Control of tomato southern blight caused by Athelia rolfsii (syn. Sclerotium rolfsii) using the soil isolate Streptomyces sasae strain GT4041

Damping off of tomato caused by Athelia rolfsii causes serious losses in the Benin Republic despite the use of chemical fungicides. To reduce pesticide dependency and provide better control, we evaluated the activity of soil isolate GT4041 against A. rolfsii in Japan for use in Benin. Isolate GT4041, applied in its PC1 culture broth, strongly inhibited A. rolfsii mycelial growth in dual culture and completely inhibited sclerotial germination. In growth chamber tests, sclerotia were pretreated with GT4041 or GT4041 was preincubated in soil before application or applied directly on sclerotia on the soil; GT4041was always used in its culture broth. Its direct application on the soil reduced disease incidence the most in the growth chamber and in the greenhouse. GT4041 inhibited mycelial growth of five other tomato fungal pathogens and also increased tomato root and shoot dry mass. GT4041 produced proteases and indole acetic and it grew optimally at 28 °C. Scanning electron microscopy of GT4041 showed cylindrical, smooth spores in flexuous chains. This is the first report of S. sasae as a biocontrol agent for tomato damping off caused by A. rolfsii.