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Banana Fusariumwilt caused by Fusarium oxysporumf. sp. cubense(Foc) is the most destructive soil-borne fungal disease. Tropical race 4 (FocTR4), one of the strains of Foc, can infect many commercial cultivars, which represents a threat to global banana production. Currently, there are hardly any effective chemical fungicides to control the disease. To search for natural product-based fungicides for controlling banana Fusariumwilt, we identified a novel strain Streptomyces yongxingensissp. nov. (JCM 34965) from a marine soft coral, from which a bioactive compound, niphimycin C, was isolated using an activity-guided method. Niphimycin C exhibited a strong antifungal activity against FocTR4 with a value of 1.20 μg/mL for EC50and obviously inhibited the mycelial growth and spore germination of FocTR4. It caused the functional loss of mitochondria and the disorder of metabolism of FocTR4 cells. Further study showed that niphimycin C reduced key enzyme activities of the tricarboxylic acid (TCA) cycle and the electron transport chain (ETC). It displayed broad-spectrum antifungal activities against the selected 12 phytopathogenic fungi. In pot experiments, niphimycin C reduced the disease indexes in banana plantlets and inhibited the infection of FocTR4 in roots. Hence, niphimycin C could be a promising agrochemical fungicide for the management of fungal diseases.

Banana Fusariumwilt caused by Fusarium oxysporumf. sp. cubense(FocTR4) is the most destructive soil-borne fungal disease. Until now, there has been a lack of effective measures to control the disease. It is urgent to explore biocontrol agents to control FocTR4 and the secretion of mycotoxin. In this study, fluvirucin B6 was screened from Streptomyces solisilvaeusing an activity-guided method. Fluvirucin B6 exhibited strong antifungal activity against FocTR4 (0.084 mM of EC50value) and significantly inhibited mycelial growth and spore germination. Further studies demonstrated that fluvirucin B6 could cause the functional loss of mitochondria, the disorder of metabolism of FocTR4 cells, and the decrease of enzyme activities in the tricarboxylic acid cycle and electron transport chain, ultimately inhibiting mycotoxin metabolism. In a pot experiment, the application of fluvirucin B6 significantly decreased the incidence of banana Fusariumwilt and the amount of FocTR4 and controlled fungal toxins in the soil. Additionally, fluvirucin B6 could positively regulate the changes in the structure of the banana rhizosphere microbial community, significantly enriching beneficial microbes associated with disease resistance. In summary, this study identifies fluvirucin B6, which plays versatile roles in managing fungal diseases and mycotoxins.