Disease Resistance In Potato Research Articles

Alternative splicing of a potato disease resistance gene maintains homeostasis between growth and immunity.

Plants possess a robust and sophisticated innate immune system against pathogens and must balance growth with rapid pathogen detection and defense. The intracellular receptors with nucleotide-binding leucine-rich repeat (NLR) motifs recognize pathogen-derived effector proteins and thereby trigger the immune response. The expression of genes encoding NLR receptors is precisely controlled in multifaceted ways. The alternative splicing (AS) of introns in response to infection is recurrently observed but poorly understood. Here we report that the potato (Solanum tuberosum) NLR gene RB undergoes AS of its intron, resulting in 2 transcriptional isoforms, which coordinately regulate plant immunity and growth homeostasis. During normal growth, RB predominantly exists as an intron-retained isoform RB_IR, encoding a truncated protein containing only the N-terminus of the NLR. Upon late blight infection, the pathogen induces intron splicing of RB, increasing the abundance of RB_CDS, which encodes a full-length and active R protein. By deploying the RB splicing isoforms fused with a luciferase reporter system, we identified IPI-O1 (also known as Avrblb1), the RB cognate effector, as a facilitator of RB AS. IPI-O1 directly interacts with potato splicing factor StCWC15, resulting in altered localization of StCWC15 from the nucleoplasm to the nucleolus and nuclear speckles. Mutations in IPI-O1 that eliminate StCWC15 binding also disrupt StCWC15 re-localization and RB intron splicing. Thus, our study reveals that StCWC15 serves as a surveillance facilitator that senses the pathogen-secreted effector and regulates the trade-off between RB-mediated plant immunity and growth, expanding our understanding of molecular plant-microbe interactions.

Determining Adaptability of Potato Genotypes in Mount Elgon Region of Uganda

Potato (Solanum tuberosum L.) in Uganda is mainly produced in the highland areas of Kabale and Kisoro in south western and Bugisu and Sebei areas on the slopes of Mt. Elgon in the eastern part of the country. However, the yields have continuously reduced due to lack of suitable high yielding and disease resistant varieties. The purpose of this study was to identify high yielding disease resistant potato genotypes adapted to Mt. Elgon region. Eight CIP potato clones were evaluated alongside ten commonly grown Ugandan varieties in RCBD for two seasons at Buginyanya station, Bulambuli District. Results showed significant differences (P<0.05) in tuber size, tuber uniformity, marketable tuber yield and the total tuber yield among genotypes. Potato clones 392797.22 and 398208.29 produced significantly (P<0.001) higher tuber yield 44.8 t/ha and 39 t/ha respectively compared to the local check Cruza with 34.5 t/ha. rAUDPC for LB showed significant differences (P<0.001) among genotypes in both seasons. The most resistant genotypes were Kinigi and clone 399985.39 with rAUDPC of 0.0135 and 0.025 respectively whereas Bumbamagara (0.413) and 396036.201 (0.392) were the most susceptible. 396036.201(0.051) and Kinigi were the most resistant genotypes for bacterial wilt while Shangi (0.66) and Cruza (0.46) were the most susceptible to BW. Generally, genotypes 392797.22 and 398208.29 were the highest yielding and disease resistant hence recommended for release as commercial varieties.

Control of potato wart disease (Synchytrium endobioticum) by fungicide soil treatments

Synchytrium endobioticum is the causative agent of potato wart disease and can remain in the soil for several years via its sporangia. Effective protection against this disease includes quarantine and the use of disease-resistant potato varieties. However, so far it has not been eradicated. The aim of this study was to determine the effect of fungicides for soil treatment to protect against potato wart. Experiments were conducted with propamocarb hydrochloride 722 SC g/l, metalaxyl M + fludioxonil 10 + 25 g/l, gimexazole 360 g/l, tolklofos methyl + thiram 30 + 30%, dimethomorph + cuproxy chloride 6 + 40WP, famoxadone + cymoxanil 22.5 + 30%, Mandipropamide + Mancoceb 5 + 60%, Zoxamide + Mancoceb 8.3 + 66.7% in the growth chamber and field conditions — showed that Famoxadone + Cimoxanil 22.5 + 30% is able to protect against the disease by 100% in both experimental conditions.

