Maris Piper Research Articles

Investigating the utility of potato (Solanum tuberosum L.) canopy temperature and leaf greenness responses to water-restriction for the improvement of irrigation management

Traits that rapidly respond to stress in important agricultural crops have the potential to provide growers with actionable feedback. Traits that respond to water-restriction could inform irrigation systems by identifying crop water status and requirements in real-time. This would be particularly useful for potato, which is extremely susceptible to drought. We conducted two pot experiments and one field experiment to evaluate the utility of two traits, canopy temperature and leaf greenness, for informing irrigation management in potatoes. We also evaluated the efficacy of Phenospex PlantEye F500 sensors for the remote sensing of leaf greenness. We found that canopy temperatures of the cvs. Maris Piper (Spring Pot Experiment, + 0.8 °C; Autumn Pot Experiment, + 5.3 °C) and Désirée (Autumn Pot Experiment, + 2.5 °C) increased with water-restriction and that the canopy temperatures of Maris Piper returned to its baseline within three days after the resumption of well-watered conditions. We also found that these responses varied between cultivars, with predictable outcomes based on reported and corroborated drought tolerance ratings. Leaf greenness was not affected by water restriction in the Spring pot experiment but had a significant interaction with sampling date and water restriction in the Autumn pot experiment. However, leaf greenness measurements from the Phenospex PlantEye F500 were significantly correlated with SPAD values, suggesting this tool might be useful in the screening for drought-tolerant cultivars in the future.

Cultivar-dependent differences in tuber growth cause increased soil resistance in potato fields.

Since soil compaction of potato fields delays shoot emergence and decreases total yield, the causes and effects of this compaction need to be better understood. In a controlled environment trial with young (before tuber initiation) plants, roots of cv. Inca Bella (a phureja group cultivar) were more sensitive to increased soil resistance (3.0 MPa) than cv. Maris Piper (a tuberosum group cultivar). Such variation was hypothesized to cause yield differences in two field trials, in which compaction treatments were applied after tuber planting. Trial 1 increased initial soil resistance from 0.15 MPa to 0.3 MPa. By the end of the growing season, soil resistance increased three-fold in the upper 20cm of the soil, but resistance in Maris Piper plots was up to twice that of Inca Bella plots. Maris Piper yield was 60% higher than Inca Bella and independent of soil compaction treatment, whilst compacted soil reduced Inca Bella yield by 30%. Trial 2 increased initial soil resistance from 0.2 MPa to 1.0 MPa. Soil resistance in the compacted treatments increased to similar, cultivar-dependent resistances as trial 1. Maris Piper yield was 12% higher than Inca Bella, but cultivar variation in yield response to compacted soil did not occur. Soil water content, root growth and tuber growth were measured to determine whether these factors could explain cultivar differences in soil resistance. Soil water content was similar between cultivars, thus did not cause soil resistance to vary between cultivars. Root density was insufficient to cause observed increases soil resistance. Finally, differences in soil resistance between cultivars became significant during tuber initiation, and became more pronounced until harvest. Increased tuber biomass volume (yield) of Maris Piper increased estimated mean soil density (and thus soil resistance) more than Inca Bella. This increase seems to depend on initial compaction, as soil resistance did not significantly increase in uncompacted soil. While increased soil resistance caused cultivar-dependent restriction of root density of young plants that was consistent with cultivar variation in yield, tuber growth likely caused cultivar-dependent increases in soil resistance in field trials, which may have further limited Inca Bella yield.

