Control Of Potato Cyst Nematodes Research Articles

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

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

PM 9/26 (1) National regulatory control system for Globodera pallida and Globodera rostochiensis

Specific scopeThis Standard describes a national regulatory control system for Globodera pallida and Globodera rostochiensis.

Allyl isothiocyanate shows promise as a naturally produced suppressant of the potato cyst nematode, Globodera pallida, in biofumigation systems

The ability of isothiocyanates to suppressGlobodera pallidawas evaluated throughin vitroassays. Several isothiocyanates increased juvenile mortality, the most effective being allyl isothiocyanate, which caused 100% mortality at both 25 and 50 ppm after 72 and 24 h exposure, respectively. In a hatching assay, allyl isothiocyanate was able to suppress hatch; in addition, replenishing allyl isothiocyanate every 3 days increased hatch suppression, and viability staining indicated that egg mortality was increased. Allyl isothiocyanate above concentrations of 50 ppm significantly affected both hatch suppression and mortality. Differing effects of isothiocyanates onG. pallidasuggest that their toxicity depends on the pest of interest and this study shows that allyl isothiocyanate is a good candidate for the control of potato cyst nematodes using biofumigation.

High-throughput diagnosis of potato cyst nematodes in soil samples.

Potato cyst nematode (PCN) is a damaging soilborne pest of potatoes which can cause major crop losses. In 2010, a new European Union directive (2007/33/EC) on the control of PCN came into force. Under the new directive, seed potatoes can only be planted on land which has been found to be free from PCN infestation following an official soil test. A major consequence of the new directive was the introduction of a new harmonized soil sampling rate resulting in a threefold increase in the number of samples requiring testing. To manage this increase with the same staffing resources, we have replaced the traditional diagnostic methods. A system has been developed for the processing of soil samples, extraction of DNA from float material, and detection of PCN by high-throughput real-time PCR. Approximately 17,000 samples are analyzed each year using this method. This chapter describes the high-throughput processes for the production of float material from soil samples, DNA extraction from the entire float, and subsequent detection and identification of PCN within these samples.

The use of liquid swine manure for the control of potato cyst nematode through soil disinfestation in laboratory conditions

In this laboratory study the effect of liquid swine manure (LSM) on Globodera rostochiensis was evaluated. The LSM was applied to 500g nematode-infested soil at 0.4, 2.0, 4.0, and 6.0% (v/w), equivalent to 31, 155, 310 and 465kg of Nha−1, in closed and open containers (microcosms sealed (S) and open (O)). The results showed that LSM in closed containers enriched the volatile fatty acids (VFAs) through partial anaerobic incubation process. Bacterial- and fungal-feeding nematodes predominated, while the least opportunistic groups had a very low occurrence. The LSM in (S) significantly decreased cyst nematode populations and percent egg hatching in contrast with opened ones (O), increasing some chemical parameters related to soil fertility. Hatching tests showed that individual VFA vary in their lethality to G. rostochiensis. Acetic and propionic acids were the most toxic, reducing hatching most effectively and irreversibly. Results suggest that soil disinfestation on laboratory tests with LSM, is an efficient way for the reduction of G. rostochiensis populations in acidic soils, due to the VFAs nematicidal action. To address management alternatives, field studies would be needed that compared these materials to the current management practices, and demonstrated that they are competitive in the field.

An evaluation of the implications of virulence in non-European populations of Globodera pallida and G. rostochiensis for potato cultivation in Europe

The potato cyst nematodes Globodera pallida and G. rostochiensis are listed in the EU Plant Health Directive 2000/29/EC and are also subject to the new EU Council Directive 2007/33/EC on the control of potato cyst nematodes, requiring unilateral suppression of these pests in Europe. At the same time there is also pressure to increase world trade in potatoes. Such pressure has to be balanced by the risks involved in the associated spread of these pests and subsequent problems in management. Populations of the potato cyst nematodes from outside Europe, in particular South America, which is considered the origin of G. pallida and G. rostochiensis, pose a risk to those European countries where limited genetic variability of these nematode species has been recorded. The development and usage of resistant cultivars under such conditions has formed a pivotal role in integrated management programmes in Europe. Molecular studies have shown that populations of G. pallida and G. rostochiensis from South America have a different genetic composition from those in Europe. The introduction of such populations would pose a threat to the use of resistant cultivars as a major tool in reducing the potential spread and damage caused by these species. At present, an inability to link precisely genetic variability to the virulence characteristics of a specific nematode population, and quickly identify the virulence status of intercepted populations for inspection purposes, strengthens the case for using plant health legislation to prevent their introduction.

