Resistant Potato Cultivars Research Articles

Resistance of potato cultivars and hybrid clones from the VIR collection to the northwestern population of <i>Phytophthora infestans</i>

Resistance of potato cultivars and hybrid clones from the VIR collection to the northwestern population of <i>Phytophthora infestans</i>

Understanding the Temporal Dynamics of Invasive Late Blight Populations in India for Improved Management Practices.

The microbial oomycete pathogen Phytophthora infestans causes severe epidemics of potato late blight in crops globally. Disease management benefits from an understanding of the diversity of pathogen populations. In this study, we explore the dynamics of P. infestans populations in the late blight-potato agro-ecosystem across the Indian subcontinent. Investigations of the macroecological observations at the field level and microbial ecological principles provided insights into future pathogen behavior. We use a comprehensive simple sequence repeat allele dataset to demonstrate that an invasive clonal lineage called EU_13_A2 has dominated populations over 14 years across India, Bangladesh, and Pakistan. Increasing levels of subclonal variation were tracked over time and space, and, for the first time, populations in Asia were also compared with the source populations from Europe. Within India, a regional pathogen population structure was observed with evidence for local migration, cross-border movement between surrounding countries, and introductions via imports. There was also evidence of genetic drift and between-season transmission of more strongly pathogenic subclones with a complete displacement of some subclonal types. The limited introduction of novel genotypes and the use of resistant potato cultivars could contribute to the dominance of the 13_A2 lineage. The insights will contribute to the management of the pathogen in these key global potato production regions.

Reaction of potato cultivars to Potato Cyst Nematodes (Globodera rostochiensis and G. pallida) under greenhouse conditions in Kenya

Several measures have been recommended in the control of potato cyst nematodes (PCN) with resistant potato cultivars being considered as the most practical and affordable for smallholder potato farmers in Kenya. However, the level of resistance in locally grown potato varieties is yet to be established. The aim of this study was to screen Kenyan potato cultivars against PCN under greenhouse conditions. Eleven potato cultivars namely Shangi, Dutch Robijn, Sherekea, Nyota, Roseline tana, Tigoni, Unica, Asante, Chulu, Kenya Mpya and Arka were screened with Desiree (susceptible variety), Manitou (resistant cultivar) as controls. For each potato cultivar, there were two sets of plants with the first set being inoculated with 50 cysts, while the second batch was nematode-free. The treatments were arranged in a completely randomized design with three replications. A scale of 1-9, with 9 indicating the highest level of resistance was used in the assessment of disease severity. Nematode infestation caused a reduction in root mass across the 11 cultivars from 20 to 100% compared to uninoculated controls. Reproductive index of PCN viable eggs across the 11 cultivars was <1 compared to control (Desiree). Potato cultivars Shangi, Tigoni, Dutch, Chulu, Asante, Unica, Arka, Kenya Mpya, and Roseline Tana had a severity score of 1-3 (>95%), hence were considered to be susceptible to PCN. The cultivars Sherekea and Nyota had a severity score of 4-6 (<25%) and hence were considered partially resistant to PCN. The findings of this study provides a basis of integrating partially resistant potato cultivars into PCN management in smallholder farms. Keywords: Cyst viable eggs, reproductive index, resistance, susceptible, smallholder farmers, severity score.

Transcriptome-Based Comparative Expression Profiling of Sweet Potato during a Compatible Response with Root-Knot Nematode Meloidogyne incognita Infection.

