Classification of apple scab resistance in two assortment orchards

The susceptibility to apple scab was evaluated in two assortment orchards in Southern Sweden, Alnarp (339 cultivars) and Balsgard (165). A scab index ranging from 0 to 4 was used and one assessment per tree was made annually from 1998 to 2000 on leaves. At Alnarp, the fruit scab was also evaluated. The over-all mean for the leaf scab index was highest at Alnarp (3.0) in 1999 when 55% of the cultivars were placed in fruit scab index 4, indicating severe scab infections. In 2000, the majority of the cultivars was grouped in classes 2 and 1. In 2000, 60.4% of the cultivars were placed in class 0, without any visible scab symptoms on the fruit. The leaf scab appeared to have a negative effect on fruit setting, since we found a lower number of cultivars bearing fruit when leaf scab index was high. The correlation between leaf and fruit scab was stronger during the first two years with high scab incidence. The most resistant cultivars or selections at Alnarp were 'Priscilla', 'Nova Easygro', 'Prima', 'Warner's King', 'Akane', 'Remo', Co-op 25, 'Liberty', 'McShay' and 'Katinka'. The over-all scab index mean at Balsgard was higher in 1998 (2.0) and 1999 (1.8) compared to 2000 (0.95). The best cultivars or selections at Balsgard were Co-op 22, 'Enterprise', 'McShay', 'Prima', 'Priscilla', 'William's Pride', 'Luke', 'Apelsinoe' and 'Judeline'.