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Nitrogen amendments are often used to alleviate damage to rice plants caused by plant-parasitic nematodes. The population development of the endoparasitic nematode Hirschmanniella oryzae was followed on irrigated rice ( Oryza sativa cv. indica IR-13240-108-2-2-3) cultivated in containers, each supplemented with one of three nitrogen amendments ( N 0 = 0, N 1 = 80 and N 2 = 160 kg ha −1 ) applied in the form of urea. The effects of nitrogen concentration on irrigated rice growth were determined with plants cultivated in soils either infested ( I 1 ) or uninfested ( I 0 ) with nematodes. Populations of H. oryzae continued to increase in both soil and roots throughout the crop cycle. Nitrogen was without effect on soil populations, but large root nematode population increases were observed with the N 1 nitrogen amendment. Interactions were observed between nematodes and nitrogen on the rice yield components, depending on the level of nitrogen applied. The average single grain weight was the main affected yield component; N 1 increased the weight of each grain, but this effect was largely reduced in the presence of H. oryzae . Even though nitrogen amendments were able to counterbalance the negative effects of H. oryzae , nitrogen applied at the N 1 level was not considered a sustainable alternative because it increased nematode populations. Root nematode populations with nitrogen applied at the N 2 level were similar to those observed with N 0 . However, at the N 2 level, nitrogen induced spikelet sterility and the plant physiological disturbances caused by excessive in-soil nitrogen would prevent multiplication of H. oryzae root populations.

Abstract An aqueous extract from leaves of Crotalaria virgulata subsp. grantiana was assayed for its effects on second-stage juveniles of Meloidogyne incognita. The biological activity was nematostatic; nematodes were not killed but were completely paralysed in a 1 mg/ml (w/v) extract: the LD50 equivalent was estimated to be 0.5 mg/ml. The effect was reversible: juveniles previously paralysed by C. grantiana extract recovered complete mobility in water and were able to infest a susceptible tomato plant. Freeze-dried aqueous extract from C. grantiana leaves added to a sterile sandy substrate at 1 mg/ml protected susceptible tomato plants from M. incognita infestation. This suggests a promising use of C. grantiana as both a green manure and natural alternative to synthetic chemicals in nematode population control, especially in integrated pest management for vegetable crops in organic agriculture of tropical and temperate areas.

The in vitro paralysis of second-stage juveniles of Meloidogyne incognita, M. javanica and M. mayaguensis by aqueous extracts of 15 West African Crotalaria species was analysed. A multivariate analysis distinguished four groups, based on their nematostatic activity: i) C. glaucoides extracts were not active; ii) the root extracts from C. goreensis, C. lathyroides and C. perrottetii were more active than the shoot extracts; iii) the shoot extracts from C. comosa and C. cylindrocarpa were more active than the root extracts; iv) both shoot and root extracts of C. atrorubens, C. barkae, C. grantiana, C. hyssopifolia, C. pallida, C. podocarpa, C. retusa, C. senegalensis and C. sphaerocarpa have nematostatic effects depending on either the Crotalaria species or plant tissue from which the extracts were derived. However, considering the greater biomass contribution of the leaves and stems compared to the roots when the plants are used as green manure, C. barkae, C. grantiana, C. pallida and C. podocarpa are the most efficient Crotalaria species, whatever the Meloidogyne species targeted.

International audience; Oral communication. Jourand P., Rapior S., Fargette M. et Mateille T. Nematostatic effects of a leaf extract from Crotalaria virgulata subsp. grantiana on Meloidogyne incognita and its use to protect tomato roots. Nematology, 6, 79-84 (2004a). Jourand P., Rapior S., Fargette M. et Mateille T. Nematostatic activity of aqueous extracts of West African Crotalaria species. Nematology, 6, 765-771 (2004b). JOURAND Philippe. Les Légumineuses du genre Crotalaria : symbiose fixatrice d’azote et activités biologiques contre les nématodes phytoparasites. - Doctorat de l'Université Montpellier II. Formation doctorale : développement et adaptation des plantes. Ecole doctorale : biologie intégrative. - Jury : B. Dreyfus (Co-directeur), S. Rapior (Co-directeur), M. Lebrun, B. Ollivier, P. Abad, G. Germani, T. Mateille. Rapporteurs : P. Abad, B. Ollivier.

