Genetic linkage map and QTL analysis in peach

A genetic linkage map of peach was constructed using 75 individuals of a BC1 population from a cross between the semidwarf peach selection IF7310828 (tolerant to powdery mildew) as female recurrent parent and an accession of Prunus ferganensis carrying a source of powdery mildew (Sphaerotheca pannosa) resistance. The current map, consisting mainly of RFLP markers, covers 460cM of the peach genome. Markers have been assigned to nine linkage groups. Twenty-one markers were in common with the saturated peach x almond map obtained by the European "Prunus mapping" group. Several morphological and agronomical traits of this population were studied during three years. The monogenic traits, leaf glands and flesh adhesion, were assigned respectively to group 7 and to group 4, both tightly linked to an RFLP marker. The polygenic traits, such as powdery mildew resistance, tree architecture, blooming and ripening time and fruit quality were analyzed for QTLs. Ten QTLs were identified by using interval-mapping analysis; some of them were consistent through the years showing that the expression of the genes influencing the traits was largely independent on the environmental conditions. The additive effect of each QTL was consistent through the years and in agreement with the parents' phenotype. In particular a major gene for powdery mildew resistance was detected in group 7 tightly linked to the marker Ag104 and to the monogenic trait "leaf glands".