Further information on Erwinia amylovora on Rubus
As stated in 'Quarantine Pests for Europe', Erwinia amylovora (EPPO A2 quarantine pest) has been isolated from diseased Rubus in USA. Because the pathogen has not been reported elsewhere on this genus, this remains slightly dubious. However, a small chapter is dedicated to fireblight in the APS Compendium of raspberry and blackberry diseases and insects. This article stated that fireblight on Rubus has been occasionally reported from Illinois, Maine and North Carolina and that more recent outbreaks have been observed in Ohio, Wisconsin and Illinois in the 1980s and in Wisconsin in 1990. The disease has been seen on red raspberry (Rubus idaeus), on wild and cultivated blackberry (Rubus fruticosus), but it is relatively uncommon and rarely of economic importance. On affected plants, water soaked lesions with abundant bacterial ooze can be seen. Diseased portions of canes become necrotic and purplish black; the tips may become curved. Infected berries do not mature and become brown, dry and very hard. It appears that strains of the bacterium isolated from Rubus can only infect Rubus and that strains from other rosaceous plants are not pathogenic to Rubus.
Sources
Ries, S.M. (1991) Fire blight.
In: Compendium of Raspberry and Blackberry Diseases and Insects, Ellis, M.; Converse, R.H.; Williams, R.N.; Williamson, B. (Eds), APS Press, St Paul, Minnesota, qUSA, 40-41.