Control of potato cyst-nematodes, Globodera rostochiensis and G. pallida, in different soils by small amounts of oxamyl or aldicarb

In eleven field trials on peaty, sandy or silt loam soils, aldicarb or oxamyl, incorporated in the soil to 15 cm deep before susceptible potatoes were planted, controlled potato cyst-nematodes (Globodera rostochiensis (Woll.) Mulvey & Stone, 1976 and G. pallida (Stone) Mulvey & Stone, 1976) better at 5–6 kg than at 3–4 or 2-2 kg a.i./ha. Incorporated in the soil to 7-5 cm deep 5–6 kg/ha of aldicarb or oxamyl controlled the nematodes less effectively at some sites. At 3–4 kg a.i./ha there was no difference in nematode control between the two incorporation depths.     

Emergence of juvenile potato cyst-nematodes Globodera rostochiensis and G. pallida and the control of G. pallida

Speed of emergence of juveniles from cysts in potato root diffusate (PRD) in vitro differed between Globodera rostochiensis and G. pallida and between populations within each species. Early emergence in vitro was slower in most populations of G. pallida than in most populations of G. rostochiensis. Fewer G. rostochiensis juveniles emerged from 4 or 6 month old than from 4 yr old cysts. More G. rostochiensis emerged in solutions of sodium metavanadate at concentrations of 10^-2 and 10^-3 M than in PRD and as many G. pallida emerged in the same solutions as in PRD. In plots of bare fallowed sandy loam, emergence of G. pallida was stimulated by 10^--³ M sodium metavanadate. The emergence of two populations of C. pallida in PRD was stimulated by the addition of benomyl at 0.1 ppm (3.4 × 10^--⁷ m). In microplots, cv. Cara potatoes grown for 8 wk decreased four populations of G. pallida by up to 93%. During a 4 wk period in PRD, more than 20 juveniles per gravid female emerged from five of 25 populations of G. pallida. In root observation boxes in which cv. Désirée was grown, oxamyl applied to the top 15 cm of a peaty loam soil greatly increased G. pallida in soil 1545 cm deep. In another peaty loam, but not in a sandy loam, the same treatment appeared to increase the nematode in soil 15–30 cm deep. Oxamyl incorporated in the uninfested top 15 cm of all three soils largely prevented nematode increase from juveniles migrating upwards from untreated heavily infested soil 15–30 cm deep. These experiments suggest that inadequate control of G. pallida increase on susceptible potatoes by an oximecarbamate nematicide of short persistence, such as oxamyl, is primarily due to the slow rate of juvenile emergence in most populations of G. pallida, with a second generation and the upward migration of juveniles from deeper untreated soil later in the growing season as potential contributory factors.     

Differential control of potato cyst-nematodes, Globodera rostochiensis and G. pallida by oxamyl and the yields of resistant and susceptible potatoes in treated and untreated soils

In sandy loam infested with Globodera rostochiensis (2–95 eggs g^-1 soil) the yield of Desiree potatoes was decreased by 8·2 t ha^-1 for every increment of 20 eggs g^-1 soil. Oxamyl incorporated in the seedbed at 5 kg ha^-1 before planting prevented significant loss of yield and damage to the tubers and minimised nematode increase. Cara and Maris Piper potatoes, which were resistant and tolerant to G. rostochiensis usually responded less to oxamyl than did susceptible cultivars. In a range of cultivars, yield responses to oxamyl treatment of soil infested with G. rostochiensis often differed from those in soil infested with G. pallida. In field experiments, oxamyl controlled G. pallida less than G. rostochiensis. In pots, such differential control of the two species by oxamyl was not observed.     

