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Meloidogyne spp. and Hirschmanniella spp. are among the most damaging plant-parasitic nematodes (PPNs). They threaten rice production, the main staple food in Asia. Cropping systems that promote natural biocontrol and plant tolerance to diseases are put forward as sustainable solutions to protect rice from these pests. In particular, cropping systems managed under conservation agriculture (CA) are promising because they improve soil health and functioning. We investigated the effects of two cropping system components in a Cambodian field, (i) CA practices, i.e., no-tillage with a cover crop Stylosanthes guianensis (cv. Nina), versus conventional plow-based tillage with no cover crop, and (ii) using IR504, IR64, Azucena and Zhonghua 11 rice varieties, on PPNs in roots and on communities (bacteria, fungi and nematodes) in the rhizosphere. We used a sequencing approach via amplicon barcoding to target microbial marker genes (16 S and ITS rRNA gene) and a microscopic approach to identify and quantify nematodes in the rhizosphere compartment. The variety had less effect than agricultural practices on the infection by PPNs and on the assembly of the three rhizosphere communities. Under CA, the abundance of PPNs extracted from the roots was reduced by 88%. Soil quality was substantially improved (+83% of total Kjeldahl nitrogen, +34% of available phosphorus, +10% of exchangeable potassium, +110% of soil organic carbon, +30% for the cation exchange capacity), thus providing more basal resources for microbial decomposers, especially fungi (+164% putative saprotrophs). Characterization of the three rhizosphere communities revealed a shift in the structure associated with soil enrichment. Both microbial richness (+3% for bacteria and +38% for fungi) and diversity (Shannon index, +11% for fungi and +5% for nematodes) increased. The relative abundance of taxa was modified by CA with notably more mycorrhizal fungi (+329% Glomeromycota spp.) and fewer Pratylenchidae nematodes (−92% Hirschmanniella spp.) in the rhizosphere. The reassembly of the communities using CA was associated with regulation of PPN populations. The reduction in Meloidogyne spp. abundance in roots (−64%) was correlated with the maturity of the food web (maturity index, +10% under CA) and with the increase in the relative abundance of omnivorous nematodes in the rhizosphere (+68% under CA). Seven years of CA in this field enabled the whole soil food web to mature thus creating a favorable niche for potentially predatory nematodes and microbes antagonistic against PPNs. This study confirms that CA is an alternative to nematicides to limit infection by PPNs in rice cropping systems.

Agroecosystem plant diversification at the field scale has been shown to enhance ecological pest regulation. We explored the effects of plant community composition and soil properties on the soil nematode community, with a particular interest in the regulation of banana plant-parasitic nematodes (PPN). We monitored banana phytometers (Cavendish Grande Naine cultivar) in 85 plots distributed along a plant richness gradient. Plant community composition, soil properties, abundance of bacterivorous, fungivorous and proportion of predaceous soil free-living nematodes, and abundance and damage of PPN ( Radopholus similis , Pratylenchus coffeae , Helicotylenchus multicinctus , and Meloidogyne spp.) in phytometer roots were measured. We used structural equation modeling to investigate ecological processes leading to PPN regulation. Low-stratum plant species richness, but not high-stratum, was positively related to microbivore nematode abundances, supposedly because it promoted qualitative diversity of organic inputs and micro-climatic effects supporting more soil microorganisms. Musa genotype and low-stratum plant species richness induced associational susceptibility because of differential susceptibility of Musa genotypes to PPN and because of polyphagia of PPN spreading outside the Musa family, respectively. We found no regulation of PPN by predaceous nematodes, probably because food web complexity prevented trophic cascades from propagating. Ultimately, fungivorous nematode abundance was negatively related to PPN abundance, suggesting apparent competition or increased regulation by antagonistic fungi. Our results suggest that, when facing generalist pests, cropped plant communities should be diversified to promote pest regulation but must be carefully assembled to limit pest susceptibility heterogeneity among crop genotypes and to exclude alternative host plant species.

International audience; Understanding the influence of soil properties and cultural practices on the communities of plant-feeding nematodes (PFNs) in agrosystems is a prerequisite for cost-efficient and environment-friendly pest control. Although plantain is a staple food crop in the Caribbean, the relationships between PFN communities and environmental factors are poorly understood in plantain agrosystems. In this study, which was conducted in Martinique (French West Indies), we quantified the PFNs in 301 root samples taken from 53 plantain fields that differed in climate, edaphic conditions, and cultural practices. The physico-chemical properties were also determined for the soil in each field. Coinertia analysis (CI) and General Linear Mixed Models (GLMMS) were used to investigate the relationships between the PFN communities, soil properties, and cultural practices. Four nematode taxa were found in plantain roots: Radopholus similis, Pratylenchus coffeae, Helicotylenchus multicinctus, and Meloidogyne spp. The lesion nematode P. coffeae was the most prominent PFN species, followed by the burrowing nematode R. similis, root-knot nematodes Meloidogyne spp., and the spiral nematode H. multicinctus. P. coffeae was significantly more abundant in ferralsols and nitisols (which have a low organic matter content and a high exchangeable cation content) than in andosols (which have a high organic matter content). Nematode abundances were apparently affected by the previous crops e.g., P. coffeae was slightly more abundant in fields where tuber plants such as sweet potato, yam, or dasheen were the previous crop; R. similis was particularly abundant in fields where banana or plantain was the previous crop; and Meloidogyne spp. were abundant in fields where a market garden was the previous crop. The results of this study will be useful for the design of PFN control methods in plantain.

Rice production in Southeast Asia is significantly affected by root-parasitic nematodes (RPN). The Green Revolution has encouraged new agricultural practices (e.g. intensive monoculture, high yielding rice variety) to respond to the high rice demand; however, these methods have promoted the spread of these pests. The recent banning of chemical nematicides resulted in a need for alternative sustainable control strategies. In the present study, we assessed the effects of a direct-seeding mulch-based cropping system (DMC) vs conventional plough-based tillages (CT) on soil properties, rice yield and RPN communities during a two-year trial in Cambodia. Our results show that on average the population densities of RPN were significantly higher in DMC than in CT. Molecular identification revealed only two RPN species associated with roots: Meloidogyne graminicola, not previously reported from Cambodia, was predominant and was present throughout the plant’s development, whereas Hirschmanniella mucronata was only found at the tillering and milky stages. We conclude that DMC had a significant positive impact on rice yield, despite higher RPN short-term pressure. In order to increase the efficiency of such cropping systems, further studies and an evaluation of the long-term relationships between DMC, the nature of cover crops used, the soil biota including RPN, and rice yield should be conducted.