Lipid transfer protein StLTPa enhances potato disease resistance against different pathogens by binding and disturbing the integrity of pathogens plasma membrane.

Potato is the third most important food crop worldwide. Potato production suffers from severe diseases caused by multiple detrimental plant pathogens, and broad-spectrum disease resistance genes are rarely identified in potato. Here we identified the potato non-specific lipid transfer protein StLTPa, which enhances species none-specific disease resistance against various pathogens, such as the oomycete pathogen Phytophthora infestans, the fungal pathogens Botrytis cinerea and Verticillium dahliae, and the bacterial pathogens Pectobacterium carotovorum and Ralstonia solanacearum. The StLTPa overexpression potato lines do not show growth penalty. Furthermore, we provide evidence that StLTPa binds to lipids present in the plasma membrane (PM) of the hyphal cells of P. infestans, leading to an increased permeability of the PM. Adding of PI(3,5)P2 and PI(3)P could compete the binding of StLTPa to pathogen PM and reduce the inhibition effect of StLTPa. The lipid-binding activity of StLTPa is essential for its role in pathogen inhibition and promotion of potato disease resistance. We propose that StLTPa enhances potato broad-spectrum disease resistance by binding to, and thereby promoting the permeability of the PM of the cells of various pathogens. Overall, our discovery illustrates that increasing the expression of a single gene in potato enhances potato disease resistance against different pathogens without growth penalty.

PotatoG-DKB: a potato gene-disease knowledge base mined from biological literature.

Potato is the fourth largest food crop in the world, but potato cultivation faces serious threats from various diseases and pests. Despite significant advancements in research on potato disease resistance, these findings are scattered across numerous publications. For researchers, obtaining relevant knowledge by reading and organizing a large body of literature is a time-consuming and labor-intensive process. Therefore, systematically extracting and organizing the relationships between potato genes and diseases from the literature to establish a potato gene-disease knowledge base is particularly important. Unfortunately, there is currently no such gene-disease knowledge base available. In this study, we constructed a Potato Gene-Disease Knowledge Base (PotatoG-DKB) using natural language processing techniques and large language models. We used PubMed as the data source and obtained 2,906 article abstracts related to potato biology, extracted entities and relationships between potato genes and related disease, and stored them in a Neo4j database. Using web technology, we also constructed the Potato Gene-Disease Knowledge Portal (PotatoG-DKP), an interactive visualization platform. PotatoG-DKB encompasses 22 entity types (such as genes, diseases, species, etc.) of 5,206 nodes and 9,443 edges between entities (for example, gene-disease, pathogen-disease, etc.). PotatoG-DKP can intuitively display associative relationships extracted from literature and is a powerful assistant for potato biologists and breeders to understand potato pathogenesis and disease resistance. More details about PotatoG-DKP can be obtained at https://www.potatogd.com.cn/.

Biotechnological Approaches to Increase the Bacterial and Fungal Disease Resistance in Potato