Observations on the distribution of potato cyst-nematodes, Globodera rostochiensis and G. pallida on two fenland potato farms

The distribution of potato cyst-nematodes, Globodera rostochiensis and G. pallida was surveyed in two widely separated fenland potato farms in Eastern England. Evidence was obtained of the suppression of G. rostochiensis and increase of G. pallida populations when Maris Piper and other potatoes with the same gene (H₁) for resistance to G. rostochiensis are grown. Numbers of G. rostochiensis and/or G. pallida in the soil could not be related directly to recent potato cropping histories of the fields. Identification of the two species of Globodera by the presence and colour of females on the roots of Désirée, Maris Piper, Cromwell (A27/20) and A25/11 potatoes were confirmed by agarose gel isoelectric focussing of general proteins. Cromwell exhibited little or no resistance to G. pallida at Woodwalton. A25/11 was more resistant to this species at Woodwalton but was susceptible to G. rostochiensis. The results of these surveys emphasise the need for carefully planned and integrated control programmes based on the use of resistant cultivars of potato, crop rotations and appropriate nematicide use to combat the growing problem of G. pallida, especially in organic soils.     

Observations on the control of potato cyst-nematodes, Globodera rostochiensis and G. pallida in 35 English potato soils in pots by oxamyl and resistant potatoes

The increase of 35 English field populations of potato cyst-nematodes (Globodera rostochiensis and/or G. pallida) was measured on Désirée, Maris Piper, Caxton (A25/11), Cromwell (A27/20) and clone 11233 ab 22 in pots of sandy, silty or peaty loam soil. Désirée was susceptible to all populations tested and, as in field soils, the final population (Pf) was inversely related to the initial population of potato cyst-nematode eggs (Pi) in the soil. Maris Piper and Cromwell were resistant to all G. rostochiensis populations, with one possible exception. Maris Piper was susceptible to all G. pallida populations. Caxton was susceptible to some and fairly resistant to other populations of G. rostochiensis, indicating the existence either of two biotypes within the one pathotype (Rol) as yet encountered in Britain, or the existence of an additional pathotype. Caxton and Cromwell were fairly resistant to G. pallida. Clone 11233 ab 22 was only moderately resistant to both species. Resistance to potato cyst-nematode increase varied considerably, especially in Caxton (to G. rostochiensis) and in 11233 ab 22 (to both species). Oxamyl greatly reduced the increase of G. rostochiensis populations on Désirée potatoes, with the notable exception of one population but it generally had much less effect on G. pallida populations, regardless of soil type. The difference in effect on the two species may be due to a longer period of hatching in G. pallida than in G. rostochiensis and also perhaps to a second generation in G. pallida.     

The resistance of six potato cultivars to English populations of potato cyst-nematodes, Globodera pallida and G. rostochiensis

Six cultivars of potato (Santé, Morag, Paladin, Glenna and Fingal bred for resistance to both potato cyst-nematodes (Globodera rostochiensis and G. pallida) and Valiant bred for resistance to G. pallida alone) were exposed to 28 English populations of G. pallida and eight English populations of G. rostochiensis in pots. Susceptible cv. Désirée potatoes served as controls for all 36 populations. Inoculum (Pi) was 12000 eggs in cysts per 400ml pot of soil. Average increase of G. rostochiensis (Pf/Pi) on cv. Désirée was 23.5 but on cvs Sante, Glenna and Fingal it was < 1.0 and on cv. Morag it was 2.2. In contrast, cvs Paladin and Valiant were susceptible (average Pf/Pi = 17.4 and 26.5, respectively). Against G. pallida populations, average Pf/Pi for cv. Désirée was 21.7; on cvs Paladin, Santé and Glenna it was 2.9, 2.6 and 2.4, respectively; cvs Morag and Fingal were less resistant (7.4 and 5.6, respectively) and cv. Valiant was quite susceptible (11.0). Resistance to the different populations of G. pallida and G. rostochiensis varied but for the most resistant cultivars (Santé, Glenna and Paladin) the variation was usually small. The value of the six resistant cultivars studied to the integrated control of potato cyst-nematodes in England and the genetic diversity of the nematode populations to which they were exposed are discussed.     

