Susceptible Potato Cultivars Research Articles

BABA-primed defense responses to Phytophthora infestans in the next vegetative progeny of potato.

The transcript of the PR1 gene accumulation as an informative marker of systemic acquired resistance (SAR) was analyzed in β-aminobutyric acid (BABA) primed potato in the short-lasting (3 days) and long-lasting (28 days) time periods after induction and in the vegetative descendants of primed plants derived from tubers and from in vitro seedlings. BABA pretreatment resulted either in minimal or no PR1 gene expression, but sequential treatment with BABA followed by virulent Phytophthora infestans provided data on the imprint of post-stress information and its duration until fertilization, in the form of an enhanced PR1 transcript accumulation and a transient increase of basal resistance to the late blight disease. The primed state for defense of the susceptible potato cultivar was transmitted to its vegetative progeny as a potentiated PR1 mRNA accumulation following challenge inoculation. However, variation was observed between vegetative accessions of the BABA-primed potato genotype in responsiveness to disease. In contrast to plants derived from tubers, potato propagated through in vitro seedlings largely lost inducible resistance traits, although itretained primed PR1 gene expression.

The expression of R genes in genetic and induced resistance to potato cyst nematode Globodera rostochiensis (Wollenweber, 1923) Behrens, 1975.

The characteristics of expression of two genes, H1 and Gro1-4, which determine the resistance to the sedentary parasitic nematode Globodera rostochiensis (Wollenweber, 1923) Behrens, 1975, in the resistant (Krepysh) and susceptible (Nevskii) potato cultivars was studied under a short-term exposure to low temperatures. Such treatment of susceptible plants at the early stages of ontogeny led to the activation of expression of H1 and Gro1-4 genes in roots and the H1 gene in leaves. The transcriptional activity of R genes was detected not only in roots but also in leaves (i.e., in tissue remote from the site of direct injury by the nematode) in the case of both genetic and induced resistance, indicating the development of a systemic defense response of plants to infection.

A cupin domain-containing protein with a quercetinase activity (VdQase) regulates Verticillium dahliae's pathogenicity and contributes to counteracting host defenses.

We previously identified rutin as part of potato root responses to its pathogen Verticillium dahliae. Rutin was directly toxic to the pathogen at doses greater than 160 μM, a threshold below which many V. dahliae pathogenicity-related genes were up-regulated. We identified and characterized a cupin domain-containing protein (VdQase) with a dioxygenase activity and a potential role in V. dahliae-potato interactions. The pathogenicity of VdQase knock-out mutants generated through Agrobacterium tumefasciens-mediated transformation was significantly reduced on susceptible potato cultivar Kennebec compared to wild type isolates. Fluorescence microscopy revealed a higher accumulation of flavonols in the stems of infected potatoes and a higher concentration of rutin in the leaves in response to the VdQase mutants as compared to wild type isolates. This, along with the HPLC characterization of high residual and non-utilized quercetin in presence of the knockout mutants, indicates the involvement of VdQase in the catabolism of quercetin and possibly other flavonols in planta. Quantification of Salicylic and Jasmonic Acids (SA, JA) in response to the mutants vs. wild type isolates revealed involvement of VdQase in the interference with signaling, suggesting a role in pathogenicity. It is hypothesized that the by-product of dioxygenation 2-protocatechuoylphloroglucinolcarboxylic acid, after dissociating into phloroglucinol and protocatechuoyl moieties, becomes a starting point for benzoic acid and SA, thereby interfering with the JA pathway and affecting the interaction outcome. These events may be key factors for V. dahliae in countering potato defenses and becoming notorious in the rhizosphere.

