE</i>, <i>fusD</i>, <i>fusC</i>, <i>fusB</i>, and <i>fusA</i> within the <i>fus</i> cluster were all involved in inhibiting fungi. This is the first time that demonstrated that <i>fusTE</i> was not essential. We first report the inhibitory mode of fusaricidin to inhibit spore germination and disrupt hyphal membranes. A biocontrol assay demonstrated that fusaricidin played a major role in controlling Fusarium wilt disease. Additionally, qRT-PCR demonstrated that fusaricidin could induce systemic resistance via salicylic acid (SA) signal against Fusarium wilt of cucumber. WLY78 is the first reported strain to both produce fusaricidin and fix nitrogen. Therefore, our results demonstrate that WLY78 will have great potential as a biocontrol agent in agriculture.