The EU43 genotype of Phytophthora infestans displays resistance to mandipropamid

AbstractMandipropamid is an active ingredient in the carboxylic acid amide group of fungicides and plays a key role in current potato late blight (Phytophthora infestans) management programmes. However, reports from Danish potato growers in 2022 suggested that mandipropamid had lost its efficacy. A study was therefore conducted to investigate the sensitivity of isolates collected from fields in which mandipropamid had been reported to be ineffective. Seventy‐two isolates of P. infestans collected from potato fields in Denmark were genotyped using microsatellite markers, revealing a dominance of the clonal lineage EU43 and fewer isolates of EU41 and ‘other’ genetically distinct genotypes. Isolates belonging to the EU43 and EU41 lineages were selected, in addition to representative isolates of clones EU36 and EU37 from Scotland, and tested for sensitivity to mandipropamid at five concentrations ranging from 0.1 to 10 μg/mL on potato leaf discs (cultivar Maris Piper). The EU43 genotype infected leaf discs at all tested concentrations, and therefore no dose–response curve could be calculated. A dose response was observed for isolates of genotypes EU36, EU37 and EU41 with EC50 values ranging from 0.35 to 0.75 μg/mL. Field experiments confirmed resistance of tested isolates of genotype EU43 to mandipropamid, with no significant difference in the area under the disease curve between the untreated and mandipropamid treatments. Analysis of the Danish population of P. infestans showed that EU43 was widely distributed across the country. To our best knowledge, this is the first report of resistance to mandipropamid in P. infestans.

Understanding the mechanical performance of raw and cooked potato cells

The micromechanics of individual potato cells comprising of cell wall and embedded native or gelatinised starch were explored. Micromanipulation can be used to compare cells of distinct strengths and study (bio)mechanical issues related to industrial processing (e.g. heat treatment). Two commercial types of potato, ‘baking’ and ‘Maris Piper’ were selected to conduct microcompression experiments. Cells isolated from ‘Maris Piper’ raw tubers appeared to be more resistant to deformation than the respective ones from the ‘baking’ cultivar. Cooked cells suffered a decrease in their turgidity which resulted in clusters of observed behaviours, with force–deformation curves showing a single or multiple bursting events. This study provides fundamental work and an insight on the behaviour of potato cells via an exploratory investigation of how different elements of the potato tissue can be measured. The results obtained can be used to relate cellular biology to mechanical properties and could also pave the way to understanding other starch-containing cells (e.g. pea, lentils, wheat).

Agronomic and physiological responses of potato subjected to soil compaction and/or drying

AbstractCompact and dry soils impede root growth and restrict plant water availability, respectively, potentially causing leaf water deficit. Although both stresses likely co‐occur in the field and limit yield, little is known about their combined impact on plant growth and physiology over a whole season, especially in a tuberous crop like potato. Field‐grown potato (Solanum tuberosum L. var. 'Maris Piper') was exposed to factorial combination of deficit irrigation (watering when soil moisture deficit reached 60 vs. 25 mm) and soil compaction (compacted with heavy machinery vs. uncompacted), with plant growth and leaf physiology measured weekly. Shoot growth was restricted by adverse soil conditions, while leaf water status, photosynthesis rates and leaf abscisic acid (ABA) levels did not vary significantly between treatments. Across all treatments, final yield was linearly correlated (R2 = 0.71) to mid‐season shoot biomass. Compared to well‐watered plants growing in loose soil, soil compaction, deficit irrigation and their combination decreased final tuber yield similarly, by 23%–34%. Surprisingly, tuber size distribution was more dependent on irrigation management than on soil strength. Plants exposed to deficit irrigation produced more, smaller potatoes than their respective control. Thus, low soil water availability and/or compact soil caused these field‐grown potatoes to restrict shoot growth rather than limit leaf gas exchange. Further research is needed to understand the role of hormonal signalling in regulating tuber growth when plants are exposed to compact and dry soils.

Nutritional Implications of Trade-Offs Between Fresh and Processed Potato Products in the United Kingdom (UK).

The UK ranks eleven among world potato producing countries with annual per capita production of about 102 kg. Since 2007, the price of potatoes has increased by 44 per cent and UK households have shown a decreasing trend on their purchases of potatoes. At the same time, retailers and manufacturers have been introducing processed potato products, which also has affected the demand for fresh potatoes. This has shifted demand from fresh potatoes to processed potatoes suggesting that consumers substitute fresh potatoes for processed ones. However, the extent to which this affect individual weekly nutritional composition is unknown. The objective of this study is to estimate the nutritional trade-offs between fresh and processed potatoes consumed in the UK using home scanner panel dataset for Great Britain in 2018. Price and expenditure elasticities were estimated using the linearized version of the Exact Affine Stone Index (EASI) Demand System. Using estimated elasticities, we analyzed the implications of substituting fresh potatoes for processed potatoes on nutrient intake. The results, in terms of the degree of substitution between fresh potatoes and processed potato products, suggest that consumers consider new potatoes baby and baking potatoes as substitutes for mashed potatoes. Maris piper potatoes and new potatoes baby are substitutes for frozen chips and other potatoes whilst white old potatoes and other vegetables and salads are complements to frozen chips and other potatoes. Finally, price reductions in the processed potatoes will increase average weekly caloric intake as well as the intakes of saturated fat and sodium. The latter has implications for public health as they are the major causes of cardiovascular diseases and certain cancers.