Cover crops are increasingly being used in agriculture, primarily for weed or erosion management. The addition of cover crops increases the primary productivity of the system and diversifies basal resources for higher trophic levels. How increases in the quality and quantity of basal resources affect bottom-up and top-down control remains a key question in soil food web ecology. We evaluated the response of the nematode community to the introduction of cover crops between rows of a banana plantation. We measured changes in nematode food web structure and inferred the prevalence of bottom-up and top-down effects on the abundance of phytophagous nematodes (i.e., plant-feeding and root-hair-feeding species) 1.5 years after plots with cover crops (Poaceae or Fabaceae species) or bare soil were established. The addition of a cover crop greatly affected the structure and the abundance of the soil nematode community 1.5 years after planting. The abundance of all trophic groups except for plant-feeding nematodes tended to increase with the addition of cover crops. The Shannon Weaver diversity index and the enrichment index increased with the addition of cover crops, indicating that opportunistic, bacterivorous and fungivorous nematodes benefited from the added resources. Plant-feeding nematodes were least abundant in plots with Poaceae cover crops, while bacterivorous, omnivorous, and root-hair-feeding nematodes were more abundant with Fabaceae cover crops than with bare soil, indicating that cover crop identity or quality greatly affected soil food web structure. Bottom-up effects on all trophic groups other than plant-feeding nematodes were evident with Poaceae cover crops, suggesting an top-down control of plant-feeding nematodes by omnivorous nematodes. Conversely, plant-feeding nematodes were evidently not suppressed in Fabaceae cover crops, perhaps because bottom-up effects on omnivorous nematodes were weaker (hence, top-down control by omnivorous nematodes was weaker), and because Fabaceae cover crops probably served as good hosts for some plant-feeding nematodes.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; Resistant rootstocks offer an alternative to pesticides for the control of soil pests. In Prunus spp., resistance loci to root-knot nematodes (RKN) have been mapped and a transformation method is needed to validate candidate genes. Our efforts have focused on the generation of transformed hairy-roots and composite plants appropriate for nematode infection assays. An efficient and reliable method using the A4R strain of Agrobacterium rhizogenes for the transformation of Prunus roots with an Egfp reporter gene is given. The rooting efficiency, depending on the genotypes, was maximal for the interspecific hybrid 253 (Myrobalan plum x almond-peach), susceptible to RKN, that was retained for subsequent studies. From the agro-inoculated cuttings, 72% produced roots, mainly at the basal section of the stem. Transformed roots were screened by microscope detection of Egfp fluorescence and molecular analyses of the integration of the transgene. The absence of residual agrobacteria in the plants was checked by the non-amplification of the chromosomal gene chvH. Egfp was expressed visually in 76% of the rooted plants. Isolated hairy roots in Petri dishes and composite plants (transformed roots and non-transformed aerial part) in soil containers were inoculated with the RKN Meloidogyne incognita. In both cases, root transformation did not affect the ability of the nematodes to develop in the root tissues. Our results showed that isolated hairy-roots can be used to validate candidate genes and the conditions in which composite plants offer a complementary system for studying the function of root genes in physiological conditions of whole plants are discussed.

Cover plant-based cropping systems have gained considerable attention over the last few years because of the recognized benefits of increasing the diversity of agrosystems to sustain services other than those pertaining to production. While agronomical tools and methods to assess these services in multispecies plant communities barely exist, trait-based approaches, originally developed in the field of comparative functional ecology, provide an appropriated framework to study the effects of plant diversity on agrosystems. The aim of this article is to discuss how a trait-based approach can be used to assess the services delivered in cover plant-based cropping system. We focus on semiperennial cropping systems based on cover plants, exemplified by the banana cropping systems. These systems are described in a first section to identify the services targeted. A second section, based on a literature survey, analyzes the processes associated with each service and identifies related effect traits of cover plants. A shortlist of markers to be used to assess agrosystem processes is proposed and hypothesis on trade-offs and synergies among services are formulated. In a third section, issues related to the scaling-up from plant traits to the services delivered by plant agricultural communities are discussed. Such an approach, originated in the field of ecology, appears highly promising to tackle agronomic issues and its application to agrosystems constitutes a challenging test of their genericity. It raises specific questions and stresses the need for new methodological developments, which could be part of a research agenda at the interface between the two disciplines.

Arabica coffees (60 % of current world coffee production) are generally sold at considerably better prices than robustas on account of superior beverage quality. However, costs of production are much higher, mainly due to more stringent demands for soil and climatic conditions, crop management, primary processing and control of several pests and diseases including the potentially very destructive coffee leaf rust (CLR) and berry disease (CBD). Breeding for disease resistance in combination with vigour, productivity and quality started in the early 1920s in India, but especially in the second half of the 20th century comprehensive breeding programmes have been implemented in several other coffee producing countries. Many of the resulting CLR- and CBD + CLR-resistant cultivars (true-breeding lines and F1 hybrids) meet the required standards of profitable and sustainable crop production. Challenges of more recent date include limited access to additional genetic resources of Coffea arabica, breakdown of host resistance to CLR, aggravating insect pest problems and the increasingly negative impact of climate change on arabica coffee production worldwide. This review discusses prospects of breeding and disseminating next generation (hybrid) cultivars of arabica coffee for sustainable coffee production under changing conditions of diseases, pests and climate. International networking on coffee breeding will facilitate sharing of resources (financial, genetic) and scientific information, application of genomics-assisted selection technologies, and pre-breeding for specific characters. Breeding and multiplication of new cultivars well adapted to the local environment will continue to be carried out at national or regional levels. A tree crop like arabica coffee does not lend itself to centralized variety development and dissemination on a global scale.

Suppression of plant-parasitic nematodes and decomposition of organic matter are important soil food web functions. The availability and nature of carbon substrates in soil drive the structure, dynamics, and activities of soil food webs and may alter the way they function in the ecosystem. In this study, we assessed the effects on nematode communities of incorporating litter from three cover crops with contrasting biochemical characteristics into soil taken from a banana field. The litter type influenced nematode taxa and functional guilds during the 90-day assay. The cellulose- and hemicellulose-rich litters of Crotalaria zanzibarica and Paspalum notatum induced similar nematode successions, causing bacterivorous and fungivorous nematode populations to increase early in the study period and promoting a fungal decomposition pathway at the end of the trial. These two litters were the most effective at decreasing the soil’s nematode infective potential with regard to major banana plant-parasitic nematodes, such as Pratylenchus coffeae , Helicotylenchus multicinctus , and Rotylenchulus reniformis . C. zanzibarica showed good potential as a green manure plant, as it increased the soil mineral nitrogen content during the 45 days following incorporation of litter. By contrast, litter from Acacia auriculiformis , which had high lignin content, induced immobilization of soil nitrogen and did not significantly increase microbivorous nematodes before day 45. This treatment failed to reduce the soil’s nematode infective potential for H. multicinctus and R. reniformis populations. Our study also showed that the dynamics of nitrogen mineralisation in soil were related to the C:N ratio of litters but not to the decomposition pathway. The biochemical characteristics of litters appear to be critical drivers of nematode ecological successions and decomposition pathways following plant litter amendments to soil taken from a banana field.

