Streptomyces hygroscopicus subsp. hygroscopicus 5-4: A Potential Biocontrol Agent for Fusarium Wilt of Banana

Fusarium wilt of banana caused by 'Fusarium oxysporum f. sp. cubense 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 'Nonomuraea', 'Kitasatospora', and 'Streptomyces'. Forty-three isolates exhibited antifungal activities against Foc TR4. The strain labeled with 5-4 isolated from roots of 'Piper austrosinense' had a broad-spectrum antifungal activity by the production of chitinase and β-1,3-glucanase and was identified as 'Streptomyces hygroscopicus subsp. hygroscopicus 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 (PAL), peroxidase (POD), pathogenesis-related protein 1 (PR-1), hydrolytic enzymes (β-1,3-glucanase), lysin motif receptor kinase 1 (LYK-1), and mitogen-activated protein kinase 1 (MPK-1). 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, 'S. hygroscopicus subsp. hygroscopicus 5-4' could be used as a potential biological agent for controlling Fusarium wilt of banana.