Growth and development of plants with potential for use as trap crops for potato cyst nematodes and their effects on the numbers of juveniles in cysts

Growth and development of three plant accessions with potential for use as trap crops for potato cyst nematodes (PCN), Solanum sisymbriifolium and two varieties of S. nigrum, were studied under 12 h and 17 h photoperiods. In pot experiments, rate of plant emergence, plant height, and shoot and root mass were greater for the S. nigrum varieties ‘90‐4750‐188’ and ‘88‐4750‐061’ than for S. sisymbriifolium and markedly greater than for a S. nigrum variety found as a weed of arable fields in The Netherlands. However, the last mentioned S. nigrum variety produced the most berries. Plant height and shoot weight of all the S. nigrum varieties were greater under the longer photoperiod, whereas the root mass was hardly affected. Plant height and shoot weight of S. sisymbriifolium also were greater under the longer photoperiod but the root weight was less. Under field conditions, with sowing dates from the end of March to mid August, S. sisymbriifolium and S. nigrum‘90‐4750‐188’ grew better than S. nigrum‘88‐4750‐061’. In contrast to S. nigrum, S. sisymbriifolium appeared resistant to night frosts in autumn. The stubbles of both S. sisymbriifolium and S. nigrum showed good regrowth after cutting the plants 5 or 10 cm above the soil surface 11 wk after sowing. In a pot experiment, all the plant accessions strongly reduced the numbers of juveniles in cysts compared with flax. Tolerance to Globodera rostochiensis of S. sisymbriifolium and S. nigrum‘90‐4750‐188’ was investigated in pot experiments under glasshouse conditions in sandy soil at pH 4.8 and 6.0. At soil infestation levels ranging from 0 to 56 juveniles ml^?1 soil, S. sisymbriifolium appeared much more tolerant than S. nigrum‘90‐4750‐188’. Shoot yield of S. nigrum decreased markedly with increasing soil infestation and root weight also decreased, except at pH 4.8 and light infestation levels. Both S. sisymbriifolium and S. nigrum grew better at soil pH 4.8 than 6.0. The proportion of lateral roots in the total root mass increased in both species with increasing PCN infestation and soil pH. However, although the proportion of lateral roots in plants grown at soil pH 6.0 was greater at PCN infestations up to 14 juveniles ml^?1 soil, the proportion of laterals in S. nigrum was considerably less at PCN infestations of 56 juveniles ml^?1 soil. The proportion of PCN juveniles hatching was similar for the two species and decreased slightly with increasing initial nematode population densities.     

Effects of potnetial trap crops and planting date on soil infestation with potato cyst nematodes and root-knot nematodes

In 1997 and 1998 the stimulation of hatch of potato cyst nematodes (PCN) by a trap crop was studied at various times during the growing season in a container and a field experiment. Solanum nigrum‘90‐4750‐188’was used as the trap crop in both experiments and was sown on 1 May, 16 June or 1 August in two successive years on different plots. Neither experiment revealed much seasonal variation in hatchability of PCN juveniles under a trap crop. In the container experiment, the hatch of the Globodera pallida Pa3 population was equally and strongly stimulated (89%) at all sowing dates in both years, except for the 1 August sowing in 1998 (when the hatch was 77% under extremely wet soil conditions). In the control treatment with non‐hosts (flax followed by barley) the total spontaneous hatch was 50% over 2 yr. In the field experiment, the hatch of PCN, averaged over the four populations, was also equally stimulated (71%) at all sowing dates in both years. In the control treatment with non‐hosts (flax‐barley) the total spontaneous hatch was 36% over 2 yr. Total hatch under the trap crop over 2 yr varied between the four PCN populations from 63% to 80%. In 1998 and 1999, control of potato cyst nematodes (PCN) by the potential trap crops Solanum sisymbriifolium and S. nigrum‘90‐4750‐188’was studied in the field. Potato was also included as a trap crop. In the 1998 experiment, potato, S. sisymbriifolium and S. nigrum strongly stimulated the hatch of PCN compared with the non‐host white mustard (Sinapis alba). Roots of potato and white mustard were mainly found in the top 10 cm of soil, whereas roots of S. sisymbriifolium and S. nigrum were also abundant at depths of 10–20 cm and 20–30 cm. In the 1999 experiment, soil infestation with PCN decreased markedly with potato and S. sisymbriifolium as trap crops. In plots moderately to severely infested with 2‐yr old cysts (2–29 juveniles ml^?1 air dried soil), potato reduced soil infestation by 87% and S. sisymbriifolium by 77%. In plots moderately to severely infested with 1‐yr old cysts the reductions were 74% and 60%, respectively. The reduction was least on plots very severely infested with PCN (110–242 juveniles ml^?1 soil): 69% and 52% for potato and S. sisymbriifolium, respectively. Soil infestations of plots that were initially slightly to severely infested with the root‐knot nematode Meloidogyne hapla were greatly reduced under fallow and S. sisymbriifolium but increased under potato. From these and previous experiments it was concluded that, for several reasons, S. sisymbriifolium is a promising trap crop.     

