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.     

Effects of growing resistant potatoes with gene H1 from Solarium tuberosum ssp. andigena on populations of Heterodera rostochiensis British pathotype A

Pure pathotype A populations of Heterodera rostochiensis produce a few females on ex andigena hybrids with the H₁ gene for resistance. As the proportion of larvae able to become female on ex andigena hybrids was not increased by reproducing the nematodes on such hybrids for 3 years, these females seem not to be genetically different from the rest of the population. The proportion increased rapidly when the initial population contained a few pathotype (species) E nematodes but again no increase in the proportion of pathotype (species) A larvae able to become female on ex andigena was detected and pathotype E replaced pathotype A.     

Interactions between Heterodera rostochiensis Woll. and Verticillium dahliae Kelb. on potatoes and the effect of CCC on both

H. rostochiensis (British pathotype A) increased the severity of the disease caused by Verticillium dahliae in potato plants grown in pots when there were more than ten eggs/g of soil and both pathogens parasitized the root system together. The growth-suppressing chemical CCC, which severely stunted plants, prevented the disease and decreased H. rostochiensis reproduction. An estimate of foliage symptoms measured the effects of the disease more precisely than did tuber yields.     

Control of potato cyst-nematode, Heterodera rostochiensis, in peaty loam soil by D-D, aldicarb and a resistant variety of potato

In peaty loam soil in Cambridgeshire, 5.2 or 10.3 kg aldicarb/ha incorporated in the top-soil before potatoes were planted controlled potato cystnematode (Heterodera rostochiensis Woll.) better than 384, 769 or 1153 kg D-D/ha injected 15 cm deep into the top-soil in the preceding autumn. 10.3 kg aldicarb/ha applied in 1968 and 1969 permitted King Edward potatoes (susceptible to H. rostochiensis) to grow well in infested soil and prevented multiplication of pathotypes of H. rostochiensis on Maris Piper potatoes (resistant to H. rostochiensis pathotype A). Although large amounts of D-D applied in 1968 and 1969 increased the yield of King Edward potatoes in both years they did not control potato cyst-nematode in the second year.     

Association between the potato cyst-nematode, Heterodera rostochiensis Woll., and Verticillium dahliae Kleb. in the early-dying disease of potatoes

Investigation of a possible association between Verticillium dahliae and H. rostochiensis (pathotype E, British notation) was based on field observations and an examination of disease development in single-stemmed potato plants grown in pots. An association was found in the distribution of the nematode and the fungus in the field, and the disease was far more severe with a combined infection than with either pathogen alone. Studies on leaf-area development and yield reduction suggest there is synergism between fungus and nematode, the reductions produced by the combined infection exceeding the sum of those produced by either pathogen alone. Fungal mycelium and the extent of host colonization by V. dahliae were greatly increased by the presence of the nematode. The possible benefits to V. dahliae in the fungus-nematode complex are discussed.     

Hatching agents for the potato cyst-nematode, Heterodera rostochiensis Woll

Of 444 compounds tested for their ability to stimulate eggs of Heterodera rostochiensis to hatch, forty-five did so to varying extents. Many compounds that hatched H. schachtii Schm. eggs did not hatch H. rostochiensis eggs. The most effective compounds with H. rostochiensis were picrolonic acid, anhydro-tetronic acid and vanadates. Tests with analogues of picrolonic and anhydro-tetronic acids suggested some structures that may be concerned in hatching H. rostochiensis and H. schachtii. The simple analogues hatched the eggs of H. schachtii but not those of H. rostochiensis. Suitably placed polarisable atoms seemed to be an essential feature. Picrolonic acid contains pairs of polarizable atoms, about 4 and 6·7 Å apart, that may respectively be associated with the hatching of H. schachtii and H. rostochiensis. Other features of the more active hatching agents were a cis and co-planar arrangement of the two polarizable atoms with respect to the rest of the molecule. The function of hatching agents is discussed.     

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.     

