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Differences in rates of infestation of root-knot nematode (Meloidogyne spp.) populations by the endospore-forming bacterium Pasteuria penetrans were not entirely due to inter/intra-specific variability of the organisms. Soil conditions, especially texture and chemical characteristics, are also involved. Focusing studies on vegetable crops, interactions between the occurrence of Meloidogyne spp. juveniles encumbered with spores of P. penetrans and some physico-chemical soil characteristics were analysed both between regions (West Africa, e.g. Burkina Faso and Senegal; South America, e.g. Ecuador; the Caribbean, e.g. Trinidad and Tobago; and Mediterranean Europe, e.g. Crete) and within Ecuador, Burkina Faso and Senegal. In Ecuador (clay or silty-clay soils), the mean proportion of infested juveniles was high (41.9%). In the sandiest soils, as in Senegal, there were very few infested juveniles (4.7%). In Crete, Burkina Faso, and Trinidad and Tobago, where the soils are siltier, the mean proportions of infested juveniles range between 14 and 24.4%. Multivariate analysis performed on the data from Senegal and Burkina Faso revealed that a significant increase of the mean clay content (1.4 and 10.5%, respectively) improved the mean proportions of infested juveniles (from 1.6 to 42.2% and from 10.7 to 79.4%, respectively). Influences of the soil texture and structure on the availability of the spores of P. penetrans to infest the juveniles of Meloidogyne spp. are discussed.

Four similar, agricultural soils with distinct nematode communities were used to determine the extent to which soil and inoculum factors affected nematode community structure. The soils all had a sandy loam texture from the same geographical area and had been in pasture or arable rotation for the last 10 years. Treatments were established in pots containing a middle layer of frozen defaunated soil, sandwiched between an inoculum that was either fresh soil from the same site ('self') or a mixture of soils to give a more diverse inoculum ('mixed'). Principal component analysis indicated that a single soil type given different inocula developed different community structures (i.e., the community under 'self' differed from that under 'mixed') suggesting an inoculum effect. It was also true that different soil types under a single inoculum soil also developed different community structures (i.e., community under 'mixed' differed with soil type), suggesting a soil effect. It is likely that the nematode community structure is influenced by a combination of antecedent land use, soil factors, species introductions and inter-species competition, which should be considered in any interpretation of nematode communities as a biotic indicator.

Recent results on the population dynamics and damage relationships of root-knot nematode (RKN, Meloidogyne incognita) and of potato cyst nematode (PCN, Globodera pallida) are modelled, and a computer-based programme is used to explore different strategies for PCN control. Damage by RKN was shown to be density dependent, to increase with increasing duration of plant growth, and to be much greater for good than poor hosts. PCN populations both increase and decline more slowly than those of RKN, and modelling suggested that, when non-hosts are grown, differences in decline rates will have an accumulative effect on the effectiveness of rotation. Similarly, differences in nematicide effectiveness will have a major effect on post-harvest PCN populations, and nematicides were shown to be most effective when PCN populations are small. Host resistance is a key component of integrated management of nematodes and, because gene flow in soil is limited, it can be durable.

