S01 - Session O9 - II - Forty years of scab resistance breeding in apple at Agroscope

Authors: Simone Buehlmann-Schuetz *, Marius Hodel, Michaela Jung, Giovanni AL Broggini, Andrea Patocchi, Markus Kellerhals

Apple scab, caused by the ascomycete Venturia inaequalis (Cke.) Wint., is the most important fungal disease in many growing areas of Malus domestica Borkh. Strong monogenic resistances originating from wild Malus species built the basis for resistance breeding. Most of these scab resistances have been mapped, and associated molecular markers are available. Within the VINQUEST network ( www.vinquest.ch ), differential hosts carrying single resistance genes ( R -genes) are monitored for resistance breakdown around the world. To date, most commercially available scab resistant varieties carry the R -gene Rvi6 ( Vf ) originating from Malus floribunda 821. However, Rvi6 has been overcome in Europe and the USA. Therefore, new varieties with durable resistance are urgently needed. Breeding for durable disease resistance against apple scab is a major goal in the Agroscope apple breeding program for almost 40 years. For effective resistance breeding, methods of stacking multiple R -genes against apple scab were implemented, such as screening with artificial scab inoculation and accelerated introgression, complemented by the use of marker-assisted breeding (MAB). MAB proved to be a useful and very efficient tool to select genotypes with stacked R -genes against apple scab. Recently, MAB in apple has progressed from using sequence-characterized amplified regions (SCAR) and simple sequence repeat (SSR) markers to more cost-effective single nucleotide polymorphism (SNP) markers. As part of the European FP7 Fruit Breedomics project, a number of SNP markers for different scab resistances ( Rvi2, Rvi4, Rvi5, Rvi6, Rvi11, Rvi12 and Rvi15 ) were identified, and an outsourced genotyping pipeline was established. Since then, the marker set has been fine-tuned and extended to resistances against other diseases (e.g., fire blight, powdery mildew) and fruit quality traits. The ongoing implementation of the combination of MAB for R -genes against various diseases with genomic selection for quantitative traits related to fruit quality, yield, and growth characteristics is a promising approach for breeding.