The effects on a population of potato-root eelworm (Heterodera rostochiensis) of growing potatoes resistant to pathotype B

The effects on a potato-root eelworm (Heterodera rostochiensis Woll.) population of growing potatoes resistant to pathotype B of the eelworm were investigated. The eelworm population, which was originally nearly entirely pathotype A, had been changed into a mixture of pathotypes A, B and C before 1961, when the experiments described in this paper began, by growing potatoes resistant only to pathotype A. The resistant potatoes grown in the years 1961 and 1962 were certain clones of the hybrid triploid species Solarium xjuzepczukii Buk., clones bred from S. multidissectum Hawkes with the gene H₂ and clones bred from S. vernei Bitt. et Wittm. In the years 1963-65 the clone used was D 40 which has both the gene H₂ from Andigena and the gene H₂ from 5. multidissectum and is resistant to both pathotypes A and B of the eelworm. The only potatoes which caused a reduction in the egg population were those bred from S. vernei. The clone D 40, although it had little effect on the egg population, appeared to have more resistance than could be accounted for from possessing genes H₁ and H₂.     

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.     

Differentiation of Closely Related Globodera pallida (Stone) Populations by Means of DNA Restriction Fragment Length Polymorphisms (RFLPs)

A small genomic library from DNA of G. pallida population Delmsen (pathotype 3) was constructed. A number of clones were tested as hybridization probes with 21 G. pallida and 6 G. rostochiensis populations. The two species were easily distinguished by their hybridization patterns. A total of 32 RFLP markers were identified which permitted the differentiation of all G. pallida populations. By means of cluster analysis of the RFLP data the genetic distances between the 21,G. pallida populations were calculated and a dendrogram was constructed. The arrangement of the 21 G. pallida populations in the dendrogram suggests a partial correlation between genetic distance and virulence according to biological pathotyping.     

Breeding for resistance to the white potato cyst-nematode, Heterodera pallida

Progenies bred from material derived from the wild potato, Solanum vernei and from the cultivated potato, S. tuberosum ssp. andigena, clone CPC 2775, were compared for their resistance to Heterodera pallida, pathotype E. The influence of additional resistance derived from the wild species, S. multidissectum, was also investigated. Both S. vernei and CPC 2775 gave progenies with variable levels of resistance and there was often no clear segregation into resistant and susceptible categories. Incorporation of gene H₂ derived from S. multidissectum increased resistance to pathotype E of H. pallida for resistant material bred from both S. vernei and clone CPC 2775. The results indicate that adequate resistance to all British populations of potato cyst-nematodes can best be obtained by combining the factors for resistance from the two Andigena clones, CPC 1673 (gene H₁) and CPC 2775 (gene H₃), and from S. multidissectum (gene H₂).     

Inorganic ions and the hatching of Heterodera spp

Of various inorganic ions tested for their ability to stimulate hatching of eggs of the cyst nematodes of cereals (Heterodera avenae Woll), carrot (H. carotae Jones), cabbage (H. cruciferae Franklin), soybean (H. glycines Ichinohe), pea (H. goettingiana Liebs.), potato (H. rostochiensis Woll.), beet (H. schachtii Schm.), tobacco (H. tabacum Lownsbery & Lownsbery) and clover (H. trifolii Goffart), some were active. Zn²⁺ hatched many eggs of seven species and some of H. goettingiana, but inhibited hatch of H. avenae to below that in water. Zinc salts are the first recorded very active hatching stimulants for H. glycines in vitro. Many other metal ions stimulated hatching of H. schachtii eggs to varying extents; these also hatched some but not all of the other species. Vanadate ions were particularly effective for H. rostochiensis, more so than Zn²⁺. No ion increased the hatch of H. avenae to above that in water. The most active ions were not those most abundant in soil. The behaviour of different ions with different species did not suggest any obvious affinities between species, but the differences between the hatching of H. tabacum and H. rostochiensis add weight to the view that, despite morphological similarities and overlapping host ranges, they are distinct species rather than pathotypes of a single species. Ions and other hatching agents may be absorbed by materials within the egg or larva and alter the structure and function of these materials. The lack of correlation between the hatching of H. schachtii by ions and the known stability sequences of various biological metal-binding systems suggests that there may be several sites of action that differ in their response.     

