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International audience; Current restrictions on the use of chemical nematicides have led to an increase in root-knot nematode (RKN) damages in horticultural crops. The effects of two sorghums as summer cover crops, Sorghum sudanense sudan-grass cv. ‘Piper’ or sudangrass hybrid [S. bicolor x S. sudanense] ‘270911’, respectively with low and high dhurrin contents, were compared in their ability to suppress RKN in a vegetable production system. The use of both sorghums ‘Piper’ and ‘270911’ as a green manure was found to be an effective strategy for decreasing RKN infestation in the soil, thereby protecting the subsequent planting of RKN susceptible crops (chard, lettuce or melon). Analytical experiments were further conducted in growth chamber and greenhouse pot experiments to investigate and compare the susceptibility of the sorghums and the factors affecting their efficacy for RKN management, in order to better explain the results obtained in the field trial. The two sorghums were poor hosts of RKN, acted as trap crops and as a biofumigant releasing hydrogen cyanide. Time of planting, time of bio-fumigation, and type of soil affected their efficacy for RKN management. For best RKN suppression, the sorghum cover crops need to be cultivated during one month or less and biofumigated for one month prior to crop planting. The trapping effect of both sorghums in clayey soil was less efficient than in sandy or sandy-loamy soils. Combining less than 30-days of sorghum culture and 10-days soil incorporation with solarization mulch was particularly efficient in suppressing nematodes. No effect relative to the sorghum type was detectable as long as they were used appropriatel.

Root-knot nematodes (RKNs) are major threats to crops through attacking the roots, which induces an abnormal development of the plant.

Meloidogyne javanica is considered as the most damaging nematode of vegetables in Morocco. Eco-friendly bionematicides are urgently required for its control. In vitro experiments were carried out to assess the direct effect of bioproducts of Peganum harmala against M. javanica. The bioassay showed extracts to be nematotoxic. Aqueous extracts of P. harmala exhibited reversible nematostatic activity. The estimated ID50 of the most active product in methanolic extracts was 368ppm. HPLC-MS of the methanolic extract revealed that total content of major alkaloids of P. harmala was approximately 12.162±0.637mg/g. Harmine (8.514±0.521mg/g) is the dominant alkaloid. In conclusion, Peganum harmala has a reversible nematostatic activity on second stage juveniles of M. javanica. The effect of P. harmala is due to its possession of a high content of β-carboline alkaloids, which warrant further experimentation. Bioproducts from P. harmala should be exploited through formulations for management of the root knot nematode.

Background Root-knot nematodes (RKN) are major pest of olive tree (Olea europaea ssp. europaea), especially in nurseries and high-density orchards. Soil samples were collected from main olive growing areas of Morocco, to characterize Meloidogyne species and to discuss the contribution of biotic and abiotic factors in their spatial distribution. Results RKN were found in 159 soil samples out of 305 from nurseries (52.1% occurrence) and in 11 out of 49 soil samples from orchards (23.2% occurrence). Biochemical and molecular characterisation (PAGE esterase and SCAR) revealed the dominance of M. javanica both in nurseries and orchards with minor presence of M. incognita only in nurseries, and M. arenaria in only one nursery. RKN were distributed on aggregated basis. Frequent presence of M. javanica in orchards might have come from nurseries. In contrast, the detection of M. incognita in nurseries alone suggests that this species could not reproduce in orchards because of either the competition with other plant-parasitic nematodes or unfit local habitats. The impact of environmental variables (climate, habitat origin and physicochemical characteristics of the substrates) on the distribution of Meloidogyne species is also discussed. Conclusion Olive nurseries in Morocco are not able to guarantee the safety of rooted plants. As a result, olive production systems are exposed to strong RKN invasion risks. Consequently, the use of healthy substrates in nurseries may prevent plant-parasitic nematode induction in orchards.

International audience; Root-knot nematodes are a growing concern for vegetable producers, because chemical nematicides are gradually disappearing. Alternative techniques based on agronomic practices are needed to solve the problem. This review analyzes the most recent studies related to these techniques and their combinations and identifies the most effective ones. Based on an agronomic point of view, the analysis focuses on a description of agricultural factors and practices, rather than on biological processes. Several alternative techniques are considered, including sanitation, soil management, organic amendments, fertilization, biological control and heat-based methods. We analyzed the effects of each practice and interactions among techniques and found large variations among studies. Many practices are only partially effective for nematode control; thus, combining control methods in a systemic analysis presents a challenge. We outline such an ongoing systemic approach and identify key future research studies.

