Potential Biological Control of Endophytic <i>Streptomyces</i> sp. 5-4 Against Fusarium Wilt of Banana Caused by <i>Fusarium oxysporum</i> f. sp. <i>cubense</i> Tropical Race 4

Abstract

Fusarium wilt of banana caused by <i>Fusarium oxysporum</i> f. sp. <i>cubense</i> tropical race 4 (Foc TR4) is one of the most disastrous fungal diseases. Biological control is a promising strategy for controlling Fusarium wilt of banana. To explore endophytic actinomycetes as biocontrol resources against Foc TR4, antagonistic strains were isolated from different tissues of medicinal plants. Here, a total of 144 actinomycetes were isolated and belonged to <i>Nonomuraea</i>, <i>Kitasatospora</i>, and <i>Streptomyces</i>. Forty-three isolates exhibited antifungal activities against Foc TR4. The strain labeled with 5-4 isolated from roots of <i>Piper austrosinense</i> had a broad-spectrum antifungal activity by the production of chitinase and β-1,3-glucanase and was identified as <i>Streptomyces hygroscopicus</i> subsp. <i>hygroscopicus</i> 5-4. Furthermore, disease index of banana wilt was significantly reduced by application of strain 5-4 in comparison with application of Foc TR4 alone. Exogenous application of strain 5-4 increased the expression levels of defense genes such as (<i>PAL</i>), peroxidase (<i>POD</i>), pathogenesis-related protein 1 (<i>PR-1</i>), hydrolytic enzymes (<i>β-1,3-glucanase</i>), lysin motif receptor kinase 1 (<i>LYK-1</i>), and mitogen-activated protein kinase 1 (<i>MPK-1</i>). The antifungal mechanism assay demonstrated that extracts of strain 5-4 inhibited spore gemination and hyphal growth of Foc TR4, and caused abnormally swollen, deformity, and rupture of Foc TR4 hypha. Thus, <i>S. hygroscopicus</i> subsp. <i>hygroscopicus</i> 5-4 could be used as a potential biological agent for controlling Fusarium wilt of banana.