SSR assessment of Phytophthora infestans populations on tomato and potato in British gardens demonstrates high diversity but no evidence for host specialization

Phytophthora infestans populations can differ in composition as a result of host specialization on tomato and potato hosts. In Great Britain many amateur gardeners grow outdoor tomatoes but there is little or no commercial tomato production outdoors. This study analysed isolates of P. infestans from British gardens with 12 multiplexed simple sequence repeat markers that are used to monitor the disease on commercial potato crops. Samples of P. infestans from tomato hosts were collected in 3 years and from potato in 1 year from across Great Britain. Seven previously unreported clonal lineages were detected in garden populations and higher frequencies of unique clonal lineages (28–40%) were present compared with populations from British commercial potato crops reported elsewhere. Garden populations had a lower proportion (11–48% less) of the most common lineages (13_A2 and 6_A1) that together made up at least 86% of the commercial potato populations during the sampling period. Host species accounted for only 2·0% of molecular variance detected between garden potato‐ and tomato‐hosted samples. No significant difference in clonal lineage composition was found between host species in Great Britain and this could be due to the whole P. infestans population overwintering on potato. British garden populations on both hosts were much more diverse than those on commercial potato crops; this finding may be influenced by less frequent fungicide use by gardeners and a higher diversity of unsprayed susceptible potato cultivars, enabling metalaxyl‐sensitive and less aggressive genotypes to survive in gardens.

Biosurfactants Have the Potential to Induce Defence Against Phytophthora infestans in Potato

Potato late blight caused by Phytophthora infestans is one of the most destructive plant diseases worldwide. Currently, its management mainly relies on the frequent use of synthetic chemicals, and there is a need to develop more sustainable strategies. Biosurfactants produced by fluorescent pseudomonads have been shown to rapidly, within 1 min, cause zoospore lyses. This study investigated if the biosurfactant-producing strain Pseudomonas koreensis 2.74 and its biosurfactants have the potential to induce resistance in potato to late blight. The experiments were performed with treatments of whole plants of the susceptible potato cultivar Bintje and the partially resistant cultivar Ovatio. A significant disease reduction and an induced secretion of proteins such as pathogenesis-related (PR) protein 1, within the leaf apoplast, were observed in the potato cultivar Ovatio after treatment with the biosurfactant at a concentration of 1 mg ml �1 . No significant effects on disease development were observed after treatment with the bacterial suspension of Pseudomonas koreensis 2.74.

Cultivation technology influences the occurrence of potato early blight (Alternaria solani) in an organic farming system

Nowadays, organically produced products have become more popular than ever and interest in them is still growing fast. The early blight causal pathogen Alternaria solani has not been considered a great threat to potato in northern climate conditions in the past and has not been routinely sprayed against. During our study early blight was evaluated in 2010 and 2011 on the plants of a potato cultivar ‘Reet’ in an organic farming experiment. In our study, both growing seasons were very favourable for early blight development. Significant differences between the two cultivation technologies were found (F1,12 = 4.84, p = 0.048). In 2010, the area under disease progress curve (AUDPC) value was 303 on cover crop (CC) plots and 990 on CC + M (manure) plots that is three times higher, whereas in 2011, the AUDPC value was 967 on CC plots and 1195 on CC + M plots. Our results confirm that potato early blight has become a serious problem in North-East European organic potato fields and thus susceptible potato cultivars cannot be recommended for growing in an organic farming system. However, it is possible to influence the development severity of early blight by selecting the proper growing technology. Since, in the changing climate conditions and in susceptible cultivars, early blight is a potato disease that can cause early defoliation of plants and crop death, there is a need for resistant potato cultivars.

Evidence of a Monogenic Nature of the Nz Gene Conferring Resistance Against Potato virus Y Strain Z (PVYZ) in Potato

Hypersensitive resistance (HR) to Potato virus Y (PVY) in potato (Solanum tuberosum) is conferred by strain-specific N genes. Two such genes have been identified in potato so far, Ny tbr conferring HR to PVYO, and Nc tbr conferring HR to PVYC. A third, putative gene Nz tbr was proposed to confer HR against a distinct strain PVYZ. However, due to the scarcity of the PVYZ isolates of PVY, no formal proof of the monogenic nature of this new gene, Nz tbr , was available until now. Here, we report on a genetic study of the Nz tbr inheritance in three crosses between cultivars Maris Bard (Ny:Nz) and King Edward (ny:nz), and Maris Bard (Ny:Nz) and Russet Norkotah (ny:nz). A fully-sequenced PVYZ isolate, L26, was used to screen the parents and progeny for a virus-induced HR phenotype in foliage. Based on the phenotypic analysis of 203 progeny, segregation of HR phenotype in the PVYZ-infected plants was found to be 1:1, indicating a monogenic, dominant nature of the Nz tbr gene. Since the PVYZ strain includes PVYNTN isolates associated with tuber necrotic ringspot disease (PTNRD) in susceptible potato cultivars, the Nz tbr gene represents a valuable source of HR against PTNRD-inducing PVY isolates. This is the first demonstration that Nz tbr is a single, dominant N gene in potato conferring resistance to the PVYZ-NTN strain.