Growth duration and root length density of Solanum sisymbriifolium (Lam.) as determinants of hatching of Globodera pallida (Stone)

Solanum sisymbriifolium is a trap crop for potato cyst nematodes (PCN). In this study, we quantified the effect of different periods of growth of S. sisymbriifolium and root length density on hatching of Globodera pallida, using potato and fallow treatments as references. One‐year‐old and 2‐year‐old G. pallida cysts were used in greenhouse experiments carried out in containers over 2 years. Two methods were used in study hatching. In the first method, 7.5‐cm‐diameter soil cores were removed and backfilled with infested soil. In the second method, cysts were buried in nylon bags. The soil cores infested with cysts used in the first method had very poor root colonisation as compared to surrounding bulk soil. Therefore, the effect of S. sisymbriifolium was strongly underestimated by the soil core method. Hatching of PCN juveniles from cysts, measured with the nylon bag method, increased with the duration of growth of S. sisymbriifolium from 47% after 6 weeks of crop growth up to 75% after 21 weeks of crop growth. Reductions per depth layer were also correlated with root length density and varied between 42.6% at 0.26 cm cm^?3 and 85.3% at 5.8 cm cm^?3. Based on a single exponential decay function, a general method is presented to estimate for any PCN management measure the average reduction in the number of years needed to ensure that the PCN population falls below a given density. Calculated reductions in the number of years ranged from 2.3 years for 59% hatching (equivalent to 90 days of S. sisymbriifolium) to 4.4 years for 75% of hatching (equivalent to 150 days of S. sisymbriifolium). These reductions were independent of initial and final population density. Our results corroborate the hatch‐inducing effect of S. sisymbriifolium, underline the importance of growth duration and root length density as determinants of the reduction in PCN population that can be achieved and draw attention to the pitfall in methodology that can arise in the study of hatch stimulation.     

Effect of the trap crop Solanum sisymbriifolium and two biocontrol fungi on reproduction of the potato cyst nematode,Globodera pallida

The potato cyst nematode, Globodera pallida, is one of the most important pests of potato worldwide. Owing to regulatory considerations and potential environmental impact, control options for this nematode are becoming increasingly limited. Solanum sisymbriifolium and biological control agents offer viable alternative options for controlling G. pallida. Therefore, experiments were conducted to determine the effect of the nematode trap crop S. sisymbriifolium, alone or in combination with the biocontrol agents Trichoderma harzianum or Plectosphaerella cucumerina, on population decline of G. pallida. Experiments were conducted for three different ‘cropping systems’: potato (Solanum tuberosum), S. sisymbriifolium, or soil only (fallow), each followed by a potato crop. Soil was amended with P. cucumerina, T. harzianum or left unamended, and then infested with nematodes at a rate of five eggs g^?1 of soil. After 16 weeks in the greenhouse, plants were removed and the soil containing cysts was refrigerated at 4°C for 8 weeks, and then planted to potato. Cysts of G. pallida were counted after an additional 16‐week period. The P_f/P_i of G. pallida was significantly reduced by 99% in potato following S. sisymbriifolium compared to both the potato‐following‐fallow and the potato‐following‐potato treatments. Amendment of soil with T. harzianum significantly reduced P_f/P_i of G. pallida by 42–47% in the potato‐following‐potato but not in either the potato‐after‐fallow nor in the potato‐after‐S. sisymbriifolium cycles which supports evidence that the plant species may play a role in the biocontrol activity of this fungus. Addition of the fungus P. cucumerina resulted in a 64% decrease in P_f/P_i in the potato‐following‐fallow in one experiment, and an 88% decrease in P_f/P_i in potato‐following‐potato but the decrease in P_f/P_i was not consistent over all experiments. However, both biocontrol fungi resulted in lower numbers of progeny cysts after an initial 16‐week incubation with potato. To look at the effect of varied population density of the nematode on efficacy of S. sisymbriifolium to reduce G. pallida populations, potato, S. sisymbriifolium, or barley were planted into soil infested with G. pallida at rates of 5, 20 or 40 eggs g^?1 soil applied as cysts (20, 80 or 160 cysts pot^?1). After 16 weeks, numbers of cysts produced in each treatment were determined for each infestation rate. No new cysts were recovered from either S. sisymbriifolium or barley treatments, confirming that neither plant is a host for G. pallida. High numbers of cysts were recovered with potato. Soil from each treatment (containing original cysts and newly‐formed cysts when present) were then planted with potato. After an additional 16 weeks, few cysts were found in the potato‐after‐ S. sisymbriifolium treatments regardless of initial infestation rate. When potato followed barley, numbers of cysts were similar to those found after a single cycle of potato, indicating that the barley crop had no effect on the survival of initial inoculum. Overall, these results suggest that S. sisymbriifolium has potential to significantly reduce G. pallida populations, and also that the cropping system (i.e. the sequence of non‐host and host plants) may play a significant role in the efficacy of fungal biological control agents.     

