Segregation of scab resistance in three apple populations: Molecular marker and phenotypic analyses

David Shupert, Purdue University
Aaron P. Smith, Purdue University
Jules Janick, Purdue University
Peter B. Goldsbrough, Purdue University
Peter M. Hirst, Purdue University


The codominant PCR marker AL07-SCAR closely linked to the Vf 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 Vf locus. Each parent was heterozygous. In two populations (CQR10T17 x 'GoldRush' and 'Pristine' x 'GoldRush') seedlings segregated 1:2:1 for fragments associated with VfVf:V fvf:vfvf as predicted by Mendelian segregation. However, in another population ('GoldRush' x '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 Vf, 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.