Integrated Reference Genetic Linkage Maps of Pear Based on SSR and AFLP Markers

Integrated genetic linkage maps of the European pear (Pyrus communis L.) cultivars 'Bartlett' and 'La France' were constructed based on SSR markers developed from pear and apple, AFLP and other markers. The map of 'Bartlett', which was constructed using an F, population derived from a cross between 'Bartlett' and 'Housui', consisted of 447 loci, including 58 loci revealed by pear SSR markers (hereafter referred to as "pear SSR loci"), 60 by apple SSR markers (hereafter referred to as "apple SSR loci") and 322 by AFLP markers (hereafter referred to as "AFLP loci"). This map covered 17 linkage groups over a total length of 1,000 cM with an average distance of 2.3 cM between markers. Another genetic linkage map of 'La France' was constructed using F, individuals obtained from a cross between 'Shinsei' and '282-12' ('Housui' x 'La France'). The map of 'La France' contained 414 loci, including 66 pear SSR loci, 68 apple SSR loci and 279 AFLP loci on 17 linkage groups encompassing a genetic distance of 1,156 cM. Using 97 common SSR markers, these two maps were well aligned together for all the 17 linkage groups, which corresponded to the basic chromosome number (n = 17). The positions of 66 SSR markers originating from apple were successfully determined in pear maps and showed a co-linearity with the saturated reference map of apple. Since the high-density genetic linkage maps of pear constructed in the present study covered almost the entire genome, they should be considered as pear reference maps. These pear reference maps may enable to identify the location of genes of interest and QTLs (quantitative trait loci), and to analyze the syntenic genome structure with other Maloideae species.