Marker-assisted selection (MAS) is an increasingly important tool in current breeding efforts for improved crop plants and animal breeds. It enables detection of favourable alleles in early developmental stages and thus may result in substantial cost savings. Until now, however, the high costs of the required chemicals and materials, together with the still very labour-intensive methods, have been an obstacle to widespread application of MAS. A new multiplex-polymerase chain reaction (PCR)-based method has been developed for reliable low-cost, high-throughput screening. By its use 3366 apple seedlings were screened with an average hands-on time from DNA extraction to data ready for analysis of <4 h per 96 plants, and at a cost below US$ 0.5 per marker per plant. Factors that have a strong effect on segregation ratios such as elevated levels of outcrossing are easily detected, as a significant correlation was observed between deviation from expected segregation ratios in some affected markers and the level of outcrossing in a cross. The new method is suitable for many crop species and, provided that suitable buffers are used for DNA extraction, for animals too.

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Zusammenfassung Qualitativ hochwertige Apfelsorten mit umfassender Krankheitsresistenz sind das wichtigste Ziel im Zuchtprogramm von Agroscope Changins-Wädenswil (ACW). Der Apfelschorf (Venturia inaequalis) ist der wichtigste Krankheitserreger im Apfelanbau. Um die Dauerhaftigkeit der Schorfresistenz zu sichern, wird eine Kombination verschiedener Resistenzgene (Pyramidisieren) angestrebt. Zudem werden Resistenzen gegen Schorf, Mehltau (Podosphaera leucotricha) und Feuerbrand (Erwinia amylovora) im gleichen Genotyp kombiniert. Die Kombination (Pyramidisieren) von Resistenzen wird am Beispiel von Kreuzungen mit zwei verschiedenen Schorfresistenzgenen (Vf und Vh2) illustriert. Kreuzungsnachkommen werden mithilfe von molekularen Markern auf Mehrfachresistenz und das Vorliegen von Resistenzgenen getestet. Die Ergebnisse des Schorfscreenings im Gewächshaus und die Markeranalysen werden miteinander verglichen und die Aufspaltung in resistente und nichtresistente Nachkommen analysiert.Schlüsselwörter Apfelzüchtung · Schorfresistenz · Apfelschorf · Venturia inaequalis · Apfelmehltau · Podosphaera leucotricha · Markergestützte Selektion · Vf · Vh2 Pyramiding scab resistances in apple breedingAbstract High quality disease resistant apples are the main breeding objective in the programme at Agroscope Changins-Wädenswil (ACW). Apple scab caused by the fungus Venturia inaequalis is still the most important disease in apple production. To ensure the durability of scab resistance we are combining different resistance genes (pyramiding). Moreover, we are incorporating also resistances against powdery mildew (Podosphaera leucotricha) and fire blight (Erwinia amylovora). Principles and methods of resistance breeding are outlined and pyramiding of resistances is illustrated by analysing crosses between two cultivars carrying different scab resistance genes (Vf and Vh2). Crosses are being analysed applying marker-assisted selection (MAS) to detect plants carrying multiple resistances. Phenotypic screening of seedlings for scab symptoms and MAS results are compared and the observed segregations into resistant and susceptible progenies discussed.