The African oil palm (Elaeis guineensis Jacq.) is grown on a total area of 16 million ha; but data on soil quality in mature oil palm plantations are fragmentary and data concerning biota are almost nonexistent. Consequently, no well-tested sampling method is available for soil diagnoses. We studied the spatial heterogeneity of the soil around the palm by measuring comprehensive soil quality in a 24-year-old oil palm plantation. Soil quality and litter were assessed in five zones with different plant cover, and different applications of herbicide or fertilizer. Physical-chemical characteristics, macrofauna, and nematofauna were analysed. A sampling method was developed and adapted to the way the cultivation practices are implemented: sampling by zone and weighting the plot mean by the respective area of each zone. The total density of macrofauna in the litter and in the 0-15 cm soil layer followed a gradient from the harvest pathway (29 ind m(-2)) to the windrow (1003 ind m(-2)). Ants (13-237 ind m(-2)), earthworms (11-120 ind m(-2)), Dermaptera (0-35 ind m(-2)), Coleoptera (3-24 ind m(-2)) and Chilopoda (0-43 ind m(-2)) were the main taxa. The termite population was very poor (3-4 ind m(-2)). The density of nematofauna was also heterogeneous (268-805 ind 100 g(-1) of soil). Heterogeneity between zones was also reflected in the density of the functional groups, mainly soil engineers, detritivores and predators for macrofauna and bacterial feeders, and phytoparasites for nematofauna. The weeded circular zone around the palm had the highest soil nutrient content (P, K, Ca, Mg, C-org CEC, base saturation). Its biodiversity was average but it contained the highest density of earthworms and nematofauna. Possible relationships between chemicals and biological groups in the food web are discussed.

Les conséquences du changement climatique sur les caféiers sont difficiles à prévoir et dépendent du système de culture (allant de monocultures artificialisées à des associations agroforestières quasi naturelles), du sol et des ressources en eau. Ces conséquences se manifestent aussi sur les maladies et ravageurs. Les recherches portant sur l'adaptation au changement climatique concerne essentiellement les céréales, et peu d' efforts portent sur les cultures pérennes tropicales, chez lesquelles le stress peut affecter le comportement de la plante pendant plusieurs saisons. Certains parasites peuvent s'adapter plus vite que ne peut réagir la plante hôte pérenne et se répandre dans de nouveaux habitats à la faveur du changement climatique. L'objectif des travaux du Cirad en amélioration génétique du caféier est de disposer de cultures " en bonne santé ", c'est-à-dire plus résilientes et plus résistantes. Nous présentons des approches intégratives portant sur le fonctionnement du génome (transcriptomique, métabolomique, génomique, épigénétique) et de la plante entière et sur la réponse adaptative aux combinaisons de stress afin de proposer des cibles pour l'amélioration variétale appliquée à la résistance à la rouille du caféier, à la lutte contre les nématodes et à f adaptation à la sécheresse.

L'introduction de biodiversité végétale dans les agroécosystèmes peut modifier la structure des réseaux trophiques du sol et les fonctions écosystémiques qu'ils assurent. Cette thèse fixe les bases d'une démarche expérimentale pour sélectionner des espèces végétales à partir de différents traits fonctionnels et pour évaluer leurs effets sur les réseaux trophiques et le fonctionnement des sols. Nous avons plus particulièrement cherché à sélectionner des plantes de services pouvant induire la régulation des nématodes parasites du bananier Radopholus similis et Pratylenchus coffeae et favoriser la décomposition des matières organiques durant l'interculture dans les bananeraies antillaises. C'est à dire durant la période séparant la destruction d'une ancienne bananeraie et la replantation d'une nouvelle. Au cours de ce travail, les réseaux trophiques du sol ont été appréhendés par une analyse fonctionnelle des communautés de nématodes. Une étude Bibliographique nous a permis de montrer que les traits fonctionnels "statut d'hôtes" vis-à-vis des nématodes phytoparasites, "composition biochimique des litières" et "productivité primaire des espèces végétales" contribuent aux effets des plantes sur les réseaux trophiques du sol et sur les deux services écosystémiques étudiés. Nous avons donc effectué une typologie des plantes de services à partir de ces traits. Puis pour étudier les effets d'apports de litières de composition biochimique contrastée sur les communautés de nématodes du sol, nous avons sélectionné les espèces végétales Paspalum notatum, Crotalaria zanzibarica et Acacia auriculiformis dont les litières présentaient des teneurs variables en hémicellulose, cellulose, azote, et lignine. Une étude en microcosmes a montré que la composition biochimique des litières détermine les successions écologiques au sein des communautés de nématodes et stimule de manière contrastée les voies de décomposition de la matière organique dans les sols. Nous avons discuté des mécanismes de régulation des nématodes parasites du bananier induits par ces apports de litières. Nous avons également montré que la culture de ces trois espèces induit une diminution des populations de R. similis dans les sols. Enfin, nous avons évalué les effets au champ de couverts de P. notatum, de C. zanzibarica et d'un couvert associant ces deux espèces. Pour cela, nous avons cultivé ces couverts durant neuf mois avant de les détruire et de restituer leurs litières à la surface des sols. Nos résultats montrent que ces couverts végétaux influencent différemment l'abondance en nématodes phytoparasites et le potentiel infectieux du sol. Ils induisent également des régulations bottom-up et top down dans leurs communautés. Après la restitution des litières, nous avons observé de fortes abondances de nématodes liées à la décomposition des litières dans la couche de surface du sol. Celle-ci fournit les couches sous-jacentes du sol en azote minéral et favorise le développement des nématodes omnivores et prédateurs. Il en résulte la formation de communautés de nématodes structurées et diversifiées concomitantes à la réduction des populations de R. similis et P. coffeae. Ces résultats étaient plus marqués pour les couverts monospécifiques de C. zanzibarica et les couverts mixtes. Nos travaux confirment que les traits fonctionnels "statut d'hôte", "production primaire", "composition biochimique des litières" sont déterminant pour sélectionner des plantes de services pour l'interculture en bananeraies.

During a survey of the nematodes associated with weeds in banana fields in Martinique, 41 weed species in 37 genera from 20 plant families were collected to extract nematodes from the roots. Results of this survey showed that 24 weed species were hosts of Radopholus similis, 23 were hosts of Helicotylenchus spp., 13 were hosts of Pratylenchus spp., 13 were hosts of Hoplolaimus seinhorsti, 29 were hosts of Meloidogyne spp. and 24 were hosts of Rotylenchulus reniformis. The presence of the burrowing nematode was more consistently found within three families, the Euphorbiaceae, Poaceae and Solanaceae. In some weed species such as Caladium bicolor, Commelina diffusa, Echinochloa colona and Phenax sonneratii, the levels of nematodes recovered were similar to, or greater than the numbers recovered from Musa roots. These results clearly show that certain weeds can be significant reservoirs of plant parasitic nematodes including R. similis in banana fields. This information is crucial in devising appropriate nematode control measures for use with rotation crops or fallow before re-planting banana fields with nematode free planting material. (c) 2005 Elsevier Ltd. All rights reserved.

