An improved genetic linkage map was constructed from a peach Ferjalou Jalousia ® × Fantasia (J×F) F 2 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.

BackgroundDomestication and breeding involve the selection of particular phenotypes, limiting the genomic diversity of the population and creating a bottleneck. These effects can be precisely estimated when the location of domestication is established. Few analyses have focused on understanding the genetic consequences of domestication and breeding in fruit trees. In this study, we aimed to analyse genetic structure and changes in the diversity in sweet cherry Prunus avium L.ResultsThree subgroups were detected in sweet cherry, with one group of landraces genetically very close to the analysed wild cherry population. A limited number of SSR markers displayed deviations from the frequencies expected under neutrality. After the removal of these markers from the analysis, a very limited bottleneck was detected between wild cherries and sweet cherry landraces, with a much more pronounced bottleneck between sweet cherry landraces and modern sweet cherry varieties. The loss of diversity between wild cherries and sweet cherry landraces at the S-locus was more significant than that for microsatellites. Particularly high levels of differentiation were observed for some S-alleles.ConclusionsSeveral domestication events may have happened in sweet cherry or/and intense gene flow from local wild cherry was probably maintained along the evolutionary history of the species. A marked bottleneck due to breeding was detected, with all markers, in the modern sweet cherry gene pool. The microsatellites did not detect the bottleneck due to domestication in the analysed sample. The vegetative propagation specific to some fruit trees may account for the differences in diversity observed at the S-locus. Our study provides insights into domestication events of cherry, however, requires confirmation on a larger sampling scheme for both sweet cherry landraces and wild cherry.

Climate change is increasing mean temperatures and in the eastern Mediterranean is expected to decrease annual precipitation. The resulting increase in aridity may be too rapid for adaptation of tree species unless their gene pool already possesses variation in drought resistance. Vulnerability to embolism, estimated by the pressure inducing 50% loss of xylem hydraulic conductivity (P50), is strongly associated with drought stress resistance in trees. Yet, previous studies on various tree species reported low intraspecific genetic variation for this trait, and therefore limited adaptive capacities to increasing aridity. Here we quantified differences in hydraulic efficiency (xylem hydraulic conductance) and safety (resistance to embolism) in four contrasting provenances of Pinus halepensis (Aleppo pine) in a provenance trial, which is indirect evidence for genetic differences. Results obtained with three techniques (bench dehydration, centrifugation and X-ray micro-CT) evidenced significant differentiation with similar ranking between provenances. Inter-provenance variation in P50 correlated with pit anatomical properties (torus overlap and pit aperture size). These results suggest that adaptation of P. halepensis to xeric habitats has been accompanied by modifications of bordered pit function driven by variation in pit aperture. This study thus provides evidence that appropriate exploitation of provenance differences will allow continued forestry with P. halepensis in future climates of the Eastern Mediterranean.