USING REAL-TIME PCR TO STUDY COMPETITION BETWEEN ERWINIA AMYLOVORA AND ERWINIA PYRIFOLIAE

Erwinia pyrifoliae, the causative agent of Asian pear blight, produces symptoms similar to fire blight caused by Erwinia amylovora in apples and pears. The two pathogens appear closely related in certain biochemical and microbiological tests and host range. However, molecular characterizations such as DNA-DNA hybridization and phylogenetic studies of the ITS or groE genes have distinguished E. pyrifoliae from E. amylovora species. Data are unavailable on the current distribution of E. pyrifoliae or on the interaction between the two species when they are present on the same host. In this study, direct real-time PCR methods that were previously developed for multiplex detection of E. amylovora, Pantoea agglomerans and Erwinia spp. bacteriophages, were used to monitor the population dynamics of E. amylovora and E. pyrifoliae on the surface of Bartlett pear blossoms. In the duplex detection system, two sets of primers and Taqman probes, one specific to each pathogen, were mixed directly with washings from inoculated blossom surfaces. A DNA extraction step was not required for this procedure. Disease appearance and severity did not differ significantly in the blossoms inoculated with individual Erwinia species or with a mixture of the two species. The population of E. amylovora was higher than that of E. pyrifoliae in both single species inoculations and in mixtures. These data suggest that E. amylovora may have greater competitive fitness on Bartlett pear blossoms than E. pyrifoliae.