Single nucleotide polymorphism (SNP) genotyping as basis for developing a PCR-based marker highly diagnostic for potato varieties with high resistance to Globodera pallida pathotype Pa2/3

Globodera pallida is a parasitic root cyst nematode of potato, which causes reduction of crop yield and quality in infested fields. Field populations of G. pallida containing mixtures of pathotypes Pa2 and Pa3 (Pa2/3) are currently most relevant for potato cultivation in middle Europe. Genes for resistance to G. pallida have been introgressed into the cultivated potato gene pool from the wild, tuber bearing Solanum species S. spegazzinii and S. vernei. Selection of resistant genotypes in breeding programs is hampered by the fact that the phenotypic evaluation of resistance to G. pallida is time consuming, costly and often ambiguous. DNA-based markers diagnostic for resistance to G. pallida would facilitate the development of resistant varieties. A tetraploid F₁ hybrid family SR-Gpa segregating for quantitative resistance to G.␣pallida was developed and evaluated for resistance to G. pallida population ‘Chavornay’. Two subpopulations of 30 highly resistant and 30 susceptible individuals were selected and genotyped for 96 single nucleotide polymorphism (SNP) markers tagging 12 genomic regions on 10 potato chromosomes. Seven SNPs were found significantly linked to the nematode resistance, which were all located within a resistance ‘hotspot’ on potato chromosome V. A haplotype model for these seven SNPs was deduced from the SNP patterns observed in the SR-Gpa family. A PCR assay ‘HC’ was developed, which specifically detected the SNP haplotype c that was linked with high levels of nematode resistance. The HC marker was only found in accessions of S.␣vernei. Screening with the HC marker 34 potato varieties resistant to G. pallida pathotypes Pa2 and/or Pa3 and 22 susceptible varieties demonstrated that the HC marker was highly diagnostic for presence of high levels of resistance to G. pallida pathotype Pa2/Pa3.Amirali Sattarzadeh and Ute Achenbach contributed equally to the work     

Effects of Zygorrhynchus moelleri on the growth of potato and reproduction of potato cyst nematodes

Laboratory, pot and field experiments investigated the effects of the fungus Zygorrhynchus moelleri on the growth of potato and on the reproduction of the potato cyst nematodes (PCN), Globodera pallida and G rostochiensis. Preliminary laboratory tests showed that Z. moelleri growth was favoured by temperatures and pH ranges commonly present in field soils. The fungus colonised potato roots in vitro and in compost or field soil. It also stimulated in vitro root growth of three potato cultivars. In pot experiments Z. moelleri stimulated potato growth, particularly in the presence of PCN attack. In field plots infested with a mixture of G pallida and G. rostochiensis, tuber yields were not increased after application of the fungus but, in G pallida‐infested plots, yields were significantly increased after drills were inoculated with Z. moelleri. The application of Z. moelleri had no apparent effects on nematode reproduction. Factors influencing the interactions between Z. moelleri, potato and potato cyst nematodes are discussed and the potential role of the fungus as a plant growth promoter in organic potato production considered.     