The conclusions of a collaborative study of the occurrence and importance of root-knot nematodes (RKN, Meloidogyne spp.) and of their control agent, Pasteuria penetrans, in parts of Europe, Africa, South America and the Caribbean are presented. Rootknot nematodes were estimated to reduce the yields of a wide range of horticultural crops by > 25% in Ecuador, Malawi and Tanzania, and by ca 10% in Trinidad and Tobago. The greatest proportion of infected crops were observed in Ecuador (205 of 207) and the least in Trinidad and Tobago (70 of 174). The mean gall index was greatest in Ecuador (5.5). Levels of galling were least in Senegal (1.6), even though 89% of crops were infested and virulent M. mayaguensis was widespread. In all countries, M. incognita and M. javanica were the most abundant species, but M. hispanica occurred widely in Burkina Faso, even in newly cultivated areas in the Sahile. Several new esterase phenotypes were detected, especially in Ecuador and Malawi. Juveniles (J2) collected from the soil during the surveys were examined for attached spores of P.penetrans. It was widespread (20 to 60% of RKN populations), except in Malawi and Tanzania (< 10% were infected), and was found for the first time in Crete (Greece). Generally, < 50% of the J2 carried spores. The occurrence of P.penetrans was sometimes correlated with soil type e.g., in Senegal it was least frequent in sandy soils. Laboratory assays of the binding of spores of isolates of P.penetrans to populations of RKN indicated large variations in specificity and substantial interactions; differences between populations within a species of RKN were sometimes almost as great as those between species. In microplot trials in which an "exotic" isolate of P.penetrans was introduced (ca 103 spores per g soil), its incidence was not increased by increasing the frequency or intensity of the growing of RKN-susceptible crops. However, in two such trials at sites in Tanzania and Ecuador naturally infected with P.penetrans, there were large increases in the proportions of spore-encumbered J2 (up to 100% encumbered) and in the yields of spores (up to 3.3 × 106 spores per mg dry root) in those plots amended with an "exotic" isolate. In these plots, numbers of J2 in the soil were decreased and damage by RKN was suppressed; gall indices were decreased (from > 8 to < 3) and yields were increased (by up to 30%). No such changes were observed in the unamended control plots. Increased suppression of RKN was also observed in a field trial, even in plots where RKN-susceptible and non-host crops were alternated. Increased suppression following amendment with the "exotic" isolate of P.penetrans was not observed at sites not previously infected with P.penetrans. Regression analysis of the results from the microplot and field trials indicated that tomato yields were decreased by > 5% for every increase of one in the gall index. Yields were increased by alternating tomato with leguminous crops in some trials, but not in others. It is proposed that, in natural infections, mutual selection produces a dynamic balance between the P.penetrans and the RKN whereby levels of infection are rarely suppressive. However, the introduction of an "exotic" isolate of P.penetrans, with a different attachment profile, can disturb this balance, resulting in a greatly increased proportion of infected J2 and females, increased yields of spores and more suppression of RKN populations. Importance des nématodes à galles tropicaux (Meloidogyne spp.) et facteurs affectant l'utilité de Pasteuria penetrans, agent de contrôle biologique - Ce travail présente les conclusions d'une étude, menée en collaboration par plusieurs équipes de recherche, sur la présence et l'importance des nématodes phytoparasites du genre Meloidogyne et de leur parasite bactérien, Pasteuria penetrans, dans certains pays d'Europe, d'Afrique, d'Amérique du Sud et des Caraïbes. Les réductions de rendement de cultures maraîchères très diverses dues à ces nématodes atteignent 25% en Equateur, Malawi et Tanzanie, et 10% à Trinidad et Tobago. La plus forte proportion de parcelles infestées a été rencontrée en Equateur (205 sur 207) et la plus faible à Trinidad et Tobago (70 sur 174). C'est en Equateur que l'indice de galles moyen (égal à 5,5) était le plus élevé. Même si cet indice était faible en moyenne au Sénégal (1,6), 89% des cultures étaient infestées dans ce pays, en grande partie par l'espèce virulente M. mayaguensis. M. incognita et M. javanica sont les plus répandues dans tous les pays prospectés. Cependant, M. hispanica est très répandu au Burkina Faso, même dans des zones récemment cultivées en maraîchage en région sahélienne. Plusieurs phénotypes estérasiques nouveaux ont été détectés, spécialement en Equateur et au Malawi. Les juvéniles de second stade (J2) extraits des échantillons de sol collectés lors des prospections ont été examinés pour détecter la présence de spores de P.penetrans sur leur cuticule. Trouvé pour la première fois en Crète (Grèce), P.penetrans est très répandu dans les autres pays prospectés, infestant 20 à 60% des populations de Meloidogyne spp., sauf au Malawi et en Tanzanie où moins de 10% des populations sont atteintes. Le plus souvent, moins de 50% de J2 portent des spores bactériennes. Le taux de parasitisme des J2 par P. penetrans est influencé par les types de sols, comme par exemple au Sénégal où il est très faible dans les sols sableux grossiers. Des expériences en laboratoire portant sur l'attachement de spores de divers isolats de P. penetrans à des populations de Meloidogyne spp. ont révélé une grande variation de la spécificité et des interactions; les différences observées pour diverses populations d'une même espèce de Meloidogyne sont parfois presque aussi marquées que celles observées entre espèces. L'incidence parasitaire d'un isolat "exotique" de P. penetrans introduit dans des microparcelles (ca. 103 sporespar g. de sol) n'a pas été accrue par l'augmentation de la fréquence ou de la densité de plantation des cultures sensibles à Meloidogyne spp. employées. Cependant, dans deux microparcelles natullement infestées en P.penetrans, situées en Equateur et en Tanzanie, l'introduction d'un isolat "exotique" s'est traduite par un accroissement de la proportion de J2 infestés (jusqu'à 100%) et de la production de spores ((jusqu'à 3, 3 × 106 spores par mg [poids sec] de racines), d'une diminution de la population de J2 dans le sol, et d'une disparition des dégâts racinaires; les indices de galles moyens ont diminué (de plus de 8 à moins de 3) et les rendements des cultures ont augmenté (jusqu'à 30%). De tels changements n'ont pas été observés dans des sols non amendés en isolats "exotiques" de P.penetrans. Un meilleur contrôle des populations de Meloidogyne spp. a également été observé au champ, même lorsque la séquence culturale alternait des cultures sensibles et des cultures non-hôtes du nématode. Dans des parcelles non infectées en P.penetrans, la baisse des populations de Meloidogyne spp. n'a pas été observée après introduction d'un isolat "exotique" de la bactérie. Des analyses de régression portant sur les données obtenues en microparcelles ou au champ montrent que les rendements en tomate diminuent de plus de 5% chaque fois que l'indice de galle augmente d'une unité. Ces rendements ont parfois été améliorés lorsque des cultures de légumineuses alternaient les cultures de tomate. Ainsi, sur la base des analyses nématologiques et agronomiques faites en fin de cycles culturaux, il est suggéré que, dans les cas d'infestations naturelles en P.penetrans, des sélections mutuelles entraîneraient un équilibre dynamique entre les populations de la bactérie et celles du nématode, représentatif d'une densité-dépendance retardée. En revanche, l'introduction inondative d'isolats "exotiques" de P.penetrans, aux propriétés parasitaires différentes de celles des populations natives, pourraient rompre temporairement cet équilibre en faveur d'un accroissement de la proportion de nématodes (J2 et femelles) infestés et de la production de spores bactériennes, ainsi qu'un meilleur contrôle des populations de Meloidogyne spp. La capacité des populations de P.penetrans à survivre dans les sols et à contrôler durablement les populations de Meloidogyne spp. dépendraient de la spécificité entre les organismes, des propriétés des sols et des systèmes de culture.

