Common scab caused by the soil-borne bacterium Streptomyces scabies is a serious disease for the potato industry. We have identified a strong source of resistance in the diploid wild relative Solanum chacoense. This resistance has been introgressed into tetraploid cultivated potato via unilateral sexual polyploidization. This paper describes three hybrid clones (M8, M16, M17) for use by potato breeding programs to enhance resistance to common scab. They were created by crossing a diploid clone (50% S. tuberosum, 50% S. chacoense) to tetraploid cultivars, producing hybrids with 75% cultivated and 25% wild germplasm. The clones are male and female fertile, and are adapted to temperate zone production environments.

Late blight of potato, tomato and some members of Solanaceae is of wide occurrence in many parts of the world leading to crop damages and yield losses. Caused by Phytophthora infestans which has a wide host range, late blight disease offers severe challenges to the crop growers in geographic localities where climatic conditions favor spread of the disease. In this study, we evaluated the susceptibility of potato (Solanum tuberosum L.), tomato (Solanum lycopersicum L.) and eggplant (Solanum melongena L.) to P. infestans. The foliar resistance of intact leaves and detached stems of three species were determined by the disease severity, incubation period and lesion area caused by the pathogen. The three crops significantly varied in response to late blight infection; potato and tomato showed severe disease symptoms, lesion area and lower incubation period. Foliage sensitivity was more evident than stems. Among the evaluated crops, eggplant was the most resistant to foliar and stem late blight disease suggesting its role in potential breeding for resistance purposes.

Somatic hybridization has been used in potato to overcome the sexual barriers between the cultivated (Solanum tuberosum L.) and wild species. To date hundreds of inter/intra-specific somatic hybrids have been produced via protoplast fusions using 23 Solanum species and characterized for multiple traits such as agronomic, disease/pest resistance, salinity, frost and others. With increasing success in recovery of fusion products, somatic hybrids have been exploited in potato genetics, breeding and genomics studies. Here, we report on progress in somatic hybridization research in potato during the past 40 years.

Long-term, sustainable management of zebra chip disease of potato, caused by ‘Candidatus Liberibacter solanacearum’ (Lso) and vectored by potato psyllids (Bactericera cockerelli Sulc [Hemiptera: Triozidae]), requires development of cultivars resistant or tolerant to infection or capable of reducing spread or both. We examined the influence that five experimental breeding clones of potato had on potato psyllids and their ability to vector Lso. The ability of these potato clones to resist aphids (green peach aphids, Myzus persicae Sulzer [Hemiptera: Aphididae]) also was examined. Due to the importance of host chemistry on plant–insect interactions, levels of primary metabolites of amino acids and sugars, as well as secondary metabolites including polyphenolics, terpenoids, and alkaloids were compared between breeding clones and a commercial cultivar. Findings for compound levels then were associated with observed changes in host susceptibility to psyllids or aphids. Psyllids oviposited less on three breeding clones than Atlantic, but no significant effects of breeding clones on psyllid feeding or choice were observed. Aphid reproduction was reduced on two clones relative to Atlantic. A05379-211 had greater sugar levels and postpsyllid amino acid levels than Atlantic. Total alkaloid and phenolic levels were greater in all breeding clones than Atlantic. Total terpenoid levels were greater in PALB03016-3 and PALB03016-6 than Atlantic, which might explain, in part, the observed resistance to psyllid oviposition and aphid reproduction. Overall, these results suggest that increased levels of certain metabolites in breeding clones could affect psyllid and aphid reproduction.

Late blight, caused by Phytophthora infestans, is an important disease of potato (Solanum tuberosum). Previous work has demonstrated that the wild diploid potato species Solanum bulbocastanum showed resistance to all known genotypes of P. infestans. In this study, the RB gene (also known as Rpi-blb1) from S. bulbocastanum was transformed and expressed into conventionally bred, late blight resistant breeding lines to evaluate the effect of pyramiding late blight resistance genes. All RB potato transformation events were confirmed by polymerase chain reaction and RB transcription was detected by reverse transcriptase-polymerase chain reaction. Multiple P. infestans genotypes were used to evaluate foliar host plant resistance using a greenhouse whole plant bioassay (WPB) and field trials. The results of the WPB were dependent on different pathogen genotypes. The RB lines derived from MSM171-A late blight resistant (LBR) parental line showed less foliar late blight than other RB lines. Field trials indicated most RB lines from three LBR parental lines had lower RAUDPC values than their parent and susceptible check line. Our results suggest that stacking of R-genes may be a viable strategy to obtain late blight resistant potato varieties.

Insight into pathogen population dynamics provides a key input for effective disease management of the potato late blight pathogen Phytophthora infestans. Phytophthora infestans populations vary from genetically complex to more simple with a few clonal lineages. The presence or absence of certain strains of P. infestans may impact the efficacy of fungicides or host resistance. Current evidence indicates that genetically, the Irish populations of P. infestans are relatively simple with a few clonal lineages. In this study, P. infestans populations were genetically characterized based on samples collected at the national centre for potato breeding during the period 2012–16. The dominance of clonal lineages within this P. infestans population was confirmed and the potential selection pressure of fungicide treatment (2013–15) and host resistance (2016) on this clonal P. infestans population was then investigated. It was found that fungicide products did not notably affect the genetic structure of sampled populations relative to samples from untreated control plants. In contrast, samples taken from several resistant potato genotypes were found to be more often of the EU_13_A2 lineage than those taken from control King Edward plants or potato genotypes with low resistance ratings. Resistant potato varieties Sarpo Mira and Bionica, containing characterized R genes, were found to strongly select for EU_13_A2 strains.

Potato is the third most important food crop in the world and is crucial to ensure food security. However, increasing biotic and abiotic stresses jeopardize its stable production. Fortunately, breeders count on a rich pool of wild relatives that provide sources for disease resistance and tolerance to environmental stresses. To use such traits effectively, breeders require tools that facilitate exploration and exploitation of the genetic diversity of potato wild relatives. Introgression programs to incorporate such alien chromatin into the crop have so far relied on cytogenetic and genetic studies to tap desired traits from these wild resources. The available genetic and cytogenetic tools, supplemented with more recent genomic technologies, can assist in the use of potato relatives in pre-breeding. This information can also facilitate cisgenesis and genome editing to improve potato cultivars. Despite the abundant and rapidly growing genomic information of potato, that of its wild relatives is still limited.

Cultivated potato (Solanum tuberosum L.) is a highly heterozygous autotetraploid that presents challenges in genome analyses and breeding. Wild potato species serve as a resource for the introgression of important agronomic traits into cultivated potato. One key species is Solanum chacoense and the diploid, inbred clone M6, which is self‐compatible and has desirable tuber market quality and disease resistance traits. Sequencing and assembly of the genome of the M6 clone of S. chacoense generated an assembly of 825 767 562 bp in 8260 scaffolds with an N50 scaffold size of 713 602 bp. Pseudomolecule construction anchored 508 Mb of the genome assembly into 12 chromosomes. Genome annotation yielded 49 124 high‐confidence gene models representing 37 740 genes. Comparative analyses of the M6 genome with six other Solanaceae species revealed a core set of 158 367 Solanaceae genes and 1897 genes unique to three potato species. Analysis of single nucleotide polymorphisms across the M6 genome revealed enhanced residual heterozygosity on chromosomes 4, 8 and 9 relative to the other chromosomes. Access to the M6 genome provides a resource for identification of key genes for important agronomic traits and aids in genome‐enabled development of inbred diploid potatoes with the potential to accelerate potato breeding.