Evaluation of Resistance of Medium Maturing Potato Clones to Fusarium Dry Rot

In the present study, resistance of 29 potato clones to fusarium dry rot disease was compared with some commercial cultivars and a susceptible check cultivar Lady Roseta. Tubers of the potato clones and cultivars were artificially inocutate with aggressive isolates of Fusarium sambucinum and F. solani and maintained in a growth chamber at 16°C and 95% relative humidity for four weeks. The experiment was in factorial with two factors of Fusarium species and potato clones, using three replications. Disease index, infected area of tubers and sprouting rate were recorded for each treatment after four weeks. Based on the results of experiment, potato clones 397009, 39709713, 39708-10, 397097-2, 397007-16, 397074-3 and cultivar Aria having the lowest disease index (ranging from 168.52 to 228.25) and lowest tuber infected area, were considered as resistant, while clones 396124-97 × 396151-15 and 396151-29 with highest disease index and tuber infected area were susceptible. Fusarium species had an invert effect on tuber sprouting so that susceptible potato clones and cultivars had the least tuber sprouting rate.

RENDIMIENTO Y ABSORCIÓN DE ALGUNOS NUTRIMENTOS EN PLANTAS DE CAMOTE CULTIVADAS CON ESTRÉS HÍDRICO Y SALINO

Sweet potato (Ipomoea batatas L.) is a low production cost crop that is grown during almost the whole year, mainly in developing countries. In arid and semiarid regions, the presence of salinity and water stress can generate yield reductions and losses in the quality of the tuber roots. To address these issues, an experiment was performed to determine yield, N, P, K, Ca, Mg and Na uptake and proline content in plants belonging to two sweet potato cultivars with a different degree of salt tolerance, grown under three (0, 8 and 14 mmol NaCl) salt and two watering regimes (watering after two and four days), during summer-fall conditions of 2009. Salinity and watering frequencies were controlled by using the soilless culture technique. Both water and salt stresses reduced tuber root yields. The yield reduction is explained by a reduction in the uptake of N, P, K, Ca and Mg with the water stress treatment, and an increased Na uptake in the high salinity treatment. The salt and water stress adjustments were reflected in an increment in proline content in leaves and tuber roots. The results confirm the tolerant cultivar as a hardy variety adaptable to abiotic stresses, whereas the non-tolerant variety had lower yield and nutrient uptake. The results did not support the hypothesis that changes in proline content might be used as fast screening tools to discriminate between tolerant and susceptible sweet potato cultivars.

In-season heat stress compromises postharvest quality and low-temperature sweetening resistance in potato (Solanum tuberosum L.)

