Survival of the fire blight pathogen, Erwinia amylovora, in calyxes of apple fruit discarded in an orchard

Abstract The survival of Erwinia amylovora from calyxes of apples discarded in an orchard over a 20-day period at flowering was determined in two consecutive years. Bacterial numbers decreased significantly in the first 4 days and then persisted at low levels for the following 16 days in both years. Spread of E. amylovora from the inoculated apples was not detected by either culture or PCR in any of the rainwater, apple flowers, leaves or insects tested over the 20-day sampling period. The results of this investigation demonstrate that populations of E. amylovora present in contaminated apple calyxes were not transferred to susceptible hosts, even when the apples were placed in close proximity to hosts that were in a receptive stage at flowering. Therefore, should populations of E. amylovora exist on exported commercial apple fruit, there is no evidence to suggest that these populations would provide inoculum for a new fire blight infection. Consequently, there is a discontinuity in the pathway for the dissemination of E. amylovora from an infested fruit to a susceptible host as the bacterial populations do not multiply and there is no demonstrated spread.