Lactobacillus plantarum protects against Erwinia amylovora infection in plants:
Lactic acid bacteria (LAB) can be a source of biological control agents (BCA) of fire blight disease. Several species of LAB are inhabitants of plants and are currently used as biopreservatives of food because of their antagonistic properties against bacteria, and are considered as generally safe. Candidates to BCA were selected from a large collection of LAB strains obtained from plant environments. Strains were first chosen based on the consistency of the suppressive effect against E. amylovora infections in detached plant organs (flowers, fruits and leaves). Lactobacillus plantarum strains PC40, PM411, TC54 and TC92 were effective against E. amylovora in most of the experiments performed. Besides, strains PM411, TC54 and TC92 had strong antagonistic activity against E. amylovora and also other target bacteria, and presented genes involved in plantaricin biosynthesis (plnJ, plnK, plnL, plnR and plnEF). The strains efficiently colonized pear and apple flowers; they maintained stable populations for at least 1 week under high RH conditions, and survived at low RH conditions. They were effective in preventing fire blight on pear flowers, fruits and leaves, as well as in whole plants and in a semi-field blossom assay. The present study confirms the potential of certain strains of L. plantarum to be used as active ingredient of microbial biopesticides for fire blight control that could be eventually extended to other plant bacterial diseases.