Susceptibility to blackheart disorder in potato tubers is influenced by sugar and phenolic profile

Abstract Blackheart (BH) is a physiological disorder of potato tubers in which internal tissue becomes discoloured during storage. The development of BH has been previously linked with general phenolic accumulation. In this study, five potato stocks cv. Maris Piper with different susceptibility to BH were selected across two consecutive seasons, whereupon targeted analysis of sugar and individual phenolic compounds in two tuber sections (flesh and heart) was conducted after storage at 1.5 °C or after one week at 15 °C. The most susceptible stock to BH had the highest accumulation of reducing sugars, while crypto- and neo-chlorogenic acids (chlorogenic acid isomers) were more abundant in flesh tissue of non-susceptible stocks. It is postulated that these metabolites may represent putative pre-symptomatic predictive biomarkers of stock susceptibility to BH.

Population dynamics of the potato cyst nematode, Globodera pallida, in relation to temperature, potato cultivar and nematicide application

The impact of increasing temperatures on the population dynamics of the soil‐dwelling nematode Globodera pallida, a persistent and economically important pest of potatoes, was investigated. The reproductive factor (final population⁄initial population) and length of life cycle were found to be temperature sensitive. Pot experiments performed over 4 months allowed comparison of the effect on development of G. pallida of two temperature regimes: an average temperature comparable to current field conditions (14.3 °C) and an average temperature above current field conditions (17.3 °C). A larger second generation of juveniles was observed at 17.3 °C compared to 14.3 °C. Multiplication of G. pallida at field sites in Shropshire and East Lothian (average soil temperatures of 15.5 and 14.1 °C, respectively, during potato cropping) was also examined. A quantitative PCR assay and visual examination of roots were used to monitor the dynamics of the G. pallida populations in both field sites at 4‐weekly intervals. Four cultivars, Desirée, Cara, Maris Piper and Estima, were grown with and without nematicide treatments. Nematicide treatments suppressed population increases at both sites. Females were observed on the roots of cvs Cara and Desirée at the end of the growing season in Shropshire, but not at East Lothian, and are likely to represent a second generation.

Post‐harvest treatment with pure (+)‐methyl jasmonate minimizes lipid oxidation in boiled potato (Solanum tuberosum L.)

Linoleic and linolenic acids are health‐promoting compounds having a number of biological properties. In the present study, oxidative degradation of these fatty acids into off‐flavor compounds in boiled potato was intended to be reduced. To that end, raw potatoes were treated by applying: (i) the commercial mixture (±)‐methyl jasmonate, (ii) pure (+)‐methyl jasmonate, and (iii) pure (−)‐methyl jasmonate, respectively. Four cultivars (i.e., Cara, Inca Sun, Mayan Gold, and Maris Piper) were included in the study. As a result, the post‐harvest application of (±)‐methyl jasmonate and (+)‐methyl jasmonate to raw potatoes during storage resulted in a significant decrease of lipid‐derived volatile compounds in boiled potato. This suggests an inhibitory effect of both the commercial enantiomeric mixture and the pure (+)‐methyl jasmonate on the lipoxygenase pathway. Stabilization of linoleic and linolenic acids against autoxidation is achieved by treatment with the enantiomeric mixture and pure (+)‐methyl jasmonate. (−)‐Methyl jasmonate however exhibited the opposite effect since it did not reduce lipid oxidation in boiled potato. The results found in the present work support earlier evidence on different effects of methyl jasmonate enantiomers on plant food composition. From a practical point of view, post‐harvest treatments with (+)‐methyl jasmonate can be used by the potato industry to obtain healthier and more pleasant products.Practical application The results found in the present study demonstrate that the practical applications of methyl jasmonate treatments minimize lipid oxidation in boiled potato. That allows us to obtain, on the one hand, tubers containing higher contents of linolenic and linoleic acids and, on the other, more pleasant flavor after boiling.The exogenous application of (+)‐MJ to raw potato during storage enabled lipid oxidation in boiled potato to be reduced. Therefore, (+)‐MJ treatment might be used by the potato industry to obtain a healthier and more pleasant product.