Field experiments in the control of Verticillium dahliae and Heterodera rostochiensis on potatoes

Potatoes were grown in soil infested with Verticillium dahliae and Heterodera rostochiensis and treated with methyl bromide, aldicarb or benomyl. Successive crops were grown in subsequent years on the same plots but without further treatment. Largest yields in the year of treatment were from plots fumigated with methyl bromide but in the second crop benomyl-treated plots yielded most. Neither methyl bromide nor aldicarb affected yields from trie third crop. After lifting the first crop, soil from plots treated with methyl bromide or benomyl contained less V. dahliae than that from plots receiving aldicarb or nothing. Soil was also less infective after the second crop following methyl bromide fumigation, but not the third. Plots treated with methyl bromide or aldicarb contained many fewer H. rostochiensis than untreated plots after the first crop, slightly less after the second and equal numbers after the third crop. H. rostochiensis were also fewer in benomyl-treated plots than in untreated after the first crop, but, surprisingly, were fewest after the second crop. The increased yield after applying benomyl to soil seems to depend more on its effect on H. rostochiensis than on V. dahliae. Fumigating with methyl bromide decreased common scab and black scurf on progeny tubers but increased infections by Oospora pustulans.     

A cereal cyst nematode (Heterodera avenae Woll.) resistance gene transferred from Aegilops triuncialis to hexaploid wheat

 The cereal cyst nematode (Heterodera avenae) is an important root parasite of common wheat. A high level of resistance was transferred to wheat from Aegilops triuncialis (TR lines) using the cross [(T. turgidum×Ae. triuncialis)×T. aestivum]. Low fertility (3–5 viable kernels per plant) was observed during the process but the surviving hybrid plants were highly vigorous. To obtain stable resistant lines further crosses to T. aestivum were performed. The resistance in TR lines seems to be transferred from the C genome of Ae. triuncialis (genomes CCUU). Ae. triuncialis was highly resistant to the two Spanish populations of H. avenae tested, as well as to four French races and two Swedish populations. The histological analysis showed a hypersensitive reaction in the roots of a resistant TR line inoculated with the Ha71 pathotype of H. avenae, whereas well-formed syncytia were observed in the roots of the susceptible control. Resistance to the H. avenae Ha71 pathotype seemed to be inherited as determined by a single dominant factor in the crosses between resistant TR lines and susceptible cultivars. Received: 11 November 1997 / Accepted: 9 December 1997     

On cyst colour changes, bionomics and distribution of potato cyst-eelworm (Heterodera rostochiensis Woll.) pathotypes in the East Midlands

Pot tests and field trials in 1966 confirmed earlier observations that pathotype A potato cyst-eelworm (Heterodera rostochiensis Woll.) showed marked colour differences from pathotypes B and C during development on the roots of susceptible potatoes. In hatching tests started in July, newly formed brown cysts of pathotype A released four times as many larvae as those of pathotypes B and C, without entering an immediate diapause; the latter produced larvae after a rest period of 18–21 days. Subsequent second-generation cyst production in glass-tube culture was greater from pathotype A. Field observations suggested that all pathotypes mature at about the same time and give rise to only one flush of cysts on both early and maincrop potatoes in the growing season. Cyst colour surveys in commercial crops, and pot and field trials using resistant potato selections, confirmed that pathotypes B and C are both dominant and widespread in the East Midlands.     

The pathogenicity and increase of Heterodera rostochiensis on tomato cultivars, self-rooted or grafted on to rootstocks.

Self-rooted tomatoes ‘Ailsa Craig’ and ‘Kingley Cross’, and scions of ‘Ailsa Craig’ grafted on to different rootstocks, were grown in soil infested with different numbers of Heterodera rostochiensis (Mainly pathotype A). Three rootstocks (RS₄, RSKN, ISKVF) tolerated damage from nematode populations of up to 125 eggs/g soil, but nematodes increased up to x45 on them. Two nematode-resistant F₁ hybrid rootstocks, B66₃₃ (ex Lycopersicon pimpinellifolium B6₁₇₃) and B6₀₁₅ (ex L. hirsutum var. glabratum B6₀₁₃), tolerated up to 125 eggs/g soil; nematode populations declined as much as 80% under B66₃₃, and increased little under B6₀₁₅. On the self-rooted ‘Ailsa Craig’ and ‘Kingley Cross' the numbers of nematodes increased markedly (maximum increase x40), and greatly affected growth and yield so that initial populations greater than 62 eggs/g soil caused crop failure.     