Field performance of Solanum sisymbriifolium, a trap crop for potato cyst nematodes. II. Root characteristics

Hatching of potato cyst nematodes is induced by root exudates of Solanaceae, such as Solanum sisymbriifolium, and is therefore related to root length distribution of this crop. A mathematical model was derived to relate the hatching potential to root length density (RLD). A series of field experiments was carried out to study actual root length distribution of S. sisymbriifolium in relation to shoot properties and to provide input into the model. Using a modified Poisson distribution formula for the three‐dimensional distribution of roots in a volume of soil, the relation between the zone of influence of hatching agents and the RLD could be derived. On this basis, the minimal RLD was estimated, which is needed to expose 75%, 90% or 95% of cysts to root exudates, as a function of the length of the zone of influence of hatching agents on cysts. The logarithm of the total root length showed a linear relation with the logarithms of above‐ground biomass and with leaf area index. Root diameter distribution was the same for all crops examined and independent of soil depth. Fine roots (<0.4 mm in diameter) constituted around 50% of total root length. Using a zone of influence of 1.00, 0.75 and 0.50 cm around the centre of each root, a minimal RLD for sufficient soil exploration (75%) was estimated. Depth at which that minimal RLD was exceeded was linearly related to total root length (km m^?2) and to above‐ground crop biomass, enabling estimations being made of the potential hatching efficacy as related to measurable properties of S. sisymbriifolium crops. The proposed approach to derive potential hatching effects from crop properties needs further validation; particularly, the distance of influence of root exudates is a critical factor.     

Climate change is predicted to alter the current pest status of Globodera pallida and G. rostochiensis in the United Kingdom

The potato cyst nematodes Globodera pallida and G. rostochiensis are economically important plant pathogens causing losses to UK potato harvests estimated at £50 m/ year. Implications of climate change on their future pest status have not been fully considered. Here, we report growth of female G. pallida and G. rostochiensis over the range 15 to 25°C. Females per plant and their fecundity declined progressively with temperatures above 17.5°C for G. pallida, whilst females per plant were optimal between 17.5 and 22.5°C for G. rostochiensis. Relative reproductive success with temperature was confirmed on two potato cultivars infected with either species at 15, 22.5 and 25°C. The reduced reproductive success of G. pallida at 22.5°C relative to 15°C was also recorded for a further seven host cultivars studied. The differences in optimal temperatures for reproductive success may relate to known differences in the altitude of their regions of origin in the Andes. Exposure of G. pallida to a diurnal temperature stress for one week during female growth significantly suppressed subsequent growth for one week at 17.5°C but had no effect on G. rostochiensis. However, after two weeks of recovery, female size was not significantly different from that for the control treatment. Future soil temperatures were simulated for medium‐ and high‐emission scenarios and combined with nematode growth data to project future implications of climate change for the two species. Increased soil temperatures associated with climate change may reduce the pest status of G. pallida but benefit G. rostochiensis especially in the southern United Kingdom. We conclude that plant breeders may be able to exploit the thermal limits of G. pallida by developing potato cultivars able to grow under future warm summer conditions. Existing widely deployed resistance to G. rostochiensis is an important characteristic to retain for new potato cultivars.     

Mode of action of fosthiazate used for the control of the potato cyst nematode Globodera pallida

Fosthiazate (Nemathorin 10G Ishihara Sangyo Kaisha Ltd, Japan) is a new nematicide approved for use on potatoes Solanum tuberosum L. in die UK for die control of die potato cyst nematodes Globodera rostochiensis (Woll). Skarbilovich and G. pallida (Stone). Fosdiiazate delayed and suppressed hatch of die potato cyst nematode Globodera pallida in bom in vitro laboratory tests and a glasshouse pot experiment. In vitro hatch was temporarily inhibited by fosdiiazate concentrations above 0.09 μg ml^-1 and increasing me fosdiiazate concentration further prolonged the duration of hatch inhibition. Analysis of fosthiazate soil concentrations, using high-pressure liquid chromatography, during me glasshouse experiment showed mat hatch was suppressed in the soil at concentrations above 0.5 mg kg^-1. Other factors such as the paralysis of hatched nematodes in the soil solution are also involved.     

