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

Abstract

Genetic linkage maps for two apple cultivars were constructed using AFLP and SSR markers and the pseudo-testcross mapping strategy. The F1-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 α = 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 (α = 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.