Identification of an Erwinia sp different from Erwinia amylovora and responsible for necrosis on pear blossoms

Necrotic pear blossoms (NPB) were found in several pear orchards of 'Ercolini' ('Coscia') and 'Tendral' in Turfs, Valencia (Spain), in April 1999, during a routine survey, in an area free of Erwinia amylovora. The symptoms resembled those of fire blight [E. amylovora] but affected only blossoms and did not progress to other parts of the tree. Erwinia-like colonies were isolated from the necrotic blossoms that year and the following 2 years, and the morphology of the colonies on CCT medium of Ishimaru and Klos, King's B medium, and sucrose nutrient agar was similar to that of Erwinia amylovora. The isolates were identified as an Erwinia sp. by their microbiological characteristics and showed API 20E, API 20NE, API ZYM, API 50CH patterns and fatty acid profiles similar, but not identical, to those of E. amylovora and Erwinia pyrifoliae. The isolates reacted as E. amylovora in immunofluorescence with several antisera and one monoclonal antibody (MAb) employed for E. amylovora detection, but did not react in the enzyme-linked immunosorbent assay against specific E. amylovora monoclonal antibodies. Polymerase chain reaction with primers from 23S rDNA sequences of E. amylovora were positive, but no signal was obtained with primers from plasmid pEa29 or from chromosomal DNA sequences of E. amylovora. The isolates were able to elicit the hypersensitive reaction on tobacco and tomato leaves and to induce necrosis in pear flowers, but were unable to develop typical fire blight symptoms in other organs of pear trees, and on various host plants of E. amylovora. The isolated Erwinia sp. strains are pathogenic and different from E. amylovora and other described bacterial species affecting pear trees.