Construction of a High-Density Simple Sequence Repeat Consensus Genetic Map for Pear (Pyrus spp.)

As an important fruit crop that is widely grown commercially in temperate regions of the world, pear (Pyrus) is a target for pursuing efficient breeding strategies. Construction of a reliable and dense genetic linkage map is critical for undertaking marker-assisted breeding. In this study, a population of 56 F-1 seedlings of 'Bayuehong'aEuro parts per thousand x 'Dangshansuli' was used to construct a high-density simple sequence repeat (SSR)-based genetic linkage map. A total of 1,756 SSR markers, including 1,341 newly designed SSRs based on whole-genome sequencing of an Asiatic pear along with 415 previously reported SSRs, were first evaluated for polymorphism. Based on 894 SSRs demonstrating polymorphism, a consensus genetic map consisting of 734 loci distributed along all 17 linkage groups (LG) was constructed, with a total length of 1,661.4 cM and with an average marker interval of 2.26 cM. Comparisons among different maps of pear and apple were then made based on positions of previously mapped SSR markers on the consensus map. As a result, homologous linkage groups LG3 and LG11, LG5 and LG10, LG9 and LG17, LG13 and LG16, LG8 and LG15 have been identified. This high-density SSR map along with a set of SSR markers covering the whole genome of pear will greatly facilitate integration of independent maps, aid in pursuing comparative genome studies, and in evaluation of different germplasm in future genetic and breeding studies.