Resistance and Resistance Breeding in Ornamentals 1

Heritability studies in ornamentals with regard to Erwinia amylovora (Burrill) Winslow et al. were started shortly after the introduction of the pathogen into northern Europe. Since that time, approximately 8,000 plants from 17 genera of Rosaceae have been tested; 7 genera were reported to be susceptible: the economically important Cotoneaster, Crataegus, Cydonia, Pyracantha, Sorbus, and, in addition, Chaenomeles and Stranvaesia. Moreover, 9,000 Cotoneaster seedlings comprising 15 cultivars were tested and the surviving individuals used for breeding purposes. The variation between these first results reported in the different European countries and some American findings is considerable because of different inoculation procedures and various epidemiological conditions. However, resistance sources have been identified and it would be desirable to start co–operation in this field on an international level.