Comparative Responses of Globodera rostochiensis and G. pallida to Hatching Chemicals

Globodera rostochiensis and G. pallida responded similarly to hatch stimulation by potato root leachate, but proportionally more second-stage juveniles (J2s) of G. rostochiensis hatched than of G. pallida in response to picrolonic acid, sodium thiocyanate, alpha-solanine, and alpha-chaconine. Fractionation of the potato root leachate identified hatching factors with species-selective (active toward both species but stimulating greater hatch of one species than the other), -specific (active toward only one species), and -neutral (equally active toward both species) activities. In a comparison of two populations of each of the two potato cyst nematode (PCN) species, however, greater similarity in response to the individual hatching factors was observed among populations of different species produced under the same conditions than among different populations of the same PCN species. Smaller numbers of species-specific and species-selective hatching factor stimulants and hatching inhibitors than of hatching factors were resolved. In a study to determine whether the different hatching responses of the two species to the same root leachate were associated with different ratios of species-selective and species-specific hatching factors, G. rostochiensis pathotype Ro1 exhibited greater hatch than did G. pallida pathotype Pa2/3 in response to leachate from older plants (more than 38 days old), while G. pallida exhibited greater hatch in response to leachate from younger plants (less than 38 days old); the response of G. pallida pathotype Pal with respect to plant age was intermediate between the other two populations. Combined molecular exclusion-ion exchange chromatography of the root leachates from plants of different ages revealed an increase in the proportion of G. rostochiensis-specific and -selective hatching factors as the plants aged.     

Characterisation of a 34 kD protein from potato cyst nematodes, using monoclonal antibodies with potential for species diagnosis

Two monoclonal antibodies, which differentially recognise the two species of potato cyst nematodes (PCN), Globodera pallida and G. rostochiensis, are described. They have been shown to have potential for quantification of these two species, recognising proteins of the same molecular weight (34 kD) in both species. Further investigation showed these proteins to have isoelectric points at pH values of 5.7 in G. pallida and 5.9 in G. rostochiensis, in common with the proteins used by Fleming & Marks (1983) to differentiate the species of PCN. They are likely to be structurally very similar, with the same physiological function (and therefore similar concentrations) in the two species. In cross-reactivity tests with a wide range of soil nematode species, the antibodies reacted strongly only with species of the genus Globodera, and thereby confirmed their potential as the basis of a quantitative immunoassay likely to be useful in management of PCN populations.     

Ribosomal DNA Comparisons of Globodera from Two Continents

Ribosomal DNA (rDNA) sequence data were compared for five species of Globodera, including G. rostochiensis, G. pallida, G. virginiae, and two undescribed Globodera isolates from Mexico collected from weed species and maintained on Solanum dulcamara. The rDNA comparisons included both internal transcribed spacers (ITS1 and ITS2), the 5.8S rRNA gene, and small portions of the 3'' end of the 18S gene and the 5'' end of the 28S gene. Phylogenetic analysis of the rDNA sequence data indicated that the two potato cyst nematodes, G. pallida and especially G. rostochiensis, are closely related to the Mexican isolates, whereas G. virginiae is relatively dissimilar to the others and more distantly related. The data are consistent with the thesis that Mexico is the center of origin for the potato cyst nematodes.     

Using SNP markers to dissect linkage disequilibrium at a major quantitative trait locus for resistance to the potato cyst nematode Globodera pallida on potato chromosome V

The damage caused by the parasitic root cyst nematode Globodera pallida is a major yield-limiting factor in potato cultivation . Breeding for resistance is facilitated by the PCR-based marker ‘HC’, which is diagnostic for an allele conferring high resistance against G. pallida pathotype Pa2/3 that has been introgressed from the wild potato species Solanum vernei into the Solanum tuberosum tetraploid breeding pool. The major quantitative trait locus (QTL) controlling this nematode resistance maps on potato chromosome V in a hot spot for resistance to various pathogens including nematodes and the oomycete Phytophthora infestans. An unstructured sample of 79 tetraploid, highly heterozygous varieties and breeding clones was selected based on presence (41 genotypes) or absence (38 genotypes) of the HC marker. Testing the clones for resistance to G. pallida confirmed the diagnostic power of the HC marker. The 79 individuals were genotyped for 100 single nucleotide polymorphisms (SNPs) at 10 loci distributed over 38 cM on chromosome V. Forty-five SNPs at six loci spanning 2 cM in the interval between markers GP21-GP179 were associated with resistance to G. pallida. Based on linkage disequilibrium (LD) between SNP markers, six LD groups comprising between 2 and 18 SNPs were identified. The LD groups indicated the existence of multiple alleles at a single resistance locus or at several, physically linked resistance loci. LD group C comprising 18 SNPs corresponded to the ‘HC’ marker. LD group E included 16 SNPs and showed an association peak, which positioned one nematode resistance locus physically close to the R1 gene family. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A DNA probe which distinguishes Globodera pallida Pa2/3 from G. rostochiensis Ro1 and other cyst-forming nematodes