Techniques for distributing non-fumigant nematicides in soil to control potato cyst-nematodes, Globodera rostochiensis and G. pallida

Potato cyst-nematodes can be controlled and potato yields increased by applying aldicarb or oxamyl in vertical bands 12.5 or 25 cm apart in the top 15 cm of infested soil and incorporating it by rotary harrowing. This new ‘Vertical Band-Roterra’ technique spreads the nematicides almost as uniformly in the soil as does spreading them on the soil surface and incorporating them by rotary cultivation, and gives equally effective nematode control. It is also faster, does not mix weathered with unweathered soil and does not smear the soil. The nematicide, or any other substance requiring incorporation in the top 15 cm of the soil, can be applied in either granule or liquid form by the new technique. Merely spreading the nematicide on the soil surface and incorporating it by rotary harrowing leaves most of the substance in the top 5 cm of the soil, lessening nematode control. Spreading the nematicide on the soil surface and in horizontal layers 5 and 10 cm deep, followed by rotary harrowing, controls the nematodes as well as does the rotary cultivation method, but is inconvenient.     

A vertical band-Dutch harrow technique for incorporating granular nematicides in soil to control potato cyst-nematodes, Globodera rostochiensis and G. pallida

In lightly infested silt loam, aldicarb at 3·3 kg ha^-1in 1985 or oxamyl at 4·5 kg ha^-1in 1986, applied to the top 12 – 15 cm of the soil by a 5 m wide Dutch harrow fitted with vertical band granule outlets 15 cm apart, increased yields of King Edward or Romano potatoes and effectively controlled increase of potato cyst-nematodes. Carbofuran at 5 kg ha^-1in 1986 was less effective. This new vertical band-Dutch harrow technique has the advantage over the vertical band-rotary harrow technique in that lateral mixing of the vertical bands of granules is not required. It is especially useful for poorly structured soils, which will not tolerate powered harrowing, and could also prove beneficial on other soils of low organic matter content.     

Changes in relative abundance of two potato cyst nematode species Globodera rostochiensis and G. pallida in one generation

Changes in relative abundance of the two potato cyst nematode species Globodera rostochiensis and Globodera pallida were studied during the 1983/84 season at two different population levels in small pots in the glasshouse and at a single population density on plants grown outdoors in 2 litre terylene cloth bags. In both environments G. rostochiensis was the more successful species. Although the ratio of the two species changed and G. pallida was at a lower level at the end of the experiment it was never eliminated. However, when the number of G. pallida in the mixture was small it did better than expected and demonstrated a frequency dependent response.     

Assessment of the losses caused to potatoes by the potato cyst nematodes, Globodera rostochiensis and G. pallida

Nine field trials were carried out from 1967 to 1973 on sandy loam soils in Staffordshire and Worcestershire to study the relationship between potato yield and numbers of potato cyst nematodes (Globodera spp.). Three (probably five) of these trial sites appeared to be infested with G. rostochiensis only, whereas both species occurred on the remaining four sites which grew the resistant variety, Maris Piper. Although mixtures of the two species occurred on some plots they tended to have different distributions within each trial site. The results from this work have been analysed, together with those from earlier work in the Eastern Counties on peat and silt soils, over two population density ranges, 0–40 eggs/g (5 sites) and 0–160 eggs/g (16 sites). There is no evidence of any difference in the regression of yield on eggs/g amongst the five sites in the lower range (b =–0.90 + 0.11) nor amongst 15 of the 16 sites in the higher range (b = -0–40 ± 0–02). Analysis of 10 sites with sufficient data in the 40–160 eggs/g range gave b = -0.24 ± 0.06. Thus the regression lines are essentially parallel for each of the two ranges, covering several potato varieties, soil textures and different potential yields and suggest that the varieties used are equally tolerant. The losses are 6.25 t/ha/20 eggs/g for the 0.40 eggs/g range, 1.67 t/ha/20 eggs/g for the 40–160 eggs/g range, and 2.75 t/ha/20 eggs/g as a mean for the whole range. A maximum loss of 22 t/ha is indicated. Peat soils are less dense than mineral soils but there was no need for adjustment in nematode counts. Losses caused by potato cyst nematodes are better expressed as actual yield losses rather than as percentage decreases.     

