Abstract: To improve the selection efficiency of potato horizontal resistance to late blight caused by Phytophthora infestans, molecularmarkers (GP179, GP76, p rp1 and GP125) of 4 quantitative trait loci (QTL)linked to potato late blight resistance and located on different chromosomeswere evaluated with 636 pedigrees
derived from 11 potato crosses with parental materials possessing horizontal resistance to late blight. The results showed that there were 6 bands produced by all the 4 markers and band distribution varied with crosses
that have different genetic background. The resistance level of the pedigrees identified in the field was significantly related to the total number of the bands yielded by the 4 markerswith a linear function. The dominant component analysis revealed that locus prp1₅₇₀ exp lained 35% of the phenotypic variance of the resistance and its linked QTL was hence classified as a dominant locus of late blight resistance. Combining the phenotypic analysis together, the experimental results have reinforced the evidence that late blight resistance is related to the number ofQTL swhen a whole potato population ( i. e. all pedigrees of a cross) is taken into account and the dominant locus determined the resistance level of individuals within this population.

Key words: Potato, Phytophthora infestans, Horizontal resistance, QTL marker