Breeding apple scab resistant cultivars in Estonia

Apple tree breeding began at the Polli Horticultural Research Centre of the Estonian University of Life Sciences in 1946. A total of 35 new apple cultivars has been obtained. A majority is more or less susceptible to apple scab. Breeding of apple scab resistant cultivars started in 1986, when Kalju Kask cross-pollinated the cultivars ‘Cortland’ and ‘Tiina’ with the apple scab resistant Crab No 23, a seedling of unknown origin. From a family of 167 seedlings he selected the cultivars ‘Kuku’, ‘Ritika’ and ‘Ruti’. The fruit of these cultivars is small, weighing about 20 g, round or slightly oblong. The flesh is dense and sweetish sour. The trees start bearing fruit early. Breeding scab resistant cultivars with large fruit started in 1997 in cooperation with the Latvian breeder Laila Ikase. Seeds of the scab resistant cultivars ‘Florina’, ‘Freedom’, ‘Imrus’, ‘Liberty’, ‘Siostra Liberty’, ‘Releta’, and ‘Remo’ and the selection BM41497 were collected. Crosses were made between cultivars: ‘Bogatyr’ × ‘Fantasia’, ‘Freedom’ × ‘Auksis’, ‘Lobo’ × ‘Remo’ and ‘Merrigold’ × ‘Stars’. Of 1372 seeds sown in spring 1998, 875 seedlings were obtained (63.8%). The trees were observed during 10 years and the ones with leaves that became infected with apple scab were removed. Out of 875 seedlings, 269 (30.7%) remained uninfected in these years. Out of these seedlings, 93 (34.6%) bore fruit by 2007. Based on the quality of fruit, 20 promising seedlings were selected. The breeding process lasted 20 years and resulted in two apple scab resistant cultivars released in 2081: ‘Virve’ and ‘Kalju’.