Abstract

A small DNA fragment (approx. 350 base pairs) from the genome of the potato cyst nematode Globodera pallida Pa2/3 was cloned in a bacterial plasmid. When used as a probe in dot-blot DNA hybridisations against a range of nematodes, the cloned DNA bound to G. pallida Pa2/3 but not to Globodera rostochiensis Rol. The cereal cyst nematode Heterodera avenae, the clover cyst nematode Heterodera trifolii, the root knot nematodes Meloidogyne hapla and Meloidogyne incognita, and the beet cyst nematode Heterodera schactii did not cross-hybridise. This probe can detect as few as six larvae of G. pallida.     

Potato cyst nematodes in England and Wales - occurrence and distribution

Potato cyst nematodes (PCN) have been known to occur in the UK for nearly a hundred years. They are the most problematic pests of potatoes and can cause severe yield losses. Previous work has shown the two species, Globodera rostochiensis and G pallida, to be distributed throughout the UK. This paper reports the results of the first structured and statistically unbiased survey undertaken to assess their occurrence and distribution in the potato growing land of England and Wales. The survey showed that PCN were present in 64% of sites sampled. Of the populations found, 67% were G pallida, 8% were G rostochiensis and 25% contained both species. The results show an increase in the incidence of PCN since previous studies were completed and confirm the perceived shift towards G pallida as the predominant species. Of the infestations found, 62% had a population density of less than 10 eggs g^?1 soil.     

Effects of a mixed-isolate mycorrhizal inoculum on the potato – potato cyst nematode interaction

Inoculation of microplants of potato cv. Golden Wonder with Vaminoc, a mycorrhizal inoculum of three arbuscular mycorrhizal fungi (Glomus spp.), resulted in an increase in in‐sand hatch of Globodera pallida, but not G. rostochiensis, within 2 weeks. By this time, mycorrhized plants also supported a larger number of feeding nematodes of both PCN species (50% higher for G. rostochiensis) than did non‐mycorrhized plants, with a higher proportion of the G. pallida population being fertilised females than for G. rostochiensis. After 12 weeks, the multiplication rate of G. rostochiensis on mycorrhized plants was significantly greater than on non‐mycorrhized plants, whereas no such difference was observed for G. pallida. The principal component of PCN multiplication affected by mycorrhization was increased cyst number per plant from 6 to 12 weeks. Over this period, there was no increase in cyst number per plant for either PCN species on non‐mycorrhized plants, whereas the value increased on mycorrhized plants for both G. rostochiensis (by almost 200%) and G. pallida (57%). Mycorrhization resulted in significant increases in the root and shoot dry weights of plants grown in the absence of PCN. Although mycorrhized plants carried a larger PCN burden than non‐mycorrhized plants when grown on PCN‐infested medium, as a result of the increased PCN multiplication rate, they produced larger root systems than did nonmycorrhized plants, suggesting increased tolerance to PCN of the mycorrhized plants, particularly to G. rostochiensis. Of morphological characters investigated in the absence of PCN, only stem height (increased) was significantly affected by mycorrhization. Colonisation by mycorrhizal fungi resulted in increased tuber yield both in the absence (significant increase) and presence (non significant) of PCN, as a result of increased tuber number per plant. These results are discussed in the light of the possible use of AMF as part of an integrated PCN management plan.     

