Screening of antagonistic bacteria against the blue mold of citrus fruit from soil by a new parallel screening method without prior isolation of single strains

• 1. Antagonistic bacteria were screened from soil without prior single colony isolation. • 2. Three antagonistic strains inhibited the blue mold of citrus fruit in vivo . • 3. The novel method is time-saving and effective. • 4. The disease incidence of blue mold was the lowest in citrus treated with Bacillus sp. Antagonistic bacteria are effective in controlling fruit and vegetable diseases. However, screening for antagonistic bacteria is time-consuming. To simplify the procedure for screening antagonistic bacteria, we developed an ameliorated method for screening antagonistic bacteria against Penicillium italicum from the soil that requires no prior isolation of single colonies. The soil supernatant was directly spread on the P. italicum plate, then the antagonistic bacterial strains were isolated from the inhibition zones on the plate and further validated by dual culture assay. By using the novel method, three antagonistic bacterial strains were isolated from soil, which showed significant antagonistic effects on P. italicum . The results of 16S rDNA sequence analysis showed that the three antagonistic strains were classified as Paenibacillus sp., Bacillus sp., and Pseudomonas sp., respectively. Compared to the control, treatments with the three antagonistic trains decreased the disease incidence of blue mold by 32.5%, 68.7%, and 42.2%, respectively. These results indicate that the ameliorated method is time-saving and effective for the screening of antagonistic bacteria.