This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

The aim of this study was to determine if the transfer pathway of E. amylovora from infected plants to fruits may have been feasible in nature. To this end, several lots of different asymptomatic fruits harvested from naturally fire blight infected trees from several origins were analyzed looking for E. amylovora.

The bacterium Erwinia amylovora was the causal agent of fire blight, a very destructive and highly infectious disease of apple, pear and other pome fruits, causing important economic losses worldwide. Due to the ability of the pathogen to persist in nature, and the difficulties for an efficient control, the fire blight disease remained a serious global threat to the pome fruit industry.

E. amylovora usually infected immature fruits, but it had been also occasionally detected in mature fruits from severely infected trees. Moreover, it was reported that E. amylovora could persist in inoculated apple and pear fruit calyces, as well as in apple pedicels, although only for short periods in a culturable state. However, the researcher had recently demonstrated that E. amylovora was able to survive for one month in mature apple fruit calyces adopting the “viable but non-culturable” (VBNC) state without causing disease symptoms. This suggested that the healthy appearance of the fruit was not always an indicative of the pathogen absence, so that asymptomatic contaminated fruit could be an unnoticed inoculum source for new fire blight infections.