Infection frequency of mature apple [Malus pumila] fruit with Erwinia amylovora deposited on pedicels and its survival in the fruit stored at low temperature

The infection frequency of mature apple fruit by Erwinia amylovora and the survival of E. amylovora in the fruit stored at low temperature were investigated. The fruit stems (pedicels) of 460 mature apple fruit were inoculated with 105 or 104cfu of bioluminescent E. amylovora, tagged with lux genes. Nine days after inoculation, 43% and 27% of the fruit inoculated with 105 and 104cfu, respectively, were infected. All infected fruit looked healthy. After 6 months of storage at 5 degrees C, almost all of the 142 infected fruit had viable E. amylovora. Of the fruit containing E. amylovora internally, 19.5% had latent infections and the rest had blight symptoms. E. amylovora was not uniformly distributed in the fruit flesh, and internal brown lesions were observed where E. amylovora was densely distributed. These findings showed that mature apple fruit may be infected with E. amylovora, especially as latent infections, and act as a source for long-range dissemination.[PUBLICATION ABSTRACT]