The goal of this research was to identify quantitative trait loci (QTLs) for potato tuber resistance to the soil‐ and seedborne bacterium Dickeya solani and for tuber starch content, to study the relationship between these traits. A resistant diploid hybrid of potato, DG 00‐270, was crossed with a susceptible hybrid, DG 08‐305, to generate the F₁ mapping population. Tubers that were wound‐inoculated with bacteria were evaluated for disease severity, expressed as the mean weight of rotted tubers, and disease incidence, measured as the proportion of rotten tubers. Diversity array technology (DArTseq) was used for genetic map construction and QTL analysis. The most prominent QTLs for disease severity and incidence were identified in overlapping regions on potato chromosome IV and explained 22.4% and 22.9% of the phenotypic variance, respectively. The second QTL for disease severity was mapped to chromosome II and explained 16.5% of the variance. QTLs for starch content were detected on chromosomes III, V, VI, VII, VIII, IX, XI, and XII in regions different from the QTLs for soft rot resistance. Two strong and reproducible QTLs for resistance to D. solani on potato chromosomes IV and II might be useful for further study of candidate genes and marker development in potato breeding programmes. The relationship between tuber resistance to bacteria and the starch content in potato tubers was not confirmed by QTL mapping, which makes the selection of genotypes highly resistant to soft rot with a desirable starch content feasible.

Potato (Solanum tuberosum L.) is the third most important crop worldwide and a staple food for many people worldwide. Genetically, it poses many challenges for traditional breeding due to its autotetraploid nature and its tendency toward inbreeding depression. Breeding programs have focused on productivity, nutritional quality, and disease resistance. Some of these traits exist in wild potato relatives but their introgression into elite cultivars can take many years and, for traits such as pest resistance, their effect is often short-lasting. These problems can be addressed by genetic modification (GM) or gene editing (GE) and open a wide horizon for potato crop improvement. Current genetically modified and gene edited varieties include those with Colorado potato beetle and late blight resistance, reduction in acrylamide, and modified starch content. RNAi hairpin technology can be used to silence the haplo-alleles of multiple genes simultaneously, whereas optimization of newer gene editing technologies such as base and prime editing will facilitate the routine generation of advanced edits across the genome. These technologies will likely gain further relevance as increased target specificity and decreased off-target effects are demonstrated. In this Review, we discuss recent work related to these technologies in potato improvement.

KEY MESSAGE: Metabolic pathway gene editing in tetraploid potato enhanced resistance to late blight. Multiallelic mutation correction of a caffeoyl-CoA O-methyltransferase gene increased accumulation of resistance metabolites in Russet Burbank potato. Late blight of potato is a devastating disease worldwide and requires weekly applications of fungicides to manage. Genetic improvement is the best option, but the self-incompatibility and inter-specific incompatibility makes potato breeding very challenging. Immune receptor gene stacking has increased resistance, but its durability is limited. Quantitative resistance is durable, and it mainly involves secondary cell wall thickening due to several metabolites and their conjugates. Deleterious mutations in biosynthetic genes can hinder resistance metabolite biosynthesis. Here a probable resistance role of the StCCoAOMT gene was first confirmed by an in-planta transient overexpression of the functional StCCoAOMT allele in late blight susceptible Russet Burbank (RB) genotype. Following this, a precise single nucleotide polymorphism (SNP) mutation correction of the StCCoAOMT gene in RB potato was carried out using CRISPR-Cas9 mediated homology directed repair (HDR). The StCCoAOMT gene editing increased the transcript abundance of downstream biosynthetic resistance genes. Following pathogen inoculation, several phenylpropanoid pathway genes were highly expressed in the edited RB plants, as compared to the non-edited. The disease severity (fold change = 3.76) and pathogen biomass in inoculated stems of gene-edited RB significantly reduced (FC = 21.14), relative to non-edited control. The metabolic profiling revealed a significant increase in the accumulation of resistance-related metabolites in StCCoAOMT edited RB plants. Most of these metabolites are involved in suberization and lignification. The StCCoAOMT gene, if mutated, can be edited in other potato cultivars to enhance resistance to late blight, provided it is associated with other functional genes in the metabolic pathway network.

Potato is regarded as the future crop for assuring food security in the developing world. Of many diseases which limit the growth and trade value of potatoes, silver scurf is emerging at an alarming rate. Potato silver scurf is a widespread disease in which silvery skin blemishes appear on the periderm of tubers. The causal agent Helminthosporium solani Durieu & Mont is an Ascomycete fungus which attacks the potato plants in the field as well as in storage. The pathogen is reported to have a hemibiotrophic or necrotrophic lifestyle. The disease which was earlier considered of minor importance has become a major cause of non-acceptance of commercial potatoes during the last two decades. Lack of resistant cultivars and emergence of thiabendazole fungicide resistant strains has made it much more devastating in potato cultivation and trade. Several new fungicide molecules have been found very effective as seed treatment chemicals in mitigating this disease. Likewise, many beneficial microbial antagonists have shown mycoparsitism and antibiosis against this pathogen. These bioagents can be utilized in an integrated disease management program. Germplasm screening for disease resistance is an important aspect that will assist the resistance breeding program for the development of silver scurf resistant potato cultivars. The pathogen has multiple cell wall degrading enzymes and several genes in glucoside hydrolase family which suggest that there is a need to reconsider the life cycle of this pathogen with special emphasis on its host range. This review draws attention to the pathogenomics, infection process and management possibilities of silver scurf disease and proposes some critical questions to be addressed in the future.