Potato (Solanum tuberosum) is a valuable cultivated vegetable with high nutritional qualities containing a variety of essential ingredients such as starch, vitamins and essential minerals. However cultivating potatoes is significantly complicated by diseases caused by a number of phytopathogens of both bacterial and fungal nature. Phytophthora infestans, Alternaria sp., Phoma exigua, Rhizoctonia solani, Fusarium sp., Verticillium sp., Clavibacter michiganensis subsp. sepedonicus, Pectobacterium sp., Dickeya sp. are considered amongst the most dangerous phytopathogens. This paper reviews the latest biotechnological approaches to the creation of potato plants resistant to a wide range of pathogens. In particular, the possibilities of applying genetic engineering methods to obtain potato plants resistant to pathogens, such as Solanum venture, S. mochiquence, S. demissum, S. bulbocastanum; avirulence genes; genes of antimicrobial peptides of plant, bacterial and animal origin by transferring the genes of resistance (R-genes) isolated from systematically related species into their genome. The review states that marker-assisted selection is suitable for obtaining varieties of S. tuberosum resistant to bacterial and fungal phytopathogens, where the R-genes or QTL regions can act as markers. Prospects for the use of genome editing technology using CRISPR/Cas9 or TALEN systems as one of the newest approaches to creating phytopathogen-resistant S. tuberosum plants have been considered. Achievements and successes in this way using these methods are analyzed in a detailed way in this review.

MANAGEMENT STRATEGIES FOR POTATO COMMON SCAB

Common scab (CS) is a major disease and quality issue in potato crops all over the world. Due to surface degradation market value is decreased. In recent years, the understanding of CS has grown significantly, allowing a better identification of the causative pathogens and a better understanding of pathogenicity processes, as well as prospective techniques for modifying pathogen response for disease resistance. Effective control of the disease, on the other hand, remains challenging, and needs a better knowledge of both the host and the pathogen. Irrigation and lowering the pH of the soil are common yet ineffective management techniques. Change in environmental conditions can affect the pathogen virulence which may results in disease reduction. Improving environmental conditions to reduce CS is, paradoxically, conducive for other diseases. Disease resistant potato varieties would be the best control approach. This review, provides an overview of potato CS caused by some Streptomyces species (viz. scabies, europaeiscabiei, turgidiscabies, that produce phytotoxins known as thaxtomins. Recent research findings on disease causes and treatment, and knowledge gaps that prevent successful control of this widespread and severe disease. This review also targets the history, symptoms and casual organisms of CS along with integrated management strategies (IMS) that includes soil amendments and agronomic practices.

Genome-Wide Profiling of DNA Methylome and Transcriptome Reveals Epigenetic Regulation of Potato Response to DON Stress.

Potato is an important food crop that occupies lesser area but has greater production than rice and wheat. However, potato production is affected by numerous biotic and abiotic stresses, among which Fusarium dry rot is a disease that has significant effect on potato production, storage, and processing. However, the role of DNA methylation in regulating potato response to Fusarium toxin deoxynivalenol (DON) stress is still not fully understood. In this study, we performed DNA methylome and transcriptome analyses of potato tubers treated with five concentrations of DON. The global DNA methylation levels in potato tubers treated with different concentrations of DON showed significant changes relative to those in the control. In particular, the 20 ng/ml treatment showed the largest decrease in all three contexts of methylation levels, especially CHH contexts in transposon regions. The differentially methylated region (DMR)-associated differentially expressed genes (DEGs) were significantly enriched in resistance-related metabolic pathways, indicating that DNA methylation plays an essential role in potato response to DON stress. Furthermore, we examined lesions on potato tubers infested with Fusarium after treatment. Furthermore, the potato tubers treated with 5 and 35 ng/ml DON had lesions of significantly smaller diameters than those of the control, indicating that DON stress may induce resistance. We speculate that this may be related to epigenetic memory created after DNA methylation changes. The detailed DNA methylome and transcriptome profiles suggest that DNA methylation plays a vital role in potato disease resistance and has great potential for enhancing potato dry rot resistance.

Snakin-2 interacts with cytosolic glyceraldehyde-3-phosphate dehydrogenase 1 to inhibit sprout growth in potato tubers.