Pathogenicity and genetic variation were investigated within a collection of 104 banana-infecting isolates of #Cylindrocladium# (teleomorph #Calonectria#) originating from different countries and representing previously described morphological taxa or species. These root-rot fungi, along with endoparasitic nematodes, have been reported to be causal agents of necrotic lesions that induce root breakage and toppling of banana plants. Little is known about the individual pathogenic effects of the species involved or their genetic diversity. In the present study, among the five morphological taxa found in the banana rhizosphere, only isolates showing an atypical morphology relative to #Cylindrocladium gracile# (named #Cy. gracile#-like isolates) and #Cy. spathiphylli# isolates were pathogenic on banana cultivar 'Grande Naine'. When comparing the latter isolates with others of the same species, but originating from different hosts, an analysis of rDNA spacer polymorphism partitioned isolates of #Cy. spathiphylli# by host into a banana - tea group and a #Heliconia# - #Spathiphyllum# group. Furthermore, isolates from Heliconia were not pathogenic on banana. A pathogenicity assessment of representative isolates from the #Cy. gracile#-like and the #Cy. spathiphylli# taxa on six different banana cultivars yielded no evidence of differential interactions between isolates and banana genotypes. Significant differences in susceptibility between banana genotypes were nevertheless detected that could potentially be exploited by breeders. Random amplified polymorphic DNA analysis revealed a genetic similarity ranging from 70% to 100% within #Cy. spathiphylli# isolates from bananas regardless of the geographic origin. Moreover, #Cy. gracile#-like isolates were highly similar but showed only 60% similarity relative to the #Cy. gracile# reference isolates, thus raising questions about their species status.

Introduction. La technique de centrifugation-flottaison permet de separer toutes les especes de nematodes, a tous les stades de developpement, des particules de sol restant et des debris de racine pour faciliter leur observation. Le principe de la methode appliquee, les principaux avantages, le materiel vegetal necessaire et le temps requis sont presentes. Materiel et methodes. Le materiel de laboratoire necessaire, ainsi que le detail des 19 etapes utilisees pour extraire les nematodes a partir du tissu vegetal avant denombrement et determination sont decrits. Les problemes potentiels sont repertories. (Resume d'auteur)

Le nématode réniforme Rotylenchulus reniformis Linford et Oliveira est en passe de devenir le nématode le plus redoutable de la culture cotonnière en Amérique du Nord et du Sud. Dans le but d'introgresser chez la principale espèce de cotonnier cultivé Gossypium hirsutum L. la résistance à ce parasite à partir de l'espèce diploïde sauvage G. longicalyx, l'hybride trispécifique G. hirsutum x G. thurberi x G. longicalyx a été créé selon la méthode pseudophylétique d'introgression. La triple hybridité du matériel produit a été mise en évidence au moyen de marqueurs microsatellites et confirmée par le comptage des chromosomes. Trois plantes hybrides évaluées en conditions d'inoculation contrôlée ont révélé un niveau de résistance à R. reniformis élevé et équivalent à celui de l'espèce diploïde donneuse.

International audience; Potato cyst nematodes induce changes in plant host gene expression following root invasion. For an accurate comparison of gene expression by reverse transcription quantitative real-time PCR (RT-qPCR), internal reference genes are necessary for transcript normalization. Very few experimental data on suitable reference genes are available for interactions between plant and root pathogens. In this study, we tested eight potential candidate reference genes for normalizing levels of potato gene transcripts by RT-qPCR after inoculation by nematodes. The ranking of candidate reference genes was performed using RefFinder WEB-based software. Four reference genes, RPN7 (26S proteasome regulatory subunit), UBP22 (ubiquitin-specific protease 22), OXA1 (OXA1 protein), and MST2 (mercaptopyruvate sulfurtransferase), were stably expressed in roots of susceptible or resistant potato plants, infected or uninfected by Globodera pallida. A normalization factor based on data from these four genes, highly homologous between potato and tomato, was used to normalize the expression of a chitinase gene, which was induced by nematodes in roots of potatoes carrying the resistance allele at a low-effect QTL, GpaXIspl. .

Tropical crop infestation by soil borne parasites (pineapple : Rotylenchulus reniformis and banana : Pratylenchus coffea e ) cann ot be controlled anymore by pes ticides in French Antillas under the new European regulations . Therefore, we investigated the possible contribution of induced systemic resistances ( ISR ) to biocontrol pests and to develop more environmentally friendly agrosystems. In Martinique ( Campus Agro - environnemental Caraïbe ), we are presently testing a strategy based on current knowledge on ISR through interaction between plants and beneficial microorganisms. The investigations are based on four main hypotheses: 1) The inoculum of soil borne parasites can be reduced introducing non - host rotation plants. Cover crops were selected on the basis of several functional traits (non - host status, high biomass), for their contribution to a balanced microfauna in the rhizos phere, and for their positive effect on soil mycorhization potential. 2) The selection of pineapple and banana varieties able to develop ISR AND adapt their metabolism to environmental changes is essential. We found differential responses against nematodes to an ISR inducer (methyljasmonate, 10 - 4 M) in several pineapple and banana varieties and we are now searching for a relation with markers of plant adaptability to environmental changes (genes for cysteine - proteases and their inhibitors phyto - cystatins). 3 ) The successful development of ISR responses is dependent on the capacity of a plant to tolerate abiotic stresses (drought, temperature, salinity...) in addition to the pathogens. As ISR may also be part of the global adaptability of plant metabolism to tol erate abiotic stresses from their habitat, we investigate the possible links between stress level and a plant's capacity to induce efficient ISR against soil - borne parasites ( ongoing ). 4) Pineapple and banana root systems bear diazotrophic bacteria (endoph ytic) that can be used as ISR inducers in the field. Seventy - five and ninety - one diazotrophic bacteria strains (endophytic) respectively for pineapple and banana were isolated from their root systems in different sites in Martinique including organic and i ntensive cropping systems. They are currently being identified (MIDI - FAME and ADNr16S sequencing) and tested as ISR inducers. Our research aims at validating the hypothesis that efficient and consistent systemic resistances to pathogens can be achieved i n the field by using selected varieties tolerant to abiotic stresses.