The effects of the inoculation of two fluorescent Pseudomonas strains (P. mendocina and Pseudomonas sp.) on the soil aggregation in the rhizosphere have been tested. Their indirect effects on the conservation of spores of Pasteuria penetrans, a bacterial endospore-forming parasite of plant-parasitic nematodes Meloidogyne spp., and on the infection of Meloidogyne javanica juveniles were investigated. The amount of rhizosphere soil adhering to the root systems was higher in the soils inoculated with both bacterial strains P. mendocina and Pseudomonas sp. However, juveniles of Meloidogyne were more numerous in the soil inoculated with Pseudomonas sp. and the multiplication rate of M. javanica did not differ regardless of the treatment. Furthermore, the proportion of juveniles infested by P. penetrans spores was highest in soil inoculated with P. mendocina (B23). The spores were distributed, following a similar pattern in the soil aggregate fractions excepted in the soil inoculated with P. mendocina (B23). In the soil inoculated with B23, about 50% of the spores present in the rhizosphere were retained in the coarser structure characterized by aggregates >200 μm. The role of the bacterial extracellular polysaccharides on soil and spores aggregation and on the Meloidogyne infection may explain these results.

Des prospections nématologiques ont été réalisées dans les régions de production maraîchère de deux pays sahéliens, le Burkina Faso et le Sénégal. Des analyses de correspondances entre quelques facteurs agronomiques et les populations de Meloidogyne spp. ont montré que les niveaux des populations telluriques et racinaires n'étaient pas exclusivement liées à la sensibilité des cultures maraîchères en place, mais dépendaient aussi des précédents culturaux ou des agrosystèmes (terres inondées ou exondées) qui prévalent dans ces régions. En outre, la présence de micro-organismes parasites des nématodes (champignons nématophages et Pasteuria penetrans) dans les agrosystèmes de terres exondées, permet d'envisager l'intégration de méthodes de contrôle biologique à l'aide d'hyperparasites indigènes aux méthodes de lutte culturale. Impact of agronomic factors on Meloidogyne spp. populations and their most common parasites in Sahelian vegetable cropping systems - Nematode surveys were carried out in vegetable producing areas in two Sahelian countries, Burkina Faso and Senegal. Correspondence analysis between agronomical factors and populations of Meloidogyne spp. revealed that vegetable susceptibility to nematodes was not the only factor responsible for soil and root infestations. Population densities would more readily depend on cropping systems (previous crops, often flooded lowlands vs well drained uplands). Natural occurrence of nematode-parasitic microorganisms (nematophagous fungi and Pasteuria penetrans) in upland agrosystems was observed and could be used together with cultural practices in an IPM approach.

Abstract L'évolution des populations de Meloidogyne javanica et de Scutellonema cavenessi a été suivie au cours de cinq cycles culturaux alternant des plantes sensibles (tomate, niébé ou plantes adventices) ou non sensibles (arachide et mil) à Meloidogyne spp. Alors que les cultures non sensibles ne permettent effectivement pas la multiplication de M. javanica, toutes les cultures sont sensibles à S. cavenessi. L'opportunité de méthodes de lutte culturale à l'aide de plantes résistantes à Meloidogyne spp. dans des systèmes de cultures susceptibles de modifier la composition des peuplements nématologiques est discutée. Development of Meloidogyne javanica and Scutellonema cavenessi populations in vegetable crop systems in Senegal - Populations of Meloidogyne javanica and Scutellonema cavenessi were analysed during five cycles alternating crops susceptible (tomato, cowpea or weeds) or not susceptible (groundnut and millet) to Meloidogyne spp. Even though the non-susceptible crops did not effectively allow the multiplication of M. javanica, all the crops were susceptible to S. cavenessi. The potential of cultural control methods with plants resistant to Meloidogyne spp. in agrosystems including crops which can modify the nematode communities is discussed.

