Potato (Solanum tuberosum L.) is among the most important upland crops cultivated for many end uses throughout Japan. Potatoes are consumed in different ways, such as table use, food processing, starch production, and others. At the same time, various cropping systems are adopted according to environmental conditions. Although potato-breeding programs in Japan are conducted by considering these demands, pest and disease resistance is one of the most important traits required for all modern cultivars. There are many pests and diseases affecting potato production in Japan, where conferring resistance against potato cyst nematodes, late blight, common scab, bacterial wilt, and viral diseases has become a main target of breeding. Artificial inoculation tests and cultivation in infested fields were traditionally conducted, in order to evaluate the levels of resistance among breeding materials. However, several DNA markers for pest and disease resistance genes have recently been developed for the selection of resistant genotypes. We have taken both approaches toward the selection of pest and disease resistant genotypes at each breeding step. This review introduces our approaches to develop new pest and disease resistant potato cultivars by using classical and molecular approaches.

We examined inoculation conditions for testing the soil rot disease resistance of sweet potato, with the aim of establishing a test method that uses the lesions in tuberous root tissue sections. In inoculation tests with mycelial agar disk inoculum of the pathogen to two sweet potato cultivars and one breeding line with different levels of resistance ('Kokei No. 14', 'Purple sweet lord', and '90IDN-47'), no significant differences were found in resistance characteristics. However, when the inoculation test was performed on tuberous root tissue sections that had been dipped into mycelial fragment suspensions of different pathogen concentrations and then buried in vermiculite with different moisture contents at 30degC, a significant difference in resistance could be observed at an inoculum suspension dilution of 1,000 times (v/w) fresh mycelial weight (approximately 10E5 CFU/ml) and a soil moisture content of 187.0% (v/w). In this inoculation condition, the inoculated sweet potato tuberous root tissue sections started to exhibit lesions 3 days after inoculation, and severities of the disease particularly became more intense from 6 to 7 days after inoculation. As a result, it was possible to clearly distinguish the levels of resistance in these cultivars and breeding line.

Selection of disease resistant potato varieties for conventional breeders is a time consuming and labor intensive process and most of the times lead to the results that are spatiotemporally inconsistent. Metabolic phenotyping was employed to develop metabolic criteria that can be used to distinguish potato genotypes with disease resistance. Tubers of potato varieties (Caesar and AC Novachip) moderately resistant and susceptible to Phytophthora infestans were inoculated with pathogen or water, and metabolites were analyzed using Gas Chromatography-mass Spectrometry (GS/MS). Disease severity was measured as the volume of diseased tissue calculated based on lesions volume at 2-day intervals after inoculation. Disease severity was 4.17 and 0.61 cm³ for varieties Caesar and AC Novachip respectively. Seventy seven metabolites were tentatively identified using Automated Mass spectral Deconvolution and Identification System (AMDIS) and univariate ANOVA showed that 37 metabolites had significant treatment effects with nine identified as resistance related and five as constitutive metabolites. Four metabolites, constitutive or induced showed significant increase in their abundance in pathogen inoculated tubers. A total of 21 metabolites were considered as pathogenesis related which showed changes in abundance after pathogen challenge. A canonical discriminant analysis of the 37 metabolites identified metabolic phenotypes correlating to disease severity phenotypes. The metabolites were mainly from sugars, fatty acids, and phenolic compounds which of some may have potential antimicrobial activity. Among resistance related metabolites, the abundances of 1H-Indole-3-acetonitrile, trihydroxybutyrate, D-Mannitol, dihydocoumarin, and propanoate were significantly higher in Caesar. The potential application of metabolic profiling technology for high throughput screening of potato breeding lines against potato late blight is discussed.