The potato tuber is the main nutrient supply and reproductive organ; however, tuber sprouting can reduce its commercial value. Snakin-2 (StSN2) was first reported as an antimicrobial peptide that positively regulates potato disease resistance. Our recent study suggested StSN2 overexpression inhibited sprout growth, while the sprouting process was accelerated in StSN2 RNAi lines. Cytoplasmic glyceraldehyde-3- phosphate dehydrogenase 1 (StGAPC1) was identified as a candidate protein that interacts with StSN2 by coimmunoprecipitation/mass spectrometry (CoIP/MS) experiments. Here, we report that the expression levels of StSN2 and StGAPC1 decreased during sprouting compared with dormancy. Coexpression of StSN2 and StGAPC1 in bud eyes and apical buds was verified by immunofluorescence analysis of paraffin sections. In addition, interaction of StSN2 and StGAPC1 was confirmed by yeast two-hybrid, coimmunoprecipitation and split luciferase complementation assays. Overexpression of StGAPC1 depressed sprout growth, which is similar to the function of StSN2, and StSN2- and StGAPC1-overexpressing lines showed decreased glucose, fructose and galactose content. The interaction of StSN2 and StGAPC1 enhanced StGAPC1 activity and decreased its oxidative modification to inhibit sprout growth. Our results suggest that StSN2 plays a regulatory role in tuber sprout growth through interaction with StGAPC1.

Genome Enhanced Marker Improvement for Potato Virus Y Disease Resistance in Potato

Potato is an important food crop worldwide and is grown in a large number of countries. As such, the crop is under disease pressures and the need for selecting disease resistance genes during breeding programs is essential. Of particular importance within Australia and other parts of the world is the potyvirus, Potato virus Y (PVY). In this paper, three commonly used PVY resistance markers, M45, RYSC3 and M6, were evaluated using existing genomic resources and phenotypic data from the Australian potato breeding program to identify a region where the PVY resistance gene, Ryadg may reside. A region of Chromosome XI was investigated, and a cluster of disease resistance genes was identified that the resistance gene Ryadg is suspected to reside within. Protein characterization was also performed on the putative resistant gene. A specific variant that had complete association with the resistance gene was identified and a single nucleotide polymorphism (SNP) assay was designed to avoid dissociation of marker and gene in future breeding programs. This SNP marker (SNP37279) was validated as a Kompetitive Allele-specific PCR (KASP) genotyping assay and was found to perform more accurately than all previously used markers for detecting Ryadg.

Comparative proteomics of three Chinese potato cultivars to improve understanding of potato molecular response to late blight disease

BackgroundLate blight disease (LBD) caused by the pathogen Phytophthora infestans (PI), is the most devastating disease limiting potato (Solanum tuberosum) production globally. Currently, this disease pathogen is re-emerging and appearing in new areas at a very high intensity. A better understanding of the natural defense mechanisms against PI in different potato cultivars especially at the protein level is still lacking. Therefore, to elucidate potato proteome response to PI, we investigated changes in the proteome and leaf morphology of three potato cultivars, namely; Favorita (FA), Mira (MA), and E-malingshu N0.14 (E14) infected with PI by using the iTRAQ-based quantitative proteomics analysis.ResultsA total of 3306 proteins were found in the three potato genotypes, and 2044 proteins were quantified. Cluster analysis revealed MA and E14 clustered together separately from FA. The protein profile and related functions revealed that the cultivars shared a typical hypersensitive response to PI, including induction of elicitors, oxidative burst, and suppression of photosynthesis in the potato leaves. Meanwhile, MA and E14 deployed additional specific response mechanism different from FA, involving high induction of protease inhibitors, serine/threonine kinases, terpenoid, hormone signaling, and transport, which contributed to MA tolerance of LBD. Furthermore, inductions of pathogenesis-related proteins, LRR receptor-like kinases, mitogen-activated protein kinase, WRKY transcription factors, jasmonic acid, and phenolic compounds mediate E14 resistance against LBD. These proteins were confirmed at the transcription level by a quantitative polymerase chain reaction and at the translation level by western-blot.ConclusionsWe found several proteins that were differentially abundant among the cultivars, that includes common and cultivar specific proteins which highlighted similarities and significant differences between FA, MA, and E14 in terms of their defense response to PI. Here the specific accumulation of mitogen-activated protein kinase, Serine/threonine kinases, WRKY transcription played a positive role in E14 immunity against PI. The candidate proteins identified reported in this study will form the basis of future studies and may improve our understanding of the molecular mechanisms of late blight disease resistance in potato.