M. incognita, a root-knot nematode (RKN), infects the roots of several important food crops, including sweet potato (Ipomoea batatas Lam.), and severely reduces yields. However, the molecular mechanisms underlying infection remain unclear. Previously, we investigated differential responses to RKN invasion in susceptible and resistant sweet potato cultivars through RNA-seq-based transcriptome analysis. In this study, gene expression similarities and differences were examined in RKN-susceptible sweet potato cultivars during the compatible response to RKN infection. Three susceptible cultivars investigated in previous research were used: Dahomi (DHM), Shinhwangmi (SHM), and Yulmi (YM). Of the three cultivars, YM had the highest number of genes with altered expression in response to infection. YM was also the cultivar with the highest susceptibility to RKN. Comparisons among cultivars identified genes that were regulated in more than one cultivar upon infection. Pairwise comparisons revealed that YM and DHM shared the most regulated genes, whereas YM and SHM shared the lowest number of regulated genes. Five genes were up-regulated, and two were down-regulated, in all three cultivars. Among these, four genes were highly up-regulated in all cultivars: germin-like protein, anthranilate synthase α subunit, isocitrate lyase, and uncharacterized protein. Genes were also identified that were uniquely regulated in each cultivar in response to infection, suggesting that susceptible cultivars respond to infection through shared and cultivar-specific pathways. Our findings expand the understanding of the compatible response to RKN invasion in sweet potato roots and provide useful information for further research on RKN defense mechanisms.

Responses of Aerial and Belowground Parts of Different Potato (Solanum tuberosum L.) Cultivars to Heat Stress

The mechanism of potato (Solanum tuberosum L.) thermotolerance has been the focus of intensive research for many years because plant growth and tuber yield are highly sensitive to heat stress. However, the linkage between the aerial and belowground parts of potato plants in response to high temperatures is not clear. To disentangle this issue, the aerial and belowground parts of the heat-resistant cultivar Dian187 (D187) and the heat-sensitive cultivar Qingshu 9 (Qs9) were independently exposed to high-temperature (30 °C) conditions using a special incubator. The results indicated that when the belowground plant parts were maintained at a normal temperature, the growth of the aerial plant parts was maintained even when independently exposed to heat stress. In contrast, the treatment that independently exposed the belowground plant parts to heat stress promoted premature senescence in the plant's leaves, even when the aerial plant parts were maintained at a normal temperature. When the aerial part of the plant was independently treated with heat stress, tuberization belowground was not delayed, and tuberization suppression was not as severe as when the belowground plant parts independently underwent heat stress. Heat stress on the belowground plant parts alone had virtually no damaging effects on the leaf photosynthetic system but caused distinct tuber deformation, secondary growth, and the loss of tuber skin colour. Transcriptome analysis revealed that the treatment of the belowground plant parts at 30 °C induced 3361 differentially expressed genes in the Qs9 cultivar's expanding tubers, while the D187 cultivar had only 10,148 differentially expressed genes. Conversely, when only the aerial plant parts were treated at 30 °C, there were just 807 DEGs (differentially expressed genes) in the D187 cultivar's expanding tubers compared with 6563 DEGs in the Qs9 cultivar, indicating that the two cultivars with different heat sensitivities have distinct regulatory mechanisms of tuberization when exposed to heat stress. The information provided in this study may be useful for further exploring the genes associated with high-temperature resistance in potato cultivars.

Status and way-forward in breeding potato (Solanum tuberosum) for resistance to late blight

Improving host resistance to late blight (Phytophthora infestans) has been a major concern of potato breeders since the Irish famine of 1840s. Since then, a number of late blight resistant potato (Solanum tuberosum L.) cultivars have been developed using both conventional and molecular techniques. However, resistance to late blight did not last long and broke down due to the emergence of more virulent races of Phytophthora infestans. This perspective paper presents the status of sources of resistance to late blight, defence mechanism of host against the pathogen and late blight resistance genes mapped, cloned, and transferred to cultivated potato. Considerable progress has been made in all aspects of breeding potato for resistance to late blight. However, a critical appraisal of the status of potato breeding for resistance to late blight suggests the continued need to identify new sources of resistance, transfer of resistance genes from diverse sources and stacking them in maximum number into individual plants. Other breeding strategies to combat this dreaded disease are also discussed.

Global transcriptome and targeted metabolite analyses of roots reveal different defence mechanisms against Ralstonia solanacearum infection in two resistant potato cultivars.