Soil nematode communities have the potential to provide unique insights into many aspects of soil processes. Since most nematodes are active in soil throughout the year, they can potentially provide a holistic measure of the biotic and functional status of soils. In contrast to other soil microbial groups, representative samples of soil nematode communities are relatively easy to obtain. However, most current nematode ecological information has been survey-based or purely observational in nature, with a persistent focus on detailed taxonomic analysis of nematode communities. The development of a Maturity Index, MI, represents a significant advance in classifying communities and it continues to be refined and developed. But, to develop a wide capacity to use soil nematode information for diagnostic and predictive purposes, particularly for agricultural soils, we need a new, more robust approach, which does not require extensive taxonomic skill and includes more functional criteria. One of the key attributes of nematodes is the relationship between structural form (principally oesophagal feeding apparatus) and function (i.e. trophic group). Nematode form is readily determinable by direct observation of extracted nematodes and high-level taxonomic skills are not needed to assign the major community components to their different trophic and ecological groups. Consequently, the trophic structure of nematode communities is relatively easy to determine and can provide an integrated measure of the status of the other groups on which they feed. Similarly, population numbers and proportions of juveniles and adults can be readily determined, permitting calculation of relative biomass and dynamics of population growth. The size distribution of individuals within the community is likely also to be an indicator of the structural status of soils from a biotic standpoint. However, fundamental gaps remain in our understanding which limit our ability to relate differences in nematode communities to functional differences. There needs to be a greater emphasis on the development and experimental testing of hypotheses, a greater integration of nematology into soil-process related studies, and the development of a specific, soil-nematode related theoretical framework for understanding epidemiological and soil colonisation processes.

