Fine mapping of Co, a gene controlling columnar growth habit located on apple (Malus×domestica Borkh.) linkage group 10

With 2 figures and 3 tables ABSTRACT: Tree architecture and shoot morphology are important factors in apple production systems. Because a columnar growth habit facilitates high‐density planting and labour‐saving fruit production methods, columnar apple breeding programmes are spreading worldwide. Columnar growth habit is controlled by a single dominant gene, Co, on linkage group 10. Fine mapping of Co was conducted using 1000 F1 progeny plants from 31 populations. Novel simple sequence‐repeat (SSR) markers were developed based on the genome sequence of apple ‘Golden Delicious’ and analysed for linkage to Co. Graphical genotyping of 22 progeny with recombination event in the vicinity of Co identified three SSR markers (Mdo.chr10.12, Mdo.chr10.13 and Mdo.chr10.14) that co‐segregated with Co. Mdo.chr10.12 and Mdo.chr10.14 are well suited for marker‐assisted selection because the sizes of the alleles linked to Co are different from those found in common ancestors of current apple breeding germplasm. The Co region was delimited to a 196‐kb region of the apple genome, between markers Mdo.chr10.11 and Mdo.chr10.15.