Temporal sampling helps unravel the genetic structure of naturally occurring populations of a phytoparasitic nematode. 2. Separating the relative effects of gene flow and genetic drift

International audienceStudying wild pathogen populations in natural ecosystems offers the opportunity to better understand the evolutionary dynamics of biotic diseases in crops and to enhance pest control strategies. We used simulations and genetic markers to investigate the spatial and temporal population genetic structure of wild populations of the beet cyst nematode Heterodera schachtii on a wild host plant species, the sea beet (Beta vulgaris spp. maritima), the wild ancestor of cultivated beets. Our analysis of the variation of eight microsatellite loci across four study sites showed that (i) wild H. schachtii populations displayed fine-scaled genetic structure with no evidence of substantial levels of gene flow beyond the scale of the host plant, and comparisons with simulations indicated that (ii) genetic drift substantially affected the residual signals of isolation-by-distance processes, leading to departures from migration–drift equilibrium. In contrast to what can be suspected for (crop) field populations, this showed that wild cyst nematodes have very low dispersal capabilities and are strongly disconnected from each other. Our results provide some key elements for designing pest control strategies , such as decreasing passive dispersal events to limit the spread of virulence among field nematode populations

The root-knot nematode producing galls on spartina altemiflora belongs to the genus Meloidogyne: rejection of Hypsoperine and Spartonema spp

International audienceRoot-knot nematodes are a major group of plant-parasitic nematodes, but their sister group within the Tylenchida remains to be identified. To find the sister group and for any investigation of the evolutionary biology of the genus Meloidogyne, it would be useful to identify the most basal species within Meloidogyninae. Meloidogyne spartinae, a root-knot nematode parasitic on cordgrass (Spartina spp.), constitutes a potentially interesting early, diverging (or at least highly divergent) root-knot nematode because it was originally described in a different genus, Hypsoperine (and later Spartonema), due to its unique anatomy and biology (although it was later pot in synonymy by some, but not all, taxonomists). We have sequenced the whole 18S rDNA of this species and compared it to other sequences of this region that are available in GenBank for numerous Meloidogyne species. Phylogenetic analysis unambiguously locates the branch corresponding to M. spartinae as a lately diverging species, more closely related to M. maritama, M. duytsi or the M. ardenensis-hapla group. Thus, the distinction of a separate genus (Hypsoperine or Spartonema) for this species is not justifie

Occurrence of the tobacco cyst nematode subspecies Globodera tabacum subsp virginiae in France

International audienceTobacco cyst nematode is a sexually diploid species composed of three subspecies, Globodera tabacum subsp. tabacum (Gtt), G. tabacum subsp. virginiae (Gtv) and G. tabacum subsp. solanacearum (Gts). In Europe, only Gtt have been reported to date. Here, we report from a plant in a French tobacco field, the identification of a mixture between cysts of the subspecies Gtt and cysts genetically different. The objective of the present study was to determine the subspecies status of those particular cysts. To this aim, we performed CAPS analyses on two genes and a principal component analysis on microsatellite data. The results obtained with both CAPS and microsatellite markers demonstrate for the first time the occurrence of G. tabacum subsp. virginiae in France

Intra-species DNA polymorphism in the tobacco cystnematode complex (Globoderatabacum) using AFLP

Amplified fragment length polymorphism (AFLP) was used to obtain information on the within-species geneticvariability of the tobacco cyst – nematode (TCN) complex. AFLP was found to be well suited to this type ofstudy. The current classification of TCN was confirmed. Results indicate that the Globodera tabacum solanacearumgroup, believed to be restricted to the U.S.A., also occurs in Mexico. The within-species variability of TCN is considerable.Populations from Mexico may form a new subgroup. AFLP group-specific markers were identified for two ofthe TCN subgroups: Globodera tabacum tabacum and Globodera tabacum solanacearum.La technique dite de l'AFLP a été utilisée sur les nématodes à kystes du tabac (TCN) afin d'acquérir des connaissances sur leur polymorphisme moléculaire intra-spécifique. L'efficience de la technique AFLP pour ce type d'études a été réaffirmée. La classification intra-spécifique des TCN communément admise est confirmée. Les résultats indiquent que le groupe Globodera tabacum solanacearum, jusqu'à présent décrit uniquement aux États-Unis, existe également au Mexique. Une variabilité intra-spécifique élargie est mise en évidence au sein des TCN. Des populations originaires du Mexique pourraient former un nouveau sous-groupe. Des marqueurs AFLP spécifiques pour deux des sous-groupes du complexe des TCN, Globodera tabacum tabacum et Globodera tabacum solanacearum, sont mis en évidence.Mots clés : Heteroderinae, classification, marqueurs, diversité génétique, distribution géographique