Factors affecting the development and control of black dot on potato tubers

Field trials were carried out over a 4 year period (2004–2007) to determine the effect of agronomic factors, specifically cultivar resistance, irrigation, crop duration and chemical control (in‐furrow application of azoxystrobin), on black dot development on potato tubers grown in fields where soilborne inoculum of Colletotrichum coccodes was present. In 2004, 2005 and 2006, two field trials were performed each year and in 2007, 19 mini‐field trials were carried out across Scotland and England. Cultivar resistance was clearly demonstrated to be an effective method of reducing black dot disease severity on tubers (described here as the percentage of unmarketable tubers, i.e. those with symptoms covering a surface area of >10%). In the four field trials carried out in 2004 and 2005, in irrigated and fungicide‐untreated plots, 43·8% of tubers of cv. Maris Piper were unmarketable, compared with 17·0% of tubers of cv. Sante. Assessments of disease development on underground plant parts (stems, stolons and roots) revealed that cultivar resistance acted only at the tuber level, as disease symptoms on other parts were often high irrespective of published disease resistance ratings. Irrigation increased the severity of disease on tubers in two trials (England 2004 and 2006), but its effect was less significant when rainfall was high. Delaying harvest by 2 weeks increased disease severity in all six trials, whilst application of azoxystrobin consistently reduced black dot severity. There were significant interactions between factors. The results clearly show how black dot disease severity can be reduced through an integrated approach to disease management.

Hypersensitive response to Potato virus Y in potato cultivar Sárpo Mira is conferred by the Ny-Smira gene located on the long arm of chromosome IX.

Potato virus Y (PVY, Potyvirus) is the fifth most important plant virus worldwide in terms of economic and scientific impact. It infects members of the family Solanaceae and causes losses in potato, tomato, tobacco, pepper and petunia production. In potato and its wild relatives, two types of resistance genes against PVY have been identified. While Ry genes confer symptomless extreme resistance, Ny genes cause a hypersensitive response visible as local necrosis that may also be able to prevent the virus from spreading under certain environmental conditions. The potato cultivar Sárpo Mira originates from Hungary and is highly resistant to PVY, although the source of this resistance remains unknown. We show that cv. Sárpo Mira reacts with a hypersensitive response leading to necrosis after PVYNTN infection in detached leaf, whole plant and grafting assays. The hypersensitivity to PVYNTN segregated amongst 140 individuals of tetraploid progeny of cvs. Sárpo Mira × Maris Piper in a 1:1 ratio, indicating that it was conferred by a single, dominant gene in simplex. Moreover, we identified five DNA markers linked to this trait and located the underlying locus (Ny-Smira) to the long arm of potato chromosome IX. This position corresponds to the location of the Ry chc and Ny-1 genes for PVY resistance. A simple PCR marker, located 1 cM from the Ny-Smira gene, can be recommended for selection of PVY-resistant progeny of cv. Sárpo Mira.

Two potato (Solanum tuberosum) varieties differ in drought tolerance due to differences in root growth at depth.