Four populations of Meloidogyne incognita were tested on 57 species of plants from temperate and tropical regions. Juveniles of one or more populations invaded, and induced galls on almost all plants. Except for the population from the West Indies which induced most galls on Nicotiana spp., there was no obvious relationship between the origins of populations and their ability to induce galls on plants from particular regions. Although most plants were hosts for all four populations, many produced only a few galls/egg masses with some of the populations. The differences in galling between populations, and the interaction with plant species were both significant (P < 0.001). Poor hosts often contained fewer juveniles and the rate of juvenile development was often decreased compared with good hosts. Solanum nigrum was an exception in that it was invaded by fewer juveniles than susceptible tomato, but rates of development were similar. The effect of host status differences in four plant species on damage by M. incognita was investigated but only the growth of susceptible tomato was decreased. The growth of the non-host Urtica dioica, of the poor host Datura metal, and of an intermediate host S. nigrum, was unaffected. Unterschiede im Wirtsstatus und ihre Bedeutung fur den durch Meloidogyne incognita verursachten Schaden - Vier Populationen von Meloidogyne incognita wurden an 57 Pflanzenarten aus gemassigten und tropischen Gebieten gepruft. Juvenile einer oder mehrerer Populationen wanderten in fast alle Pflanzen ein und induzierten Gallen. Mit Ausnahme der Population von den Westindischen Inseln, die an Nicotiana spp. die meisten Gallen induzierte, bestand keine deutliche Beziehung zwischen der Herkunft der Populationen und ihrer Fahigkeit, an Pflanzen bestimmter Gebiete Gallbildung zu induzieren. Obwohl die meisten Pflanzen Wirte fur alle vier Populationen waren, bildeten viele von ihnen mit einigen Populationen nur wenige Gallen/Eimassen. Die Unterschiede zwischen den Populationen in Bezug auf Gallbildung und auf Wechselwirkungen mit den Pflanzen waren beide significant (P < 0.001). Schlechte Wirte enthielten oft weniger Juvenile als gute Wirte, und die Entwicklungsrate der Juvenilen war oft vermindert im Vergleich zu guten Wirten. Solanum nigrum bildete insofern eine Ausnahme, als weniger Juvenile eindrangen als in anfallige Tomaten, die Entwicklungsraten aber ahnlich waren. Die Wirkung der Unterschiede im Wirtsstatus auf die Schadigung durch M. incognita wurde an vier Pflanzenarten untersucht. Nur das Wachstum von anfalligen Tomaten wurde vermindert. Das Wachstum des Nichtwirtes Urtica dioica, des schlechten Wirtes Datura metal und des massig guten Wirtes S. nigrum wurde nicht beeinflusst.