Late blight of potato causes significant yield losses and poses severe threat to potato production in Pakistan. Screening potato genotypes for resistance to Phytophthora infestans is the most effective and environmental friendly way to prevent widespread devastation by late blight. The present experiment was carried out to examine the level of field resistance to late blight, caused by Phytophthora infestans (Mont.) de Bary, in the local cultivated potato germplasm. Eighteen potato cultivars were screened under the field conditions in the Research Area of the Institute of Horticultural Sciences, University of Agriculture, Faisalabad, Pakistan after inoculation with highly virulent race of pathogen. The results revealed variable responses of all the cultivars towards the pathogen. Five potato cultivars viz. FD35-36, Diamond, Cardinal, Rossana and FD37-13 exhibited highly resistant reaction. Two cultivars NARC-46, FD63-4 exhibited moderately resistant response while FD69-1, SH103, FD65-4 and FD7-2 responded moderately susceptible response. The cultivars FD49-62, 394055-40, TPS9801, FD96-19, FD48-54 and FD50-1 were susceptible while the single cultivar Desiree exhibited highly susceptible response towards the disease. These resistant sources could further be exploited in breeding program for the development of disease resistant commercial cultivars against late blight pathogen.

International audience | The oomycete Phytophthora infestans causes late blight of potato, which can completely destroy the crop. Therefore, for the past 160 years, late blight has been the most important potato disease worldwide. The identification of cultivars with high and durable field resistance to P. infestans is an objective of most potato breeding programs. This type of resistance is polygenic and therefore quantitative. Its evaluation requires multi-year and location trials. Furthermore, quantitative resistance to late blight correlates with late plant maturity, a negative agricultural trait. Knowledge of the molecular genetic basis of quantitative resistance to late blight not compromised by late maturity is very limited. It is however essential for developing diagnostic DNA markers that facilitate the efficient combination of superior resistance alleles in improved cultivars. We used association genetics in a population of 184 tetraploid potato cultivars in order to identify single nucleotide polymorphisms (SNPs) that are associated with maturity corrected resistance (MCR) to late blight. The population was genotyped for almost 9000 SNPs from three different sources. The first source was candidate genes specifically selected for their function in the jasmonate pathway. The second source was novel candidate genes selected based on comparative transcript profiling (RNA-Seq) of groups of genotypes with contrasting levels of quantitative resistance to P. infestans. The third source was the first generation 8.3k SolCAP SNP genotyping array available in potato for genome wide association studies (GWAS). Twenty seven SNPs from all three sources showed robust association with MCR. Some of those were located in genes that are strong candidates for directly controlling quantitative resistance, based on functional annotation. Most important were: a lipoxygenase (jasmonate pathway), a 3-hydroxy- 3-methylglutaryl coenzyme A reductase (mevalonate pathway), a P450 protein (terpene biosynthesis), a transcription factor and a homolog of a major gene for resistance to P. infestans from the wild potato species Solanum venturii. The candidate gene approach and GWAS complemented each other as they identified different genes. The results of this study provide new insight in the molecular genetic basis of quantitative resistance in potato and a toolbox of diagnostic SNP markers for breeding applications.

The potato is one of the top staple foods in the world and is an important crop regarding food security. The potato's ease of cultivation and high energy content make it a valuable crop for millions of farmers. Climate changes mean that potato production is increasingly vulnerable to a wide range of pathogens (including Phytophthora infestans (late blight), nematodes, bacteria, viruses and insects and environmental stresses (drought, heat, cold and salinity). The publication of the genome sequence is a major step in understanding potato biology and is accelerating the breeding of new cultivars. The use of genetics-based selection methods is promising and the technology to exploit the genome sequence immediately is already being applied in the UK and elsewhere. An understanding of the genetic blueprint for potato gives us the option of introducing desirable characteristics into existing cultivars more efficiently, such as enhanced pest and disease resistance and improved tuber quality characteristics. Marker-assisted selection (MAS) can be effectively used to identify major genes and QTLs that exhibit significant effects. However, there are also a number of important and complex traits, such as yield and quality that are influenced by a large number of individual small effect genes dispersed across the genome making the application of MAS difficult. Progeny testing and using pedigree information in the analysis can provide effective identification of the inherent factors that underpin these complex traits. This paper discusses recent advances in potato breeding and how their application to simple and complex traits is improving the efficiency of potato breeding programs.