The effects of soil temperature during tuber development on physiological processes affecting retention of postharvest quality in low-temperature sweetening (LTS) resistant and susceptible potato cultivars were investigated. 'Premier Russet' (LTS resistant), AO02183-2 (LTS resistant) and 'Ranger Russet' (LTS susceptible) tubers were grown at 16 (ambient), 23 and 29 °C during bulking (111-164 DAP) and maturation (151-180 DAP). Bulking at 29 °C virtually eliminated yield despite vigorous vine growth. Tuber specific gravity decreased as soil temperature increased during bulking, but was not affected by temperature during maturation. Bulking at 23 °C and maturation at 29 °C induced higher reducing sugar levels in the proximal (basal) ends of tubers, resulting in non-uniform fry color at harvest, and abolished the LTS-resistant phenotype of 'Premier Russet' tubers. AO02183-2 tubers were more tolerant of heat for retention of LTS resistance. Higher bulking and maturation temperatures also accelerated LTS and loss of process quality of 'Ranger Russet' tubers, consistent with increased invertase and lower invertase inhibitor activities. During LTS, tuber respiration fell rapidly to a minimum as temperature decreased from 9 to 4 °C, followed by an increase to a maximum as tubers acclimated to 4 °C; respiration then declined over the remaining storage period. The magnitude of this cold-induced acclimation response correlated directly with the extent of buildup in sugars over the 24-day LTS period and thus reflected the effects of in-season heat stress on propensity of tubers to sweeten and lose process quality at 4 °C. While morphologically indistinguishable from control tubers, tubers grown at elevated temperature had different basal metabolic (respiration) rates at harvest and during cold acclimation, reduced dormancy during storage, greater increases in sucrose and reducing sugars and associated loss of process quality during LTS, and reduced ability to improve process quality through reconditioning. Breeding for retention of postharvest quality and LTS resistance should consider strategies for incorporating more robust tolerance to in-season heat stress.

Potato Late Blight and Tuber Yield: Results from 30 Years of Field Trials

During 1983–2012, three field trials per year were performed in each of the three southernmost counties in Sweden to test different fungicide programmes aiming to control late blight, primarily in the very susceptible potato cultivar Bintje. A dataset with results from these field trials was used (i) to examine possible changes in the appearance and behaviour of late blight attack over the years, (ii) to investigate the relationship between late blight in foliage and tuber blight, (iii) to investigate the relationship between late blight and tuber yield and (iv) to identify any correlations between different variables in the dataset. Late blight reached epidemic proportions, i.e. 75% disease severity in the untreated control, in the majority of the field trials. The estimated first attack of late blight was earlier in many field trials after 1998. Differences between years and regions were great in terms of date of the first attack and how the attack developed during the season. For example, in 2002–2005 and 2007, the first attack occurred 40–55 days after planting (DAP), compared with 95–108 DAP in 1994 and 1996. In 1994, 2006 and 2009–2011, the attacks increased from first symptoms to 65% disease severity in the untreated control within 16–21 days, compared with 35–40 days in 1995, 1999 and 2002. The relationship between foliage late blight and tuber blight was weak with the best match found at high disease severity late in the growing season (r = 0.33; p < 0.001). The relationship between blight-free tuber yield and start of the first attack indicated a yield increase of 287 kg/day (R 2 = 0.27) for every day’s delay in first attack. Using the DAP for 65% disease severity in the untreated control improved the correlation (R 2 = 0.64) and indicated a yield increase of 534 kg/day for every day’s delay in first attack. The later the onset of attack, the higher the blight-free tuber yield in treated plots. In general, significant correlations were found between blight-free tuber yield, size fractions of tuber yield, date of first late blight attack, date of different degrees of disease severity, disease severity, date of treatment, treatment measures and maintenance.

Tuber respiratory profiles during low temperature sweetening (LTS) and reconditioning of LTS-resistant and susceptible potato (Solanum tuberosum L.) cultivars

Potato cultivars Premier Russet, GemStar Russet, Defender and Russet Burbank differ substantially in resistance to low temperature sweetening (LTS) and associated metabolism. ‘Gemstar Russet’ and ‘Premier Russet’ have moderate and high resistances, respectively, while ‘Defender’ loses processing quality progressively during storage at 9°C, and similar to ‘Russet Burbank’, has virtually no resistance to LTS at 4°C. The different mechanisms of LTS resistance or susceptibility in these cultivars were indicated by changes in sucrose (Suc), fructose (Fru) and glucose (Glc) concentrations in relation to tuber respiratory profiles during wound healing (9°C), LTS (4°C) and reconditioning (16°C). At 4°C, ‘Premier Russet’ tubers maintained low levels of Suc and reducing sugars (RS, Glc+Fru), while ‘GemStar Russet’ tubers accumulated Suc with little inversion to RS. ‘Defender’ and ‘Russet Burbank’ tubers accumulated RS during LTS but only moderate levels of Suc. Changes in RS content reflected the combined activities of acid invertase and its endogenous inhibitor. In response to an immediate drop from 9°C to 4°C, tuber respiration decreased to a minimum and then increased to a new maximum over the next approximately 5 days, before decreasing to a constant basal rate at 4°C. Relative changes in respiration from the minimum to maximum rate during cold acclimation (respiratory acclimation response, RAR) were 80% for ‘GemStar Russet’ and ‘Defender’, 51% for ‘Russet Burbank’ and 26% for ‘Premier Russet’. The RARs correlated with total sugar (Suc+Glc+Fru) accumulation during LTS and likely reflected the metabolic energy required to catabolize starch to Suc, Glc and Fru. The relative ratio of Fru/Glc was also demonstrative of LTS-resistance, discriminating genotypes that accumulated Suc versus RS under LTS conditions. Changes in carbohydrates, invertase, respiration rates and RARs in response to temperature over the wound healing, LTS and reconditioning phases of storage characterized the LTS phenotypes unique to each cultivar, and revealed different mechanisms of resistance to LTS.

