Antagonistic activity and mechanism of a novel Bacillus amyloliquefaciens MB40 strain against fire blight

Fire blight caused by Erwinia amylovora is an important disease affecting most types of rosaceous trees and represents a significant threat to fruit cultivation in many parts of the world. The effectiveness of antagonistic bacteria Bacillus amyloliquefaciens strain MB40 to inhibit the growth of Erwinia amylovora strain 1E IMIV was evaluated under in vitro conditions. B. amyloliquefaciens MB40 was isolated from leaves of fire blight host mature apple trees (cultivar ‘Zarya Alatau’) sampled in the Almaty region of Kazakhstan. Local isolate of the fire blight causative agent E. amylovora was used as pathogen inoculum in laboratory trials. Erwinia amylovora and Bacillus amyloliquefaciens were identified using morphological and biochemical tests, and the pathogenicity of E. amylovora 1E IMIV was demonstrated in a bioassay on immature pear fruits. B. amyloliquefaciens MB40 showed high antagonistic activity against the pathogen. Biological efficiency of the applied culture broth of B. amyloliquefaciens was 90.6% (95% confidence interval [CI] = 74.1 to 107.2). Analysis of active substances produced by the antagonistic bacterium disclosed high amounts of acetoin (3-hydroxybutanone) - 53.7 ± 1.8% and and 2,3-butanedione - 34.4 ± 3.6%. The inhibitory activity of the latter was demonstrated. The possible mechanism of its action is discussed, suggesting that B. amyloliquefaciens MB40 is a novel antibacterial strain with potential application in controlling E. amylovora in fruit growing.