Abstract A targeted survey of vegetable production areas in Crete, Greece, showed that the majority of infestations of rootknot nematodes (RKN) were Meloidogyne javanica. M. incognita appeared to be limited to areas growing pepper that is a host for M. incognita but not for M. javanica. Tests with resistant tomato carrying the Mi gene showed that the M. incognita and the majority of the M. javanica populations were avirulent, and that virulent nematodes could not be selected from them. However, three populations of M. javanica, including some previously identified, were virulent. An AFLP study of the DNA from 22 populations of M. javanica produced 264 scorable amplification products and gave a very high mean similarity (99.4%) between populations, indicating that both virulent and avirulent populations probably derived from the same founder population. Mi-resistant tomato and pepper appear to have considerable utility in the integrated management of RKN in Crete, provided care is taken to monitor the species and virulence or reproductive ability of the nematode populations. Die Variation bei Wurzelgallennematoden (Meloidogyne spp.) auf Kreta in Bezug auf ihre Bekampfung mit resistenten Tomaten und Paprika - Eine gezielte Untersuchung von Gemuseanbaugebieten auf Kreta Griechenland, ergab, dass die Mehrzahl der von Wurzelgallennematoden (RKN) befallenen Flachen mit Meloidogyne javanica verseucht war. M. incognita was offentsichtlich auf Gebiete des Paprikaanbaus beschrankt. Paprika ist ein Wirt fur M. incognita aber nicht fur M. javanica . Versuche mit resistenten Tomaten, die das Mi-Gen besassen, zeigten, dass M. incognita und die Mehrzahl der Populationen von M. javanica avirulent waren, und dass aus ihnen keine virulenten Nematoden selektiert werden konnten. Drei Populationen von M. javanica, darunter schon einige schon vorher identifizierte, waren virulent. Eine AFLP-Untersuchung der DNA von 22 Populationen von M. javanica ergab 264 unterscheidbare Amplifikationsprodukte und zeigte eine hohe mittlere Ahnlichkeit (99,4%) zwischen den Populationen. Dies deutete daraufhin, das virulente and avirulente Populationen wahrscheinlich von der gleichen Grunderpopulation abstammten. Mi-resistente Tomaten und Paprika sind offensichtlich von betrachtlichen Nutzen bei der integrierten Bekampfung von RKN auf Kreta. Voraussetzung ist, dass die Arten und die Virulenz oder die Vermehrungsfahigkeit der Populationen sorgfalting festgestell werden.

The relationship between initial population density of Globodera pallida and yield was examined for five genotypes of potato at four different experimental sites; two in Scotland and two in England. The experiments at each site were conducted in two stages. The experimental area was first manipulated using resistant and susceptible potato cultivars to give plots with different nematode population densities to act as the initial populations (P i ) for the second stage. The main experiment was conducted using a range of host genotypes that differed in their tolerance and susceptibility. The utility of an inverse linear model relating yield to initial population density was confirmed as were differences in cultivar tolerance. Site differences in yield loss were also observed. It was found that the model could be modified to include the partitioning of genotype and site effects. The implications of this in terms of developing further models to predict yield loss and nematode population dynamics are discussed.

Forty populations of Globodera pallida originating from either South America or field sites in Europe were tested for their reproductive ability on a susceptible potato cultivar and five genotypes with quantitative resistance from either Solanum vernei or S. tuberosum ssp. andigena CPC 2802 in a glasshouse pot experiment. The results showed that there was a wide and continuous range of virulence (85% to 4% reproduction) to all the resistant genotypes. This range was as broad within the European populations as within those from S. America. There was a significant host clone x nematode population interaction, largely accounted for by grouping the clones according to the source of resistance and the populations by their continent of origin. Populations from Europe were relatively more virulent on genotypes derived from S. vernei. In contrast, populations from S. America were relatively more virulent on genotypes derived from S. tuberosum ssp. andigena CPC 2802. Examination of the data from the European populations also showed a significant host x population interaction tending to separate British from mainland European populations.

Four random probes from a Globodera pallida DNA library and one rDNA repeat probe from flax were used to highlight specific fragments in total DNA restricted with the endonucleases Bam HI, Eco RI, Eco RV, and Hind III, from 26 potato cyst nematode (PCN) populations (G. rostochiensis and G. pallida). The percentage similarity between species was low (%sm = 45.6). Cluster and principal coordinate analysis allowed us to hypothesise about the epidemiology of these populations. In the G. rostochiensis group, the populations representing pathotypes Ro2, Ro3, Ro4 and Ro5 may have been derived from the same introduction. Canarian populations R1, R2, R6, R7, and R10 were distinct from all the controls but R4 and R5 were close to the British Ro1 population. In the G. pallida group, the Luffness population was distinct from all others suggesting that it may represent a distinct introduction of PCN into the British Isles. Canarian population P9 had ten markers which were absent from the European control populations and it is possible that this population represents a distinct introduction of G. pallida into the Island of Tenerife.