The susceptibility of bananas to phytoparasitic nematodes, the damages caused by nematodes, and the plant defense reactions can be evaluated respectively by the multiplication rate of parasites, the plant growth and metabolism, and the modifications of the secondary metabolism. The comparison, through multivariate analyses, of these four groups of parameters between two banana cultivars (Poyo and Gros Michel), differently susceptible to nematodes, helps to hierarchize the importance of these groups. So, the variables associated with shoot and root growth and the variables associated with plant physiology (photosynthesis, carbon metabolism, nitrogen and mineral absorption) are quite bad parameters because they evolve anarchically with the initial nematode population pressure. On the opposite, the final nematode population pressure and the variables associated with host defense reactions (secondary metabolism) are more reliable because they give more homogeneous results. It is then possible to assess the usefulness of the parameters describing banana susceptibility to nematodes and to give reliable criteria to geneticians for nematode resistance breeding programs. Key words: banana, defense reactions, phytoparasitic nematodes, resistance, tolerance, cultivar behaviour. [Traduit par la rédaction]

Les recherches menees sur l'incidence des nematodes sur la croissance et la physiologie des plantes parasitees concernent essentiellement la nutrition minerale, en relation avec l'alimentation hydrique, la photosynthese, la respiration et les biosyntheses qui lui sont liees. D'autres etudes, a la frontiere entre la biologie du nematode et son impact parasitaire, concernent les mecanismes d'attraction des nematodes par les exsudats racinaires. Enfin, la nutrition azotee, dependante de l'association de symbiotes avec la plante, et, elle aussi, sujette a des perturbations par les nematodes phytoparasites. Bien que les connaissances acquises a ce jour soient eparses, et les mecanismes physiologiques mis en cause tres vastes, les niveaux d'invervention des nematodes sur la biologie des plantes sont divers et vraisemblablement lies. La litterature presente de nombreux resultats sur les mecanismes de defense des plantes contre les nematodes parasites, mais les syntheses sont rares. L'objectif de cette revue bibliographique est, d'une part d'actualiser les recherches menees dans ce domaine, d'autre part de structurer les connaissances acquises afin d'en degager un principe plus general. Cette analyse decrit l'intervention d'un metabolisme hormonal, mettant en jeu des regulations auxiniques, cytokiniques ou ethyleniques, et d'un metabolisme phenolique, qui mene a la formation de substances i) directement toxiques envers les nematodes (e.g. phytoalexines), ii) regulatrices des reactions de defense (balance monophenols-polyphenols), iii) modifiant la structure tissulaire (e.g. lignines). Ces deux metabolismes sont sous la dependance de regulations enzymatiques (peroxydases, polyphenol oxydases, ammonia-lyases) qui repondent a la penetration et a la migration des nematodes dans les racines, et dont l'activite definit le degre de resistance des plantes aux nematodes.

Adventitious budding can be induced on two types of Pinus pinaster Ait. organs. Cotyledons (10-mm-long), derived from 8 to 10-day-old seedlings, show morpho-genetic response when an appropriate mineral solution is used (NH4+/K+= 1). Of the various cytokinin concentrations added to this optimal mineral medium, 0.8 μM BAP (6-benzylaminopurine), with 5 nM NAA (1-naphtaleneacetic acid), promoted organogenesis best. Buds were induced from outer mesophyll layers. Short shoots and the elongating needles (70-mm-long) were collected from cuttings of a mature tree (10-years-old). These cuttings benefited from physiological advantages of a well-developed root system (by heating the substrate). In order to stimulate in vitro organogenesis, they had been sprayed every week from March to May with 10 μM BAP. When cultivated in the presence of 10 μM BAP and 25 nM NAA, 79% of the explants produced buds from dome-shaped meristematic cell clusters that pre-existed at the top of the short shoots. Moreover, among these, 42% gave rise to adventitious buds induced from proliferating mesophyll cells at the needle base. The morphologies of the two kinds of shoots were similar. Adventitious budding on these two different explants should allow vegetative multiplication of selected seedlings and elite trees.

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.

