Segregation of Scab Resistance in Three Apple Populations: Molecular Marker and Phenotypic Analyses

The codominant PCR marker AL07-SCAR closely linked to the V f gene for scab resistance was used to genotype seedlings in three apple populations in which each parent (`GoldRush', `Enterprise', `Pristine', and CQR10T17) was resistant to apple scab. The marker was used to predict the genotype at the V f locus. Each parent was heterozygous. In two populations (CQR10T17 × `GoldRush' and `Pristine' × `GoldRush') seedlings segregated 1:2:1 for fragments associated with V f V f :V f v f :v f v f as predicted by Mendelian segregation. However, in another population (`GoldRush' × `Enterprise') the ratio was 1.5:1:1.5, suggesting some type of selection against heterozygotes. Fruiting seedlings were rated for the presence of fruit scab. No scab was observed on seedlings homozygous for the PCR marker linked to V f , a small amount of scab was observed on one heterozygous seedling out of 35, and 22 of 26 seedlings that were homozygous recessive, had fruit scab.