Susceptibility of twenty-two apple cultivars to apple scab in Sweden

Twenty-two apple cultivars and selections were ranked according to their susceptibility to foliar apple scab in order to Find possible alternatives for organic growing. The ranking was based on unsprayed observation trials for new apple cultivars planted at three places in southern Sweden: Alnarp (southwest); Kivik (southeast) and Ranna/Skovde (central) in July 2000. The most resistant cultivars were 'McShay' and 'Sansa' followed by 'Pimona', 'Redsleeves', Tiros', BM54859, BM44044 and 'Pikant', 'Jupiter', 'Elise' and 'Majda', 'Birgit Bonnier', 'Aroma' and 'Pinova'. The least resistant group included 'Pilot', 'Astramel', 'Arlet', 'Bountiful', 'Eva-Lotta" 'Rubinette', BM55196 and 'Cadel'. Scab infection periods were monitored during the growing seasons 1999 and 2000 at Alnarp. A sample of apples from five cultivars were weighed, and classified in four different scab levels. There were great differences in scab level classification, both between the 2 years and among the cultivars. In the second year, scab infection appeared later and was less severe than in the first year. The correlation coefficient was calculated for apple scab symptoms, regarding leaves/fruit in Alnarp. At the Alnarp location, a scab lesion was documented on a 'McShay' fruit, indicating that the Vf-resistance (Vf gene from Malus floribunda 821) was broken in 1999 - the first ever recorded in Sweden.