Molecular markers applied to apple breeding: analysis of oligogenic and single gene resistances.

摘要

The use of molecular markers can dramatically improve apple breeding by increasing selection efficiency. Two examples are presented of how DNA markers have been successfully applied to prove that the Venturia inaequalis resistance gene present in the cultivar Nova Easygro (said to be Vr) is tightly linked to Vf and is most probably Vf itself. Homozygous resistant plants were detected and it was shown that those plants are on average more resistant than the heterozygous ones. In a population obtained by crossing a powdery mildew (Podosphaera leucotricha) resistant selection (A679-2) and a susceptible one (Iduna), resistance to powdery mildew introgressed from Malus zumi (Pl2) was studied. Genetic linkage maps of the two parental plants were constructed. By analysing quantitative trait loci (QTL) two major genomic regions containing genes controlling the resistance were detected. Several other minor regions have been detected both in the resistant and in the susceptible parents. The analysis of a larger sample and repeated observations over several years will enable a more precise localisation of the QTLs and evaluation of the importance of the genomic regions containing putative loci controlling powdery mildew resistance.