Colonization Patterns of an mCherry-Tagged Pectobacterium carotovorum subsp. brasiliense Strain in Potato Plants

Pectobacterium carotovorum subsp. brasiliense is a newly identified member of the potato soft rot enterobacteriaceae. The pathogenesis of this pathogen is still poorly understood. In this study, an mCherry-P. carotovorum subsp. brasiliense-tagged strain was generated to study P. carotovorum subsp. brasiliense-potato plant interactions. Prior to use, the tagged strain was evaluated for in vitro growth, plasmid stability, and virulence on potato tubers and shown to be similar to the wild type. Four potato cultivars were evaluated for stem-based resistance against P. carotovorum subsp. brasiliense. Confocal laser-scanning microscopy and in vitro viable cell counts showed that P. carotovorum subsp. brasiliense is able to penetrate roots of a susceptible potato cultivar as early as 12 h postinoculation and migrate upward into aerial stem parts. Due to the phenotypic differences observed between tolerant and susceptible cultivars, a comparison of P. carotovorum subsp. brasiliense colonization patterns in these cultivars was undertaken. In the susceptible cultivar, P. carotovorum subsp. brasiliense cells colonized the xylem tissue, forming "biofilm-like" aggregates that led to occlusion of some of the vessels. In contrast, in the tolerant cultivar, P. carotovorum subsp. brasiliense appeared as free-swimming planktonic cells with no specific tissue localization. This suggests that there are resistance mechanisms in the tolerant cultivar that limit aggregation of P. carotovorum subsp. brasiliense in planta and, hence, the lack of symptom development in this cultivar.

Identification of Late Blight Resistance-Related Metabolites and Genes in Potato through Nontargeted Metabolomics

Late blight of potato (Solanum tuberosum) caused by Phytophthora infestans significantly reduces the productivity of potato around the world. Resistance to late blight in potato is either qualitative or quantitative. Qualitative resistance governed by race-specific single R genes is well characterized and gives complete resistance, but is not durable. Quantitative resistance governed by polygenes gives partial resistance, but is durable in nature. However, the quantitative resistance mechanisms are poorly studied and are not efficiently exploited in potato breeding. A nontargeted metabolic profiling of resistant (F06037) and susceptible (Shepody) potato cultivars, using high-resolution liquid chromatography–mass spectrometry, was applied to elucidate the quantitative resistance mechanisms against P. infestans (US-8 genotype). The hydroxycinnamic acid amides (HCAAs) of the shunt phenylpropanoid pathway were highly induced following pathogen inoculation in F06037. In parallel, the transcript abundances of genes that catalyze the biosynthesis of these metabolites, such as 4-coumarate:CoA ligase, tyrosine decarboxylase, ornithine decarboxylase, tyramine hydroxycinnamoyl transferase, and putrescine hydroxycinnamoyl transferase, were also higher in the resistant genotype. Sequencing of the coding genes of these enzymes revealed single-nucleotide polymorphisms between resistant and susceptible genotypes, and the amino acid changes caused missense mutations altering protein functions. HCAAs deposited at host cell walls inhibit pathogen colonization, thus reducing lesion expansion. In addition, these also act as phytoalexins, leading to the reduced biomass of the pathogen. Following validation, the HCAAs can be used as biomarker metabolites for late blight resistance. The putative candidate genes can be either used to develop allele-specific markers for marker-assisted breeding programs or suitably stacked into elite cultivars through cisgenic approaches, following validation.