Nematodes belonging to the genus Meloidogyne are the most ubiquitous and widespread plant-parasitic nematodes. They occur worldwide, are polyphagous and can parasitize most cultivated plants leading to reduced crop yields. They are especially harmful in developing countries because of the lack of suitable and feasible management strategies. Among all the control practices (chemicals, physical techniques, cultural practices, resistance), the use of natural enemies as biological control agents is the most recently developed. Pasteuria penetrans which is an obligate Gram-positive, endospore-forming bacterium, is perhaps the most promising plant-parasitic nematode biocontrol agent. Despite much research conducted on prey–predator interactions (host–parasite specificity, mechanisms of attachment, field efficacy), the influence of the soil environment on host–parasite interactions is poorly understood even when the soil appears to be the key factor. Beyond common studies on the influence of climatic conditions on the attachment of endospores of P. penetrans to nematodes, more knowledge about the systemic interactions between plants, soil water dynamics, soil texture and structure, and other biota on the parasitism of nematodes by P. penetrans would improve their utilization as biological control agents. The aim of this review is to analyze the literature dealing with the influence of the soil on nematode – P. penetrans interactions in order to suggest a helpful conceptual model based on partitioning the Pasteuria population in sub-populations according to their soil habitat (dispersible and non-dispersible aggregates, microporosity, macroporosity), not all of them being available for attachment and infection on nematodes. Such concerns should be taken into account by epidemiologists for improving biological management strategies based on the use of this bacterium.

International audience; Knowing which factors affect the distribution of organisms provides useful insights for the management of biodiversity. For root-knot nematodes Meloidogyne (RKN), a critical threat in agriculture, an understanding of the constraints that impact their diversity is a fundamental prerequisite for their control. RKN are reported to be major pests on olive trees, mainly in high-density orchards and in nurseries. This study was undertaken in order to characterise the Meloidogyne species associated with olive trees in Morocco and to consider how anthropogenic stresses and some edaphic and climatic factors may be involved in their spatial distribution. A soil sampling was conducted in the main olive growing areas in Morocco, including wild, feral and cultivated olive trees. RKN were detected in 12.2% of the samples. The analysis of biochemical (esterase patterns) and molecular (SCARS, D2D3) markers revealed the occurrence of M. javanica (as the predominant species), M. arenaria, M. hapla,M. spartelensis and of an undescribed species Meloidogyne n.sp. Some esterase variability was detected in M. javanica and M. hapla populations. The RKN species were distributed everywhere on an aggregated basis. However, M. javanica was recorded in high abundance throughout the cultivated areas in Morocco in high-density and traditionally cultivated olive orchards and rarely on some feral olive, while the other species were detected in low abundance on wild olive in mountain plant refuge areas in northern and southern Morocco. Nevertheless, the large distribution of M. javanica in cultivated areas could be primarily due to widespread introductions from nurseries, followed by multiple founder processes favoured by local conditions such as irrigation and planting density. In contrast, the detection of the other species hosted by wild olive only in plant refuge areas suggest that these areas host ancestral nematode species that did not disperse in the absence of human activities.

Farming activities that are likely to induce the development of emerging pests increasingly disturbs the Argan Biosphere in Morocco. Considering that plant-parasitic nematodes strongly contribute to the decrease in plant growth production, a survey was conducted in the Argan Biosphere in order to assess nematode diversity and distribution. It was established that the parasitic nematofauna was rich, with 70 species belonging to 34 genera and 12 families. Species with high plant decay potential belonging to Longidoridae, Heteroderidae, Hoplolaimidae, Meloidogynidae, Paratylenchidae and Pratylenchidae are present in the argan forest. Telotylenchus sp., Paratylenchus microdorus and Paratylenchus veruculatus , Xiphinema italiae and Xiphinema pachtaicum (virus-transmitting nematodes), and Helicotylenchus crassatus are the most dominant species. Populations of root-knot ( Meloidogyne spp.) and lesion ( Pratylenchus spp.) nematodes are also present. Climate forces have driven the structuration of the argan forest to topoclimatic landscapes that led the diversity of the plant-parasitic nematodes communities. The north–south typology of the arid climate affects the richness and the taxonomic and functional diversity of nematodes, while the west–east temperature typology mainly affects the abundance of nematodes, especially of colonizing species. The emergence of plant-parasitic nematode problems as a consequence of intensive agroforestry or argan orchard development is considered.

