The two most important bacterial diseases of cultivated potato, blackleg of stems and tuber soft rot, are caused by Erwinia species. Genetic resistance currently present in cultivars is insufficient to protect the crop. New sources of polygenic resistance to Erwinia carotovora ssp. atroseptica (van Hall) Dye (Eca) have been selected in diploid hybrids originating from intercrossing Solanum tuberosum L with the wild species S. chacoense Bitter and S. yungasense Hawk. One F1 hybrid population derived from these materials was used to locate, on the molecular map of potato, quantitative trait loci (QTL) for resistance of tubers and leaves to Eca. A linkage map was constructed based on AFLP and RFLP markers including three resistance‐gene‐like (RGL) markers. Clustering of AFLP markers in putative centromeric regions was observed. QTL analysis revealed complex inheritance of resistance to Eca. Genetic factors affecting resistance to Eca were located on all 12 potato chromosomes. Putative QTL for tuber resistance were identified on 10 chromosomes. The QTL with the largest and most reproducible effect on tuber resistance mapped to chromosome I. Effects on leaf resistance were less reproducible than effects on tuber resistance. Putative QTL for leaf resistance were identified on 10 chromosomes. Inheritance of tuber and leaf resistance to Eca was largely independent. Several QTL for resistance to Eca were linked to RGL loci. Four of those QTL mapped to genomic segments that have been shown to contain factors for qualitative and quantitative resistance to different pathogens in potato, tomato (Lycopersicon esculentum Mill.), or tobacco (Nicotiana tabacum L.).

Solanum nigrumis a self-pollinating, hexaploid weed and one of a fewSolanaceaespecies native to Europe. It used to be described as a non-host forPhytophthora infestans. However, now it is known that, like its distant relatives: potato (Solanum tuberosumL.) and tomato (Solanum lycopersicumL.),S. nigrumcan suffer from potato late blight caused by this pathogen. Both susceptible and resistantS. nigrumgenotypes have been previously identified and inheritance of resistance originating from one accession has been described based on population of F₂plants and 15 F₃lines. The goal of this study was to evaluate resistance of three families of F₃lines, originating from crosses between a susceptible and three different resistantS. nigrumaccessions followed by two self-pollinations. Parental accessions were tested for the spectrum of late blight resistance against 48P. infestansisolates. The three families consisted of 106, 96 and 115 F₃lines, respectively, and from each line 20 plants were tested for resistance toP. infestans. Laboratory detached leaf assays were performed in two dates and two replications of three leaves each. Segregation of the trait within the line allowed us to distinguish hetero- and homozygous lines. In one F₃family, the ratio of resistant homozygotes: heterozygotes: susceptible homozygotes was 1:2:1, indicating that a single gene is most likely underlying the late blight resistance in this case. In the other two, observed segregations of the trait significantly deviated from this model suggesting more complex inheritance patterns.