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Le nématode à kyste du soja (NKS), Heterodera glycines, est un nématode phytoparasite causant des pertes de rendement considérables dans la culture de soja. Il a été détecté pour la première fois au Québec en 2013. Nous présentons ici les résultats d’une enquête visant à déterminer les régions affectées par ce ravageur et la densité de populations présentes au Québec. Au cours des trois dernières années (2013-2015), le NKS a été détecté dans 54 échantillons (32 % des champs testés) répartis dans les 10 régions productrices de soja du Québec. Les densités de populations trouvées étaient par contre très faibles, à la limite de détection. Parmi les régions testées, l’Estrie présentait la plus forte proportion de champs positifs (63 %). Étonnamment, cette proportion n’était que de 7 % en Montérégie-Ouest, là où la première détection a pourtant eu lieu et où se concentre la production de soja. Dans l’ensemble, la qualité des kystes récupérés était pauvre et le nombre d’oeufs très faible. Même si les populations sont encore négligeables, le NKS est bel et bien présent au Québec et il ne pourra pas être éradiqué. Diverses mesures devraient donc être mises en oeuvre afin de limiter la dispersion et l’accroissement des populations de ce ravageur important., The soybean cyst nematode (SCN), Heterodera glycines, is a plant parasite that causes considerable yield loss in soybean crop. It was detected for the first time in Quebec in 2013. Here, we present the results of a survey aimed at identifying the regions affected by this pest and the density of its populations in Quebec. Over the last 3 years (2013-2015), SCN was detected in 54 samples (32% of fields tested) from the regions that produce soybean in Quebec. However, population density was very low, barely reaching the point of detection. Among the tested regions, the Eastern Townships had the highest proportion of fields that tested positive (63%). Surprisingly, this proportion was only 7% in Montérégie-Ouest, the centre of soybean production in Quebec, where SCN was first detected. Overall, the quality of the cysts collected was poor and the number of eggs was very low. Even if its populations are still low, SCN is present in Quebec and will not be eradicated. Therefore, different measures should be enforced to limit the spread and population growth of this important pest.

Background In hyperspecialized parasites, the ability to grow on a particular host relies on specific virulence factors called effectors. These excreted proteins are involved in the molecular mechanisms of parasitism and distinguish virulent pathogens from non-virulent related species. The potato cyst nematodes (PCN) Globodera rostochiensis and G. pallida are major plant-parasitic nematodes developing on numerous solanaceous species including potato. Their close relatives, G. tabacum and G. mexicana are stimulated by potato root diffusate but unable to establish a feeding site on this plant host. Results RNA sequencing was used to characterize transcriptomic differences among these four Globodera species and to identify genes associated with host specificity. We identified seven transcripts that were unique to PCN species, including a protein involved in ubiquitination. We also found 545 genes that were differentially expressed between PCN and non-PCN species, including 78 genes coding for effector proteins, which represent more than a 6-fold enrichment compared to the whole transcriptome. Gene polymorphism analysis identified 359 homozygous non-synonymous variants showing a strong evidence for selection in PCN species. Conclusions Overall, we demonstrated that the determinant of host specificity resides in the regulation of essential effector gene expression that could be under the control of a single or of very few regulatory genes. Such genes are therefore promising targets for the development of novel and more sustainable resistances against potato cyst nematodes. Electronic supplementary material The online version of this article (10.1186/s12864-019-5853-4) contains supplementary material, which is available to authorized users.

Studying phenotypic and genomic modifications associated with pathogen adaptation to resistance is a crucial step to better understand and anticipate resistance breakdown. This short review summarizes recent results obtained using experimentally evolved populations of the potato cyst nematode Globodera pallida. In a first step, the variability of resistance durability was explored in four different potato genotypes carrying the resistance quantitative trait loci (QTL) GpaV(vrn) originating from Solanum vernei but differing by their genetic background. The consequences of the adaptation to resistance in terms of local adaptation, cross-virulence and virulence cost were then investigated. Finally, a genome scan approach was performed in order to identify the genomic regions involved in this adaptation. Results showed that nematode populations were able to adapt to the QTL GpaV(vrn), and that the plant genetic background has a strong impact on resistance durability. A trade-off between the adaptations to different resistant potato genotypes was detected, and we also showed that adaptation to the resistance QTL GpaV(vrn) from S. vernei did not allow adaptation to the colinear locus from S. sparsipilum (GpaV(spl)). Unexpectedly, the adaptation to resistance led to an increase of virulent individual's fitness on a susceptible host. Moreover, the genome scan approach allowed the highlighting of candidate genomic regions involved in adaptation to host plant resistance. This review shows that experimental evolution is an interesting tool to anticipate the adaptation of pathogen populations and could be very useful for identifying durable strategies for resistance deployment.

International audience; Trade-offs between virulence (defined as the ability to infect a resistant host) and life-history traits are of particular interest in plant pathogens for durable management of plant resistances. Adaptation to plant resistances (i.e., virulence acquisition) is indeed expected to be associated with a fitness cost on susceptible hosts. Here, we investigated whether life-history traits involved in the fitness of the potato cyst nematode Globodera pallida are affected in a virulent lineage compared to an avirulent one. Both lineages were obtained from the same natural population through experimental evolution on resistant and susceptible hosts, respectively. Unexpectedly, we found that virulent lineages were more fit than avirulent lineages on susceptible hosts: they produced bigger cysts, containing more larvae and hatching faster. We thus discuss possible reasons explaining why virulence did not spread into natural G. pallida populations.

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. .

International audience; In order to identify genes involved in pathogenicity, we compared the closely related species Globodera pallida (GP) and Globodera "mexicana" (GM) that have different host ranges and are able to produce viable and fertile hybrids. Three pioneer genes were previously identified as differentially expressed between GP and GM: GPLIA7 and GPLIB3 were found to be more highly expressed in GP, whereas GMLIVG9 was found more highly expressed in GM. In this study, we showed that Ia7 and IVg9 genes probably encode products secreted by the subventral oesophageal glands and the dorsal oesophageal gland, respectively. No Blast homolog was found in the databases, but a metridin-like ShK (Stichodactyla helianthus) toxin domain was identified in the Ia7 sequence. Analysis of the full-length sequences of these 2 genes between GP and GM revealed a high level of interspecies variability (8% for the Ia7 transcript and 17% for the IVg9 transcript) and a high proportion (90%) of nonsynonymous mutations among the substitutions observed. This suggested that these 2 pioneer genes are under strong diversifying selection pressures and therefore may be involved in pathogenicity. Further investigations of the sequence polymorphism of Ia7 and IVg9 genes were conducted in GP x GM hybrid lines that were selected in laboratory conditions for their different ability to develop on potato and black nightshade. As similar sequences were obtained for all the hybrid lines tested independently of their pathogenicity status, no correlation could be established between IA7 and IVG9 amino acid changes and the host range differences observed between GP and GM