Effective transgenic resistance to Globodera pallida in potato field trials

A cysteine proteinase inhibitor expressed in potato plants provides the first demonstration that transgenic resistance to nematodes such as the potato cyst nematode Globodera pallida can be effective under field conditions. The highest level of resistance obtained in the field for one of the four transformed lines of the normally fully susceptible Solanum tuberosum tuberosum cv. Désirée was 70±9%. The partially resistant cv. Sante that is currently of commercial use in the UK showed a resistance of 85±3%. In containment experiments a change in G. pallida population to one known to be virulent against cv. Sante caused a significant loss of its resistance from 80±4% to only 51±6%. In contrast, the resistance of transgenic Désirée was similar for challenge by the avirulent and virulent populations with values of 68±6% and 71±4%, respectively. Constitutive expression of the cystatin had no detrimental effect on either number or weight of tubers and the weight of the haulm for 3 of the 4 lines in the field. The results establish that transgenic field resistance against G. pallida can be achieved. Clearly food and environmental safety must be assured before commercialisation can be contemplated. However, a prima facie case can be made that the technology is benign and can reduce the use of environmentally hazardous nematicides.     

Control of potato cyst nematodes and economic benefits of application of 1,3-dichloropropene and granular nematicides

The two species of the potato cyst nematodes (PCN) Globodera pallida and G rostochiensis are the most problematic pests of the potato crop in the UK. There are no commercially available cultivars with full resistance to G. pallida and both crop rotation and granular nematicides are less effective at controlling this species than G. rostochiensis. In situations of very high PCN levels it may be possible to reduce populations and yield losses by using an autumn application of the soil fumigant 1,3-dichloropropene (1,3-D) followed by a spring application of a granular nematicide. Two field experiments were done to look at the integration of methods for the control of PCN. The Common Field experiment (G. rostochiensis infested) compared the use of 1,3-D with the granular nematicides aldicarb, oxamyl and fosthiazate when growing the susceptible cv. Estima. The Four Gates experiment (infested with both PCN species but mainly G rostochiensis) compared the performance of cv. Santé (partially resistant to G. pallida, fully resistant to G. rostochiensis) with that of the susceptible cv. Estima when treated with 1,3-D and oxamyl at full and half-rates. The results of the experiments show that an integrated approach to nematode control on heavily infested sites, including granular and fumigant nematicides and cultivar resistance, can lead to significant decreases in nematode population densities and reduce yield losses. An economic evaluation of the experiments modelled the gross margins from the different nematicide treatments. In Common Field, the highest gross margins were achieved with the combined use of fumigant and granular nematicides. In Four Gates, there was a clear economic benefit for both cultivars from the use of 1,3-D. In this experiment, oxamyl was of economic value to Estima but not to Sante and full-rate oxamyl was of more benefit than half-rate to Estima.     

Mapping of resistance to the potato cyst nematode Globodera rostochiensis from the wild potato species Solanum vernei

A population of diploid potato (Solanum tuberosum) was used for the genetic analysis and mapping of a locus for resistance to the potato cyst nematode Globodera rostochiensis, introgressed from the wild potato species Solanum vernei. Resistance tests of 108 genotypes of a F₁ population revealed the presence of a single locus with a dominant allele for resistance to G. rostochiensis pathotype Ro1. This locus, designated GroV1, was located on chromosome 5 with RFLP markers. Fine-mapping was performed with RAPD and SCAR markers. The GroV1 locus was found in the same region of the potato genome as the S. tuberosum ssp. andigena H1 nematode resistance locus. Both resistance loci could not excluded to be allelic. The identification of markers flanking the GroV1 locus offers a valuable strategy for marker-assisted selection for introgression of this nematode resistance.Abbreviations BSA bulked segregant analysis - RAPD random-amplified polymorphic DNA - RFLP restriction fragment length polymorphism - SCAR sequence-characterized amplified region     

Control of potato cyst nematode (Globodera pallida) by host plant resistance and nematicide

Seven trials conducted over four years on sites naturally infested with the white potato cyst nematode established that potato clones bred for resistance to Globodera pallida allowed significantly less nematode multiplication than conventional cultivars under field conditions. Nematode multiplication was inversely related to initial infestation level. The nematicide, aldicarb, significantly reduced nematode multiplication. However, nematode multiplication on nematicide treated susceptible cultivars was greater than on untreated partially resistant clones, indicating that resistance may offer more effective control of G. pallida than chemical treatment. Integration of host plant resistance and nematicide treatment is discussed.