The epidemiology of Pasteuria penetrans, parasite of Meloidogyne javanica, was studied in a field cultivated with an African egg-plant (Solanum aethiopicum) in Senegal. Abiotic and biological parameters were analyzed from 100 soil samples. Soil physical characteristics were studied with principal component analysis (PCA). Similarity between the parameters according to biotic and abiotic variables was established by hierarchical classification and corroborated by Discrimin analysis (AFD). The coarser fractions (> 200 mu m) were positively correlated to intensive irrigation, whereas finest fractions (< 20 mu m) and spores of P. penetrans were abundant in the areas moderately irrigated. Furthermore, the proportion of Pasteuria-infected juveniles was positively correlated to the presence of finest texture and high water holding capacity. The abundance of M. javanica was associated with coarse sands and potassium. Based on these results, laboratory experiments were attempted on the influence of irrigation and soil texture on the distribution of P. penetrans in cultivated and bare soils. The results showed that 53% of the spores inoculated were leached by water flow in the sandy soil, but only 14% in the sandy-clay soil and 0.1% in the clay soil. No nematodes survived in the clay soil, while the population increased both in the sandy and the sandy-clay soils. More M. javanica were infected by P. penetrans in the sandy-clay soil than in the sandy soil. Comparing different combinations of bare soils containing 1.1-57% clay, the best spore percolation/retention balance occurred in soils textured with 10-30% clay.

International audience; Soil is a component of primary importance in crop production, even if it is often neglected, or only regarded as a physical support for the growth of plants. However, with the increasing societal concerns for the sustainability of agriculture, soil must be considered as a living system. Its quality results from the multiple interactions among physicochemical and biological components, notably the microbial communities, primordial for soil function. Crops are threatened by soil-borne diseases. These are often difficult to control, because of the “hidden” status of the pathogens and also because of the absence, noxiousness or lack of efficacy of chemical treatments. In this context, there is a renewed interest for cultural practices such as the use of organic amendments. These practices have a strong influence on soil health, which takes into account plant health, through both changes of physicochemical characteristics and influence on soil microbial communities. Cultural practices are used to improve soil health, and can, in some cases, increase soil disease suppression. The effects of these practices on soil properties have been studied, but the relationship between these properties and soil suppressiveness has not been always very clear. Many different soil descriptors, either abiotic or biotic, have been used to describe the soil health and suppressiveness, but there is a lack of identified, reliable and consistent indicators. One aim of this review is to show that, despite the age of the soil health concept and all the studies that have been conducted, there are still no guidelines for assessment of soil quality from the plant health point of view. Obviously, the extreme diversity of situations makes any generalisation from a given case-study difficult. However, based on what has already been done in related fields, a methodology to search for indicators of soil health can be proposed. In this review we will present (i) how a healthy soil can be defined and what are the concepts hidden behind the words “soil health,” (ii) which cultural practices have been used to control soil-borne diseases and their limitations, (iii) which soil parameters have been measured when studying soil suppressiveness, and which relationships have been found between these parameters, and finally (iv) how these descriptors could become indicators of soil health, using appropriate analytical and statistical methods.

