In the framework of a CAOBISCO sponsored project the genetic bases of resistance to several species of Phytophthora have been studied. Different significant QTL identified make it possible to accumulate various genes to improve varietal resistance. Markers closely linked to QTL could allow to control at early stages the presence of resistance alleles in progenies. Several applications or strategies using QTL analyses could be considered to improve the resistance level. - Creation of genotypes homozygous for resistance alleles. The most resistant clones, as SCA6 and SNK413, could have the resistance genes in a homozygous condition. The identification of a QTL means a heterozygous condition of the resistance gene identified in the parent studied. By selfing the genotypes and using Marker Assisted Selection (MAS) it is possible to produce and screen selfed progenies for plants that are homozygous for the resistance alleles. These clones will have a higher resistance level and a better combining ability to produce resistant hybrids. - Accumulation of various resistance genes and other genes of interest. Various resistance genes could be accumulated using MAS by crossing clones for which different QTL of resistance have been identified. It is also possible to use MAS to break linkage between favourable and unfavourable alleles located in the same chromosome region. - Early selection for resistance and other traits. Increased selection efficiency in pre-breeding, at the nursery stage, would be possible by applying MAS on a limited number of resistance QTL (the stronger QTL, QTL for resistance to several Phytophthora species...) and to have available more plants to apply selection for other traits of interest in the field. - Combined use of marker information and phenotypic selection to constitute a selection index. Information on a larger number of QTL could be combined with phenotypic selection related to resistance traits (e.g. intrinsic resistance revealed by leaf test