To test the hypothesis that root growth at depth is a key trait explaining some genotypic differences in drought tolerance in potato (Solanum tuberosum L.), two varieties (Horizon and Maris Piper) differing in drought tolerance were subjected to different irrigation regimes in pots in a glasshouse and in the field under a polytunnel. In the glasshouse, both cultivars showed similar gas exchange, leaf water potential, leaf xylem ABA concentration and shoot biomass independently of whether plants were grown under well watered or water deficit conditions. Under well watered conditions, root growth was three-fold higher in Horizon compared with Maris Piper, 3 weeks after emergence. Water deficit reduced this difference. In the polytunnel, applying 60% or less irrigation volume compared with full irrigation significantly decreased tuber yield in Maris Piper but not in Horizon. This was coincident with the higher root density of Horizon in deep soil layers (>40cm), where water content was stable. The results suggest that early vigorous root proliferation may be a useful selection trait for maintaining yield of potato under restricted irrigation or rainfall, because it rapidly secures access to water stored in deep soil layers. Although selecting for vigorous root growth may assist phenotyping screening for drought tolerance, these varieties may require particular environmental or cultural conditions to express root vigour, such as sufficiently deep soils or sufficient water shortly after emergence.

A locus conferring effective late blight resistance in potato cultivar Sárpo Mira maps to chromosome XI

Late blight of potato, caused by Phytophthora infestans, is one of the most economically important diseases worldwide, resulting in substantial yield losses when not adequately controlled by fungicides. Late blight was a contributory factor in The Great Irish Famine, and breeding for resistance to the disease began soon after. Several disease-resistant cultivars have subsequently been obtained, and amongst them Sárpo Mira is currently one of the most effective. The aim of this work was to extend the knowledge about the genetic basis of the late blight resistance in Sárpo Mira and to identify molecular markers linked to the resistance locus which would be useful for marker-assisted selection. A tetraploid mapping population from a Sárpo Mira × Maris Piper cross was phenotyped for foliar late blight resistance using detached leaflet tests. A locus with strong effect on late blight resistance was mapped at the end of chromosome XI in the vicinity of the R3 locus. Sárpo Mira’s genetic map of chromosome XI contained 11 markers. Marker 45/XI exhibited the strongest linkage to the resistance locus and accounted for between 55.8 and 67.9 % of variance in the mean resistance scores noted in the detached leaflet assays. This marker was used in molecular marker-facilitated gene pyramiding. Ten breeding lines containing a late blight resistance locus from cultivar Sárpo Mira and the Rpi-phu1 gene originating from the late blight resistant accession of Solanum phureja were obtained. These lines have extended the spectrum of late blight resistance compared with Sárpo Mira and it is expected that resistance in plants containing this gene pyramid will have enhanced durability.

Dynamics and management of the white potato cyst nematodeGlobodera pallidain commercial potato crops

Eight trials were conducted in commercial potato fields infested with the white potato cyst nematode (wPCN, Globodera pallida) and one in a field infested with the yellow PCN (yPCN, Globodera rostochiensis). Our aims were to produce data to validate and refine a computer-based program (The Model) for the long-term management of PCN, to determine nematicide effectiveness and to assess rates of PCN population decline between potato crops. Prior to planting, each farmer applied an overall nematicide treatment to his field, except for ten untreated plots that were widely spaced to encompass a range of PCN population densities. Each untreated plot was paired with a similar plot in the adjacent treated area and all plots were intensively sampled for PCN population densities at planting (Pi) and again at harvest (Pf) when tuber yields were determined. Four trials were re-sampled 2–4 years later to determine PCN population decline rates. Regressions that form the basis of ‘The Model’ and described the relationship between Pi and tuber yield and PCN population density at harvest were fitted to the results from both the untreated and nematicide treated plots. These regressions also enabled us to estimate the yield potential at each site in the absence of PCN and showed that nematicide treatment generally did not increase yield potential and that both tuber yield and PCN multiplication decreased with increasing Pi. However, there were major differences between sites and cultivars. When untreated, the yield of cv. Maris Piper was hardly affected in a highly organic soil with Pi > 200 eggs g−1 whereas the yield of partially resistant cv. Sante was decreased from a potential of c. 60 t ha−1 to c. 20 t ha−1 in a light silt with Pi = 20 egg g−1 soil. Similarly, untreated wPCN multiplication rates at a low Pi ranged from 46-fold to >100-fold. Nematicide effectiveness was estimated from the regressions and, at several sites, yield was decreased despite nematicide treatment. Control of wPCN multiplication was even poorer. In only two of seven trials planted with susceptible cultivars was more than 50% control achieved – maximum populations in treated plots usually exceeded 250 eggs g−1. Partially resistant Sante decreased the multiplication rate of wPCN in the two trials where it was planted. An alternative analysis using Genstat indicated that The Model tended to underestimate the maximum multiplication rate and overestimate the maximum population density. When four sites were re-sampled 2–4 years after harvest the populations of wPCN had declined by between 15% and 33.5% per annum with a mean of 26% per annum. Modelling indicated that rotations longer than 8 years were required to control wPCN unless other effective control measures, such as growing a partially resistant cultivar, were used.