Root-knot nematodes are globally the most aggressive and damaging plant-parasitic nematodes. Chemical nematicides have so far constituted the most efficient control measures against these agricultural pests. Because of their toxicity for the environment and danger for human health, these nematicides have now been banned from use. Consequently, new and more specific control means, safe for the environment and human health, are urgently needed to avoid worldwide proliferation of these devastating plant-parasites. Mining the genomes of root-knot nematodes through an evolutionary and comparative genomics approach, we identified and analyzed 15,952 nematode genes conserved in genomes of plant-damaging species but absent from non target genomes of chordates, plants, annelids, insect pollinators and mollusks. Functional annotation of the corresponding proteins revealed a relative abundance of putative transcription factors in this parasite-specific set compared to whole proteomes of root-knot nematodes. This may point to important and specific regulators of genes involved in parasitism. Because these nematodes are known to secrete effector proteins in planta, essential for parasitism, we searched and identified 993 such effector-like proteins absent from non-target species. Aiming at identifying novel targets for the development of future control methods, we biologically tested the effect of inactivation of the corresponding genes through RNA interference. A total of 15 novel effector-like proteins and one putative transcription factor compatible with the design of siRNAs were present as non-redundant genes and had transcriptional support in the model root-knot nematode Meloidogyne incognita. Infestation assays with siRNA-treated M. incognita on tomato plants showed significant and reproducible reduction of the infestation for 12 of the 16 tested genes compared to control nematodes. These 12 novel genes, showing efficient reduction of parasitism when silenced, constitute promising targets for the development of more specific and safer control means., Author Summary Plant-parasitic nematodes are annually responsible for more than $100 billion crop yield loss worldwide and those considered as causing most of the damages are root-knot nematodes. These nematodes used to be controlled by chemicals that are now banned from use because of their poor specificity and high toxicity for the environment and human health. In the absence of sustainable alternative solutions, new control means, more specifically targeted against these nematodes and safe for the environment are needed. We searched in root-knot nematode genomes, genes conserved in various plant-damaging species while otherwise absent from the genomes of non target species such as those of chordates, plants, annelids, insect pollinators and mollusks. These genes are probably important for plant parasitism and their absence from non-target species make them interesting candidates for the development of more specific and safer control means. Further bioinformatics pruning of this set of genes yielded 16 novel candidates that could be biologically tested. Using RNA interference, we knocked down each of these 16 genes in a root-knot nematode and tested the effect on plant parasitism efficiency. Out of the 16 tested genes, 12 showed a significant and reproducible diminution of infestation when silenced and are thus particularly promising.

The genus Musa is not native to Africa. It evolved in tropical Asia, from southwest India eastward to the island of New Guinea. There is a growing circumstantial evidence which suggests that the East African Highland banana and the tropical lowland plantain were cultivated on the African continent since before 1 AD. It is also probable that ABB cooking and AB and AAB dessert cultivars were brought to the continent from India by Arabian traders from 600 AD, and that these were disseminated throughout East Africa. During the colonial era, the main centres of distribution for banana cultivars were botanical gardens, such as Zomba in Malawi, Entebbe in Uganda and Amani in Tanzania. It appears that the very early introductions of Highland banana and plantain arrived in Africa as a relatively clean material without the conspicuous pests and diseases that affect them in Asia. In contrast, several devastating problems now impact the crop in Africa, including nematodes, the borer weevil and diseases, most notably banana bunchy top, banana streak, Sigatoka leaf spots, Xanthomonas wilt and Fusarium wilt. We (a) provide chronological overviews of the first reports/observations of different Musa pests and pathogens/diseases in Africa, (b) highlight specific examples of when a pest or pathogen/disease was introduced via planting materials and (c) give recent examples of how the pests and pathogens spread to new regions via planting materials. In total, these production constraints threaten banana and plantain production throughout the continent and impact those who can ill afford lost production, the small-holder producer. Our intent in this review is to highlight the significance of these problems and the great importance that infested planting materials have played in their development.

Sedentary plant-parasitic nematodes maintain a biotrophic relationship with their hosts over a period of several weeks and induce the differentiation of root cells into specialized feeding cells. Nematode effectors, which are synthesized in the esophageal glands and injected into the plant tissue through the syringe-like stylet, play a central role in these processes. Previous work on nematode effectors has shown that the apoplasm is targeted during invasion of the host while the cytoplasm is targeted during the induction and the maintenance of the feeding site. A large number of candidate effectors potentially secreted by the nematode into the plant tissues to promote infection have now been identified. This work has shown that the targeting and the role of effectors are more complex than previously thought. This review will not cover the prolific recent findings in nematode effector function but will instead focus on recent selected examples that illustrate the variety of plant cell compartments that effectors are addressed to in order reach their plant targets.

Earthworms can ingest large amounts of soil and litter and thus many nematodes. Several studies have actually shown a decrease in nematode populations in the presence of earthworms. We studied interactions between earthworms (the tropical peregrine Pontoscolex corethrurus) and plant-parasitic nematodes (Heterodera sacchari and Pratylenchus zeae) in the laboratory. In the presence of earthworms, we observed a significant decrease in populations of P. zeae in the rhizosphere of Oryza sativa after 6 weeks (1st generation), and 12 weeks (2nd generation), respectively, in comparison to a control with no earthworms. A parallel experiment with H. sacchari and P. corethrurus showed that H. sacchari cysts were ingested by earthworms with the soil, and the interaction between the gut and the gut contents of P. corethrurus and H. sacchari showed that i) populations of cysts had decreased 5 weeks (1st generation) after the start of the experiment, and ii) the total number of eggs and infesting larvae (J2 alive) had decreased.

Plantains are among the crops that enhance food security in Cameroon. However, plantain yields remain low because of several constraints of parasites such as Radopholus similis, a nematode that can cause losses up to 75% in fields when no protection measures are taken. In most cases, the sensitivity of local plantain varieties to R. similis is unknown; which generally results to low yields despite the control technique used. This limits their up scaling in the country. This work was undertaken to study the sensitivity of two varieties, Essong and Big Ebanga, to R. similis. To this effect, the parasitic activity of R. similis on the varieties Essong and Big Ebanga was assessed in vivo. The variety Grande naine known to be very sensitive to R. similis was used as the control. According to the results obtained, local varieties Essong and Big Ebanga were found to be sensitive to R. similis with the variety Essong being the most sensitive.

Plant-parasitic nematodes possess a large number of proteins that are secreted in planta, allowing them to be successful parasites of plants. The majority of these proteins are synthesized mainly in the nematode subventral and dorsal glands as well as in other organs. To improve the immunovisualization of these proteins, we adapted a methacrylate embedding method for the localization of proteins inside nematode tissues, and extracellularly when secreted in planta or within plant cells. An important advantage is that the method is applicable for all nematode stages: preparasitic as well as parasitic stages, including large mature females. Herein, the method has been successfully applied for the localization of four nematode secreted proteins, such as Mi-MAP-1, Mi-CBM2-bearing proteins, Mi-PEL3, and Mi-6D4. In addition, we could also localize 14-3-3 proteins, as well as two cytoskeletal proteins, by double-immunolabeling on preparasitic juveniles. Superior preservation of nematode and plant morphology, allowed more accurate protein localization as compared with other methods. Besides excellent epitope preservation, dissolution of methacrylate from tissue sections unmasks target proteins and thereby drastically increases antibody access.

