Local European cultivars as sources of durable scab resistance in apple

The Vf resistance gene has been widely used in apple breeding programmes to control Venturia inaequalis, the causal agent of scab, the major apple disease. Since the appearance of new strains that are able to overcome this major gene, research in Europe has been focused on durable resistance. The objective of one task of the European DARE project was to find cultivars which show a broad spectrum of resistance to the different scab races. This collaborative work involved 6 partners who tested 36 cultivars with various local scab inocula collected in the participating countries and with 8 monoconidial strains belonging to known races or isolated and characterized in the frame of the DARE project. Tests were performed each year from 1998 to 2001. Symptoms were assessed using macroscopic scoring scales. Some microscopic observations were performed; these resulted in a better knowledge of the host/pathogen interaction. Very diverse and complex resistance behaviours were found: the cultivars which showed the widest range of resistance were mostly local cultivars and some newly selected hybrids combining major genes and partial resistance. It would be worthwhile to include these individuals as parents in apple breeding programmes to improve the durability of scab resistance. Some methodologies and strategies to reach this goal will be proposed.