Molecular Detection and Differentiation of Erwinia pyrifoliae and Host Range Analysis of the Asian Pear Pathogen

Abstract

The recently described pathogen Erwinia pyrifoliae, isolated from Nashi pear fruit trees in Korea, resembles the fire blight pathogen Erwinia amylovora in some of its properties. The two pathogens were classified into different species by DNA hybridization kinetics and microbiological criteria. From the nucleotide sequences of the 16S rRNA and the internal transcribed spacer (ITS) region as well as extracellular polysaccharide (EPS)-encoding genes, polymerase chain reaction (PCR) primers were designed that specifically detect E. pyrifoliae but not the fire blight pathogen Erwinia amylovora, and these primers were also applied to identify E. pyrifoliae in necrotic plant material. The genomes of several strains were digested with the restriction enzyme SpeI, and the DNA fragments were analyzed by pulsed-field gel electrophoresis (PFGE). Three groups of patterns could be distinguished for the isolated E. pyrifoliae strains, all different from various E. amylovora strains, which produce a relatively homogeneous PFGE pattern after SpeI digests. Typical fire blight host plants were assayed in a growth chamber or an experimental field for their susceptibility to E. pyrifoliae. A strong preference was found for pear varieties, whereas apple, cotoneaster, hawthorn, or raspberry rarely produced necrotic symptoms. E. pyrifoliae was readily detected in samples from pear orchards in South Korea during 1995 to 1998; however, the Asian pear pathogen was not recovered in necrotic plant tissue from 1999 and 2000.