Recreation of the Edinburgh Potato Solanum ×Edinense Berthault

Solanum ×edinense Berthault, is a spontaneously occurring hybrid between S. demissum Lindl. and the cultivated potato, S. tuberosum L., found near potato fields in Mexico. Although not described until 1911, this hybrid was in cultivation at the Royal Botanic Garden Edinburgh shortly after the Irish Potato Famine of 1845–1849 and proved to be highly resistant to late blight, Phytophthora infestans. In the mid-19th century late blight caused widespread failure of the potato crop across Europe and played a central role in the Irish Potato Famine. Using the parent species in controlled crosses we have recreated the hybrid that was named by Berthault in recognition of the Royal Botanic Garden Edinburgh as the source of his plant material. We have also researched the early history of this hybrid potato in Edinburgh and demonstrated disease resistance through field exposure during the outbreak of late blight in Edinburgh in 2019. This work underlines the important role of this hybrid in the breeding of disease resistant potato cultivars.

New Findings on the Resistance Mechanism of an Elite Diploid Wild Potato Species JAM1-4 in Response to a Super Race Strain of Phytophthora infestans.

Late blight is a devastating potato disease worldwide, caused by Phytophthora infestans. The P. infestans strain 2013-18-306 from Yunnan is a "supervirulent race" that overcomes all 11 known late blight resistance genes (R1 to R11) from Solanum demissum. In a previous study, we identified a diploid wild-type potato JAM1-4 (S. jamesii) with high resistance to 2013-18-306. dRenSeq analysis indicated the presence of novel R genes in JAM1-4. RNA-Seq was used to analyze the late blight resistance response genes and defense regulatory mechanisms of JAM1-4 against 2013-18-306. Gene ontology enrichment and KEGG pathway analysis showed that many disease-resistant pathways were significantly enriched. Analysis of differentially expressed genes (DEGs) revealed an active disease resistance mechanism of JAM1-4, and the essential role of multiple signal transduction pathways and secondary metabolic pathways comprised of SA-JA-ET in plant immunity. We also found that photosynthesis in JAM1-4 was inhibited to promote the immune response. Our study reveals the pattern of resistance-related gene expression in response to a super race strain of potato late blight and provides a theoretical basis for further exploration of potato disease resistance mechanisms, discovery of new late blight resistance genes, and disease resistance breeding.

Producing of potato varieties resistant to fusarial wilt by cell selection

The experiment has determined the characteristic features of callusogenesis, regeneration as well as of receiving resistant to fusariosis of potatoes cell lines in simulated conditions of biotic stress. The technologic elements of potato cell selection towards its resistance to Fusarium oxysporum and Fusarium sabucinum were presented. We succeeded in separating the lines which during a 3-year period of research were characterised by a higher resistance point as compared to the original varieties Gurman and Tyras. The plants-regenerants received on the selective medium were characterised by higher resistance (by 10–35%) to the pathogens action as compared to the regenerants of a control variant. The received lines were estimated on their yield capacity and starch content. The lines deviations on economically valuable indices either increased or decreased as to characteristic value. Herewith, the deviation upward is 25–75% depending on characteristics. The combination of maximal characteristic values was found in lines 12 and 28 of Gurman variety. The received lines were given to the selection-breeding plot for further testing. Key words: Potatoes; Culture in vitro; Cell selection; Selective medium; Phytotoxic metabolites; Plants-regenerants. References Behnke, �?. (1980). General resistance to late blight of Solanum tuberosum plants regenerated from callus resistant to culture filtrates of Phytophthora infestans. Theor. and Appl. Genet., 9, 151–152. Bolic, M., Foroughi-Wehr, B., & Kohler, F. (1986). In vitro selection for disease resistance in potato and barley. Nuclear Technigues and in vitro Culture for Plant Improvement, 12, 275–285. Kalashnikova, E.A. (2003). Cell selection of plants on their resistance to fungus diseases. Thesis of Doctoral Dissertation. Moscow (in Russian). Murashige, T. & Scoog, A. (1962). A revised medium for rapid growth and bioassays with tobacco tissue cultures. Physiol. Plant., 15, 473–497. Podgayetskiy, A.A. & Gorbas, S.B. (2013). The feasibility of getting high-starch forms from among the progeny from crossing of interspecific hybrids. Bulletin of Sumy National Agrarian University, 3(25), 224–228 Polozhenets, V.M., Tymoschuk, O.A. & Zhuravska, I.A. (2006). Fusarium dry rot of potatoe. Quarantine and plants protection, 8, 13–15. Zaharchuk, N.A. (2013). The effectiveness of potatoe selection in vitro on its resistance to Fusarium oxysporum and Fusarium sambucinum. Bulletin of Sumy National Agrarian University, 11 (26), 188–228.