Summary In Senegal, a study was carried out in a field cultivated with African egg-plant ( Solanum aethiopicum ) in order (1) to determine soil size fractions infested both with Meloidogyne javanica and Pasteuria , (2) to compare the efficacy of soil fraction dispersion methods in the recovery of both organisms and (3) to estimate the concomitant distribution of the two organisms in the different soil fraction sizes. Samples were taken from four areas: severely-infested (M+) with M. javanica with a high percentage (I+) of Pasteuria -infected juveniles, severely-infested (M+) with a low percentage of infected juveniles (I−), minimally-infested (M−) with a high percentage of infected juveniles (I+) and minimally-infested (M−) with a low percentage of infected juveniles (I−). The samples were dispersed and fractionated using two different techniques in order to evaluate soil aggregation (size fractions >200, 50–200, 20–50 and 0–20 μm). The numbers of free entities of Pasteuria penetrans were estimated per size fractions. The proportion of Pasteuria -infected juveniles (biological detection of P. penetrans ) was estimated in order to correlate the infection rate to the distribution of free entities of P. penetrans . Regardless of sampling area, the 50–200 μm size fraction predominated, followed by largest particle (>200 μm) size. The distribution of Pasteuria spores in the soil was not linearly correlated to the distribution of Pasteuria -infected juveniles. The influence of the soil characteristics on the relationship between the two organisms is discussed.

Pasteuria penetrans, a bacterial parasite of plant-parasitic nematodes, is used to control root-knot nematode Meloidogyne spp. populations in vegetable crops. But its efficiency is variable, mostly because of the patchy distribution of the bacteria in arable fields. As the infective P. penetrans are non-motile bacteria in soil, abiotic soil factors can affect the bacteria–nematode relationships. An epidemiological study, conducted in a vegetable field, showed that abiotic factors such as irrigation, soil water holding capacity and texture, affected the efficiency of P. penetrans. A correspondence analysis between these abiotic factors and the density of P. penetrans spores in the soil, and the proportion of Meloidogyne javanica juveniles infected by the bacteria, revealed that irrigation affected directly the distribution of the spores in soil pores related to their passive transport by water flow. Laboratory experiments conducted on the passive transport of spores confirmed that intensive irrigation leached the spores down the soil profile and decreased the percentage of infected Meloidogyne juveniles.

The transport of the spores of Pasteuria penetrans was studied in three contrasted textured soils (a sandy, a sandy-clay and a clay soils), cultivated with tomato, inoculated with juveniles of Meloidogyne javanica and watered with 25 or 150 mm day−1. One month after inoculation of the nematodes, 53% of the spores inoculated were leached by water flow in the sandy soil but only 14% in the sandy-clay soil and 0.1% in the clay soil. No nematodes survived in the clay soil, while the population was multiplied both in the sandy and in the sandy-clay soils. But juveniles of M. javanica were more infected by P. penetrans in the sandy-clay soil than in the sandy soil. Comparing different combinations of bare soils containing 1.1–57% of clay showed that the best spore percolation and retention balance occurred in soils amended with 10–30% clay. However, the spore recoveries decreased when the soil was enriched with more than 30% clay. The role of clay particles on the extractability of spores and on their availability to attach to the nematode cuticle in the soil is discussed.

International audience; Plant-parasitic nematodes affect significantly the production of susceptible plants, including olive trees. In this context, nematode communities were determined in soil samples collected from 23 olive growing sites in the Haouz and Souss regions (southern Morocco). These sites corresponded to various modalities: wild (Olea europaea L. ssp. sylvestris) or cropped olive (Olea. europaea L. ssp. europaea), traditional or high-density cropping, rainfed or irrigated. Even free-living nematodes prevailed in most of the sites, high population levels of plant-parasitic nematodes were observed in rainfed cropping systems than in irrigated systems. Ten nematode families and 14 genera were identified. The most important plant-parasitic nematodes detected, in order decreasing frequency of infestation (percentage of samples), were spiral nematodes Helicotylenchus spp. (100%) and Rotylenchus spp. (87%), lesion nematodes Pratylenchus spp. (100%) and root-knot nematodes Meloidogyne spp. (40%). Most of the nematode species were assigned to more or less colonizer nematodes, whereas only one family (Longidoridae) was assigned to persistent nematodes. Considering the two producing areas, plant-parasitic nematodes were significantly more abundant in the Souss region than in the Haouz region, but nematode diversity was higher in the second one. The prevalence of Meloidogyne spp. in the Haouz region would be related to the predominance of irrigated cropping systems in this region. Hoplolaimidae nematodes (Helicotylenchus spp. and Rotylenchus spp.) are better adapted to rainfed conditions that prevail in the Souss region. Co-inertia analysis showed the importance of soil physic-chemical characteristics (e.g., pH, texture and nutrients) on the structure of the plant-parasitic nematode community patterns. The high occurrence of Helicotylenchus spp. in olive orchards may be induced by fertilization. Aphelenchoides spp., Gracilacus spp., Pratylenchus spp., Rotylenchidae and Tylenchidae were supported by coarse textures as it was observed in the Souss region.