Ralstonia solanacearum (Rs), the causal agent of bacterial wilt disease in an unusually wide range of host plants, including potato (Solanum tuberosum), is one of the most destructive phytopathogens that seriously reduces crop yields worldwide. Identification of defence mechanisms underlying bacterial wilt resistance is a prerequisite for biotechnological approaches to resistance breeding. Resistance to Rs has been reported only in a few potato landraces and cultivars. Our in vitro inoculation bioassays confirmed that the cultivars 'Calalo Gaspar' (CG) and 'Cruza 148' (CR) are resistant to Rs infection. Comparative transcriptome analyses of CG and CR roots, as well as of the roots of an Rs-susceptible cultivar, 'Désirée' (DES), were carried out two days after Rs infection, in parallel with their respective noninfected controls. In CR and DES, the upregulation of chitin interactions and cell wall-related genes was detected. The phenylpropanoid biosynthesis and glutathione metabolism pathways were induced only in CR, as confirmed by high levels of lignification over the whole stele in CR roots six days after Rs infection. At the same time, Rs infection greatly increased the concentrations of chlorogenic acid and quercetin derivatives in CG roots as it was detected using ultra-performance liquid chromatography - tandem mass spectrometry. Characteristic increases in the expression of MAP kinase signalling pathway genes and in the concentrations of jasmonic, salicylic, abscisic and indoleacetic acid were measured in DES roots. These results indicate different Rs defence mechanisms in the two resistant potato cultivars and a different response to Rs infection in the susceptible cultivar.

Neocosmospora rubicola, a stem rot disease in potato: Characterization, distribution and management.

Potato (Solanum tuberosum L.) is one of the most important crops in maintaining global food security. Plant stand and yield are affected by production technology, climate, soil type, and biotic factors such as insects and diseases. Numerous fungal diseases including Neocosmospora rubicola, causing stem rot, are known to have negative effects on potato growth and yield quality. The pathogen is known to stunt growth and cause leaf yellowing with grayish-black stems. The infectivity of N. rubicola across a number of crops indicates the need to search for appropriate management approaches. Synthetic pesticides application is a major method to mitigate almost all potato diseases at this time. However, these pesticides significantly contribute to environmental damage and continuous use leads to pesticide resistance by pathogens. Consumers interest in organic products have influenced agronomists to shift toward the use of biologicals in controlling most pathogens, including N. rubicola. This review is an initial effort to carefully examine current and alternative approaches to control N. rubicola that are both environmentally safe and ecologically sound. Therefore, this review aims to draw attention to the N. rubicola distribution and symptomatology, and sustainable management strategies for potato stem rot disease. Applications of plant growth promoting bacteria (PGPB) as bioformulations with synthetic fertilizers have the potential to increase the tuber yield in both healthy and N. rubicola infested soils. Phosphorus and nitrogen applications along with the PGPB can improve plants uptake efficiency and reduce infestation of pathogen leading to increased yield. Therefore, to control N. rubicola infestation, with maximum tuber yield benefits, a pre-application of the biofertilizer is shown as a better option, based on the most recent studies. With the current limited information on the disease, precise screening of the available resistant potato cultivars, developing molecular markers for resistance genes against N. rubicola will assist to reduce spread and virulence of the pathogen.

CRISPR/Cas9-Mediated Targeting of Susceptibility Factor eIF4E-Enhanced Resistance Against Potato Virus Y.

Potato (Solanum tuberosum L.) is an important staple food around the world, and potato virus Y (PVY) is a major constraint for potato production. The VPg protein of PVY interacts with the translation initiation factor eIF4E of the host that works as a susceptibility factor during infection. The interaction between eIF4E and VPg was disrupted by CRISPR/Cas9. The homozygous conserved region of eIF4E of the potato variety “Kruda” was mutated by CRISPR/Cas9. Tracking of insertion, deletion, and conversion events was performed by Sanger sequencing with ∼15% editing efficiency. Truncated and mutated eIF4E proteins were unable to interact with VPg, and the virus was not able to exploit the host machinery for replication and systemic spreading. Mutated eIF4E lines showed enhanced resistance to PVYO strain. DAS-ELISA and RT-PCR were used for validation of the observed resistance. PVY resistance in tetraploid lines via CRISPR/Cas9 provides a route to develop novel resistant potato cultivars.