Effects of the nematicide 1,3-dichloropropene on weed populations and stem canker disease severity in potatoes

The soil fumigant 1,3-dichloropropene (1,3-D) has been used in the UK for the control of potato cyst nematodes (PCN), Globodera pallida (Stone) and Globodera rostochiensis (Wollenweber), but its potential herbicidal activity has not been extensively investigated in this country. Field and glasshouse studies were therefore conducted to evaluate the potential of 1,3-D for the control of weeds in potatoes, and observations were made on the severity of potato stem canker, caused by the fungus Rhizoctonia solani Kühn [teleomorph: Thanatephorus cucumeris (Frank) Donk]. Autumn application of 1,3-D at 211.5 L active substance (a.s.) ha −1 significantly suppressed the number of germinating weeds and the percentage of weed ground cover by 83% and 79%, respectively, relative to controls. There were also species-specific significant decreases (field pansy, Viola arvensis, in particular) in the number of weed seeds germinating in field soil in the glasshouse post-1,3-D treatment. The effect of 1,3-D declined in time and single (autumn or spring) or combined application produced a slight, but not significant, reduction in the number of weeds germinated on potato ridges relative to those recorded in untreated soil. The severity of stem canker on potato plants was not significantly reduced by 1,3-D but both mean number and weight of stems per plant were significantly increased compared with plants from untreated plots. These studies demonstrated that 1,3-D, in addition to giving PCN control, has efficacy against weeds; implications are the potential for reduced herbicide input in the crop rotation with accompanying economic and environmental benefits.

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

SummaryThe 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.

Interactions between nematophagous fungi and consequences for their potential as biological agents for the control of potato cyst nematodes

The efficacies of three nematophagous fungi, Paecilomyces lilacinus, Plectosphaerella cucumerina and Pochonia chlamydosporia, for controlling potato cyst nematodes (PCN) as part of an Integrated Pest Management (IPM) regime were studied. The compatibility of the nematophagous fungi with commonly used chemical pesticides and their ability to compete with the soil fungi Rhizoctonia solani, Chaetomium globosum, Fusarium oxysporum, Penicillium bilaii and Trichoderma harzianum were tested in vitro. Paecilomyces lilacinus was the most successful competitor when the ability to grow and inhibit growth of an opposing colony at both 10 and 20 degrees C was considered. P. lilacinus also showed potential for control of the soil-borne fungal pathogen R. solani, releasing a diffusable substance in vitro which inhibited its growth and caused morphological abnormalities in its hyphae. Pochonia chlamydosporia was least susceptible to growth inhibition by other fungi at 20 degrees in vitro, but the isolate tested did not grow at 10 degrees. Plectosphaerella cucumerina was a poor saprophytic competitor. Radial growth of Paecilomyces lilacinus and Plectosphaerella cucumerina was slowed, but not prevented, when grown on potato dextrose agar incorporating the fungicides fenpiclonil and tolclofos-methyl, and was not inhibited by the addition of pencycuron or the nematicide oxamyl. Radial growth of Pochonia chlamydosporia was partially inhibited by all the chemical pesticides tested. The efficacy of Paecilomyces lilacinus as a control agent for R. solani was further investigated in situ. Treatment with P. lilacinus significantly reduced the symptoms of Rhizoctonia disease on potato stems in a pot trial. The effectiveness of P. lilacinus and P. cucumerina against PCN was also tested in situ. Three application methods were compared; incorporating the fungi into alginate pellets, Terra-Green inoculated with the fungi and applying conidia directly to the tubers. Both formulations containing P. lilacinus and formulation mixtures alone, particularly alginate pellets, significantly reduced multiplication of PCN in soil. We conclude that P. lilacinus showed the greatest potential for use in combination with selected fungicides and nematicides as part of an IPM programme for the control of PCN, but further work is required to confirm whether it is effective against PCN in soil.

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

SummaryIn 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.

Toxicity of 1,3‐dichloropropene and fosthiazate to wireworms (Agriotes spp.)

