Inhibition of cucumber Pythium damping-off pathogen with zoosporicidal biosurfactants produced by Bacillus mycoides

Pythium species causes seedling damping-off on numerous plants, resulting in severe economic losses to growers worldwide. The present study is to evaluate the control of cucumber damping-off by biosurfactants produced by Bacillus mycoides. Experiment has demonstrated the ability to produce biosurfactants by B. mycoides, as well as the potential use as a biocontrol agent for controlling cucumber seedling damping-off caused by Pythium aphanidermatum. A B. mycoides strain isolated from rice rhizosphere was capable of producing biosurfactants, one of which was identified as a novel compound closely resemble surfactin A based on HPLC coupling with electrospray ionization-mass spectrometer analysis. The presence of yeast extract suppressed the accumulation of biosurfactants, whereas peptone or glucose increased the accumulation of biosurfactants. The addition of plant oils into medium greatly reduced surface tension, but increased the production of biosurfactants. Co-application of B. mycoides culture with P. aphanidermatum suppressed the release and caused lysis of Pythium zoospores. Application of B. mycoides culture completely suppressed the formation of water-soaked lesions on cucumber leaves and reduced Pythium damping-off by 35% in greenhouse. This study provides valuable information in determining the importance and practicability of utilizing B. mycoides as a biocontrol means in controlling plant diseases.