EPIPHYTIC ERWINIAS TO CONTROL FIRE BLIGHT

Abstract

Several epiphytic bacteria isolated from healthy apple and pear flowers were characterized by their phenotypic properties and by DNA sequence comparisons. Selected epiphytes from Australia and South Africa induced hypersensitive response (HR) on tobacco leaves and produced the exopolysaccharide levan. Sequence comparison of 16S rRNA and the housekeeping genes recA and gapDH showed a close relationship of these epiphytes to Erwinia amylovora and to other plant pathogenic bacteria of the genus Erwinia, however, the epiphytes form a separate group and are not pathogenic to apple and pear. Another close relative of E. amylovora, the epiphyte Erwinia billingiae did not produce levan and HR on tobacco, but it synthesized an acyl-homoserine lactone (AHL). The epiphytic strains from Australia and South Africa were antagonists against E. amylovora in assays on immature pear slices and on apple flowers. E. billingiae also showed significantly antagonism against E. amylovora. Using Real-Time PCR and plating samples on selective agar, we demonstrated that the epiphytic isolates provided effective growth suppression of the pathogen when apple flowers were co-inoculated with a high concentration of the epiphytes and low concentrations of E. amylovora. These epiphytes could possibly be used for biological control of fire blight.