Dans un contexte de mutation rapide de l'agriculture, la conception de systèmes de culture répondants aux nouvelles exigences des agriculteurs et de la société est une nécessité. L'agriculture doit répondre au double enjeu : être productive et respecter l'environnement. La conception de systèmes de culture innovants repose à la fois sur i) des recherches cognitives, visant à comprendre les processus impliqués dans l'agroécosystème et ii) leur intégration dans des systèmes complexes et l'évaluation multicritère de ces systèmes. J'ai développé une approche de modélisation permettant d'intégrer les connaissances existantes sur le fonctionnement des agroécosystèmes à base de bananiers, d'identifier les connaissances manquantes, et de fournir des outils de pilotage afin de permettre la définition de systèmes de culture durables. Les outils de modélisation développés simulent le fonctionnement biophysique de l'agroécosystème, incluant certaines spécificités, comme la prise en compte d'un peuplement cultivé hétérogène (caractère semi-pérenne des bananiers) et la dynamique des bioagresseurs (nématodes phytoparasites et charançons). Ces modèles ont été couplés à des outils d'évaluation des risques environnementaux (risque de pollution par les pesticides), permettant in fine, d'évaluer systèmes de culture existants ou innovants sur la base de critères de performances agronomiques, économiques et environnementales. Afin d'assister le prototypage de systèmes de culture innovants, ces outils de modélisation ont été utilisés afin de tester un grand nombre de règles de décisions des agriculteurs et d'optimiser les combinaisons les plus prometteuses. Mon projet de recherche traite de la question du rôle de la diversité biologique dans la productivité et la stabilité des systèmes de culture. Je propose de mobiliser des modèles de réseaux trophiques afin de prendre en compte la complexification biologique des systèmes cultivés. Au niveau méthodologique, lier les modèles de culture utilisés par les agronomes, avec les modèles de réseaux trophiques utilisés par les écologues, représente un cadre adapté pour simuler le fonctionnement du continuum sol-plante-atmosphère, la régulation biologique des bioagresseurs, et les feedbacks des différentes communautés sur les propriétés du sol. Ce cadre devrait permettre de faire le lien entre les pratiques culturales des agriculteurs, incluant la composante économique et décisionnelle, avec les propriétés émergentes de ces systèmes complexes. La seconde partie de ce projet de recherche concerne l'étude de la dimension spatiale dans la régulation des bioagresseurs. Il s'agit notamment d'étudier comment l'hétérogénéité spatiale et la diversité des ressources influencent la dispersion et la régulation des bioagresseurs par prédation.

Les producteurs de banane antillais sont engagés en partenariat avec l'Institut Technique Tropical et le CIRAD dans une démarche de réduction de l'emploi des intrants chimiques. Les innovations accompagnant cette démarche reposent principalement sur des techniques alternatives à la lutte chimique pour le contrôle des nématodes phyto-parasites et du charançon du bananier. Ces techniques font appel à l'intégration dans le système de culture de plantes de service afin de restaurer des mécanismes de régulation biologique des bio-agresseurs, à un contrôle de l'assainissement des parcelles par des tests biologiques, à l'utilisation de matériel végétal sain (vitroplants) pour la replantation des bananeraies et à la mise en place de pièges attractifs à phéromones pour la capture du charançon du bananier. Ces techniques sont intégrés dans des prototypes de systèmes de culture mis au point et testés en milieu réel dans le cadre d'une démarche de conception et d'évaluation participative impliquant les producteurs, les services techniques et la recherche.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; Plant-parasitic nematodes are injurious crop pests that have been managed mainly by chemical nematicides. However, safe and alternative methods such as those based on organic materials need to be developed. Our study has evaluated (i) the effects of four organic amendments with different biochemical compositions that are abundantly produced in the study area (Guadeloupe, French West Indies) on soil nematode communities and (ii) some of the suppression mechanisms of banana parasitic nematodes, especially those involving the soil food web. This study is based on a microcosm experiment comparing sugarcane bagasse, sugarcane sludge, plant residues and sewage sludge. All amendments except sewage sludge decreased the root abundances of plant-parasitic nematodes, by 96% in the case of sugarcane bagasse. For this treatment, soil densities of carnivorous nematodes were six times higher than the treatments without organic amendment. Plant residues and bagasse were mainly composed of materials that are difficult to decompose, namely cellulose and lignins. These organic materials favored a fungal decomposition pathway and permitted development of carnivorous nematode populations and increased the Channel Index (CI). Pratylenchus coffeae control after sugarcane refinery sludge application remains unexplained. Lastly, sewage sludge, composed mainly of easily degradable compounds, did not permit nematode control, and only bacterivorous nematode populations were enhanced by this treatment. (C) 2011 Elsevier B.V. All rights reserved.

In late 2009, a European Food Safety Authority (EFSA)-funded project (Prima phacie) began work to review and test methodologies for conducting pest risk assessment by means of case studies on three phytoplasmas (Candidatus Phytoplasma mali, Ca. P. prunorum, Ca. P. pyri); two bacteria (Acidovorax avenae subsp. citrulli, Xanthomonas citri [=X. axonopodis] pv. citri); two fungi (Guignardia citricarpa, Mycosphaerella dearnessii); two nematodes (Meloidogyne chitwoodi, M. fallax); and an insect (Anoplophora glabripennis). Multiple risk assessment schemes and methods will be applied to each of the case study pests, allowing for a comparative assessment of methods. Methods to assess the effectiveness of possible risk management options for each pest will also be evaluated. The project will further develop the scientific basis for pest risk assessment within the European Community and identify methodologies most suitable for conducting risk assessments and for evaluating the effectiveness of possible risk management options by the EFSA Panel on Plant Health in order to support European decision making. The project lasts 29 months, and is being conducted by an international consortium of 11 partners consisting of phytosanitary organizations, research institutes and a university. Results will be disseminated via conventional publications and at a workshop in March 2012.

Les nématodes parasites des plantes sont de minuscules vers qui vivent principalement dans le sol et les racines. Dans les cultures de bananiers, les espèces provoquant le plus de ravages passent la plus grande partie de leur cycle biologique dans les tissus racinaires et dans ceux du rhizome des bananiers. La prolifération de ces nématodes perturbe l'alimentation en eau et en nutriments, retarde la croissance et cause la verse des plants de bananiers parasités. Jusqu'à présent, la plupart des méthodes conventionnelles pour lutter contre les nématodes du bananier reposaient sur l'utilisation de nématicides chimiques. La plupart de ces produits ont progressivement été interdits en Europe. Ce guide passe en revue les principales étapes pour une gestion intégrée et alternative des nématodes parasites des bananiers aux Antilles. Cette démarche intègre i) des mesures d'assainissement du sol vis-à-vis des nématodes foreurs Radopholus similis telles que la mise en jachère améliorée, la création de fossés d'isolation hydrique permettant d'évacuer les eaux contaminées pour protéger les jachères et les parcelles assainies d'un risque de recontamination, ainsi que l'utilisation de culture de plantes non-hôtes incluant des cultures de rente, des graminées fourragères et des légumineuses. ii) un diagnostic de la qualité d'assainissement du sol vis-à-vis des nématodes avant la plantation de nouvelles cultures de bananiers. iii) l'utilisation de matériel de plantation sain, principalement des plants issus de culture in-vitro. iv) l'utilisation de variétés tolérantes aux nématodes et, à moyen terme, celles de variétés résistantes aux nématodes. v) une intégration plus poussée de ces stratégies et la réintroduction d'une plus grande biodiversité pour favoriser un contrôle durable de ces nématodes.

