Suppressive effect of secondary metabolites from Streptomyces plumbeus isolate F31D against Fusarium oxysporum f. sp. lycopersici, the causal agent of Fusarium wilt of tomato

Fusarium wilt of tomato, a disease caused by the soilborne fungus Fusarium oxysporum f. sp. lycopersici, causes major losses to tomato production. Chemical fungicides and resistant cultivars are the main control strategies, but new races of the pathogen appear to be able to overcome resistance genes in currently grown cultivars. Therefore, there is a need to identify natural antifungal compounds and develop new agents to control F. oxysporum f. sp. lycopersici. The culture filtrate (F31D-CF) from isolate F31D, a bacterial isolate collected from paddy field soil in Shimane Prefecture in 2019, significantly inhibited in vitro conidial germination of F. oxysporum f. sp. lycopersici, indicating a fungicidal effect against this pathogen. The amount of the inhibitory compound in F31D-CF increased from 1 to 3 days of incubation. F31D-CF significantly suppressed disease development in tomato plants. Sequence analysis of the 16S rDNA region of the isolate revealed 99% similarity with the type strain of Streptomyces plumbeus. Thin layer chromatography-bioautography of F31D-CF showed that the compound inhibiting F. oxysporum f. sp. lycopersici growth had an Rf of 0.57. The effective compound in F31D-CF has a molecular weight of > 3000 and is heat stable below 100 degrees C. Our results suggest that secondary metabolites of isolate F31D have potential for developing a new fungicidal agent against F. oxysporum f. sp. lycopersici.