Spherical swelling of germ tubes and hyphae of Fusarium oxysporum by the treatment with 5-fluoroindole

In our attempts to develop effective chemical control agents for soil-borne phytopathogenic bacteria of tomato, we found that indole and its related compounds (3-indolepropionic acid and 3-indoleacrylic acid) were capable of inhibiting the multiplication of Pseudomonas solanacearum, the pathogen causing the bacterial wilt of tomato, and have clarified the correlation between chemical structures of these compounds and their antibacterial activities. These compounds were examined for their antifungal spectra against a variety of tomato pathogens, Cladosporium fulvum, Botrytis cinerea, Erysiphe cichoracearum, Fusarium oxysporum f. sp. lycopersici, Rhizoctonia solani, Pythium aphanidermatum, Verticillium albo-atrum and Phytophthora infestans, and were shown to be effective only to E. cichoracearum. Recently, 5-fluoroindole (5-FI) was found to inhibit the growth of some soil-borne pathogens, such as F. oxysporum, R. solani and P. aphanidermatum. In the present study, we report the spherical swelling of germtubes and vegetative hyphae of F. oxysporum f. sp. lycopersici by the treatment with 5-FI and discuss the antifungal activity of this compound.