Mapping quantitative trait loci controlling peach leaf curl resistance

Inheritance and linkage studies were conducted with 125 molecular markers (73 RFLPs and 52 RAPDs) in the F1 progeny of an interspecific cross between two heterozygous Prunus [P. persica (L.) Batsch cv ‘Summergrand’ and a related species P. davidiana clone 1908]. The segregating progeny of 77 plants was also analysed for peach leaf curl resistance in order to map the genes involved in their expression. Evaluation for resistance was carried out under severe natural infection conditions, in two locations, during a four-year period and with artificial contamination. Two maps were established, (one for each parent) with MAPMAKER/EXP software (LOD> 5.0, recombination fraction< 0.4). The P. davidiana map contains 97 markers distributed among 9 linkage groups and covering 471 cM. The 'Summergrand' map contains 23 markers, distributed into 3 linkage groups and covering 159 cM. Nine additional markers remain unlinked. QTLs for peach leaf curl resistance were detected in six linkage groups of the P. davidiana map (MAPMAKER/QTL LOD > 2.0) and expressed with different magnitude according to experimental conditions. Two QTLs, located in linkage groups 3 and 6, were detected in nearly all the conditions, with an important phenotypic effect. The total variation explained ranged between 19% and 54%. No QTL was detected in the 'Summergrand' map.