Hatching Behavior of Potato Cyst Nematodes from the Canary Islands

The present work investigated early hatching differences in naturally occuring field populations and newly reared populations of potato cyst nematodes from the Canary Islands. Hatching behavior of the two species appears to be distinct, with more juveniles hatched from G. pallida that hatch earlier and over a shorter time than G. rostochiensis. The hatching rate of 3-year-old PCN populations was more than double (mean 44.5% ñ 1) that shown by newly reared populations (mean 19.1% ñ 12.5), and those that could be classified as pathotype Pa 1 (Pa 1 and P 13) were found to hatch particularly poorly. Significant differences were also observed in the juveniles released in tap water between newly reared populations of both species, with mean hatch significantly higher for G. rostochiensis. The results are discussed in relation to the implication that these findings may have for competition between the two species of PCN in the field.     

Observations on periodicity of hatching of eggs of the potato cyst nematode, Heterodera rostochiensis Woll.

Soil containing new-generation cysts of Heterodera rostochiensis was taken from the field at monthly intervals during late summer and autumn and kept in various conditions for up to a year. The number of eggs that hatched in the stored cysts was compared each month with the number that hatched in cysts taken directly from the field. Eggs did not hatch readily when stimulated during the late autumn and early winter, although more did so in cysts taken from the field before August than after. A few more eggs hatched in cysts stored in air-dried soil than in cysts stored in moist soil. Some cysts were kept at 15 or 20 °C continuously and others at 5, 15 or 30 °C for 6 weeks followed by 20 °C continuously. Storage at 30 °C caused eggs to hatch sooner, but otherwise the temperature of storage had little effect on hatch at any time of the year. Warmth also increased the hatch of H. cruciferae sooner, and some synthetic hatching agents did so with both of these species. When freed from new cysts, more eggs of H. rostochiensis hatched than in intact cysts and hatch was further increased when the fragments of tanned cyst-wall were left with the freed eggs. Puncturing the cyst-wall of new brown cysts had little effect on the hatch in potato root diffusate. Like eggs in new cysts, those in 1-year-old cysts stored out of doors ceased to hatch during the autumn and winter. The term ‘dormancy’ is inadequate to describe the inability of eggs of H. rostochiensis and other Heterodera spp. to hatch in the appropriate stimulant and the term ‘facultative diapause’, as applied to insects, better fits the phenomenon.     

Resistance to the potato cyst-nematode, Heterodera rostochiensis, in the plant genus Lycopersicon

Forty-eight lines of Lycopersicon and four lines of Solanum were screened for resistance to twelve Heterodera rostochiensis populations of known patho-type(s). Plant lines were assessed for resistance first by examining the outside of the root ball for cysts and later by washing the root ball to extract all cysts. Possible resistant plant selections were re-tested against three eelworm populations, including the one to which they were first shown resistant. Resistance was discovered in two lines of Lycopersicon pimpinelli-folium, two L. esculentum L. pimpinellifolium crosses, L. esculentum var. cerasiforme, six lines of L. peruvianum, in L. peruvianum var. humifusum, L. hirsutum var. glabratum, and in Solanum indicum. Because resistance was found most commonly in L. peruvianum and because it has already been used as a resistant parent in breeding programmes to incorporate resistance to root-knot nematode (Meloidogyne spp.) in tomato, L. peruvianum seems to be the best source of resistance among plants tested so far. The host-parasite relationships of resistant L. hirsutum var. glabratum (B 6013) were compared with those of a commercial, susceptible tomato, L. esculentum‘Ailsa Craig’. Plants were inoculated with three eelworm isolates; the extent of eelworm invasion, plant reaction and eelworm development were studied. Larvae invaded and penetrated roots of the resistant plant as freely and in as large numbers as they penetrated roots of the susceptible tomato. In the latter, numerous larvae matured while, in contrast, few larvae matured in the roots of L. hirsutum var. glabratum. L. hirsutum var. glabratum was shown to possess a root diffusate as active in hatching larvae of Heterodera rostochiensis as that of L. esculentum‘Ailsa Craig’. The existence of pathotypes of H. rostochiensis, identifiable by their differing abilities to increase on resistant tomato lines, was not clearly revealed in the experiments.