PROGRESS IN PYRAMIDING DISEASE RESISTANCES IN APPLE BREEDING
Durability of disease resistance in apple under severe disease pressure has proved to be vulnerable. In many areas of middle and northern Europe it has become difficult to grow apple cultivars carrying only the Rvi6 (Vf) scab resistance without a complete fungicide spray program as isolates of Venturia inaequalis have emerged that are able to overcome this type of resistance. Similar resistance breakdown was reported for powdery mildew resistance such as Pl1 and Pl2 and others. Fruit quality is the primary objective in our breeding program. To develop high quality cultivars with durable disease resistance suitable for sustainable production systems, molecular marker analysis was applied, depending on the cross, at different stages in the breeding process and combined with a stringent phenotypic evaluation and selection. We present an approach to combine in the same genotype several major resistance genes towards apple scab (V. inaequalis) and also to incorporate resistance to powdery mildew (Podosphaera leucotricha) and to fire blight (Erwinia amylovora). Marker-Assisted Breeding based on SSR and SCAR markers closely linked to resistance loci was used to detect progeny genotypes with combined resistance to scab and mildew and enhanced resistance to fire blight. Depending on the number of resistance loci considered, it was possible to reduce the analyzed progeny to the individuals with a pyramided set of loci which corresponded to 5, 9, 12 and 18%, respectively of the original progeny size. Promising advanced selections were developed with pyramided resistance against scab and resistance against powdery mildew and fire blight. Those selections are supposed to display commercial fruit quality. Problems associated to linkage drag derived from the original resistance donors in the pedigree will be discussed.
Kellerhals, M., Baumgartner, I.O., Leumann, L., Frey, J.E. and Patocchi, A. (2013). PROGRESS IN PYRAMIDING DISEASE RESISTANCES IN APPLE BREEDING. Acta Hortic. 976, 487-491
Malus × domestica, marker-assisted selection, apple scab, powdery mildew, fire blight