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

▪ Abstract Most apomictic root-knot nematodes (RKN; Meloidogyne spp.) have host ranges that encompass the majority of flowering plants, and M. incognita is possibly the world's most damaging crop pathogen. The ancestors, age, and origins of the polyphagous RKN are obscure, but there is increasing evidence that M. incognita, M. javanica, and M. arenaria are closely related, heterogeneous species with a recent, hybrid (reticulate) origin. If so, they must owe much of their current worldwide distributions to spread by agriculture. Host resistance appears to be generally durable in the field, but laboratory studies suggest that apomixis does not prevent evolution in response to selection by a parasitic bacterium (Pasteuria penetrans) and host resistance. Maintaining general fitness may be the evolutionary priority for most populations of polyphagous RKN, and a wide host range, important in the field but not in the laboratory, may be conserved by apomixis. Several factors may help confer a wide host range, including suppression of host resistance, perhaps as a consequence of the strength of the induced susceptible response. Resistance genes effective against RKN appear not to have resulted from coevolution. Rates of juvenile invasion and/or development are low in many wild and some crop plants, with the result that they are both poor hosts and sustain less damage. Overall, it is suggested that greater coordination, particularly of fundamental research, is required.

In tropical regions the parthenogenetic Meloidogyne spp. are major crop pests. The presence of populations in West Africa which overcome resistance in cultivars as diverse as tomato cv. ‘Rossol’, sweet potato cv. ‘CDH’ and soya bean cv. ‘Forrest’ has been reported (Prot, 1984; Fargette and Braaksma, 1990). The relationship of these populations to other tropical Meloidogyne spp. was investigated as the nature of such resistance breaking populations has implications both for integrated control and for appropriate quarantine measures. At a broader level, variation within the various tropical Meloidogyne spp. is also of interest to gain an understanding of the extent of genetic variation in this important group of pests.

(1) This paper aims to compare alternative models for the population dynamics of the potato cyst nematode Globodera pallida Behrens using data from a field experiment in which nematode egg densities were observed before planting and after harvest of six potato genotypes with different degrees of resistance to G. pallida. (2) Four population models are fitted to the data. These are the models of Jones & Kempton (1978) and Seinhorst (1970, 1984), and two modifications of the Jones & Kempton model which are found to fit the data more closely. (3) The parameter values of the models and the equilibrium densities are interpreted in terms of the resistance and tolerance of the potato genotypes.

Potato plants growing in soil heavily infested with potato cyst nematode (PCN) contained less N, P and K in their leaf dry matter than plants growing in the same soil treated with a nematicide. These differences were less in tolerant than intolerant cultivars. Applying additonal fertiliser increased the growth of untreated plants more than that of nematicide-treated plants and nematicides increased growth most in plots receiving the lowest rate of fertiliser. Overall, the results are consistent with the hypothesis that damage by invading juveniles of PCN decreases the effectiveness of the potato root system leading to a chronic deficiency of one or more nutrients and a consequential reduction in the rate of top growth.

Where one organism lives on or within and is dependent upon another there may be a range of relationships from symbiosis (mutualism) to predator/prey. Between are the parasite/host and, if the parasite damages its host, the pathogen/host relationship. Cyst nematodes cause damage and are therefore pathogens, but Koch’s postulates cannot readily be applied to them; in part this is because they multiply and spread much less rapidly than many other plant pathogens and, in part, because the damage they cause is usually proportional to their population density at planting.

The cuticle is a major barrier prohibiting the infection of nematodes against micro-organisms. The attachment of bacterial spores of the nematode hyperparasite Pasteuria penetrans (PP1) to field populations of root-knot nematodes (RKN, Meloidogyne spp.) from Burkino Faso, Ecuador, Greece, Malawi, Senegal and Trinidad and Tobago were assayed in standard attachment tests. The attachment of spore population PP1 to different field populations of root-knot nematode showed that the rates of attachment differed between countries. Similar tests were also undertaken on P. penetrans spores from these countries against 2 species of RKN, M. incognita and M. arenaria. The results showed a high degree of variability in spore attachment with no clear distinction between the 2 species of nematode. It has been hypothesized that Pasteuria spore attachment is linked to nematode species designations and this study clearly shows that this is not the case. Further tests showed that variation in spore attachment was not linked to nematode phylogeny. The results therefore beg the question of how do parthenogenetic root-knot nematodes maintain cuticle variability in the face of such an aggressive hyperparasite.