Genetic linkage maps of two apple cultivars (Malus x domestica Borkh.) based on AFLP and microsatellite markers

Genetic linkage maps for two apple cultivars were constructed using AFLP and SSR markers and the pseudo-testcross mapping strategy. The F-1-mapping population was produced by crossing the cultivar 'Braeburn' to the cultivar 'Telamon' and consisted of 257 individuals. Out of the 182 AFLP primer combinations screened, a total of 48 were selected. Using these, 463 AFLP markers segregating 1: 1 in the progeny were identified, of which 231 were heterozygous in 'Telamon' and 232 in 'Braeburn'. Eighty-five AFLP markers present in both cultivars ( 3: 1 segregation) were scored in the whole mapping population. Twenty-one SSR primer pairs were tested, which clearly screened 23 loci ( some multi-locus markers). This resulted in the identification of 3 loci heterozygous only in 'Telamon' ( 1: 2: 1), 5 loci heterozygous only in 'Braeburn' ( 1: 2: 1) and 15 loci which were heterozygous in both cultivars ( 1: 1: 1: 1). Two linkage maps were produced. The 'Telamon' map comprised 259 markers ( 242 AFLPs and 17 SSRs) divided into 17 linkage groups. The total map length was 1039 cM with a marker density of 4.0 cM. At alpha = 0.05, 8.9% of the mapped loci showed distorted segregation. The ` Braeburn' map consisted of 264 markers ( 245 AFLPs and 19 SSRs) mapped on 17 linkage groups and spanning 1245 cM. The average distance between two markers was 4.7 cM and segregation distortion was observed for 18.6% of the mapped markers (alpha = 0.05). Fourty-six markers common to both maps ( 32 AFLPs and 14 SSRs) allowed the identification of 16 homologous linkage groups. The seventeenth pair of homologous linkage groups from 'Telamon' and ` Braeburn' was identified by 2 SSR markers which were in common to the genetic linkage maps of ` Fiesta' and 'Discovery', two other apple cultivars.