Marker-assisted selection in apple breeding

Apple breeding is aimed at creating varieties with high fruit quality, regular and high yields and durable disease and pest resistance. Traditional breeding is time and labour consuming. DNA markers for traits related to fruit quality, productivity and resistances will allow early and precise selection for desired characters. Within the framework of an EU apple genome project and the Swiss Science Foundation priority programme biotechnology we have focussed mainly on molecular markers related to scab and mildew resistance. CAPS and SCAR-markers were developed which allow to determine the allelic status of the Vf locus coding for scab resistance. Progeny plants obtained from crosses with two Vf-resistant parents were used. Markers for the Vbj scab resistance originating from Malus baccata jackii have been developed and will allow the combination of Vf and Vbj resistance in the same genotype in order to increase durability of resistance. The segregation for mildew resistance in the progeny Iduna x A 679-2 comprising 400 individuals was assessed. Quantitative trait loci (QTL)-analysis using the nonparametric Kruskal-Wallis test was performed. Major QTLs controlling mildew resistance were detected in the A 679-2 genome. A linkage map was constructed using a random subpopulation of 189 individuals of Iduna x A 679-2 using random amplified polymorphic DNA. The linkage map of A 679-2 contains 142 RAPD-markers and 9 microsatellites arranged in 15 linkage groups. Routine application of marker-assisted selection for scab resistance is being investigated also for economical feasibility.