Inhibition of the Growth of Ascosphaera Apis by Bacillus and Paenibacillus Strains Isolated from Honey

The fungus Ascosphaera apis, the causative agent of chalkbrood disease in honeybee larvae, occurs throughout the world and is found in many beekeeping areas of Argentina. The potential as biocontrol agents of 249 aerobic spore-forming bacterial antagonists isolated from honey samples was evaluated. Each isolate was screened against A. apis by a central disk test assay. Ten bacterial strains that showed the best antagonistic effect to A. apis were selected for further study and identified as Bacillus cereus (m363, mv86, mv81, mv75), Bacillus circulans (Fr231, m448b), Bacillus megaterium (m435), Bacillus pumilus (m354), Bacillus subtilis (m329), and Paenibacillus alvei (m321). For testing the efficiency of the selected strains, a paired culture test was used with 5 replicates of each combination bacterial antagonist/A. apis strain, and 5 replications for each control on 4 different culture media. The analysis of variance and posterior comparison of means according to LSD method showed that the best antagonists when using YGPSA medium were B. subtilis (m329) and B. megaterium (m435), and in the case of MYPGP medium the most efficient were B. circulans strains Fr 231 and m448b.