Screening of Antifungal Bacteria by a Dual Culture Bioassay

The antagonistic activity of bacterial strains isolated from rhizospheres against F. graminearum was evaluated by a dual culture bioassay (Lam et al., 2000). A mycelial plug (5 mm diameter) of F. graminearum was placed at the center of the PDA plate and the bacterial strains were inoculated at four cardinal points 25 mm from the center of the plate. As control, only F. graminearum was inoculated. After 4 days of incubation at 25°C, the inhibition zone was measured. Inhibition was graded by relating the inhibited growth area per inoculation streak to the total area of the Petri dish. The following scale was used: -, no visible inhibition; ^∗, no fungal growth on 0.1–3% of plate area/bacterial streak; ^∗∗, no fungal growth on 3–8% of plate area/bacterial streak; ^∗∗∗, no fungal growth on >8% of the plate area/bacterial streak. All data were obtained from three replicates.