Control of fire blight (Erwinia amylovora) by a novel strain 49M of Pseudomonas graminis from the phyllosphere of apple (Malus spp.)

A bacterial isolate called 49M, showing protective activity against fire blight caused by the bacterium Erwinia amylovora, was selected from a large collection of isolates obtained from the apple phyllosphere and was identified as Pseudomonas graminis, based on its phenotype and sequence analysis of the 16S rRNA and rpoD genes. The efficacy of strain 49M under laboratory and greenhouse conditions to protect apple blossoms and apple terminal shoots was equal or even higher than that of the reference strains A506 of Pseudomonas fluorescens and C9-1 of Pantoea vagans, as well as the bioproducts BlightBan A506, Blossom Protect and Hortocyna 18 SP (streptomycin), used for comparison. However, its activity on pear fruitlets was slightly less effective, but significantly better (over 10 %) than that of BlightBan A506. When strain 49M was introduced onto apple blossoms in orchards, it effectively colonised them during the entire bloom period, in different weather conditions, including rain. The strain showed no pathogenicity towards plant tissue (pear fruitlets, apple blossoms, tobacco leaves) and is therefore, a potential candidate for the development of a new biopesticide against fire blight.