Exogenous SA Initiated Defense Response and Multi-signaling Pathway in Tetraploid Potato SD20

Salicylic acid (SA) is an important signaling substance that plays an important role in plant growth, development and disease resistance. In order to further understand the role of the SA pathway in potato disease resistance and identify SA signaling key genes, gene expression profiling of the late blight resistance genotype SD20 was performed under exogenous SA application. A total of 28 572 unigenes were assembled, of which 4 564 were differentially expressed. Analysis of differentially expressed genes (DEGs) showed that multiple signaling pathways such as SA, jasmonic acid, ethylene, abscisic acid, auxin, and brassinolide were involved in response to exogenous SA. Many plant defense signal-related genes involved in protein serine/threonine kinase activity and plant-pathogen interaction, were significantly enriched. These were consistent with the interaction results of SD20 and Phytophthora infestans in our previous study, indicating that exogenous SA stimulated the resistance response and initiated a similar defense pathway compared to pathogen infection in SD20, which confirmed crosstalk of the SA signaling pathway with a pathogen-induced disease resistance signal pathway in plant. Moreover, transcriptome analysis revealed that ROS1 was positively regulated by SA in potato for the first time. SA-induced gene expression profiling provides insight into SA signaling and its mechanisms in disease defense systems.

Plant Viruses in Gilgit-Baltistan (GB) Pakistan: Potential Future Research Direction

Potato is becoming the most economically important crop in GB because its production is expanding more rapidly than that of most other crops primarily because it generates hugh incomes to the farming community. The disease resistant potato cultivars were replaced by the high yielding varieties, consequently the potato crops has become vulnerable to numerous diseases. Among the diseases viral diseases may play a major role in reducing the yield of potato crops. There are no proper regulatory policies intended to prevent introduction of plant viruses, introduction has still occurred through the potato tubers from the other provinces of Pakistan. Furthermore, the vectors such as aphid’s population have increased. These plant viruses have considerable effects on potato crops range from mere curling and chlorosis of leaves to demise of entire potato crops from the fields. These plant viruses may be major yield limiting factor and therefore there is need to identify the viruses on farms and to determine the severity as well as their impacts on potato yield. Theses plant viruses are major future threats to GB’s food security. There are no wellestablished plant pathology laboratories as a result their identification and estimation of losses to potato crops, they pose still remain a challenge. In conclusion, the viruses are the future constraints to food security in GB, this review paper uses some plant viruses as a case study to illustrate their key influences on the yield of potato crop.

