Effect of crop rotation on Globodera rostochiensis and on potato yield1

A crop rotation field study was conducted in 1981–1989 to assess the effect of six crop rotation sequences on a soil population of potato cyst nematode (PCN), Globodera rostochiensis, and on potato yield. In the plots with potato monoculture, the tuber yield decreased from 35 to 4.6 t ha^?1. All other cropping systems maintained the yield at the original or an even higher level. In monoculture, the population density of the nematode was raised during the first 3 years from 0.1 to 265 larvae g^?1 soil, and the density fluctuated afterwards between 30 and 136 larvae g^?1 soil. Three of the cropping systems, (1) susceptible potato once in 5 years, (2) susceptible potato once in 4 years, and (3) potato once in 3 years using resistant (H1) and susceptible cultivars alternately, decreased the nematode density under the economic threshold or even under the level of detection. The nematicide treatments (oxamyl) did not control nematode multiplication but prevented yield losses. No nematicide is currently registered nor needed for the control of PCN in Finland. The nematode can be controlled effectively with crop rotation, resistant cultivars and early harvesting.     

Potential impacts of climate change on the threat of potato cyst nematode species in Great Britain

Potato cyst nematode (PCN) species have different temperature optima for various life cycle stages, therefore a risk assessment of the threat of PCN species under future climates is essential to guide adaptation strategies. Data defining the spatial coverage of potato crops in Great Britain were combined with probabilistic climate change data and a newly developed PCN life cycle model to project the future risk to potato crops from PCN. The model was based on the results of controlled environment experiments to investigate the effect of temperature on survival to female maturity using three PCN populations: Globodera pallida (Lindley) and G. rostochiensis from the James Hutton Institute PCN collection, and a field population of G. pallida (S‐Fife). It was found that projected increases in soil temperature could result in increased survival to female maturity for all three PCN populations, with greater increases expected for Scotland, followed by Wales then England. The largest projected increases in Scotland were for G. pallida, whereas G. rostochiensis showed the largest increases in Wales and England. The potential impact of several agronomic adaptation strategies on projected PCN risk were also investigated. The results from the model suggest that soil infestation levels would have to be reduced by up to 40% in order to negate projected increases in PCN risk, and that advancing the start date of the growing season or modifying planting patterns could be successful strategies to reduce future PCN risk.     

Consistent action of two partially effective loci conferring resistance to Globodera pallida Pa2/3 across multiple nematode field populations

The potato cyst nematodes (PCN) Globodera rostochiensis and Globodera pallida are significant pests of potatoes worldwide. The most effective control methods are crop rotation and the deployment of resistant varieties. Complete resistance to G. rostochiensis based on a single resistance gene has successfully been integrated into many varieties. However, resistance to G. pallida has not been as successful to date, with current varieties only exhibiting partial resistance. Combining partially effective quantitative trait loci (QTLs) for resistance can increase the strength and breadth of the resistance. An additive effect on resistance has previously been demonstrated on combining two QTLs from Solanum tuberosum subsp. andigena (GpaIV^s_adg) and Solanum vernei (Gpa5). However, populations of G. pallida can be quite divergent and it was unclear whether the relative effects of the individual QTLs and the combined additive effect would be consistent across different G. pallida Pa2/3 populations. Using a mapping population segregating for both QTLs, the effect of the QTLs individually and combined was examined on four UK‐derived field populations of G. pallida pathotype Pa2/3, and the relative effects of the individual QTLs and the additive effect of the combination found to be consistent across all populations.     

Seed-potato production of cultivars resistant to Globodera rostochiensis in Poland1

Changes in the production of Polish seed potatoes of cultivars that are resistant to potato cyst nematodes have been followed. Over the period from 1972 to 1998, 35 cultivars resistant to Globodera rostochiensis (pathotype RO₁) were introduced. Among them, one (Drop) was also resistant to Globodera pallida (PA₃) and a number had multiple resistance to diseases and nematodes. Planting of seed potatoes of these resistant cultivars concerned only 0.4% of the total potato area. Against a background of much reduced seed-potato production, the area planted with resistant cultivars fell by 47% over the years 1989/1997). However, the share of resistant cultivars in the total seed-potato area increased from 16% in 1989 to 47% in 1997, the most important cultivars being Lawina, Orlik, Ibis and Irga. In 1992/1993, resistant cultivars occupied only 6–8% of the total potato area.     

