Biological control of pests and pathogens is one of the top priorities in plant protection. In particular, soil-borne pathogens, including wilting diseases, are notorious pathogens to control. Previously we noticed the lack of filamentous fungal growth on the rhizospheric samples that were collected from high-yield saffron crocus fields. We hypothesized that suppressive-soil microbiota are involved in this interesting phenomenon. Therefore, we isolated the rhizobacteria from the soil samples and tested their antifungal activities both in in vitro and in in vivo assays. From 10 rhizobacteria, two showed antifungal activity against Fusarium equiseti, Fusarium foetens, and Exserohilum mcginnisii, three fungal pathogens that cause wilting diseases in plants. In particular, Bacillus pumilus showed strong antifungal activity. Furthermore, this species significantly increased the biomass and height of sesame seedlings by 28% and 18%, respectively. Seeking for the antifungal mechanisms, we tested the antifungal properties of the extracellular substances and volatile organic compounds (VOCs) of B. pumilus. Results showed that VOCs, but not extracellular substances, are the main antifungal compounds of B. pumilus. The second bacteria, Metabacillus galliciensis, showed moderate antifungal activity, which is not reported before. Our results suggest B. pumilus as a biological agent to control wilting diseases, and also as a growth promoting bacteria.

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