Molecular characterization of Algerian Erwinia amylovora strains by VNTR analysis and biocontrol efficacy of Bacillus spp. and Pseudomonas brassicacearum antagonists

Samples of pear shoots, blossoms and leaves showing typical fire blight symptoms were collected from diseased pear trees during spring and summer over a period of 3 years from orchards situated in the Mitidja region, a main pear producing area in Northern Algeria. From all collected plant samples, thirty-seven putative Erwinia amylovora strains were isolated and identified by biochemical, serological and molecular tests. Molecular typing of these strains was performed using six variable number of tandem repeats sequences (VNTRs). Minimal spanning trees showed that four different haplotypes were present within the bacterial population analyzed. The efficacy of twenty potential bacterial antagonists was evaluated in vitro against two E. amylovora pathogenic strains. Four antagonists ( Bacillus amyloliquefaciens, Bacillus methylotrophicus and two Pseudomonas brassicaceaurum ) were selected to perform a biocontrol assay on immature pear fruits. Results showed that the two Pseudomonas strains were the most effective for preventive treatment on pear fruits, leading to a necrosis reduction of up to 90%. No curative effect was observed. The four selected antagonists were characterized for features linked to biocontrol activity, such as biofilm, siderophores and biosurfactant-production, motility, and effect of environmental conditions on bacterial growth.