Human activities increasingly frequent and persistent in ecosystems on one hand, and cropping system intensification on the other hand partly with radical methods to control pests and diseases of crops, raise questions about the ecological risks related to biotop changes, including disturbances of living organism communities. Plant-parasitic nematodes (PPN), microscopic round soil-borne worms that cause significant losses of crop production, are everywhere present in communities. They respond quickly to external forces (e.g. human and environmental) by changing the structure of their communities. In this thesis, we seek to better understand the effect of the factors involved in the assemblage of PPN species in communities associated with the Mediterranean olive tree and to determine the response of these communities to forces imposed by olive domestication, by crop intensification and by various environmental factors. The study was conducted in all olive-growing regions in Morocco (traditional low density and high density orchards), in refugia areas for wild olive (oleaster) and on feral olive trees. The soil and climatic factors that characterize the sampling sites were also considered. The analysis of the nematofauna revealed a wide species diversity, many species being described for the first time on olive tree, and a new species (Meloidogyne spartelensis) have been discovered. The diversity, the species / trophic / functional structure of the communities, the dominance of the taxa, and the community patterns are strongly affected by the various forces considered. The increasing anthropogenic gradient (wild vs feral vs traditional cultivation vs high-density cultivation) is the variable that mostly impacts the diversity by reducing the species richness and increasing the abundance of PPN. A particular attention was attributed in this study to the diversity of root-knot nematodes Meloidogyne, a major pest of the olive tree. It revealed that M. javanica is widespread in orchards and olive feral, while other species (M. arenaria, M. hapla and M. spartelensis) are confined in oleaster refuge areas. In order to analyse the genetic diversity, morphological and molecular markers have revealed a significant diversity between and within different Meloidogyne populations. These thesis studies confirm that both the diversity and the structure of the PPN communities could be relevant indicators to assess soil health in agro and ecosystems, by correlating diversity and pathogenicity of communities. They therefore emphasize the importance of parasite diversity as a main variable to consider for inspiring pest control strategies based on the concept of diversity resilience (even if it concerns parasites) for sustainable management of PPN communities and for environment preservation., Les interventions humaines de plus en plus fréquentes et persistantes dans les écosystèmes d'une part, et l'intensification des systèmes de cultures d'autre part qui s'accompagne pour partie de méthodes radicales pour combattre les bio-agresseurs des cultures, nous posent de multiples questions au sujet des risques écologiques liés aux changements des milieux, dont les perturbations induites sur les communautés d'organismes vivants. Les nématodes phytoparasites (NPP), vers ronds microscopiques telluriques qui occasionnent des pertes de production végétale importantes, sont partout présents en communautés. Ces nématodes répondent rapidement aux forçages extérieurs (e.g. anthropiques et environnementaux) par des modifications de la structure de leurs communautés. Par ce travail de thèse, nous cherchons à mieux comprendre l'effet des facteurs impliqués dans l'assemblage des espèces de NPP en communautés associées à l'olivier méditerranéen et à déterminer la réponse de ces communautés aux forçages imposés par la domestication de l'olivier, par l'intensification de sa culture et par différents facteurs environnementaux. L'étude a été réalisée au Maroc dans toutes les régions oléicoles (vergers traditionnels à faible densité et vergers à haute-densité), dans les zones refuge d'olivier sauvage (oléastre) et sur olivier féral. Les facteurs pédoclimatiques qui caractérisent les sites d'échantillonnage ont également été pris en considération. L'analyse de la nématofaune a révélé d'une grande diversité spécifique, de nombreuses espèces étant décrites pour la première fois sur olivier, et une nouvelle espèce (Meloidogyne spartelensis) ayant été découverte. La diversité, la composition taxonomique, trophique et fonctionnelle, la dominance des taxons, les patrons de communautés sont fortement affectés par les différents forçages pris en compte. Le gradient d'anthropisation croissante (sauvage vs féral vs cultivé traditionnel vs cultivé haute-densité) est la variable qui impacte le plus la diversité par réduction de la richesse spécifique et l'augmentation de l'abondance en NPP. L'étude a également porté une attention particulière sur la diversité des nématodes à galles des racines du genre Meloidogyne, un des principaux ravageurs de l'olivier. Elle a indiqué la dispersion de M. javanica dans les vergers et sur olivier féral, alors que d'autres espèces (M. arenaria, M. hapla et M. spartelensis) sont confinées dans les zones refuge des oléastres. Afin d'analyser la diversité génétique, des marqueurs morphologiques et moléculaires ont dévoilé d'une diversité importante entre et au sein des différentes populations de Meloidogyne. Les études diligentées dans le cadre de cette thèse confirment que la diversité et la structure des communautés de NPP pourraient être des indicateurs pertinents pour évaluer la santé des sols dans les agro et écosystèmes, en corrélant diversité et pathogénicité des communautés. Elles soulignent donc l'importance de la diversité parasitaire comme variable prioritaire à prendre en compte pour inspirer des stratégies de gestion des parasites basées sur le concept de résilience de la diversité (même s'il s'agit de parasites), pour une gestion durable des communautés de NPP et la préservation des milieux.