Late Blight Resistance Conferred by Rpi-Smira2/R8 in Potato Genotypes In Vitro Depends on the Genetic Background

Potato production worldwide is threatened by late blight, caused by the oomycete Phytophthora infestans (Mont.) de Bary. Highly resistant potato cultivars were developed in breeding programs, using resistance gene pyramiding methods. In Sárpo Mira potatoes, five resistance genes (R3a, R3b, R4, Rpi-Smira1, and Rpi-Smira2/R8) are reported, with the latter gene assumed to be the major contributor. To study the level of late blight resistance conferred by the Rpi-Smira2/R8 gene, potato genotypes with only the Rpi-Smira2/R8 gene were selected from progeny population in which susceptible cultivars were crossed with Sárpo Mira. Ten R8 potato genotypes were obtained using stepwise marker-assisted selection, and agroinfiltration of the avirulence effector gene Avr4. Nine of these R8 genotypes were infected with both Slovenian P. infestans isolates and aggressive foreign isolates. All the progeny R8 genotypes are resistant to the Slovenian P. infestans isolate 02_07, and several show milder late blight symptoms than the corresponding susceptible parent after inoculation with other isolates. When inoculated with foreign P. infestans isolates, the genotype C571 shows intermediate resistance, similar to that of Sárpo Mira. These results suggest that Rpi-Smira2/R8 contributes to late blight resistance, although this resistance is not guaranteed solely by the presence of the R8 in the genome.

Susceptibility assessment and genetic population structure associated with Rhizoctonia solani AG3-PT - Potato stem canker disease

Rhizoctonia solani Kühn AG3-PT causes stem canker (SCD), and significantly impacts potato, Solanum tuberosum L. production globally. However, up to date, there are few resistant or tolerant potato cultivars to R. solani. Given the importance of the subject, we screened ninety-two potato genotypes to SCD, R. solani in the field and greenhouse conditions. Of which, fifty genotypes were subjected to genetic diversity analyzing using 20 Inter Simple Sequence Repeats (ISSR) primers. SCD severity on genotypes ranged from 5 to 73% in the field, and out of 20 used ISSR primer pairs, 14 primers generated 485 loci, of which 216 (45%) showed polymorphic bands. The highest percentage (67%) of polymorphisms was in uBC834 primer. Polymorphism information content value varied from 0.262 to 0.459 with an average of 0.338. Nei's measure of average population genetic diversity per locus ranged from 0.06 to 0.5. Effective number of alleles, Nei's genetic diversity and Shannon's Information Index were 1.530, 0.266, and 0.392, respectively. uBC834 and uBC811 primers identified the most polymorphic loci. According to simple-matching coefficient, the highest similarity (99%) was among “KSG64”, “KSG82”, ‏“KSG81”, ‏“KSG21”, “KSG31”, and “KSG109”, and lowest similarity (54%) in “8708/177” and “KSG300”. Thus, resistant sources can play a significant role in disease management in an integrated pest management planning program. Moreover, diverse potato resistant/susceptible genotypes reported in this study will be useful to generate mapping populations for potato and work in breeding programs for developing and releasing new resistant cultivars for SCD, R. solani infection.

Large-Scale Protein and Phosphoprotein Profiling to Explore Potato Resistance Mechanisms to Spongospora subterranea Infection.

Potato is one of the most important food crops for human consumption. The soilborne pathogen Spongospora subterranea infects potato roots and tubers, resulting in considerable economic losses from diminished tuber yields and quality. A comprehensive understanding of how potato plants respond to S. subterranea infection is essential for the development of pathogen-resistant crops. Here, we employed label-free proteomics and phosphoproteomics to quantify systemically expressed protein-level responses to S. subterranea root infection in potato foliage of the susceptible and resistant potato cultivars. A total of 2,669 proteins and 1,498 phosphoproteins were quantified in the leaf samples of the different treatment groups. Following statistical analysis of the proteomic data, we identified oxidoreductase activity, electron transfer, and photosynthesis as significant processes that differentially changed upon root infection specifically in the resistant cultivar and not in the susceptible cultivar. The phosphoproteomics results indicated increased activity of signal transduction and defense response functions in the resistant cultivar. In contrast, the majority of increased phosphoproteins in the susceptible cultivar were related to transporter activity and sub-cellular localization. This study provides new insight into the molecular mechanisms and systemic signals involved in potato resistance to S. subterranea infection and has identified new roles for protein phosphorylation in the regulation of potato immune response.

