Reaction of apple cultivars to abiotic and biotic stress factors

The study was carried out in 2015-2017 at the Institute of Agriculture - Kyustendil. The aim was to evaluate some apple cultivars from а collection at the Institute as to response to stresses (late spring frost and susceptibility of leaves and fruit to apple scab and powdery mildew). ‘Rosana’, ‘Fuji Nagafu 6’, ‘Charden’, ‘Prima’ and the new Bulgarian cultivar ‘Siyana’ had the best resistance to late spring frosts (-4°C). Fruit damage according to the phenological stage code 72 on the BBCH-scale, i.e., fruit size up to 20 mm, in these cultivars were around 40-50%. The most sensitive were ‘Rubinola’, ‘Belgoden’, ‘Braeburn’, ‘Čadel’, ‘Oregon Spur’ and ‘Super Chief’ with injuries between 80 and 90%. ‘Rubilola’, ‘Teser T219’ and ‘Siyana’ showed resistance to scab and a weak sensitivity to powdery mildew, while the remaining cultivars were sensitive to these diseases.