Apple breeding for resistance to the aphids Dysaphis plantaginea and Aphis pomi in Bulgaria

Infestations by the green-apple aphid, Aphis pomi, and the rosy-apple aphid, Dysaphis plantaginea, have caused serious damage to apple trees in Bulgaria. Resistance to major pests and diseases has been considered one of the most important goals of apple breeding programmes. From 2011 to 2013, experiments were conducted in an orchard of apple hybrids where no pesticides were applied and under controlled conditions (in pots). Various hybrid combinations, selected for high resistance to scab and low susceptibility to powdery mildew from 2006 to 2010, were tested for tolerance to aphids. 'Golden Delicious' was used as a susceptible reference cultivar. Artificial infection was carried out in two trials, under field conditions and on trees of cultivars and hybrids budded on M.26 rootstock and grown in pots. Some hybrids showed tolerance to the rosy-apple aphid and the others to the green-apple aphid. Resistance to A. pomi and tolerance to D. plantaginea under field conditions was observed in plants of the hybrid 'Dayton' × 'Vista Bella' N 45. It was also confirmed that 'Florina' and 'Prima' are good donors of resistance to these aphids.