Comparative Metabolomic Profiling of Compatible and Incompatible Interactions Between Potato and Phytophthora infestans.

Late blight is one of the main biological stresses limiting the potato yield; however, the biochemical mechanisms underlying the infection process of Phytophthora infestans remain unrevealed. In this study, the late blight-resistant potato cultivar Ziyun No.1 (R) and the susceptible cultivar Favorita (S) were inoculated with P. infestans. Untargeted metabolomics was used to study the changes of metabolites in the compatible and incompatible interactions of the two cultivars and the pathogen at 0, 48, and 96 h postinoculation (hpi). A total of 819 metabolites were identified, and the metabolic differences mainly emerged after 48 hpi. There were 198 and 115 differentially expressed metabolites (DEMs) in the compatible and incompatible interactions. These included 147 and 100 upregulated metabolites during the compatible and incompatible interactions, respectively. Among them, 73 metabolites were identified as the P. infestans-responsive DEMs. Furthermore, the comparisons between the two cultivars identified 57 resistance-related metabolites. Resistant potato cultivar had higher levels of salicylic acid and several upstream phenylpropanoid biosynthesis metabolites, triterpenoids, and hydroxycinnamic acids and their derivatives, such as sakuranetin, ferulic acid, ganoderic acid Mi, lucidenic acid D2, and caffeoylmalic acid. These metabolites play crucial roles in cell wall thickening and have antibacterial and antifungal activities. This study reports the time-course metabolomic responses of potatoes to P. infestans. The findings reveal the responses involved in the compatible and incompatible interactions of potatoes and P. infestans.

Quantitative Trait Loci for Resistance to Potato Dry Rot Caused by Fusarium sambucinum

Tuber dry rot is an important disease of potato caused by soil and seed-borne pathogens of the Fusarium genus leading to losses that may reach 60% of the yield. The goal of this work was to study the inheritance of the dry rot resistance in two diploid potato hybrid populations (11–36 and 12–3) with complex pedigrees, including several wild Solanum spp. We used an aggressive isolate of F. sambucinum for phenotyping both progenies, parents, and standard potato cultivars in laboratory tuber tests, in three subsequent years. The QTL for dry rot resistance were mapped by interval mapping on existing genetic maps of both mapping populations. The most important and reproducible QTL for this trait was mapped on chromosome I and additional year- and population-specific QTL were mapped on chromosomes II, VII, IX, XI, and XII, confirming polygenic control of this resistance. This is the first study mapping the loci affecting tuber dry rot resistance in potato genome that can contribute to better understanding of potato-F. sambucinum interaction and to more efficient breeding of resistant potato cultivars.

Traditional Selection Potato Varieties and Their Resistance to the 28-punctata Potato Ladybug Henosepilachna vigintioctomaculata (Coleoptera: Coccinellidae) in the Southern Russian Far East

Background: Henosepilachna vigintioctomaculata is a polytrophic pest, causing the greatest damage to plants from the nightshade family. The study aimed to research the resistance of potato cultivars that are promising for breeding to damage by a potato ladybug in laboratory and field experiments. Methods: In laboratory experiments, the indicators of fertility, mortality and duration of development, morphological anomalies and the effect of potato varieties on the composition of Epilakhna’s hemolymph were studied. The sample consisted of 50 individuals with a slight predominance of females. The experiment used 13 varieties of potatoes. Result: A specific dependence of the frequency of phytophage anomalies on the variety was revealed. The influence of nutrition on survival and the timing of ontogenesis has been established. The results obtained indicate the high breeding value of the material when recommending it for cultivation in regions with a high number of pests, as well as when creating new varieties.