Potato late blight, caused by Phytophthora infestans, is one of the main diseases in potato production, causing major losses in yield. Applying environmentally harmful fungicides is the prevailing and classical method for controlling late blight, thus contaminating food and water. There is therefore a need for innovative research approaches to produce food sustainably. Here, we used a systems approach to identify sustainable management strategies for disease control in potato production in the Netherlands. We focussed not only on ecological processes, the classical approach, but also on decision-making concerning disease management. For that, we performed a literature study, stakeholder interviews and modelling using fuzzy cognitive mapping. Interviews were carried out with farmers, representatives of breeding companies and experts. The fuzzy cognitive map allows to identify major concepts and their influence on late blight management. Three management scenarios were analysed using the fuzzy cognitive map. Results show that published research on the control of potato late blight focusses on agronomic practices, plant breeding for resistance to late blight and chemical-based disease suppression. Farmers are strongly influenced by corporate (such as traders, breeders and retail) and public institutes and policies, each pushing their own objectives and interests. The fuzzy cognitive map showed that social and ecological processes are tightly related. The scenario analysis showed that increasing stakeholder cooperation and a change in market demands towards resistant cultivars could improve sustainability of late blight management. In contrast, policies restricting the use of fungicides would result in increased disease severity if no alternative strategies were implemented. Adoption of such strategies would require social-institutional support and facilitation. We conclude that our systems approach improves the understanding of the system dynamics which is necessary for developing and deploying effective strategies for controlling P. infestans.

Rhizoctonia solani is an important root infecting pathogen of a range of food staples worldwide including wheat, rice, maize, soybean, potato, legumes and others. Conventional resistance breeding strategies are hindered by the absence of tractable genetic resistance in any crop host. Understanding the biology and pathogenicity mechanisms of this fungus is important for addressing these disease issues, however, little is known about how R. solani causes disease. The data described in this article is derived from applying mass spectrometry based proteomics to identify soluble, membrane-bound and culture filtrate proteins produced under wheat infection and vegetative growth conditions. Comparisons of the data for sample types in this set will be useful to identify metabolic pathway changes as the fungus switches from saprophytic to a pathogenic lifestyle or pathogenicity related proteins contributing to the ability to cause disease on wheat. The data set is deposited in the PRIDE archive under identifier PRIDE: PXD002806.

Late blight caused by Phytophthora infestans is a devastating disease affecting potato production worldwide. The quantitative resistance is durable, but the underlying molecular and biochemical mechanisms are poorly understood, limiting its application in breeding. Integrated transcriptomics and metabolomics approach was used for the first time to study the hierarchies of molecular events occurring, following inoculation of resistant and susceptible potato genotypes with P. infestans. RNA sequencing revealed a total of 4216 genes that were differentially expressed in the resistant than in the susceptible genotype. Genes that were highly expressed and associated with their biosynthetic metabolites that were highly accumulated, through metabolic pathway regulation, were selected. Quantitative real-time PCR was performed to confirm the RNA-seq expression levels. The induced leucine-rich repeat receptor-like kinases (LRR-RLKs) are considered to be involved in pathogen recognition. These receptor genes are considered to trigger downstream oxidative burst, phytohormone signalling-related genes, and transcription factors that regulated the resistance genes to produce resistance related metabolites to suppress the pathogen infection. It was noted that several resistance genes in metabolic pathways related to phenylpropanoids, flavonoids, alkaloids and terpenoid biosynthesis were strongly induced in the resistant genotypes. The pathway specific gene induction provided key insights into the metabolic reprogramming of induced defence responses in resistant genotypes.