ANALYSIS OF MOLECULAR MARKERS ASSOCIATED WITH POWDERY MILDEW RESISTANCE GENES IN PEACH (PRUNUS-PERSICA (L) BATSCH) X PRUNUS-DAVIDIANA HYBRIDS

A progeny of 77 hybrids issued from a cross between two heterozygous P runus, peach [P. persica (L.) Batsch] (variety 'Summergrand') and a re lated species, P. davidiana (clone 1908), was analysed for powdery mil dew resistance in five independent experiments. This population was al so analysed for its genotype with isoenzyme and RAPD markers in order to map the genes responsible for resistance. A genetic linkage map was generated for each parent. The 'Summergrand' linkage map is composed of only four linkage groups including 15 RAPD markers and covering 83. 1 centiMorgans (cM) of the peach nuclear genome, whereas the P. davidi ana linkage map contains 84 RAPD markers and one isoenzyme assigned to ten linkage groups and covering 536 cM. Significant associations betw een molecular markers and powdery mildew resistance were found in each parent. For P. davidiana, one major QTL with a very strong effect and five other QTLs with minor effects were located in different linkage groups. For 'Summergrand', three QTLs for powdery mildew resistance, w ith minor effects, were also detected. Consequently, evidence is given here that the powdery mildew resistance of P. davidiana clone 1908 an d P. persica variety 'Summergrand' is not a monogenic character but is controlled by at least one major gene and several minor genes.