Identification of co-dominant RAPD markers tightly linked to fruit skin color in apple.

A simple genetic basis for the red/yellow skincolor polymorphism in apple was verified using DNA markers. Bulked segregant analysis identified one 10-base oligomer that generated different fragments in each of the bulks. After testing the primer in four populations, two fragments were found to be associated with red skin color and another two fragments associated with yellow skin color. Three of the fragments (1160, 1180, and 1230 bp) were partly sequenced and found to share high sequence homology, suggesting these were generated from the same locus. A pair of universal primers were designed to amplify the fragments. In the 'Rome Beauty' x 'White Angel' population, two fragments were associated with red skin color; one fragment designated as A(1) (1160 bp) was from 'Rome Beauty' and another fragment (A(2), 1180 bp) was from 'White Angel'. Progeny possessing both fragments, or either one, had red fruit. Both parents displayed an alternate fragment, a(1) (1230 bp), associated with yellowskinned fruit. In three other crosses tested, only fragment A(1) co-segregated with red skin color; two fragments, a(1) and a(2) (1230 bp and 1320 bp), were associated with yellow skin color. Our results are consistent with the hypothesis that the red/yellow dimorphism is controlled by a monogenic system with the presence of the red anthocyanin pigmentation being dominant. There was no indication that other modifier genes could reverse the effect of the locus (R f ) linked to the markers. Examination of amplification products in 56 apple cultivars and advanced breeding selections demonstrated that the universal primers could be used to correctly predict fruit skin color in most cases.