The First Report of Globodera rostochiensis Pathotypes Ro5 Occurrence in Poland.

Potato (Solanum tuberosum L. subsp. tuberosum) is one of the most important crops in Poland. During vegetation season, pests and pathogens including a quarantine-significant nematode Globodera rostochiensis (Woll.) Behrens can infect growing plants. Regional surveys have revealed potato cyst nematodes (PCN) to be widely distributed in Poland, with the highest infestation throughout the northwest of the country. Since 1946, only pathotype Ro1 of G. rostochiensis has been recorded. Previous data revealed the occurrence of pathotype Ro5 in three separate provinces. In recent surveys, 22 soil samples from infested fields in northern and western parts of Poland were collected. Each sample comprised 10 kg of soil collected in a grid pattern. Samples of approximately 2 kg were dried for extracting nematodes. The cysts were obtained with an automatic cyst extractor (Mekku Gmbh). A molecular test was performed as a first step to discriminate G. rostochiensis from G. pallida. DNA from 30 cysts per sample was extracted with DNeasy Blood and Tissue KIT (Qiagen). Multiplex PCR analysis with two pairs of primers, GroR-GroF and PaR-PaF (1), was employed. The PCR resulted in a single 315-bp DNA fragment specific for G. rostochiensis. No amplification was shown with primers specific for G. pallida. Bioassays on differential genotypes of potato were carried out to identify the pathotype of G. rostochiensis. Five genotypes of potato: S. vernei hybr. 58.1642/4, S. vernei hybr. 62.33.3, S. vernei hybr. 65.346/19, S. multidissectum hybr. P 55/7, S. kurtzianum hybr. 60.21.19, and two varieties, Desiree and Maris Piper, were inoculated with 22 populations of G. rostochiensis cysts (2). Tests were performed in three replications. Eighteen of the cyst populations were pathotype Ro1 and four were pathotype Ro5. The abundance of cysts in locations where the new pathotype was detected suggests that there is a threat of further spread of G. rostochiensis. Consequently, producers and farmers need to grow resistant potato cultivars to keep nematode population below damaging level. To our knowledge, this is the first report of Globodera rostochiensis Ro5 in Poland.

Concentrations of Free Amino Acids and Sugars in Nine Potato Varieties: Effects of Storage and Relationship with Acrylamide Formation

Acrylamide forms during cooking and processing predominately from the reaction of free asparagine and reducing sugars in the Maillard reaction. The identification of low free asparagine and reducing sugar varieties of crops is therefore an important target. In this study, nine varieties of potato (French fry varieties Maris Piper (from two suppliers), Pentland Dell, King Edward, Daisy, and Markies; and chipping varieties Lady Claire, Lady Rosetta, Saturna, and Hermes) grown in the United Kingdom in 2009 were analyzed at monthly intervals through storage from November 2009 to July 2010. Acrylamide formation was measured in heated flour and chips fried in oil. Analysis of variance revealed significant interactions between varieties nested within type (French fry and chipping) and storage time for most free amino acids, glucose, fructose, and acrylamide formation. Acrylamide formed in chips correlated significantly with acrylamide formed in flour and with chip color. There were significant correlations between glucose or total reducing sugar concentration and acrylamide formation in both variety types, but with fructose the correlation was much stronger for chipping than for French fry varieties. Conversely, there were significant correlations with acrylamide formation for both total free amino acid and free asparagine concentration in the French fry but not chipping varieties. The study showed the potential of variety selection for preventing unacceptable levels of acrylamide formation in potato products and the variety-dependent effect of long-term storage on acrylamide risk. It also highlighted the complex relationship between precursor concentration and acrylamide risk in potatoes.