SummaryWireworms (Agriotes spp.) are sporadic but increasingly important pests of potatoes, sugar beet and cereals. Whilst effective chemical control is possible, the granular organophosphates normally require high rates of application and the seed dressings containing lindane (gamma‐HCH) have been withdrawn from use.The soil fumigant 1,3‐dichloropropene (1,3‐D as Telone II) and the granular nematicide fosthiazate (Nemathorin 10G) are currently used for the control of potato cyst nematodes. We investigated the effects of both of these chemicals on wireworms. Air‐vapour phase toxicities for 1,3‐D against wireworm were LD50 2.74 mg.litre.day and LD99 5.05 mg.litre.day. The in vitro soil phase toxicity was LD99 8.15 mg.litre.day. 1,3‐D soil phase activity against wireworm may be associated more with air‐vapour phase than a soil‐water phase activity. In glasshouse experiments 16.0 mg.litre.day of 1,3‐D gave 75% control. Fosthiazate, which is applied at approximately 2 μg g−1 of soil for potato cyst nematode control, achieved an LC50 at 3.20 μg g−1.In both in vitro and glasshouse studies 1,3‐dichloropropene showed high toxicity to wireworm at dosages below the current commercial application rate for potato cyst nematode control and fosthiazate also showed useful efficacy. These chemicals may therefore prove to be valuable additional tools for limiting initial wireworm plant damage or reducing wireworm populations.

Aspects of the enhanced biodegradation and metabolism of ethoprophos in soil

Enhanced biodegradation of ethoprophos was evident in a soil from a previously treated field in Northern Greece. However, enhanced biodegradation was specific to ethoprophos and there was no cross-enhancement leading to rapid degradation for any of the other organophosphorus (cadusafos, fenamiphos, fonofos, isazofos) or carbamate (aldicarb, oxamyl) nematicides registered in Greece for the control of potato cyst nematodes. Studies with radio-labelled ethoprophos showed that the adapted microflora in the soil from the previously treated field was able to degrade [propyl-1-14C]ethoprophos rapidly and mineralized about 60% of the initially applied nematicide. When [ethyl-1-14C] ethoprophos was applied, the reduction in extractable radioactivity in the previously treated soil was coupled with evolution of lower amounts of [14C] carbon dioxide and was similar to the amounts produced from the previously untreated soils. It is suggested that degradation of ethoprophos in the soil from the previously treated field proceeds via hydrolysis of the P-S bond in the -S-propyl moiety of the ethoprophos molecule, which is then further mineralized by the adapted micro-organisms. Enhanced biodegradation of ethoprophos in this specific previously treated soil in Northern Greece and under the local environmental conditions was still evident two years after the last ethoprophos field application. It appears that, once established, enhanced biodegradation of ethoprophos can be quite stable. A possible solution to this problem might be the introduction of a rotation scheme where other nematicides like fenamiphos, cadusafos, aldicarb or oxamyl are used as alternatives with ethoprophos application restricted to only once every three or four years. © 2000 Society of Chemical Industry

Screening of non‐tuber bearing Solanaceae for resistance to and induction of juvenile hatch of potato cyst nematodes and their potential for trap cropping

SummaryNinety accessions of non‐tuber bearing Solanaceae were screened for (i) resistance to and (ii) stimulatory effect on juvenile hatch of potato cyst nematodes, and (iii) their growth under temperate climatic conditions. All plant species belonging to the genus Solanum tested induced hatching but this effect was most pronounced for plant species of the Solanum nigrum complex. Hatching of juveniles was hardly or not stimulated by other plant genera of the Solanaceae. Solanum sisymbriifolium combined a high hatching effect with complete resistance to both Globodera rosiochiensis and G pallida. Two S. nigrum varieties showed full resistance to G rostochiensis and a high level of resistance to G pallida. Moreover, S. sisymbriifolium and the two varieties of S. nigrum performed very well under Dutch field conditions and, therefore, they are suggested as candidate trap crops for the control of potato cyst nematodes.

Management of Potato Cyst Nematodes in the UK: An Integrated Approach?

Potato cyst nematodes (PCN) are the most problematic pest faced by potato growers in the UK. Both species of PCN were brought to Europe from South America, but one, Golobodera pallida, now predominates because it is more refractive to control measures. Despite sometimes poor results, considerable reliance is placed on nematicides for the control of PCN, but this situation may have to change if potato retailers in the form of supermarkets continue to insist on ever tighter restrictions on the use of nematicides.

