Thierry Mateille

Nematode interactions in nature : Models for sustainable control of nematode pests of crop plants?

van der Putten, W. H., Cook, R., Costa, S., Davies, K. G., Fargette, M., Freitas, H., Hol, W. H. G., Kerry, B. R., Maher, N., Mateille, T., Moens, M., de la Pena, E., Piskiewicz, A., Raeymaekers, A., Rodriguez-Echeverria, S., van der Wurff, A. W. G. (2006). Nematode interactions in nature: models for sustainable control of nematode pests of crop plants? Advances in Agronomy, 89, 227-260.

Fast assembly of the mitochondrial genome of a plant parasitic nematode (Meloidogyne graminicola) using next generation sequencing

Little is known about the variations of nematode mitogenomes (mtDNA). Sequencing a complete mtDNA using a PCR approach remains a challenge due to frequent genome reorganizations and low sequence similarities between divergent nematode lineages. Here, a genome skimming approach based on HiSeq sequencing (shotgun) was used to assemble de novo the first complete mtDNA sequence of a root-knot nematode (Meloidogyne graminicola). An AT-rich genome (84.3%) of 20,030 bp was obtained with a mean sequencing depth superior to 300. Thirty-six genes were identified with a semi-automated approach. A comparison with a gene map of the M. javanica mitochondrial genome indicates that the gene order is conserved within this nematode lineage. However, deep genome rearrangements were observed when comparing with other species of the superfamily Hoplolaimoidea. Repeat elements of 111 bp and 94 bp were found in a long non-coding region of 7.5 kb, as similarly reported in M. javanica and M. hapla. This study points out the power of next generation sequencing to produce complete mitochondrial genomes, even without a reference sequence, and possibly opening new avenues for species/race identification, phylogenetics and population genetics of nematodes.

Nematostatic effects of a leaf extract from Crotalaria virgulata subsp. grantiana on Meloidogyne incognita and its use to protect tomato roots

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.

Nematostatic activity of aqueous extracts of West African Crotalaria species

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.

Influence of irrigation on the distribution and control of the nematode Meloidogyne javanica by the biocontrol bacterium Pasteuria penetrans in the field

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

Effect of different West African species and strains of Arthrobotrys nematophagous fungi on Meloidogyne species

Different species ofArthrobotrys nematophagous fungi and several strains ofA. oligospora have been studied for their antagonistic effects against nematodes of the genusMeloidogyne, important pests of vegetables. All fungi trappedM. mayaguensis andM. incognita juvenilesin vitro but had no effect on the juveniles ofM. javanica. In pot experiments withM. mayaguensis, all fungi reduced the nematode populations and stimulated the growth of tomato seedlings. In a field trial, a strain of A.oligospora, isolated in Senegal and incorporated into compost blocks, was efficient in increasing the tomato seedling growth. The introduction of nematophagous fungi in compost blocks as a biological biocontrol technique against phytophagous nematodes adapted for developing countries is discussed.RésuméDifférentes espèces d’Arthrobotrys, champignon nématophage, et plusieurs souches d’A.oligospora, isolées au Sénégal et au Burkina Faso, ont été étudiées pour leur effets antagonistes envers les nématodes du genreMeloidogyne, parasites importants des cultures maraîchères en Afrique de l’Ouest. Toutes les souches utilisées ont piégé les juvéniles deM. mayaguensis etM. incognita in vitro mais n’ont eu aucun effet surM. javanica. Testées sur culture de tomate en pots, toutes les souches ont diminué le développement des populations deM. mayaguensis et ont permis un meilleur développement des plantes. Testée sur culture de tomate au champ, une souche d’A.oligospora isolée au Sénégal et incorporée à des mottes de compost a permis une meilleure croissance des plantes. La production de plants maraîchers en mottes de compost combinée à l’incorporation de champignons nématophages aux mottes est proposée comme une technique de lutte biologique contre les nématodes phytoparasites adaptée aux pays en voie de développement

Indirect effects of the bacterial soil aggregation on the distribution of Pasteuria penetrans, an obligate bacterial parasite of plant-parasitic nematodes

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.

Control and Management of Plant Parasitic Nematode Communities in a Soil Conservation Approach

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

Multisite survey of soil interactions with infestation of root-knot nematodes (Meloidogyne spp.) by Pasteuria penetrans

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

Plant-parasitic Nematodes Associated with Olive Tree in Southern Morocco

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