First Report of Rhizoctonia solani AG2-2IIIB Infecting Potato Stems and Stolons in the United States.

Rhizoctonia solani is an important pathogen of potato (Solanum tuberosum) causing qualitative and quantitative losses. It has been associated with black scurf and stem canker. Isolates of the fungus are assigned to one of 13 known anastomosis groups (AGs), of which AG3 is most commonly associated with potato disease (2,4). In August 2011, diseased potato plants originating from Rupert, ID (cv. Western Russet) and Three Rivers, MI (cv. Russet Norkotah) were received for diagnosis. Both samples displayed stem and stolon lesions typically associated with Rhizoctonia stem canker. The presence of R. solani was confirmed through isolation as previously described (4) and the Idaho and Michigan isolates were designated J11 and J8, respectively. AG was determined by sequencing the rDNA internal transcribed spacer (ITS) region using primers ITS5 and ITS4 (3). The resulting sequences of the rDNA ITS region of isolates J8 and J11 (GenBank Accession Nos. HE608839 and HE608840, respectively) were between 97 and 100% identical to that of other AG2-2IIIB isolates present in sequence databases (GenBank Accession Nos. FJ492075 and FJ492170, respectively). Koch's postulates were confirmed for each isolate by carrying out the following protocol. Each isolate was cultured on potato dextrose agar for 14 days. Five 10-mm agar plugs were then placed on top of seed tubers (cv. Maris Piper) in 1-liter pots containing John Innes Number 3 compost (John Innes Manufacturers Association, Reading, UK). Pots were held in a controlled environment room at 18°C with 50% relative humidity and watered as required. After 21 days, plants were removed and assessed for disease. Typical Rhizoctonia stem lesions were observed and R. solani was successfully reisolated from symptomatic material. To our knowledge, this is the first report of AG2-2IIIB causing disease on potatoes in the United States. In the United States, AGs 2-1, 3, 4, 5, and 9 have all been previously implicated in Rhizoctonia potato disease (2). AG2-2IIIB should now also be considered a potato pathogen in the United States. Knowledge of which AG is present is invaluable when considering a disease management strategy. AG2-2IIIB is a causal agent of sugar beet (Beta vulgaris) root rot in Idaho (1). Sugar beet is commonly grown in crop rotation with potato and such a rotation could increase the risk of soilborne infection to either crop by AG2-2IIIB.

Bio-fortification of potato tubers using foliar zinc-fertiliser

SummaryWorldwide, many people are zinc (Zn)-deficient. Dietary Zn intake can be increased by producing crops with higher concentrations of Zn in their edible portions. This can be achieved by applying Zn-fertilisers to varieties with an increased ability to acquire Zn and to accumulate Zn in their edible portions. Potato (Solanum tuberosum L.) is an important food crop and is, therefore, a target for bio-fortification with Zn. Field trials incorporating a core collection of 23 potato genotypes, performed over 4 years (2006 – 2009), indicated significant genotypic effects on tuber Zn concentration and suggested that tuber Zn concentration was influenced by environmental effects, but also found that genotype × environment (G × E) interactions were not significant. Tuber Zn concentrations averaged 10.8 mg kg–1 dry matter (DM), and the ratio between the lowest and the highest varietal tuber Zn-concentration averaged 1.76. Tuber Zn concentrations could be increased by foliar Zn-fertilisation. Tuber yields of ‘Maris Piper’ were unaffected by foliar applications of < 1.08 g Zn plant–1. The relationship between tuber Zn concentration and foliar Zn application followed a saturation curve, reaching a maximum at approx. 30 mg Zn kg–1 DM at a foliar Zn application rate of 1.08 g plant–1. Despite a 40-fold increase in shoot Zn concentration compared to the unfertilised controls following foliar Zn-fertilisation with 2.16 g Zn plant–1, only a doubling in tuber Zn concentration was observed. This suggests that the bio-fortification of tubers with Zn was restricted by the limited mobility of Zn in the phloem. A significant positive linear relationship between tuber Zn concentration and tuber N concentration supported the hypothesis of co-transport of Zn and N-compounds in the phloem.