Soil degradation has led crop yield to decline in many Sahelian countries and is a fundamental agricultural and economical threat for local populations. In Saria, Burkina Faso, long-term experiments are being performed to find efficient soil management practices that could improve soil fertility. A randomized block experiment comprising organic amendment (unamended control, straw at 8.3 t ha(-1), manure at 10 t ha(-1)) coupled with mineral fertilization (no urea, urea at 60 kg ha(-1)) was started in 1980 with a continuous sorghum (Sorghum bicolor) cropping system. Twenty-six years after the settlement of the treatments, we compared their effects on nematode populations, community structure, and ecological indices, as well as soil physical and chemical properties at three stages of sorghum's cropping cycle. The addition of manure led to significantly higher soil C, N, and P content and produced a higher sorghum grain yield in comparison to unamended or straw-amended soils. The number of plant-parasitic nematodes (mainly Pratylenchus and Tylenchorhynchus) was significantly higher in plots fertilized with manure in comparison to unamended or straw-amended plots. They were also significantly more abundant when urea was added. Mineral nitrogen fertilization had little impact on free-living nematodes, regardless of S. bicolor development stage, whereas organic amendment significantly raised the abundance of bacterivorous and fungivorous nematodes. Moreover, microphagous nematodes were significantly more numerous in plots amended with straw than with manure. Our results show that, on the long-term, only manure amendment seemed able both to store C and nutrients whereas both manure and straw led to greater microphagous nematode communities.

Au cours de mon expérience, je me suis intéressé à différents aspects de l'écologie des bioagresseurs allant de l'étude de leurs traits de vie jusqu'à leurs interactions avec l'agroécosystème. Les organismes que j'ai étudiés sont variés : depuis différentes espèces de mouches des fruits, d'aleurodes, de nématodes phytophages jusqu'au charançon du bananier. Deux axes principaux ont structuré mes recherches : un premier concernant la biodémographie et le comportement des bioagresseurs, et un second sur les interactions entre espèces en étudiant en particulier plusieurs espèces envahissantes. Dans le premier axe, j'ai conduit une série de travaux dans lesquels j'ai étudié les traits de vie de différentes espèces au laboratoire et mis en évidence sur le terrain leurs relations avec certains facteurs environnementaux (température, pluviosité, gamme et type de plantes hôtes, type de sol...). Une partie des travaux de ce premier axe a également porté sur la mise au point de systèmes de piégeage contre certains de ces bioagresseurs, et l'étude des biais en termes de structure en âge des populations capturées par ces systèmes. Enfin, des études sur les comportements liés à dispersion du charançon du bananier ont été menées. Dans le second axe, j'ai étudié le lien entre les traits de vie de ravageurs envahissants (mouches des fruits et biotypes d'aleurode) et leur aptitude à l'invasion dans une communauté résidente. Certains traits de vie comme une durée de vie plus longue, une plus grande taille des adultes et des oeufs, permettent une meilleure aptitude à la compétition interspécifique (par exploitation et interférence). L'étude de la distribution géographique de différentes espèces en compétition (mouches des fruits, aleurodes et nématodes phytophages) en fonction des différents facteurs environnementaux a permis de caractériser leurs niches écologiques. Celles-ci conditionnent les possibilités de coexistence des espèces, notamment pour les espèces de bioagresseurs envahissants introduits dans une communauté d'espèces déjà établies dans un environnement hétérogène. Deux nouveaux projets de recherche sont proposés dans la continuité de cette synthèse. Le premier projet porte sur la caractérisation de l'habitat, la dynamique et la dispersion des populations des bioagresseurs en milieux hétérogènes. Le deuxième projet s'intéresse à la caractérisation du réseau trophique du charançon du bananier, et à sa modification par les pratiques culturales. Il s'agit notamment d'identifier les liens trophiques entre espèces et la façon dont ils peuvent être modifiés en vue d'augmenter la régulation du bioagresseur.

9th International Congress on Molecular Epidemiology and Evolutionary Genetics of Infectious Diseases OCT 30-NOV 01, 2008 Irvine, CA; International audience; The tropical and subtropical parthenogenetic plant-parasitic nematodes Meloidogyne are polyphagous major agricultural pests. Implementing proper pest management approaches requires a good understanding of mechanisms, population structure, evolutionary patterns and species identification. A comparative analysis of the mitochondrial vs nuclear diversity was conducted on a selected set of Meloidogyne lines from various geographic origins. Mitochondrial co2-16S sequences and AFLP markers of total DNA were applied because of their ability to evidence discrete genetic variation between closely related isolates. Several distinct maternal lineages were present, now associated with different genetic backgrounds. Relative discordances were found when comparing mitochondrial and nuclear diversity patterns. These patterns are most likely related to crosses within one ancestral genetic pool, followed by the establishment of parthenogenesis. In this case, they mirror the genetic backgrounds of the original individuals. Another aspect could be that species emergence was recent or on process from this original genetic pool and that the relatively short time elapsed since then and before parthenogenesis settlement did not allow for lineage sorting. This could also be compatible with the hypothesis of hybrids between closely related species. This genetic pool would correspond to a species as defined by the species interbreeding concept, but also including the grey area of species boundaries. This complex process has implications on the way genotypic and phenotypic diversity should be addressed. The phenotype of parthenogenetic lines is at least for part determined by the ancestral amphimictic genetic background. A direct consequence is, therefore, in terms of risk management, the limited confidence one can have on the direct association of an agronomic threat to a simple typing or species delineation. Risk management strategies and tools must thus consider this complexity when designing quarantine implementation, resistance breeding programmes or molecular diagnostic

The stability and positive functions (such as pest regulation) of intensively managed agroecosystems can be enhanced by increasing biodiversity (in particular, by introducing cover plants or associated crops). Therefore, understanding modes of interspecific interactions among the phytophagous species, such as coexistence via host-plant partitioning, may allow manipulation of the balance between pest and non-pest species. In the present study, we tested the hypothesis that a community of six plant-feeding nematode species in banana agroecosystems is structured by host plants. This was done using extensive data on the abundance of the different nematodes species on banana and associated weeds in Martinique. Because the purpose of this study was to focus on host-plant range, we eliminated the effects of temperature, rainfall, and soil type using a partial canonical correspondence analysis. Host plants in banana agroecosystems have a marked influence on the plant-feeding nematode community structure. Host plants allow niche partitioning between some but not all pairs of species. The most evident pattern is the niche partitioning among the three nematodes considered long established in Martinique. For pairs of species showing no host-plant niche partitioning, additional information regarding the colonisation and population dynamics over time both at the root and agroecosystem scale would allow better understanding of the equilibrium among species of the plant-feeding nematode community. For management purposes, the modification of abundance of some host plants, which could be used as cover plants in the field, could change the balance among nematode species.

