233 USING RAPDs TO INVESTIGATE GENE INTROGRESSION IN APPLE
DNA was extracted from leaves of various Malus genotypes and used to screen synthetic decamer oligonucleotide primers. Samples from the following two groups were bulked: 1) seven scab-susceptible apple cultivars, and 2) 15 scab-resistant apple genotypes derived by introgressive hybridization from the previous group of cultivars. A third sample consisted of DNA extracted from Malus floribunda Sieb. clone 821, the original source of apple scab resistance for all genotypes in the second group. A total of 59 primers from kits A, L, and R (Operon Technologies) were screened. Amplified fragments were obtained for 93% of the primers tested, while random amplified polymorphic DNA (RAPD) fragments were detected among samples for 76% of the primers. One primer, A15, amplified a unique band in both M. floribunda clone 821 and the bulked scab-resistant sample. This RAPD marker, designated OA15900, identifies an amplified, introgressed fragment that likely corresponds to a region of the genome that may serve as a modifier for the scab resistance gene block V, derived from M. floribunda clone 821.