Three-year (2006, 2008 and 2009) QTL detection studies were conducted at INRA-Bordeaux (France) on a sweet cherry F-1 progeny population derived from the cross between 'Regina' and 'Lapins'. 'Regina' is a very late blooming and ripening variety with low fruit cracking susceptibility. 'Lapins', one of the first widely commercialised self-fertile varieties, blooms relatively early, has an intermediate ripening date, and is relatively susceptible to fruit cracking. The progeny is composed of 124 F-1 individuals planted on their own roots in the orchard and their duplicates were grafted on Tabel (R) Edabriz and planted in pots. A partially saturated linkage map was constructed with 89 and 72 SSR markers for both parents, 'Regina' and 'Lapins', respectively. Traits were measured during 2 or 3 years, including bud break date, bloom and ripening dates, cracking susceptibility, fruit weight, and fruit firmness. Fruit cracking (% of cracked fruits), based on the observation of 100 randomly selected fruits, was evaluated on individuals planted in the orchard and on individuals planted in pots, according to different tests. The first test was conducted using the potted trees grown in a plastic tunnel with an automatic irrigation system. The trees were moved into the tunnel at the period of maximum cracking susceptibility and constant amounts of water were sprayed over the trees for five consecutive days. For the second test, trees planted in the field were used and fruits were harvested at physiological maturity. Finally, these same trees were used for the classical Christensen test. The strongest and most stable QTLs were found for the following traits: bloom and ripening dates (LG4 and LG5), mean fruit weight (LG2 and LG3), and fruit firmness (LG2). QTLs for cracking susceptibility were relatively weak and variable across years. Implications for sweet cherry breeding and the use of marker-assisted selection are discussed.

The sugar/acid ratio is an essential component of the organoleptic quality for fruits in the Rosaceae family. The D gene, controlling the non-acid trait in peach, is dominant and segregates as a Mendelian character. Using a mapping progeny of 208 F-2 individuals derived from a cross between two peach varieties 'Ferjalou Jalousia (R)' and 'Fantasia', the D gene was mapped on linkage group 5. Using the BSA-AFLP method with 960 primer combinations, 12 AFLP markers were identified within 10 cM around the D gene. Two of them co-segregate with the D gene. The fine mapping of the region around the D gene, based on the analyses of an extended F-2 progeny of 1510 seedlings, is in progress. Three AFLPs were transformed into codominant SCARs and will be used to screen a new BAC library obtained from the F-1 hybrid that is the parent of the F-2 progeny. Screening of the BAC library with the flanking markers of the D gene will allow the identification of the clones containing the D and d alleles.

The sweet cherry (Prunus avium) is one of the most popular temperate fruit crops. However, compared with others, such as the apple and peach, progress in breeding for improvement of sweet cherry has been slow. The long generation time and the large size of cherry trees severely limit the classical breeding method. Consequently, the integration of molecular markers in breeding programmes should be a powerful tool. Inheritance and linkage studies were conducted with microsatellite markers in an F, progeny including 133 individuals of a cross between 'Regina' and 'Lapins', which were chosen as parents for their distinct agronomic characters and especially because they allowed the study of resistance to fruit cracking, which is a limiting factor in sweet cherry production. 'Regina' is relatively resistant, and 'Lapins' is susceptible to fruit cracking. 'Lapins' is self-compatible, whereas 'Regina' is self-incompatible; moreover, they differ for several other characters: blooming and maturity dates, peduncle length, fruit colour, weight, firmness, titratable acidity and refractive index. These characters were measured at commercial and physiological maturity. For mapping, 337 Prunus microsatellites were tested for polymorphism: 249 (74%) give amplification, 76 were heterozygous in 'Regina', 63 in 'Lapins' and 44 in both parents. sMaps were constructed for each parent. The comparison of these cherry maps with other Prunus maps gives additional evidence for the high level of synteny within the Prunus genus. The two sweet cherry maps will be used for detection of QTLs involved in fruit quality.

An improved genetic linkage map was constructed from a peach Ferjalou Jalousia® × Fantasia (J×F) F2 population. Ferjalou Jalousia® is a flat low-acidity clingstone peach, and Fantasia is a round, normally acidic freestone peach. This population is segregated for six Mendelian characters: pollen sterility, peach or nectarine fruit, flat or round fruit, clingstone, or freestone fruit. It also segregates for the D major gene controlling the fruit’s low acidity. A new character is reported here for the first time that segregates as a Mendelian character: trees bearing aborting fruits. These trees have flowers, but fruits start to fall 2 months after blooming. This recessive character has been named Af. We demonstrate that it is linked to the flat shape of the fruit. The previous map obtained from this cross was constructed using 63 individuals, whereas the present map was constructed using 207 individuals. Moreover, 82 simple-sequence repeat (SSR) markers, including 10 expressed sequence tag-SSRs, and 43 amplified fragment length polymorphism (AFLP) markers were added. Molecular markers linked to the six Mendelian characters were identified, and one of them has already been used for marker-assisted selection. This map will be used for detection of quantitative trait loci controlling organoleptic and nutritional fruit quality in peach.

Inheritance and linkage studies were carried out with microsatellite [or simple sequence repeat (SSR)] markers in a F(1) progeny including 101 individuals of a cross between Myrobalan plum ( Prunus cerasifera Ehrh) clone P.2175 and the almond (Prunus dulcis Mill.)-peach ( Prunus persica L. Batsch) hybrid clone GN22 ["Garfi" (G) almond x "Nemared" (N) peach]. This three-way interspecific Prunus progeny was produced in order to associate high root-knot nematode (RKN) resistances from Myrobalan and peach with other favorable traits for Prunus rootstocks from plum, peach and almond. The RKN resistance genes, Ma from the Myrobalan plum clone P.2175 and R(MiaNem) from the 'N' peach, are each heterozygous in the parents P.2175 and GN22, respectively. Two hundred and seventy seven Prunus SSRs were tested for their polymorphism. One genetic map was constructed for each parent according to the "double pseudo-testcross" analysis model. The Ma gene and 93 markers [two sequence characterized amplified regions (SCARs), 91 SSRs] were placed on the P.2175 Myrobalan map covering 524.8 cM. The R(MiaNem) gene, the Gr gene controlling the color of peach leaves, and 166 markers (one SCAR, 165 SSRs) were mapped to seven linkage groups instead of the expected eight in Prunus. Markers belonging to groups 6 and 8 in previous maps formed a single group in the GN22 map. A reciprocal translocation, already reported in a G x N F(2), was detected near the Gr gene. By separating markers from linkage groups 6 and 8 from the GN22 map, it was possible to compare the eight homologous linkage groups between the two maps using the 68 SSR markers heterozygous in both parents (anchor loci). All but one of these 68 anchor markers are in the same order in the Myrobalan plum map and in the almond-peach map, as expected from the high level of synteny within Prunus. The Ma and R(MiaNem)genes confirmed their previous location in the Myrobalan linkage group 7 and in the GN22 linkage group 2, respectively. Using a GN22 F(2) progeny of 78 individuals, a microsatellite map of linkage group 2 was also constructed and provided additional evidence for the telomeric position of R(MiaNem) in group 2 of the Prunus genome.