Development of somatic hybrids Solanum × michoacanum Bitter. (Rydb.) (+) S. tuberosum L. and autofused 4x S. × michoacanum plants as potential sources of late blight resistance for potato breeding

Key message Phytophthora infestans resistant somatic hybrids of S. × michoacanum (+) S. tuberosum and autofused 4 x S. × michoacanum were obtained. Our material is promising to introgress resistance from S. × michoacanum into cultivated potato background. Solanum × michoacanum (Bitter.) Rydb. (mch) is a wild diploid (2n = 2x = 24) potato species derived from spontaneous cross of S. bulbocastanum and S. pinnatisectum. This hybrid is a 1 EBN (endosperm balance number) species and can cross effectively only with other 1 EBN species. Plants of mch are resistant to Phytophthora infestans (Mont) de Bary. To introgress late blight resistance genes from mch into S. tuberosum (tbr), genepool somatic hybridization between mch and susceptible diploid potato clones (2n = 2x = 24) or potato cultivar Rywal (2n = 4x = 48) was performed. In total 18,775 calli were obtained from postfusion products from which 1,482 formed shoots. The Simple Sequence Repeat (SSR), Cleaved Amplified Polymorphic Sequences (CAPS) and Random Amplified Polymorphic DNA (RAPD) analyses confirmed hybrid nature of 228 plants and 116 autofused 4x mch. After evaluation of morphological features, flowering, pollen stainability, tuberization and ploidy level, 118 somatic hybrids and 116 autofused 4x mch were tested for late blight resistance using the detached leaf assay. After two seasons of testing three somatic hybrids and 109 4x mch were resistant. Resistant forms have adequate pollen stainability for use in crossing programme and are a promising material useful for introgression resistance from mch into the cultivated potato background.

ROS and salicylic acid (SA) play roles on the resistance establishment of the potato cultivar Zihuabai to Phytophthora infestans

Due to its high resistant to potato late blight, Zihuabai has become the most popular potato variety in the Inner Mongolia region of China. In this study, experiments were carried out to investigate the resistance mechanism of potato cultivar Zihuabai to late blight. Accumulation of reactive oxygen species (ROS), activities of oxygen scavenging enzymes, and transcription level of some resistance genes were determined in both resistant and susceptible potato cultivars inoculated with Phytophthora infestans, which causes potato late blight. Our results show that both ROS accumulation and oxygen scavenging enzymes activities were quicker and higher in the resistant cultivar Zihuabai compared to those of the susceptible cultivar Shepody. In addition, transcript levels of genes which are involved in resistant signaling pathways (salicylic acid and jasmonic acid pathways) were detected through RT-PCR. Our data indicated that together ROS and SA are the main signaling molecules regulating the resistance of potato cultivar Zihuabai to P. infestans.

Management of Bacterial Wilt [Rhalstonia solanacearum Yabuuchi et al., 1995] of Potatoes: Opportunity for Host Resistance in Kenya

This article gives a general overview of bacterial wilt of potatoes and its management. It also highlights the potential of host resistance as an important component of integrated management of bacterial wilt in Kenya. Bacterial wilt has spread to all potato growing areas in Kenya, affecting over 70% of potato farms and causing yield losses of between 50 to 100%. This disease has no effective means of control because crop protection chemicals are ineffective and expensive and biological control agents are ineffective. In addition, phytosanitary methods such as quarantine are either expensive or difficult to apply and cultural methods such as crop rotations are largely impractical because the farms are too small to allow effective rotation, the pathogen has a wide host range, and it persists for long in the soil. Development of resistant cultivars could therefore play an important role in managing the disease. More resistant potato clones have recently been identified by CIP scientists, and this resistance needs to be incorporated into the popular but susceptible Kenyan potato cultivars so as to increase potato production in Kenya. For better results, use of high resistant varieties may be coupled with use of disease-free tubers and clean fields.