Assessing resistance levels of potato cultivars in South Africa against Alternaria alternata

Brown leaf spot caused by Alternaria alternata (Fries) Keissler is one of the most devastating fungal diseases of potato. Management of this disease relies mostly on fungicide applications. However, fungicides are becoming less effective due to the development of fungal resistance to specific chemicals. Additionally, there is limited information on resistance in potato cultivars in South Africa against brown leaf spot. This study aims to evaluate ten commercial potato cultivars for brown leaf spot resistance using detached leaf, tuber and whole plant screening techniques under controlled conditions. The experiment was conducted in 2016 and repeated in 2017. The whole plant assay showed that Labadia, Almera, Sifra, Mondeo, Up-To-Date and Lanorma are resistant to brown spot. Resistance levels in Labadia, Almera, Sifra and Up-To-Date were consistent in the 2016 and 2017 experiments. The detached leaf assay showed Almera, Sifra, Up-To-Date and Mondeo as moderately resistant, while Innovator, Mondial and Markies were moderately susceptible. However, in the tuber assay all cultivars were highly susceptible. Cultivar resistance varied based on the screening technique used, although results suggest that the detached leaf and whole plant assays could be used in potato disease screening programs.

Association mapping to detect Phytophthora infestans resistance in tetraploid potato

AbstractPhytophthora infestans (Mont.) de Baryis found in all areas of potato (Solanum tuberosum L.) production in Argentine. Association mapping uses the existing diversity in a a population to identify loci responsible of phenotypic variation of a character. The studied population was formed by 159 genotypes of the germplasm collection of the Instituto Nacional de Tecnología Agropecuaria (INTA) Estación Experimental Agropecuaria (EEA) Balcarce potato breeding program. These genotypes are part of a larger population that was previously analyzed using single‐nucleotide polymorphism (SNP). Phenotypic assessment was carried out in two locations over 3 yr. Environmental conditions allowed the presence of the disease in all year × location combination. Phenotypic variability was found for relative area under disease progress curve (RAUDPC) and yield parameters as, Total weight and Seed weight. Association mapping was carried out on 159 genotypes. Eight significant associations were found using Bonferroni methodology, with values of −log(p) ranging between 4.61 and 5.42 located at chromosomes 3 (solcap_snp_c2_16679), 4 (solcap_snp_c1_6126 and solcap_snp_c2_38243, solcap_snp_c2_54077), 5 (solcap_snp_c2_42374), 6 (solcap_snp_c2_33228), 7 (solcap_snp_c1_7407), and 10 (solcap_snp_c2_63) and eleven significant associations using permutation tests with values of −log(p) between 4.5 and 6.42 located at chromosomes 1(solcap_snp_c1_5150), 2 (solcap_snp_c1_13923), 4 (solcap_snp_c1_4178, and solcap_snp_c2_50004), 5 (solcap_snp_c2_11829 and solcap_snp_c2_50532), 7 (solcap_snp_c2_35057 and solcap_snp_c1_10011), and 9 (solcap_snp_c2_1915). Some of the SNPs detected are adjacent to genes that encode enzymes that participate in metabolic pathways that are activated in response to interaction with pathogens. Those markers might be included in breeding programs related to improve late blight resistance in potato cultivars.

Evaluation of potato varieties and hybrids on the resistance against black scab under conditions of Ukraine’s Polissia

