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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.

National audience; Root-knot nematodes, Meloidogyne spp., are extremely polyphagous plant parasites worldwide. Since the use of most chemical nematicides is being prohibited, genetic resistance is an efficient alternative way ta protect crops against these pests. However, resistance genes (R-genes) are limited and nematode populations are able ta overcome them with time. Good management of these valuable resources is thus a key point of R-gene durability. ln pepper, Me3 is a dominant major resistance gene, currently used in breeding programs, that control M. arenario, M. incognito and M. javanica, the three main root-knot nematodes species. ln this study, it was introgressed in either a susceptible or a partially resistant genetic background in either homozygous or heterozygous allelic status. Confronting these genotypes with a high inoculation pressure of an avirulent M. incognito isolate or a Me3 virulent laboratory-selected population (obtained by successive re-inoculation on a Me3 R-pepper line) demonstrated i) that the genetic background plays an important raie, Me3 being overcome more easily in a susceptible genetic background than in a partially resistant one, ii) that the allelic status has no effect. These results are in good agreement with concepts recently developed from the analysis of very different plant-pathogen interactions: pepper-virus (Palloix et al., 2009) or rapeseed-Leptosphaeria (Brun et al., 2012). Experiments are now underway ta detect and localise genes or loci providing partial resistance (QTLs = Quantitative Trait Loci) ta root-knot nematodes explaining the differences observed between susceptible and partially resistant genetic backgrounds, and ta determine the effectiveness of their « protective » raie on the major R-genes. Ali these results are of main importance for the creation of new varieties by breeders who have to take into account the plant material used and the resistance gene they want ta introgress.

Expanding genomic data on plant pathogens open new perspectives for the development of specific and environment friendly pest management strategies based on the inhibition of parasitism genes that are essential for the success of infection. Identifying such genes relies on accurate reverse genetics tools and the screening of pathogen knock-down phenotypes. Root-knot nematodes are major cosmopolitan crop pests that feed on a wide range of host plants. Small interfering RNAs (siRNAs) would provide a powerful tool for reverse genetics of nematode parasitism genes provided that they could (1) target genes expressed in inner tissues of infective nematodes and (2) target genes expressed during parasitism. In this study, we show that siRNAs can access inner tissues of the infective juveniles during soaking and accumulate in the esophagus, amphidial pouches and related neurons of the nematode. We provide evidence that siRNAs can trigger knock-down of the parasitism gene Mi-CRT, a calreticulin gene expressed in the esophageal glands of Meloidogyne incognita. Mi-CRT knock-down in infective juveniles affected nematode virulence. However, Mi-CRT knock-down was not persistent after plant infection, indicating that siRNA-mediated RNAi is best suited for functional analysis of genes involved in pre-parasitic stages or in the early steps of infection.

Afin de pouvoir développer à grande échelle une lutte biologique par Trichogramma chilonis contre le foreur de la canne à sucre, il est nécessaire d’en diminuer les coûts. Savoir stocker les auxiliaires avant leur utilisation sur le terrain représente un avantage indispensable, tant au niveau de la biofabrique que des professionnels sur le terrain. A cet effet, un nouveau programme de recherche, financée par le Ministère Français de l’Agriculture et de la Pêche, est en cours. L’objectif est de déterminer les conditions optimales (T°, HR, photopériode, stade de développement) pour mettre en place un arrêt de développement (quiescence ou diapause). Les premiers résultats obtenus montrent déjà la possibilité de stocker au froid pendant 2 mois, sous forme de quiescence, les Trichogramma produits.

L’importance de la prédation des oeufs du foreur de la canne à sucre, Chilo sacchariphagus, à la Réunion est démontrée et joue un rôle essentiel dans le contrôle naturel de ce ravageur. Elle est principalement exercée par les fourmis de l’espèce Pheidole megacephala. La stratégie de lutte biologique que nous avons mise au point depuis quelques années prend en compte cette action prédatrice qui est particulièrement bénéfique sur des champs de canne âgés de 6 à 12 mois. Toutefois, nos résultats montrent que la prédation des fourmis peut aussi avoir un effet néfaste sur l’auxiliaire utilisé, Trichogramma chilonis, au cours des lâchers. En effet, de par leur comportement très actif et leur petite taille, elles arrivent à pénétrer dans les différents conditionnements testés et à attaquer les oeufs hôtes et les parasitoïdes en cours de développement. Pour limiter cet impact négatif, il est nécessaire d’optimiser le conditionnement, le temps que les trichogrammes émergent et aillent parasiter les oeufs du ravageur.

National audience; La recherche et le développement de nouvelles méthodes de lutte biologique nécessitent un investissement important sur l’optimisation de l’élevage d’insectes (auxiliaires, hôtes ou prédateurs). Cet article décrit les procédures d’élevage d’un parasitoïde, Psyttalia lounsburyi, et de son hôte de substitution Ceratitis capitata. Cet article présente également quatre expérimentations complémentaires visant à mieux documenter la biologie de P. lounsburyi, auxiliaire potentiel de lutte biologique contre la mouche de l’olive, Bactrocera oleae, qui reste le principal ravageur de l’olivier. L’âge de l’hôte, la forme du support de ponte et la présence de mâles adultes sur la production de parasitoïdes sont plus particulièrement étudiés. L’apport de ces informations pour l’optimisation de la production est discuté