Late blight, caused by the oomycete Phytophthora infestans, is the most devastating disease in potato-producing regions of the world. Cultivation of resistant varieties is the most effective and environmentally friendly way to control potato late blight disease, and identification of germplasms with late blight resistance and clarification their genetic relationship would promote the development of the resistant varieties. In this study, a diverse population of 189 genotypes with potential late blight resistance, consisting of 20 wild species and cultivated Solanum tuberosum Andigenum group and Chilotanum group, was screened for the presence of late blight resistance by performing challenge inoculation with four Phytophthora infestans isolates including one 13_A2 isolate, CN152. Ten elite resources with broad-spectrum resistance and 127 with isolate-specific resistance against P. infestans were identified. To improve the available gene pool for future potato breeding programs, the population was genotyped using 30 simple sequence repeat (SSR) markers covering the entire potato genome. A total of 173 alleles were detected with an average of 5.77 alleles per locus. Structure analysis discriminated the 189 potato genotypes into five populations based on taxonomic classification and genetic origin with some deviations. There was no obvious clustering by country of origin, ploidy level, EBN (endosperm balance number) value, or nuclear clade. Analysis of molecular variance showed 10.08% genetic variation existed among populations. The genetic differentiation (Fst) ranged from 0.0937 to 0.1764, and the nucleotide diversity (π) was 0.2269 across populations with the range from 0.1942 to 0.2489. Further genotyping of 20K SNP array confirmed the classification of SSRs and could uncover the genetic relationships of Solanum germplasms. Our results indicate that there exits abundant genetic variation in wild and cultivated potato germplasms, while the cultivated S. tuberosum Chilotanum group has lower genetic diversity. The phenotypic and genetic information obtained in this study provide a useful guide for hybrid combination and resistance introgression from wild gene pool into cultivated species for cultivar improvement, as well as for germplasm conservation efforts and resistance gene mining.

Die Kartoffel (Solanum tuberosum) ist weltweit eine der wichtigsten Nahrungspflanzen. Sie ist eine Kulturart mit vielfältigen Verwendungsmöglichkeiten und einem hohen Wertschöpfungspotenzial. Allerdings wird die Kulturkartoffel auch von einer Vielzahl an Schaderregern befallen. Die Kraut- und Knollenfäule (Phytophthora infestans) sowie verschiedene Viren verursachen beträchtliche Ertrags-und Qualitätseinbußen. Daher ist die Resistenzzüchtung gegen diese Schaderreger schon seit langem von entscheidender Bedeutung. Sie stehen ebenfalls im Fokus der Züchtungsforschung und Resistenzprüfung am Julius Kühn-Institut. Heute kommen neben klassischen Züchtungsmethoden, zunehmend Techniken der markergestützten Selektion im Zuchtprozess zur Anwendung. Auch Methoden der Genomeditierung können möglicherweise in Zukunft eingesetzt werden um gesunde und ertragsstabile Kartoffelsorten zu entwickeln. | Potato (Solanum tuberosum) is one of the most important staple foods worldwide carrying versatile opportunities in utilisation and high added value. Cultivated potato is threatened by various diseases and pests. Late blight caused by Phytophthora infestans and various viruses cause high losses in yield and quality. Since many decades breeding for disease resistance is of high importance. Thus at Julius Kühn-Institute breeding research and resistance testing are focussed on them. Besides classical breeding methods marker assisted selection becomes of increasing importance in the breeding process yet. In future methods of genome editing possibly will be introduced into the breeding process for healthy and high valuable potatoes.

Potato apical leaf curl disease (PALCD) caused by ToLCNDV has emerged as a serious threat to potatocultivation in India. Host resistance to the virus is the potent strategy to curb the menace of this disease. Identification ofpotato germplasm free from ToLCNDV is a major challenge for healthy seed production and also for an effective resistancebreeding programme. Novel and simple agro-inoculation of ToLCNDV was done to select resistant genotypes of potatoes. Aset of 9 advanced hybrids and 4 control varieties were evaluated for resistance to ToLCNDV under controlled conditions atICAR-Central Potato Research Institute, Shimla. Clear symptoms were visible in susceptible genotypes within 30 days afterthe first inoculation. Based on symptoms of the disease, a scale (0-5) was developed for ToLCNDV resistance screening.Phenotyping results showed the resistant reaction of SM/00-42, SM/00-120 and VMT5-1 to ToLCNDV. However, virus loadquantification of inoculated plant samples revealed low virus load in LBY 18, VMT5-1 and SM/00-42. All the four controlvarieties showed moderately susceptible to susceptible reaction with Kufri Pukhraj showing the highest virus load amongall genotypes. The hybrid, SM/00-42 was found to promising due to its resistant reaction and very low virus load. This canbe effectively utilized in ToLCNDV resistance breeding or direct deployment after agronomic evaluation. Moreover, thescale developed in the present study could be used in preliminary screening for the disease.

The oomycete Phytophthora infestans is responsible for the disease known as late blight in potato and tomato. It is the plant pathogen that has caused the greatest impact on humankind so far and, despite all the studies that have been made, it remains the most important in this crop. In Spain during the last years a greater severity of the disease has been observed in both, potato and tomato, probably due to genetic changes in pathogen populations described recently. The aim of this study was the characterization of the physiological strains of 52 isolates of P. infestans obtained in different potato-growing areas in Spain. For this purpose, inoculations on detached leaves were performed in order to determine compatibility or incompatibility reactions. A total of 17 physiological races were found. The less frequent virulence factors were Avr5 and Avr8. By studying the epidemiology of the pathogen, a specific breeding program for late blight resistance can be implemented.