Virulence assessment of Portuguese isolates of potato cyst nematodes (Globodera spp.)

Identification of species and virulence groups of potato cyst nematodes (PCN), Globodera pallida and G. rostochiensis , present in field populations is important in the control of these nematodes by means of resistant cultivars. In order to characterize the virulence of Globodera spp. isolates from Portugal, 43 G. rostochiensis and three G. pallida isolates were evaluated by measuring their multiplication rates on a susceptible potato cultivar and five differential potato genotypes in a growth chamber pot experiment. Principal Component Analysis and Hierarchical Cluster Analysis showed that the reproduction rates were different in terms of both the numbers of eggs and the numbers of cysts produced. Portuguese isolates of PCN were more virulent on genotypes derived from Solanum vernei than on genotypes derived from other Solanum resistance sources, and there was a significant nematode isolate × host genotype interaction. The virulence bioassay clearly distinguished the two PCN species but failed to differentiate isolates into pathotypes. There was a wide and continuous range of virulence to the resistant genotypes, especially in G. rostochiensis isolates.

Nematodes as a Limiting Factor in Potato Production in Scandinavia

Plant parasitic nematodes associated with potato feed on roots and/or tubers. About 70 species, representing 24 genera, have been reported from potato. Since nematodes attack underground plant parts, there are no reliable foliar symptoms to show that nematodes may be the major cause of poor growth and reduced tuber yields. Potato roots damaged by nematodes may show lesions, abnormal proliferation of lateral roots, emerging white females and brown cysts. Nematode attacks may render plants vulnerable to other pathogens, so disease caused by microorganisms may have nematodes as an etiological component. Therefore, nematode damage may often have been attributed to other factors. In Scandinavia, potato cyst nematodes (Globodera rostochiensis and Globodera pallida) are by far the most important nematodes on potato. In Norway, the cost of compensations schemes due to imposed statutory regulations of potato cyst nematodes may some years exceed the compensation for any other pests or diseases organism in agriculture. Other important nematodes include root lesion nematodes (Pratylenchus spp.), stubby root nematodes (Trichodorus spp. and Paratrichodorus spp.), and potato rot and stem nematodes (Ditylenchus spp.). Root knot nematode Meloidogyne hapla is considered less important. Meloidogyne chitwoodi and Meloidogyne fallax are not known to be present in Nordic countries. In the control, crop rotations using non-host crops, alternating susceptible and resistant potato cultivars, are an important control measure. However, the use of resistant potato cultivars requires knowledge of the species and pathotypes present in the field.

Differential gene induction in resistant and susceptible potato cultivars at early stages of infection by Phytophthora infestans

Sarpo Mira, a potato variety with high resistance against the late blight pathogen Phytophthora infestans, is being used in breeding programs to increase late blight resistance in commercial varieties. Discovering genes that are important for P. infestans resistance will assist in the development of molecular markers for the selection of new resistant cultivars and the use of resistant varieties will reduce the environmental, health and financial costs associated with the use of pesticides. Using complementary DNA amplified fragment length polymorphism analyses, differentially expressed genes involved in the potato-P. infestans interaction were identified in the susceptible Bintje and in the resistant Sarpo Mira potato cultivars. Forty-eight differentially expressed transcript derived fragments (TDFs) were cloned and sequenced. The expression profiles of some of these genes were analyzed in detail using quantitative RT-PCR at seven time points: 1, 4, 17, 24, 30, 41 and 65 hours after inoculation (hai). We found that five transcripts with homologies to pathogenesis/defense-related genes and two TDFs with homology to transcription factors were significantly induced to higher levels in the resistant cultivar at very early stages of the infection (1 hai). Interestingly, most of these genes showed different expression profiles throughout the whole infection process between both cultivars. Particularly during its biotrophic growth phase, P. infestans triggered the down-regulation of infection responsive genes in the susceptible but not in the resistance cultivar. Our results suggest that these newly identified early-induced transcripts may be good candidates for conferring Sarpo Mira's resistance to late blight and they could be useful molecular markers for the selection of new resistant cultivars.