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.

New developments in the estimation of free spores of #Pasteuria penetrans$, a hyperparasite of plant-parasitic nematodes, including #Meloidogyne$ spp., have been tested in contrasted textured soils. They were dedicated to improving the recovery of spores. Different methods of increasing energy of aggregate dispersion were compared in their efficiency in recovering spores inoculated in a sandy clay soil and a clay soil. The dispersion of the soils by the less energetic method (method A) allowed only 50% and 20% of the spore inoculum to be recovered from the sandy clay soil and clay soil, respectively. For these soils, 76% and 81% of the particle-size fraction (0-20 micrometers) isolated by this method were still aggregated in coarser structures. With increasing energy (methods B and C), these coarse aggregates disappeared entirely in both soils. At the same time, the recovery of spores increased sharply, representing about 87% and 75% of the inoculum of the sandy clay soil and clay soil, respectively. Therefore, at most 25% of the pool of spores remained undetectable. The formation of artificial aggregates during the enumeration procedure could not be advocated to explain this result, since the dispersion of the fraction collected for the enumeration did not improve spore recovery. (Résumé d'auteur)

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.

Plant-parasitic nematodes are involved in soil fatigue processes in coastal foredunes and, therefore, have an impact on the growth of plants such as marram grass ( Ammophila arenaria ) that enhance sand accretion and the stabilisation of dunes. Transects were sampled in European Atlantic and Mediterranean foredunes at different locations. Plant-parasitic nematode communities and physico-chemical soil properties were analysed, and multivariate techniques were used to link them. Although all the dunes are of sandy texture, the Atlantic and Mediterranean dunes mainly differ by their ratio of coarse and fine sands. Mediterranean dunes, although more disturbed by storms than the Atlantic dunes, have fine-textured soils that can accumulate organic matter. They trap a large amount of minerals and have a high carbonate concentration due to the salinity of the Mediterranean Sea. As a result of the higher content of coarse sand in the top horizons, probably due to a higher accretion of sand, Atlantic foredune soils are low in organic matter and minerals. Soils from North and Irish Sea dunes have intermediate characteristics. These soil contrasts lead to specific plant-parasitic nematode communities. Thus, nematodes such as Hemicycliophora spp., Neodolichorhynchus spp., Longidorus spp. and Merlinius spp. generally colonise the carbonated and mineralised soils of the Mediterranean dunes, and do not seem to be affected by high salinity. Conversely, populations of Meloidogyne spp. and Pratylenchus spp. nematodes are more commonly found in coarse textured soils and the oligotrophic conditions that occur in Atlantic dunes. Specific local conditions such as the presence of paleosols do not seem to disturb them. Considering that both nematode species are major pests in cropping systems, higher population levels due to their fit to such soil characteristics can explain their contribution to soil fatigue encountered in Atlantic dunes.