Influence of temperature on the hatch of Heterodera avenae Woll. populations from Algeria

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Intra-species DNA polymorphism in the tobacco cyst – nematode complex (<i>Globodera</i> <i>tabacum</i>) using AFLP

International audienceAmplified fragment length polymorphism (AFLP) was used to obtain information on the within-species genetic variability of the tobacco cyst - nematode (TCN) complex. AFLP was found to be well suited to this type of study. The current classification of TCN was confirmed. Results indicate that the Globodera tabacum solanacearum group, believed to be restricted to the U.S.A., also occurs in Mexico. The within-species variability of TCN is considerable. Populations from Mexico may form a new subgroup. AFLP group-specific markers were identified for two of the TCN subgroups: Globodera tabacum tabacum and Globodera tabacum solanacearum

New information about the phenotypic and genetic variability in the cereal cyst nematode complex

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Validation of two laboratory methods for beef intramuscular fat quantification

International audienceMany studies on beef nutritional qualities require the quantification of intramuscular fat. To reduce the sample amount, solvent use and time of analysis, two alternative methods to the Folch et al. (1957) reference method were studied: a miniaturised Folch's method and a near-infrared spectroscopic method. Performances and acceptability limits were evaluated with accuracy profiles for each of the methods. Equations to correct bias between the alternative and reference methods were calculated. Uncertainties associated with measurements were determined, and the validity domains were defined. From a previous set of studies, the ability of each method to discriminate samples from bovines of different breeds or receiving diverse treatments was tested. The validity domain of the miniaturised Folch's method ranged from 1.9 to 13.8 g of total lipids/100 g of tissue, and that of the near-infrared spectroscopic method ranged from 4.8 to 13.8 g of total lipids/100 g of tissue, with less than 20% difference from the reference method's results. Thus, the two alternative methods could be used depending on the research objectives: the miniaturised Folch's method could be used for detailed quantification of intramuscular fat and the near-infrared spectroscopic method for a quick classification of a large number of muscles. The precise knowledge of uncertainties associated with each measurement was determined, and perfect continuity with the results obtained so far with the reference Folch's method was confirmed

Origin and genetic diversity of Western European populations of the potato cyst nematode (Globodera pallida) inferred from mitochondrial sequences and microsatellite loci

International audienceNative to South America, the potato cyst nematode Globodera pallida is one of the principal pests of Andean potato crops and is also an important global pest following its introduction to Europe, Africa, North America, Asia and Oceania. Building on earlier work showing a clear south to north phylogeographic pattern in Peruvian populations, we have been able to identify the origin of Western European populations with high accuracy. They are all derived from a single restricted area in the extreme south of Peru, located between the north shore of the Lake Titicaca and Cusco. Only four cytochrome b haplotypes are found in Western Europe, one of them being also found in some populations of this area of southern Peru. The allelic richness at seven microsatellite loci observed in the Western European populations, although only one-third of that observed in this part of southern Peru, is comparable to the allelic richness observed in the northern region of Peru. This result could be explained by the fact that most of the genetic variability observed at the scale of a field or even of a region is already observed at the scale of a single plant within a field. Thus, even introduction via a single infected potato plant could result in the relatively high genetic variability observed in Western Europe. This finding has important consequences for the control of this pest and the development of quarantine measures

New information about the phenotypic and genetic variability in the cereal cyst nematode complex

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