Simulating crop-disease interactions in agricultural landscapes to analyse the effectiveness of host resistance in disease control: The case of potato late blight

Disease-resistant potato varieties can play a key role in sustainable control of potato late blight. However, when these varieties are more widely used, resistance breakdown can occur as a result of pathogen adaptation. Here we focussed on potato cultivation in the Netherlands, where new (single gene) resistant varieties have been introduced over the last ten years. This new generation of late blight resistant varieties has moderate yield levels and does not meet all market requirements. As a result, adoption rates for resistant varieties have been low so far. We developed a spatially explicit agent-based model to simulate potato production, disease spread and pathogen evolution at the landscape level. We analysed how late blight severity, resistance durability and potato yield are affected by the spatial deployment of a resistant variety, with a lower potential yield than susceptible varieties. The model was applied to an agricultural region in the Netherlands (596 km2) and was run for a period of 36 years using daily weather data as input for crop growth and disease dynamics. The short- and long-term effects of the deployment of a resistant variety were analysed with the model. With respect to short-term dynamics, years were analysed independently to study between year variation. The model demonstrated that in most years, susceptible fields without fungicide application suffered severe yield losses and resistant fields performed better despite their lower potential yield. Resistance breakdown was observed in a small fraction of fields with the resistant variety, but this did not affect mean potato yield or disease incidence in the short term since it occurred at the end of the growing season. Increasing the fraction of potato fields with the resistant variety strongly reduced late blight infection within a landscape. With respect to the long-term effects, the model showed the emergence and spread of a virulent strain over time. The virulent strain gradually took over the pathogen population, decreasing mean potato yields from fields with the resistant variety. This occurred in all landscape compositions where the resistant variety was deployed to different extents. It was found that low as well as high proportions of fields with the resistant variety could increase durability of resistance. With these findings, the model provided more insight into the opportunities and risks related to the use of plant resistance in disease control, an important and sustainable disease management strategy.

Germplasm evaluation and molecular selection of potato (Solanum tuberosum L.) cultivars with disease resistance in China

Foreground and background selections are two important aspects that need to be carefully considered by plant breeders during field selection. In this article, we used 7 disease resistance markers, including four late blight and three potato virus disease resistance gene markers, and 12 microsatellite markers to evaluate the disease resistance and genetic diversity of 76 potato cultivars in total which were collected from 15 provinces of China. The foreground selection results showed that a number of materials, clustered separately, contained more than two late blight resistance markers or pyramided late blight and virus disease resistance gene markers together. A lot of them were collected from the southwest of China. Additionally, the genetic backgrounds of all cultivars were relatively narrow and a limited number of cultivars (15.8%) contained both potato late blight and potato virus Y resistance markers. Also, only two accessions (Yunshu 103 and Lishu 7) contained both late blight and potato virus X resistance markers. In conclusion, this comprehensive evaluation of genetic resources will shed the light on potato disease resistance breeding in the future.

Toughing It Out--Disease-Resistant Potato Mutants Have Enhanced Tuber Skin Defenses.

Common scab, a globally important potato disease, is caused by infection of tubers with pathogenic Streptomyces spp. Previously, disease-resistant potato somaclones were obtained through cell selections against the pathogen's toxin, known to be essential for disease. Further testing revealed that these clones had broad-spectrum resistance to diverse tuber-invading pathogens, and that resistance was restricted to tuber tissues. The mechanism of enhanced disease resistance was not known. Tuber periderm tissues from disease-resistant clones and their susceptible parent were examined histologically following challenge with the pathogen and its purified toxin. Relative expression of genes associated with tuber suberin biosynthesis and innate defense pathways within these tissues were also examined. The disease-resistant somaclones reacted to both pathogen and toxin by producing more phellem cell layers in the tuber periderm, and accumulating greater suberin polyphenols in these tissues. Furthermore, they had greater expression of genes associated with suberin biosynthesis. In contrast, signaling genes associated with innate defense responses were not differentially expressed between resistant and susceptible clones. The resistance phenotype is due to induction of increased periderm cell layers and suberization of the tuber periderm preventing infection. The somaclones provide a valuable resource for further examination of suberization responses and its genetic control.

Breeding of Pest and Disease Resistant Potato Cultivars in Japan by Using Classical and Molecular Approaches

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 consider- ing 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 breed- ing 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.