Morphological and molecular identification of potato and cereal cyst nematode isolates from Algeria and their phylogenetic relationships with other populations from distant theirgeographical areas

A nematode survey conducted in 2013 in Algeria, revealed that potato cyst nematodes (PCN) and cereal cyst nematodes (CCN) are widely distributed in several potato and cereal growing regions of the country. Sixteen PCN populations from five localities and five CCN populations from four of these localities were collected and characterized at the morphological and molecular levels. The PCN populations were identified as Globodera rostochiensis and G. pallida occurring separately or in mixed populations. Two species of CCN were detected. Heterodera avenae was found in four localities, whereas H. hordecalis only in one locality in association with H. avenae. The morphological and morphometric identification of PCN and CCN was confirmed by diagnostic ITS-RFLP profiles and sequencing. Phylogenetic analysis of the ITS, D2-D3 expansion domains of the 28S rRNA gene and 18S rRNA gene was made for PCN and CCN populations. Globodera pallida and G. rostochiensis from Algeria show great similarity with European and South American populations. Because of the high divergence among Algerian populations of G. pallida and G. rostochiensis it can be assumed that they were multi-introduced in Algeria. The most divergent population of G. pallida, that formed a well-separated group with some populations from Chile and Peru, suggests a later or independent introduction of this population into Algeria. Heterodera avenae and H. hordecalis formed a well-supported cluster with the corresponding populations.     

The Basis of Predictive Modelling for Estimating Yield Loss and Planning Potato Cyst Nematode Management

The basis of modelling yield loss and population dynamics relations of potato cyst nematodes is that both are strongly density-dependent. Potato cyst nematodes (PCN; Globodera pallida and G. rostochiensis) are particularly suitable for analysing such relationships because they have only one generation per year, potato is their only field host, the juvenile nematodes within the egg are very durable (up to 20 years persistence), and they hatch mainly in response to specific chemicals exuded from host roots. Small populations increase the most, up to 50-fold, when a potato crop is grown. Multiplication rates decrease as the population density increases because damage decreases root system size and increases competition so that very large populations may actually be decreased when potatoes are grown. The newly formed eggs have a ‘half-life’ of c.two years when non-host, rotational crops are being grown. Control is achieved largely by the use of rotation, the application of nematicidal chemicals, and growing resistant cultivars. As rotations are shortened, so PCN populations will be increased, and crop damage becomes more likely. Thresholds for damage vary with both soil type (greatest on sandy soils) and potato cultivar. Cultivars differ in their tolerance of PCN damage depending on how vigorously they grow, on their root sensitivity to damage from the PCN juveniles which invade close to root tips, on cultivar resistance which decreases the parasitic effect by reducing the numbers of developing PCN females, and on various environmental factors such as the amounts of fertiliser applied. The dependence of the yield-loss relationship on population density, soil type and cultivar effects has been described in a simple equation and assessed using field-trial data. Effects on yield are described in proportion to the PCN-free yield but the addition of information on expected yield (in tonnes ha⁻¹) in the absence of PCN renders this equation predictive. Nematicides are widely applied to infestations of potato cyst nematodes, both to prevent the crop from being damaged and to prevent population increase which could hazard the next potato crop in the rotation, but they are generally more effective at preventing the former than the latter. A complex equation has also been developed to model the population dynamics of PCN. This equation incorporates a factor for host-crop growth and tolerance (from the yield-loss equation) and also the effects of host resistance. This latter is particularly relevant to G. pallida, where all the resistance currently available is determined by minor genes and hence is ‘quantitative’ or ‘partial’. Effects of rotation and of nematicides can also be incorporated into this model. To provide a realistic prediction also requires accurate information on PCN population densities, species composition and distributions, and rates of PCN population decline between potato crops.     