Goal. Assess potato varieties and hybrids for resistance against rhizoctonia disease and identify highly resistant varieties.
 Methods. The fundamental principle of the existing methodology for evaluating varieties is to test varieties, hybrids and species of potatoes on natural or artificial infectious backgrounds using a pure culture of the fungus Rhizoctonia solani Kuhn. The culture grown in Petri dishes was introduced when the tubers were planted in the soil. The assessment of the degree of damage to tubers and stems was carried out according to the damage to the underground organs of plants, the yield of potatoes, and then the level of variety samples was determined by resistance to the disease. Evaluation of potato varieties and hybrids for resistance against the causative agent of the disease Rhizoctonia solani Kuhn was carried out on a nine-point scale, where score 9 — no damage to stems and tubers, 7 — disease development up to 10% (high resistance); 5 — disease progression 11—25% (medium resistance); score 3 — disease progression 26—50% (low resistance).
 Results. Based on the test of potato varieties and hybrids for resistance against rhizoctonia, Dubravka, Vesta, Lugovska, Obriy, Serpanok, Yavir, Scarbnytsia, Tyras and hybrids P.207.407 (Zov × Polisska Rozheva), 205.17-24 (Adretta × 23-16s/73) and others; to medium-resistant (5 points) — Chervona Ruta, Povin, Vodogray, Horlytsia, Zov, Cupava, Nadiyna, Belarossa, Olvia, Svitanok Kyivskyi, Ukrainska Rozheva, Beregynia, Charunka, Okolytsia, Slutch, hybrids P.210.14-23 (Adretta × Posvit), 211.20-31 (Prolisok × Lugovska); to susceptible — 51, or 32.9% of the tested varieties.
 Conclusions. We have proved that mid-early ripening and early ripening cultivars as well as selection hybrids are more infected with black scab than mid-ripening, mid-late ripening and late ripening cultivars. These relatively resistant potato cultivars and hybrids are expedient to use in the selection on the resistance against black scab.

Characterization of Superoxide Dismutase from the Potato Cyst Nematode, Globodera pallida.

Potato cyst nematodes (PCNs), such as Globodera pallida and Globodera rostochiensis, are some of the most agriculturally and economically important pests of potato. Upon nematode infection, a principal component of plant defense is the generation of the reactive oxygen species (ROSs). ROSs are highly toxic molecules that cause damage to pathogens and host alike. To infect the plant, nematodes protect themselves from ROSs by activating their own antioxidant processes and ROS scavenging enzymes. One of these enzymes is a superoxide dismutase (SOD; EC 1.15.1.1), which prevents cellular damage by catalyzing conversion of the superoxide radical (O2-·) to hydrogen peroxide (H2O2) and molecular oxygen (O2). We have isolated a putatively secreted isoform of a Cu-Zn SOD (SOD-3) from G. pallida and localized the expression of this gene in the posterior region of the nematode. Furthermore, we studied the expression of the SOD-3 gene during early parasitic stages of infection (24 to 72 h) in the susceptible potato cultivar Desiree, the resistant potato cultivar Innovator, and an immune host, Solanum sisymbriifolium. The SOD-3 gene was significantly upregulated, regardless of the host type; however, the expression pattern differed between the susceptible and the resistant or immune hosts. This finding suggests that SOD-3 gene is responding to infection in plant roots differently depending on whether the nematode is experiencing a compatible or an incompatible interaction.

Evaluation of potato virus X resistance in potato cultivars and identification of an innate immunity-independent resistance phenotype

Potato virus X (PVX) is a widely distributed viral pathogen that causes significant losses in potato production by co-infecting with potato virus Y or potato virus A. In this study, the resistance of 23 potato cultivars to PVX was dissected in detail using a PVX infectious clone containing a yellow fluorescent protein (YFP). Among them, four potato cultivars (Longshu-3, Eugene, Atlantic and Waiyin-2) were found to carry an Rx gene that confers extreme resistance to PVX; one cultivar (Waiyin-1) displayed partial resistance and was able to delay PVX infection by ~ 5 days; while the rest eighteen potato cultivars were susceptible to PVX. Moreover, we found that the replication but not cell-to-cell or long-distance movement of PVX was inhibited in Waiyin-1. Finally, we determined that the expression of pathogenesis-related (PR) genes in Waiyin-1 was not triggered by PVX infection at early infection stage, whereas they were triggered in the Rx-carrying cultivar Atlantic during this period of time. In conclusion, our results confirm that Rx is a major type of resistance gene in potato cultivars in the Northeast part of China. Furthermore, the possible mechanism underlying Waiyin-1 resistance to PVX is discussed.