Phytophthora infestans causes an economically important disease of potato called late blight. The epidemic is controlled chemically but resistant potatoes can become an environment-friendly and financially justified alternative solution. The use of diploid Solanum tuberosum derived from European tetraploid cultivars enabled the introgression of novel genes encoding foliage resistance and tuber resistance from other species into the modern cultivated potato gene pool. This study evaluated the resistance of the obtained hybrids, its quality, expression in leaflets and tubers and its relation to the length of vegetation period. We also identified genetic loci involved in late blight resistance and the length of vegetation period. A family of 156 individuals segregating for resistance to late blight was assessed by three laboratory methods: detached leaflet, tuber slice and whole tuber test, repeatedly over 5 years. Length of vegetation period was estimated by a field test over 2 years. The phenotypic distributions of all traits were close to normal. Using sequence-specific PCR markers of known chromosomal position on the potato genetic map, six quantitative trait loci (QTLs) for resistance and length of vegetation period were identified. The most significant and robust QTL were located on chromosomes III (explaining 17.3% of variance observed in whole tuber tests), IV (15.5% of variance observed in slice tests), X (15.6% of variance observed in leaflet tests) and V (19.9% of variance observed in length of vegetation period). Genetic characterization of these novel resistance sources can be valuable for potato breeders and the knowledge that the most prominent QTLs for resistance and vegetation period length do not overlap in this material is promising with respect to breeding early potatoes resistant to P. infestans.