Potato cyst nematodes in the Canary Islands: an epidemiologic model for the Mediterranean region1

This work describes studies done on the Canary Islands in order to support the elaboration of quarantine and control legislation for potato cyst nematodes which take into account the special agroecological characteristics of the Mediterranean region. The interest of the islands for epidemiological studies is based on the occurrence of the oldest potato crops in the Old World and the use of several local cultivars and traditional management cropping systems. Also, the environmental conditions allow field experiments to be performed throughout the year. The phytonematological problems of the potato crop on the Canary Islands is reported and the absence of Ditylenchus destructor, D. dipsaci, Nacobbus aberrans, Rotylenchulus reniformis and trichodorids pointed out. The cyst nematodes, Globodera rostochiensis and G. pallida were found to cause severe damage to the crop and were studied in detail by field trials at Tenerife. Continuous growing of the cv. Cara, with the H1 gene conferring resistance to G. rostochiensis (pathotypes Ro1 and Ro4), exerted selection pressure for G. pallida. Under the edaphic and climatic conditions of Tenerife, nematicide application was found to be inefficient for controlling potato cyst nematodes. Alternative control techniques based on traditional management systems and on the use of environmentally adverse conditions were investigated.     

A biotechnological strategy involving monoclonal antibodies for improvement of potato farming by identification and quantification of potato cyst nematodes in soil samples1

The two closely related nematode species Globodera rostochiensis and G. pallida are one of the major problems encountered in potato cultivation. There is a spectrum of potato plant genes known, which confer resistance to these species and their pathotypes. Potato growing in The Netherlands has to follow strict rules to control spread of the pests. Since distinction between the two nematode species is difficult, a rapid and reliable identification method is needed to allow better use of existing and forthcoming resistant potato cultivars. The aims of this project were: (1) identification and partial purification of species-specific proteins from the nematodes, (2) production of species-specific monoclonal antibodies, and (3) development of a screening test for qualitative and quantitative determination of Globodera spp. in soil samples.     

Evaluation of PCR,IEF and ELISA techniques for the detection and identification of potato cyst nematodes from field soil samples in England and Wales

Effective management of potato cyst nematodes (PCNs) requires simple, rapid and accurate identification and quantification of field populations. Soil samples from a survey of 484 fields in potato rotations in England and Wales were used to compare the identification and quantification of PCNs using IEF, PCR, ELISA and bait plant tests. The cyst counts and bait plant test revealed that 64.3% of field samples contained PCNs. Bait plant tests increased the detection rate of PCNs in field samples by 4–6.4%. This means that some infestations are cryptic and would not normally be detected by standard counts. IEF, PCR and ELISA methods distinguished between Globodera rostochiensis and G pallida and were able to register mixed populations; however they were not in full agreement. All methods suggested that G pallida is the dominant species in the field samples tested. The PCR results indicated that 66% of field samples contained pure G pallida, 8% contained pure G rostochiensis and 26% contained mixtures of the two species. Estimates of the relative process times taken per sample in the PCR, IEF and ELISA techniques are given. © 2001 Society of Chemical Industry     

Identification of <Emphasis Type="Italic">Globodera rostochiensis</Emphasis> and <Emphasis Type="Italic">G. pallida</Emphasis> in the Ukraine by PCR

Multiplex polymerase chain reaction was used to identify the potato cyst nematodes in soil samples from the Ukraine. The results show the occurrence of Globodera pallida in the Uzhhorod region (Zakarpatska oblast), where only G. rostochiensis had been previously reported. In the mixed potato cyst nematode (PCN) populations, G. pallida was less prevalent (2–5%) than G. rostochiensis (95–98%). A phylogenetic analysis based on ribosomal DNA internal transcribed spacer sequences showed that the Ukrainian population of G. pallida had >99% sequence identity with other G. pallida pa2/3 isolates from Europe. This study has demonstrated that polymerase chain reaction-mediated amplification of specific regions of the potato cyst nematode genome is not only highly effective as a species diagnostic tool but is also a sensitive method which can be used for taxonomic purposes with cyst collections which vary in age.     

Differential hatching of the potato cyst nematodes Globodera rostochiensis and G. pallida in root diffusates and water of differing ionic composition

The hatching differences ofGlobodera rostochiensis andG. pallida were assessed in potato root diffusate (PRD) of cv. Bintje, cv. Elkana and clone ZB35-29.G. pallida hatched better in the PRDs thanG. rostochiensis. It was shown that the experimental test conditions strongly influenced the hatching results. The water type used in the hatching tests had a significant discriminating effect on the species;G. rostochiensis reached hatch percentages of 60 to 90% in demineralized and tap water, whereasG. pallida never exceeded the 15%. These differences were independent of the various batches that were used or the different years the tests were carried out. Silver sand percolate had a inhibiting effect on the hatching of both nematode species. Boron and a high electrical conductivity may be responsible for this. The results are discussed from an ecological point of view as well as for research consequences.     

