Genetic Linkage Maps of Japanese and European Pears Aligned to the Apple Consensus Map

Abstract

Genetic linkage maps of the Japanese pear (Pyrus pyrifolia Nakai) cultivar 'Housui' and the European pear (Pyrus communis L.) cultivar 'Bartlett' were constructed based on Amplified Fragment Length Polymorphism markers (AFLPs), Simple Sequence Repeat markers (SSRs) (from pear, apple and Prunus), isozymes, and phenotypic traits by using their F 1 progenies. The map of the female parent 'Bartlett' consisted of 256 loci including 178 AFLPs, 76 SSRs (32 pear, 39 apple, 5 Prunus SSRs), 1 isozyme and a self-incompatibility locus on 19 linkage groups over a total length of 1020 cM. The map of 'Housui' contained 180 loci including 110 AFLPs, 64 SSRs (29 pear, 29 apple, 6 Prunus SSRs), 2 phenotypic traits and 4 other markers on 20 linkage groups encompassing a genetic distance of 995 cM. These 2 pear maps were aligned using 37 co-dominant markers that showed segregating alleles in both parents. Out of 80 tested SSR markers developed from apple, more than four-fifth could produce discrete amplified fragments in pear. Thirty-eight apple SSR markers showed 39 segregating loci in the linkage map of 'Bartlett', while 27 markers produced 29 loci in 'Housui'. All pear linkage groups could be successfully aligned to the apple consensus map by at least 1 apple SSRs, suggesting that positions and linkages of SSR loci were well conserved between pear and apple. The selfincompatibility locus (S locus) was mapped to linkage group 17 in Japanese and European pears as well as apple. Our results are the first major effort in comparative mapping of pear and apple. INTRODUCTIONPear (Pyrus spp.) is one of the most important fruits, which has been cultivated in Asia and Europe for 2000 to 3000 years. Presently, pear is cultivated commercially in all the temperate regions in more than 50 countries around the world. However, there is very little information on genome research, i.e., genetic linkage maps, development of molecular markers, and genetic analysis on phenotypic traits.In this study, we constructed genetic linkage maps of the European pear cultivar 'Bartlett' and the Japanese pear cultivar 'Housui' using AFLP markers and SSR markers developed in pear, apple and Prunus. Both maps are aligned to the apple consensus map by using apple SSRs as anchor loci. Genetic synteny between pear and apple is discussed.

Identification of a major QTL together with several minor additive or epistatic QTLs for resistance to fire blight in apple in two related progenies

“…The QTLs for resistance to fire blight identified in the present analysis can be compared to those of a previous study conducted in pear (Dondini et al 2004). The use of common microsatellite markers and the remarkable synteny between apple and pear (Yamamoto et al 2004) enables the apple and pear maps to be aligned. In pear, four QTLs have been identified on LGs 2, 4 and 9 (Dondini et al 2004), two of which have been mapped at positions similar to those of epistatic QTLs identified in apple.…”

Linkage map positions and allelic diversity of two Mal d 3 (non-specific lipid transfer protein) genes in the cultivated apple (Malus domestica)

“…The fact that these two genes are located on homoeologous chromosomes is clear evidence that Mal d 3.01 and Mal d 3.02 have originated from different ancestral genomes. Because the genome constitution of apple and pear is highly similar (Yamamoto et al 2002(Yamamoto et al , 2004Hemmat et al 2003), we expected to locate: (1) the known pear nsLTP gene (Pyr c 3, accession AF221503), which is 93% identical to Mal d 3.02 (Fig. 6), on linkage group 4; and (2) another yet unidentified pear nsLTP gene on linkage group 12.…”

The genome of the domesticated apple (Malus × domestica Borkh.)

“…Similarly, the collinearity between Pyrus and Malus genetic maps 31,36 suggests that the Pyreae genome reorganization occurred before the divergence of the two genera. A rapid genome rearrangement after polyploidization is expected in species lacking the Ph1-like function that prevents the pairing of homologous chromosomes in wheat 37 .…”