Genetic control of root-knot nematodes (RKNs) is an essential part of an integrated pest management as the use of resistant cultivars or rootstocks constitutes an easy, inexpensive, non-polluting method of control. This chapter presents the results achieved in understanding the genetic basis of coffee resistance to Meloidogyne spp. in Latin America, and in using genetic resistance in breeding programmes. The context of breeding for improving coffee resistance is firstly described. This is followed by an overview of works published on the identification of resistance sources among the genetic resources preserved in collections worldwide. The methods of resistance evaluation are discussed, and a standardized method is proposed in order to improve the reliability of resistance evaluation trials. The results obtained from studies on the genetics of resistance to RKNs are then given for the main species that parasitize coffee. So far, only one resistance gene has been identified and mapped in the coffee genome, the gene Mex-1 of resistance to M. exigua. The advent of large-scale molecular genomics will provide an access to previously inaccessible sources of genetic variation which could be exploited in breeding programmes. Strategies for using resistance sources are finally proposed in the context of coffee breeding.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; New crop systems have been developed in the French West Indies that combine fallow or rotation crops with nematode-free vitro-plants to avoid the massive application of nematicides in banana fields. In these new banana fields, recontamination by the burrowing nematode Radopholus similis can then happen either by run-off or irrigation water. To understand these phenomena, we studied the vertical dissemination of R. similis by water leaching using soil cylinders and rainfall simulations. Steel drums were used to collect cylinders of soil (around 14.3 dm3) with a backhoe. The soil cylinders were placed in an aspersion chamber, saturated with water, and a R. similis suspension was placed on the soil surface. Afterwards, rainfalls ranging from 12 to 540 mm were simulated. Nematodes were then extracted from different soil layers (0–5 to 20–25 cm depth) using either (i) a Seinhorst elutriator followed by a Baermann funnel or (ii) centrifugation–flotation combined with Meldola blue staining. Results showed that dissemination of R. similis at the scale of the decimetre in nitisoil is limited: less than 8% of the applied nematodes reached layers deeper than 10 cm after exceptional rainfalls that represent several times the poral volume of the soil. Dissemination below 25 cm depth seemed to be limited to very few individuals, from 0.1 to 0.2%. Among leached nematodes, the percentage of non-active and dead nematodes increased significantly with depth. It seems that R. similis have developed a behaviour to escape leaching. These findings question the generally accepted idea that water dissemination of plant-parasitic nematodes is mainly a passive phenomenon.

Breeders develop an increasing number of new crop varieties with potentially interesting characteristics in regards to their resistance or tolerance to pests. Nevertheless, the long-term assessment often requires heavy multi-local in-field measurements. Furthermore, the interactions between two or more pest many limit the relevance of field results on the long-term. Here, we present a methodology that use cropping system model to evaluate both the long-term evolution of the pest dynamics and the overall sustainability of the cropping systems based on include new varieties. We illustrate our method with the case of the new synthetic banana hybrid FB920 (Musa spp., AM group) - plant-parasitic nematodes complex. FB920 was designed to be resistant to the Sigatoka Disease and Black Leaf Streak Disease, caused respectively by Mycosphaerella musicola and Mycosphaerella fijiensis. Herein, we used the SIMBA model (a model to simulate phenology, growth, and plant-parasitic nematode/banana interactions) to examine the population dynamics of plant-parasitic nematodes in cropping systems with this new synthetic hybrid FB920 in various initial conditions. We used short term experiments to calibrate the SIMBA model to account for the growth and the development of the FB920 variety and to simulate the dynamics of the burrowing nematode (Radopholus similis) and the spiral nematode (Helicotylenchus multicinctus). Results from simulations show that in the long term the spiral nematode populations can overtake the burrowing nematode populations and that nematodes populations are smaller than in Cavendish banana fields. (Texte intégral)

The synthetic banana hybrid FB920 (Musa spp., AAA group) has been designed to be resistant to Sigatoka and Black Leaf Streak Diseases, caused respectively by Mycosphaerella musicola and Mycosphaerella fijiensis. In addition to these features, the hybrids seem less susceptible to plant-parasitic nematodes, especially the burrowing nematodes (Radopholus similis) and the lesion nematode (Pratylenchus coffeae) than classic Cavendish cultivars, such as Williams, Grande Naine, or Poyo. This genetic modification drastically reduces pesticide use. Herein, we used the SIMBA model (a model to simulate phenology, growth, and plant-parasitic nematode/banana interactions) to examine the population dynamics of plant-parasitic nematodes in cropping systems with hybrid FB920 in various initial conditions. Results from field observations and simulations show that in the long-term, the spiral nematodes (Helicotylenchus multicinctus) can overtake the burrowing nematodes and that nematode populations are smaller than in Cavendish banana fields. This reduced capacity of FB920 to support multiplication of R. similis reduces the use of pesticides and thus re-creates favourable conditions for fauna, thereby increasing the global sustainability and resilience of banana agro-ecosystems.

CIRAD (Montpellier, France) develops research activities centered on tropical and sub-tropical agricultural systems. Among others crops, cotton is the fucus of a series of research programs in different disciplines from economics to breeding. Major areas in genetics and breeding relate to (1) genetic diversity, (2) cultivar development through classical and molecular breeding, and (3) applied genomics. An important but under-exploited reservoir of genetic diversity exists within the genus Gossypium. With over 3000 accessions CIRAD has one of the few important gene banks worldwide. It includes cultivars, landraces , and wild Gossypiurn species. DNA molecular markeTs have shawn their usefulness and validity for fingerprinting plant resources and for structuring diversity of large collections. In our case, after a preliminary step centered on the screening of microsatellite markers over a limited set of accessions of the gene bank (a genotyping kit has been proposed) , our future plans include the use of high-throughput methods of genotyping (a DArT platform will soon be available in our unit). Opportunities for exploiting this large diversity relate to the development core-collections and of genetic association studies for a given set of traits (fiber quality, stress response) . After a past and fruitful period of collaboration in different tropical countries (varieties co-obtained by ClRAD are cultivated on over 2. 5 million hectares worldwide), CIRAD has more recently engaged research programs in molecular genetics. Focus has initially been on fiber quality as a target trait and on markerassisted interspecific breeding for introgressing fiber quality traits from G. barbadense into G. hirsutUtn. Achievements in this area (genetic maps, fiber quality QTLs) have been published and are posted on the web. The database of CIRAD, TropGene DB (available at http, lltropgenedb. cirad. h l ) is regularly updated and presently displays various genetic maps as well as QTL data. Based upon QTL detected in the BCI and BC2 (backcross to the Gh parent) generations, marker-assisted selection in further generations (BC3 to BCG) was conducted and advanced lines introgressed with 3 ~ 5 QTLs were tested under tropical conditions. Using the same material, libraries of segmental introgression lines are being created for a few specifie target chromosomes. More recently , through collaboration with Embrapa (Brazil), CIRAD has initiated research on disease and nematode resistances in order to clarify the genetic basis of resistance; prepare segregating populations, and develop marker-assisted selection programs. A new collaborative project coordinated by CIRAD on the genetics and genomics of cotton fiber quality has been launched in 2007. CIRAD and its partners, Bayer CS and CSIRü, are engaged in ambitious research aimed at elucidating the genetic basis of fiber quality. The project is centered on an interspecific RIL population (a cross between 2 weil studied parents , Guazuncho 2 (G. hirsuturn) and VH8 (G. harhadense)) . It is innovative by the approach combining (1) phenotypic assessment of fi ber quality from field and greenhouse experiments on four continents, and (2) transcriptome profiling using complementary platforms, hybridization-based (microarrays) and PCR-based (cDNA-AFLP). Comparison of QTL and eQTL results is expected to help in identifying candidate genes important in fiber quality.