Control methods for potato nematodes in Ukraine1

Control of Globodera rostochiensis in Ukraine depends on the use of resistant potato cultivars. In the last 2 years, the proportion of resistant entries in the official Ukrainian list has increased from 27% to 45%, and the number of Ukrainian-bred resistant cultivars has increased from 3 to 12. It is now suggested that resistant cultivars are classified into the categories‘resistant and tolerant’ and ‘resistant but only relatively tolerant’. The choice of these cultivars should depend on the nematode population of the soil. Control of Ditylenchus destructor is also considered, on the basis of prophylactive and agrotechnical measures.     

The use of isoelectric focusing as a tool in the identification and management of potato cyst nematode populations1

Isoelectric focusing on thin layers of polyacrylamide or agarose gels may be used to separate proteins from the potato cyst nematodes Globodera rostochiensis and G. pallida. General protein patterns may be used to identify the two species, even from single cysts. Densitometry of species-specific protein bands may be used to assess the proportions of G. rostochiensis and G. pallida in potato cyst nematode samples. Staining for the enzymes phosphoglucomutase and phosphoglucose isomerase also revealed species-specific patterns, and variation among G. pallida populations was observed. Thus calculations of coefficients of similarity based on six enzymes, phosphoglucose isomerase, phosphoglucomutase, glycerol-3-phosphate dehydrogenase, enolase, hexokinase and malate dehydrogenase and the construction of a dendrogram for several Northern Ireland populations indicated clear separations between G. pallida (Pa1), G. pallida (Pa3) and G. rostochiensis (Ro1). The use of the technique of isoelectric focusing as a routine research and advisory tool in nematology, and as a means of further understanding the genetic basis of pathotype schemes, is discussed.     

Testing potato clones for resistance to Globodera rostochiensis (Ro1) and Globodera pallida (Pa2 and Pa3) by root-ball screening1

Clones from the international test assortment were tested for resistance to Globodera pallida (Pa2 and Pa3) and estimated by root-ball counting and by extraction of the total number of cysts to show the practicability of the root-ball test. New clones in a breeding programme were tested by root-ball counting for resistance to Globodera rostochiensis (Ro1) and G. pallida (Pa2 and Pa3), and the statistical aspects are discussed. The conclusion is that testing new clones early in a breeding programme by root-ball counting of cysts with four to five replicates is a sufficient method to separate the susceptible clones from resistant and moderately resistant ones.     

Hsp90 gene, an additional target for discrimination between the potato cyst nematodes, Globodera rostochiensis and G. pallida, and the related species, G. tabacum tabacum

The heat-shock gene, Hsp90, was targeted as a new variable genomic region to supplement other DNA-based tests for identification and discrimination of Globodera pallida, G. rostochiensis and G. tabacum tabacum. Populations of the potato cyst nematodes, G. pallida and G. rostochiensis (PCN), originating from Canada, France, Belgium and USA, together with two populations of G. tabacum tabacum from the USA and France were used for the amplification of a fragment of the Hsp90 gene. General and specific primers and probes for each species were derived from the consensus and non-consensus regions of the aligned sequences, respectively. A triplex conventional PCR assay, using a general forward and reverse or three specific reverse primers, as well as a real-time PCR using general primers and specific TaqMan probes, were developed. Melting curve analysis and restriction fragment polymorphisms using high resolution electrophoresis were explored for identifying PCR amplicons that characterized and discriminated the three Globodera species in both pure and mixed samples. Results from the different molecular assay strategies confirmed the usefulness of Hsp90 as a new additional gene target and showed that several different test options could be used for discrimination of PCN.     

Photosynthesis,transpiration and plant growth characters of different potato cultivars at various densities of Globodera pallida