The effects of deep cultivation and oxamyl on control of potato cyst-nematode, Globodera rostochiensis

Soil compaction associated with frequent cultivation of potatoes was partly removed with a deep winged-tine coulter. This increased the yield of tubers of cv. Cara in 1987 and 1988 and of cv. Désirée in 1987 in soil which was heavily infested with potato cyst-nematode, Globodera rostochiensis (Woll.), and which was treated with oxamyl at 5.6 kg ha^-1. In 1988, in soil not treated with oxamyl, deep cultivation significantly decreased the yield of cv. Cara. In both years, oxamyl decreased numbers of G. rostochiensis eggs in the soil following cv. Désirée potatoes but not following cv. Cara which were resistant to the nematode.     

Potato cyst nematodes Globodera rostochiensis and G. pallida

TaxonomyPhylum Nematoda; class Chromadorea; order Rhabditida; suborder Tylenchina; infraorder Tylenchomorpha; superfamily Tylenchoidea; family Heteroderidae; subfamily Heteroderinae; Genus Globodera.BiologyPotato cyst nematodes (PCN) are biotrophic, sedentary endoparasitic nematodes. Invasive (second) stage juveniles (J2) hatch from eggs in response to the presence of host root exudates and subsequently locate and invade the host. The nematodes induce the formation of a large, multinucleate syncytium in host roots, formed by fusion of up to 300 root cell protoplasts. The nematodes rely on this single syncytium for the nutrients required to develop through a further three moults to the adult male or female stage. This extended period of biotrophy—between 4 and 6 weeks in total—is almost unparalleled in plant–pathogen interactions. Females remain at the root while adult males revert to the vermiform body plan of the J2 and leave the root to locate and fertilize the female nematodes. The female body forms a cyst that contains the next generation of eggs.Host rangeThe host range of PCN is limited to plants of the Solanaceae family. While the most economically important hosts are potato (Solanum tuberosum), tomato (Solanum lycopersicum), and aubergine (Solanum melongena), over 170 species of Solanaceae are thought to be potential hosts for PCN (Sullivan et al., 2007).Disease symptomsSymptoms are similar to those associated with nutrient deficiency, such as stunted growth, yellowing of leaves and reduced yields. This absence of specific symptoms reduces awareness of the disease among growers.Disease controlResistance genes (where available in suitable cultivars), application of nematicides, crop rotation. Great effort is put into reducing the spread of PCN through quarantine measures and use of certified seed stocks.Useful websitesGenomic information for PCN is accessible through WormBase ParaSite.     

Superoxide dismutase polymorphism in field populations of the potato cyst nematodes Globodera rostochiensis and G. pallida

Superoxide dismutase (SoDase) polymorphism in reference populations of potato cyst nematodes (PCN) was studied by isoelectric focusing and compared with the banding pattern obtained from 26 English field populations of PCN. Qualitative and quantitative differences were found between the reference populations: a band detected only in the G. rostochiensis Ro4 and Ro5 reference populations was found in four field populations of varying pathotype composition and two field populations of G. rostochiensis Rol possessed extra bands that were not detected in the other field populations. Analysis of the band differences showed little correlation between pathotype and banding pattern in the field populations.     

Glucose phosphate isomerase polymorphism in field populations of the potato cyst nematodes, Globodera rostochiensis and G. pallida

The isozymic variation of glucose phosphate isomerase (GPI) was compared in 20 field populations of potato cyst-nematode (PCN) and related to variation in reference pathotypes of PCN. Populations pathotyped as G. rostochiensis Ro 1 by conventional differential cultivar tests were found to be different from populations of G. pallida. Variation within populations pathoptyped as G. pallida was seen and three populations were found to be similar to the reference G. pallida Pal pathotype. This seemed to be confirmed for two populations using cysts formed on a cultivar resistant to the Pa 1 pathotype when an isoenzyme pattern characteristic of G. palida Pa2 and Pa3 was found. The feasibility of the use of isozyme identification of PCN pathotypes is discussed in the light of these results.     