Infection of Second Stage Juveniles of Potato Cyst Nematodes By the Nematophagous Fungus Hirsutella Rhossiliensis in Dutch Potato Fields

The infection of second stage juveniles of potato cyst nematodes (PCN) by fungal parasites was studied in populations extracted from soil by centrifugal flotation. Soil was collected from five experimental plots which had annual crops of potatoes for at least nine years. The percentage of fungus-infected juveniles ranged from 10 to 60%. After 12 weekly additions of Globodera pallida juveniles, the percentage of infected individuals increased to 45-90%. The endoparasitic nematophagous fungus Hirsutella rhossiliensis was the only fungal parasite found. The fungal infection of juveniles of PCN was also studied in soil samples from 20 fields in a starch potato growing area in northeastern Netherlands where potatoes are intensively grown (once every two years). Infection by H. rhossiliensis was observed in 17 of the 20 field populations of free-living juveniles, with an average infection percentage of 15%. After 12 weekly additions of G. pallida juveniles, the average infection percentage increased to 25% and extended to 100% of the samples. Again H. rhossiliensis was the predominant parasite. In a laboratory experiment most of the juveniles added to pasteurized soil at weekly intervals were recovered after 12 weeks when H. rhossiliensis was not present but few were recovered when H. rhossiliensis was present, probably because of the rapid disintegration of infected juveniles. Detached conidia of H. rhossiliensis did not adhere to the juvenile cuticle on agar plates, but newly formed conidia, attached to conidiophores, adhered to and infected juveniles. The possible role of H. rhossiliensis in the biological control of potato cyst nematodes and other plant parasitic nematodes is discussed.

Isolation and Screening of Fungi for the Biological Control of Potato Cyst Nematodes

Using observation chambers, fungal parasites of young potato cyst nematode females growing on potato roots were isolated from fourteen field soils. Cylindrocarpon destructans was the most commonly occurring fungus. Eight of the ten fungi selected for screening gave significant control of the nematode when cultured on milled wheat straw and added to soil. Methods of culturing influenced the amount of control achieved, but three fungi, C. destructans, Fusarium oxysporum and F. sambucinum, were particularly effective in decreasing nematode populations. The problems of selecting suitable control treatments, and the advantages and disadvantages of two different screening methods, are discussed.

Changing Concepts and Molecular Approaches in the Management of Virulence Genes in Potato Cyst Nematodes

Patterns emerging from molecular and virulence studies (2, 5, 9, 50, 64, 68, 74) challenge the prevailing view that breeding for resistance against plant parasitic nematodes is a lost arms race. The general idea is that control by means of resistance is unavoidably a short-term approach owing to the appearance of populations of resistance-breaking nematodes. This pervasive myth has been stimulated and maintained by traditional trial and error approaches in breeding as well as in growing of resistant cultivars. Recent advances in research (5,9,50,58,68), however, may improve the image of resistance genes in the control of plant parasitic nematodes. Changing concepts and molecular approaches provide opportunities to develop rational and refined control strategies. In this chapter it is argued that a well-chosen form of resistance, including single dominant genes, can be very effective against plant parasitic nematodes. Although this concept is mainly illustrated for the control of potato cyst nematodes in Europe, it also applies, with appropriate restrictions, to other parasites and pathogens having low repro­ duction capacities and poor dispersal abilities.

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

Summary 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.

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.

Integrated control of potato cyst nematodes using small amounts of nematicide and potatoes with partial resistance

SUMMARYThe control of potato cyst nematode (PCN) by less than approved amounts of nematicide combined with partially resistant potato clones was studied in a series of field experiments. On a site heavily infested with Globodera pallida only the most resistant clone (12380ac2) decreased the population density in untreated soil. With aldicarb at its full approved rate (3·36 kg ha‐1) numbers of PCN were decreased under all the genotypes, including the non‐resistant Maris Piper. Aldicarb at 1·68 kg ha‐1significantly decreased populations on all clones except 12380ac2. Aldicarb at 0·84 kg ha‐1still significantly decreased population densities and multiplication rates of G. pallida on two clones with intermediate resistance (12243acl and 11233ab22). At two G. rostochiensis sites with light infestations nematode multiplication rates were greater and the control given by aldicarb and partially resistant genotypes of potato was not as great as that at the site with G. pallida.Tuber yields were not increased by the application of aldicarb at the G. rostochiensis infested sites. However, at the site heavily infested with G. pallida the yield of the most intolerant genotype (12380ac2) was increased seven‐fold by the full rate of aldicarb (3·36 kg ha‐1) and four‐fold by the quarter rate (0·84 kg ha‐1)‐Yield of the most tolerant genotype (12243acl) was unaffected by the application of aldicarb.