Variation in in vitro hatch of potato cyst nematodes in response to different potato cultivars inoculated with isolates of arbuscular mycorrhizal fungi

AbstractSix potato (Solanum tuberosum) cultivars (Home Guard, Bintje, British Queen, Maris Piper, Pentland Dell and Saturna) were inoculated with Vaminoc (a commercial mixture of three selected arbuscular mycorrhizal fungal (AMF) isolates) and with two of the individual AMF isolates present in Vaminoc, Glomus intraradices (BioRize BB-E) and Glomus mosseae (isolate BEG 12). Root length colonisation by AMF at 6 weeks after shoot emergence ranged from 49 to 54%, with Vaminoc exhibiting the highest percentage. In comparison with control plants, AMF-inoculated plants accelerated the in vitro hatch (21% mean increase) of the potato cyst nematode (PCN) species Globodera pallida (but not of G. rostochiensis) in potato root leachate collected 3 weeks after shoot emergence. The effects of mycorrhization on PCN hatch were broadly similar across the six potato cultivars. This consistency supports the potential use of AMF inoculation of potato plants as part of an integrated pest management strategy for G. pallida.

The Golden Potato Cyst Nematode Globodera rostochiensis Pathotype Ro1 in the Saint-Amable Regulated Area in Quebec, Canada.

The golden potato cyst nematode, Globodera rostochiensis (Wollenweber, 1923) Behren, is an economically important parasite of potato (Solanum tuberosum L. subsp. tuberosum) and is recognized as a quarantine pest internationally (2). This pest attacks potato plants and causes stunting of the haulm and the root system, leaf yellowing, and tuber yield losses (2). The pathotype scheme proposed by Kort et al. distinguishes five pathotypes (Ro1, Ro2, Ro3, Ro4, and Ro5) of G. rostochiensis using differential Solanum clones (1). Several resistance genes and quantitative trait loci (QTL) that have been identified in wild Solanum species confer resistance to different G. rostochiensis pathotypes and have been introgressed into commercial potato cultivars (2). Determining G. rostochiensis pathotype(s) is essential to implement efficient management strategies, which include using resistant potato varieties. G. rostochiensis was discovered in the municipality of Saint-Amable, Quebec (QC), Canada in 2006 (3) and was subsequently characterized (4). In this study, cysts were collected from 11 representative infested fields and confirmed to be G. rostochiensis (3). The pathotypes of these nematodes were assessed on seven differential clones (S. tuberosum subsp. tuberosum cv. Desiree, S. tuberosum × S. andigena cv. Maris Piper, S. kurtzianum hybrid 60.21.19, S. vernei hybrid 62.33.3, S. vernei hybrid 58.1642/4, S. vernei hybrid 65.346/19, and S. multidissectum hybrid P55/7) in 2007 and 2009. Briefly, in each 1-liter plastic pot containing 907 g (2 lbs) of soil (3:1 loam/grit v v-1), a single differential Solanum clone was planted and 15 cysts from 1 of 11 fields were inoculated. Five replicates were set up for each Solanum-nematode combination and the pots were arranged in a completely randomized design in a greenhouse at 22°C with a 16-h light period per day. Nine weeks after inoculation, cysts were extracted from each pot and counted. Reproduction factor (Rf) for each replicate was calculated (Rf = Pf/Pi; Pf is the final cyst number and Pi is the initial cyst number added to each pot). Rf values were used to categorize the differential clones into two groups, "susceptible" leading to increase in nematode numbers (Rf > 1) and "resistant" resulting in decrease in nematode numbers (Rf ≤ 1) (1). Our results in 2007 and 2009 were consistent and the pathotype of the nematodes collected from all the fields were identified as Ro1. To our knowledge, this is the first time that the pathotype of G. rostochiensis in the Saint-Amable regulated area was identified. Accordingly, potato cultivars carrying genes or QTL resistant to G. rostochiensis pathotype Ro1 can be used to reduce the nematode numbers in infested fields in the Saint-Amable area, QC.