International audience; Little is known about the variations of nematode mitogenomes (mtDNA). Sequencing a complete mtDNA using a PCR approach remains a challenge due to frequent genome reorganizations and low sequence similarities between divergent nematode lineages. Here, a genome skimming approach based on HiSeq sequencing (shotgun) was used to assemble de novo the first complete mtDNA sequence of a root-knot nematode (Meloidogyne graminicola). An AT-rich genome (84.3%) of 20,030 bp was obtained with a mean sequencing depth superior to 300. Thirty-six genes were identified with a semi-automated approach. A comparison with a gene map of the M. javanica mitochondrial genome indicates that the gene order is conserved within this nematode lineage. However, deep genome rearrangements were observed when comparing with other species of the superfamily Hoplolaimoidea. Repeat elements of 111 bp and 94 bp were found in a long non-coding region of 7.5 kb, as similarly reported in M. javanica and M. hapla. This study points out the power of next generation sequencing to produce complete mitochondrial genomes, even without a reference sequence, and possibly opening new avenues for species/race identification, phylogenetics and population genetics of nematodes.; Il existe peu de connaissances sur la variation des génomes mitochondriaux de nématodes, car leur séquençage avec une approche PCR reste difficile du fait de fréquentes réorganisations génomiques et de la faible similitude de séquence entre des lignées divergentes. Nous avons utilisé une approche d’écrémage de génome pour assembler la première séquence mitochondriale complète d’un nématode à galles (Meloidogyne graminicola). Un génome riche en AT (84,3 %) de 20 030 paires de bases (pb) a été obtenu avec une profondeur de séquençage supérieure à 300. Trente-six gènes ont été identifiés selon une approche semi-automatisée. La comparaison de cette séquence avec la carte physique du génome mitochondrial de M. javanica indique que l’ordre des gènes est conservé chez Meloidogyne. Toutefois, des réarrangements génomiques importants ont été observés entre genres de la superfamille Hoplolaimoidea. Des éléments répétés de 111 et 94 pb ont été détectés dans une longue région non codante d’environ 7500 pb, comme rapporté chez M. javanica et M. hapla. Cette étude montre le potentiel du séquençage de nouvelle génération pour produire rapidement des génomes mitochondriaux complets, même en l’absence de séquence de référence. Ceci ouvre des perspectives dans les domaines de l’identification d’espèces/races, de la phylogénie et de la génétique des populations de nématodes.

Different species ofArthrobotrys nematophagous fungi and several strains ofA. oligospora have been studied for their antagonistic effects against nematodes of the genusMeloidogyne, important pests of vegetables. All fungi trappedM. mayaguensis andM. incognita juvenilesin vitro but had no effect on the juveniles ofM. javanica. In pot experiments withM. mayaguensis, all fungi reduced the nematode populations and stimulated the growth of tomato seedlings. In a field trial, a strain of A.oligospora, isolated in Senegal and incorporated into compost blocks, was efficient in increasing the tomato seedling growth. The introduction of nematophagous fungi in compost blocks as a biological biocontrol technique against phytophagous nematodes adapted for developing countries is discussed.

Two strains (ORS 18692 S7 and ORS 18692 S5) of the nematophagous fungus Arthrobotrys oligospora have been isolated for the first time in Senegal. In vitro, both strains trapped 98% of groups of 7-day-old Meloidogyne mayaguensis juveniles within 48 h. Their optimal growth occurred at 25-30 C and at a pH of 5.6, but salinity inhibited their development. In order to test the fungi on M. mayaguensis in pots and in mixed populations of Meloidogyne spp. on tomato in the field, the fungus was incorporated into compost blocks before sowing and subsequent transplanting. In pot experiments during the cool season (28 C), both strains reduced nematode populations and stimulated seedling growth. In field trials during the hot season (35 C), both strains were efficient in reducing Meloidogyne populations. The feasibility of combining the use of compost blocks with the introduction of A. oligospora is discussed. Pour la premie re fois, deux souches du champignon ne matophage Arthrobotrys oligospora (souches ORS 18692 S5...

The susceptibility of two acacias (Acacia holosericea and A. seyal) against the root-knot nematode Meloiodogyne javanica has been studied. The nematode was inoculated at different rates (1000, 5000 and 10,000 second stage juveniles per seedling). In both acacias, M. javanica inhibited seedling height, shoot and root biomass and the density of root tips per mg of root. In terms of nematode development, the increase of M. javanica was greater on A. holosericea than on A. seyal when the inoculum rate was 1000 J2 per seedling indicating that A. holosericea is a better host for M. javanica than A. seyal.

Root-knot nematodes belonging to the Meloidogyne genus are ubiquitous plant-parasitic pests, especially on vegetables. The Pasteuria penetrans bacterium is an obligate parasite of nematodes, parasitizing most of the Meloidogyne species. Spatial distributions of Meloidogyne javanica populations infested or not by P. penetrans and of bacterial populations were studied in a vegetable plot naturally infested by these organisms. It was observed that distributions of M. javanica populations, of populations infested by P. penetrans, and of free bacteria populations were not overlapped. Soil factors involved were investigated. Soil texture and water flow in porosity are concerned, as they directly influence the level of the pool of bacteria and then the chances of both organisms to meet. The soil solution has a direct effect on the attachment of the bacterium on the nematode cuticle.