Plants of four potato (Solanum tuberosum L.) cultivars were grown in pots in a greenhouse at five densities ofGlobodera pallida between 0 and 300 eggs per gram of soil. Photosynthesis and transpiration of selected leaves were measured at 30, 37, 49 and 60 days after planting. Stem length was recorded at weekly intervals. Plants were harvested 70 days afteer planting and various plant variables were determined.At 30 days after planting, when second and third stage juveniles were present in roots, both photosynthesis and transpiration rates were severely reduced byG. pallida. In the course of time these effects became less pronounced. Water use efficiency was reduced byG. pallida between 30 and 49 days, but not at 60 days after planting. The results suggest independent effects ofG. pallida on stomatal opening and on photosynthesis reactions. There were no consistent differences among cultivars in the response of leaf gas exchange rates and water use efficiency to nematode infection. Reduction of photosynthesis byG. pallida appeared additive to photosynthesis reduction due to leaf senescence.Total dry weight was reduced by 60% at the highestG. pallida density. Weights of all plant organs were about proportionally affected. Shoot/root ratio was not affected and dry matter content was reduced. Stem length and leaf area were most strongly reduced during early stages of plant-nematode interaction. The number of leaves formed was only slightly reduced byG. pallida, but flowering was delayed or inhibited. Reduction of total dry weight correlated with reduction of both leaf area and photosynthesis rate. Leaf area reduction seems the main cause of reduction of dry matter production. Tolerance differences among cultivars were evident at 100 eggs per gram of soil only, where total dry weight of the intolerant partially resistant cv. Darwina was lower than that of the tolerant partially resistant cv. Elles and of the tolerant susceptible cv. Multa. The tolerance differences were not correlated with leaf photosynthesis and transpiration. Apparently these processes are not part of tolerance of plants.     

Plant parasitic nematodes as pests of potatoes in Poland1

Only two plant parasitic nematode species have practical importance in potato crops in Poland. They are Ditylenchus destructor and Globodera rostochiensis pathotype Ro1. Control of D. destructor is done permanently by the elimination of infested seed potatoes and sowing of cereals in the infested fields. Damage to potatoes is observed rather seldom. G. rostochiensis is widely distributed throughout Poland. It is controlled by non-host crops and by resistant potato cultivars. Chemical control of potato nematodes is not put into practice in Poland.     

Quantification of Globodera rostochiensis and G. pallida in mixed populations using species-specific thermostable proteins

A method has been developed to quantify species ratios in mixed populations. The method is based on the separation of species-specific thermostable proteins by SDS-PAGE. Densitometric analyses of the 17 kD protein ofGlobodera pallida and the 18 kD protein ofG. rostochiensis revealed a high correlation (R ²=0.93) with the species ratio in the mixed samples. Within the limits of 10 to 90% of each species, one can estimate with 95% reliability the species composition with 3 to 6% deviation.Samenvatting Een methode is ontwikkeld om de samenstelling van soortenmengsels vanGlobodera rostochiensis enG. pallida te kwantificeren. Bij deze methode wordt gebruik gemaakt van de soort-specifieke thermostabiele eiwitten die met behulp van SDS-PAGE gescheiden worden. De kleurintensiteit van het 17 kD eiwit vanG. pallida en het 18 kD eiwit vanG. rostochiensis is per gel-laan bepaald m.b.v. een densitometer en heeft een lineair verband met de soortsverhouding in de mengsels (R ²=0.93). Binnen het bereik van 10 tot 90% van elke soort kan men met deze ijklijn met 95% betrouwbaarheid de soortsamenstelling bepalen op 3 tot 6% nauwkeurig.     

Interactions Between the Potato Cyst Nematode Globodera rostochiensis and Diseases Caused by Rhizoctonia solani AG3 in Potatoes Under Field Conditions

Findings from 2 years of field experiments investigating the relationship between Globodera rostochiensis and Rhizoctonia solani on unique field sites are reported. In 2000, a field experiment was positioned on land that had previously been used for experimental work investigating integrated potato cyst nematode (PCN) management methods. This study had produced an ‘untypical’ mosaic of PCN population densities ranging from 5 to 221 eggs g⁻¹ soil. In 2001, the field experiment was conducted on a different field site and overlaid on a focus of G. rostochiensis population densities ranging from 11 to 108 eggs g⁻¹ soil. In each experiment, potatoes (cv. Désirée) were grown in plots with similar population densities of G. rostochiensis that were either uninoculated or inoculated with R. solani. A series of potato plant harvests were undertaken to investigate the effects of nematode infestation on the incidence and severity of R. solani diseases and the associated development of plants. In both experiments, a clear relationship was found between the density of G. rostochiensis juveniles present in potato roots and the incidence of stolons infected by R. solani, 6 weeks after planting. For the first time this interaction has been determined under field conditions. The results of the study suggest that the interaction between nematode and fungus is indirect and possible mechanisms are discussed.     

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.