Use of resistant and susceptible potato cultivars in the trap cropping of potato cyst nematodes, Globodera pallida and G. rostochiensis

The effects of planting date and growing period of potato cultivars on their efficiency as trap crops for potato cyst nematodes (PCN) were studied. Plots were planted with susceptible or resistant cultivars in April, June and August and these were grown for 5, 6 or 7 wk before removal of the plants by hand lifting. Crops planted in June provided the best overall reductions in PCN population density of up to 95%, with cv. Santé significantly more effective than the other cultivars. Population reductions from the August planting were only slightly less than from planting in June but the tuber yields obtained were much greater: Maris Piper and Maris Bard produced 16.4 and 21.4 t ha^-1 respectively, with 37% and 43% respectively, of a size useful for canning (i.e. between 20 and 40 mm diameter).     

Effects of rotation length and oxamyl on potato yield and the potato cyst-nematode, Globodera rostochiensis, in a sandy loam soil

In sandy loam infested with golden potato cyst-nematode, Globodera rostochiensis, oxamyl at 5.6 kg a.i. ha^-1 incorporated in the top 15 cm of the soil just before planting potatoes greatly reduced nematode population increase on susceptible cv. Désirée grown six, seven or eight years after the last susceptible potato crop, but did not significantly increase tuber yields. In four-course and two-course rotations, oxamyl also controlled increase of G. rostochiensis and greatly increased yields of both cv. Désirée and resistant cv. Maris Piper. Oxamyl maintained tuber yields in a four-course rotation at the same level as in a six to eight-course rotation. Decline of G. rostochiensis in the soil was much faster under barley in some two-course rotations than under barley in four-course rotations.     

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.     

Effects of the nematicide oxamyl on life cycle stages of Globodera rostochiensis

Hatched second stage juveniles of Globodera rostochiensis were found to be more sensitive than either unhatched juveniles or adult males to low concentrations of oxamyl (EC₅₀ value for activity 0.5 μg oxamyl ml^-1). Development of juveniles in roots was significantly inhibited by 2.0 μg oxamyl ml^-1 probably due to impairment of normal feeding activity. The behavioural events necessary for orientation of juveniles towards roots for invasion and orientation of males towards females for fertilisation were found to be impaired by 0.5 and 1.0 μg oxamyl ml^-1 respectively. A comparison with previous work on Meloidogyne incognita showed G. rostochiensis juveniles to be more sensitive to oxamyl.     

Basal fertiliser application method, tuber initiation nitrogen, foliar NPK and the tolerance of potatoes to infection by the potato cyst nematodes Globodera rostochiensis and G. pallida

The effects of broadcast granular, placed liquid and foliar fertilisers on the tolerance of potatoes to infection by potato cyst nematodes were investigated. The tolerance of the potato cv. Pentland Dell was not significantly improved by fertiliser application type but placed liquid fertiliser, with or without foliar applications, increased the concentrations of N, P and K measured in whole plant dry matter of PCN infected plants. The tolerance of the potato cv. Sante was not statistically improved by altering the balance of fertiliser nitrogen applications between planting and tuber initiation or by applying foliar nitrogen. Nitrogen applications of 120 kg N ha^-1 at planting and a further 120 kg N ha^-1 at tuber initiation supplemented with foliar N, however, achieved a larger tuber yield than the same nitrogen programme without foliar N and gave a significantly greater yield than the application of 240 kg N ha^-1 at planting plus foliar N. The emergence of both cultivars was delayed in the absence of oxamyl. N, P and K concentrations within whole plant dry matter were significantly higher in plants from oxamyl treated plots and both N and K concentrations were significantly increased by increasing the quantity of N at planting, at 56 DAP. Splitting the fertiliser N between planting and tuber initiation appears to be important in maintaining the availability of this nutrient to PCN infected plants throughout the season.     

The identification of the potato cyst nematodes Globodera rostochiensis and G. pallida by isoelectric focusing of proteins on polyacrylamide gels

Isoelectric focusing on thin layers of polyacrylamide gel was used to separate proteins from the potato cyst-nematodes Globodera rostochiensis and G. pallida. General protein patterns could be used to identify the two species, even from. single cysts. Staining for the enzyme phosphoglucomutase (PGM) also produced species specific patterns and the presence of PGM variation among G. pallida populations was revealed. The potential of isolectric focusing as a routine research and advisory tool in nematology is discussed.