The nematodes specificities and their interactions with plants are reviewed, considering host plants quality and compatibility. The potentials of nematode resistance and diversity of antagonists and parasitism are discussed, in relation to host specificity and obligate multitrophic relationships. The ecology and management of nematode communities are also reviewed, focusing on soil health approaches and new paradigms for plant protection.

Tsetse flies transmit African trypanosomes, responsible for sleeping sickness in humans and nagana in animals. This disease affects many people with considerable impact on public health and economy in sub-Saharan Africa, whereas trypanosomes' resistance to drugs is rising. The symbiont Sodalis glossinidius is considered to play a role in the ability of the fly to acquire trypanosomes. Different species of Glossina were shown to harbor genetically distinct populations of S. glossinidius. We therefore investigated whether vector competence for a given trypanosome species could be linked to the presence of specific genotypes of S. glossinidius. Glossina palpalis gambiensis individuals were fed on blood infected either with Trypanosoma brucei gambiense or Trypanosoma brucei brucei. The genetic diversity of S. glossinidius strains isolated from infected and noninfected dissected flies was investigated using amplified fragment length polymorphism markers. Correspondence between occurrence of these markers and parasite establishment was analyzed using multivariate analysis. Sodalis glossinidius strains isolated from T. brucei gambiense-infected flies clustered differently than that isolated from T. brucei brucei-infected individuals. The ability of T. brucei gambiense and T. brucei brucei to establish in G. palpalis gambiensis insect midgut is statistically linked to the presence of specific genotypes of S. glossinidius. This could explain variations in Glossina vector competence in the wild. Then, assessment of the prevalence of specific S. glossinidius genotypes could lead to novel risk management strategies.

International audience; The current restrictions on the use of chemical nematicides have contributed to increased root-knot nematodes (Meloidogyne spp.) problems in horticultural crops. In this context, plant resistance (R) appears as the most effective method of control, but the restricted number of cultivated vegetable species with root-knot nematode R-genes available (tomato, pepper), and the possible occurrence of virulent nematodes able to reproduce on R-plants may constitute a severe threat to this control strategy. To increase the sustainability of the protection, a scientific challenge exists in building cropping strategies based on the combination of genetic resistance with cultivation practices. Our projects aimed at assessing such innovative strategies in a multi-site device in research stations and commercial farms. First, we looked at three components of crop protection, i.e., R-efficiency, R-durability, and sustainability of rotating cultivation. Overall, a constant hierarchy of management strategies was observed, with Pyramyding > Alternating > Mixture of R-genes > Sequential use of a single R-gene introgressed in a susceptible background. We are currently analysing (1) the impact of agronomic practices on the parasite pressure in the soil and on ecological diversity including other nematode species, (2) the linkage between reduction of Meloidogyne populations in the soil and increase of R-genes durability, and (3) the sustainability assessment of such varietal and technical innovations. Multidisciplinary approaches were combined to foster synergistic and long-term goals. The diversity of partners and associated forces brought all the complementary expertise needed for answering specific short-term questions as well as generic mid- to long-term expectations.

A été étudiée l'action d'isolats bactériens au champignon nématophage #Arthrobotrys oligospora$ ORS 18692 S7 isolé au Sénégal sur le développement du champignon (croissance saprophytique et activité prédatrice), la multiplication d'une population de #Meloidogyne mayaguensis$ sur des plants de tomate, et la croissance de la plante hôte. Trois isolats bactériens ont été capables de stimuler in vitro l'activité prédatrice du champignon et de réduire le développement d'une population de #M. mayaguensis$ sur des plants de tomate cultivés en pots. Ces bactéries ont été nommées bactéries auxiliaires de champignons nématophages (BAN). Les critères permettant de distinguer ces organismes des autres bactéries rhizosophériques n'ont pu être mis en évidence. L'utilisation des BAN pour le contrôle biologique des nématodes est discutée. (Résumé d'auteur)

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.