Transmission de descendants entre saisons culturales chez Leptosphaeria maculans selon la taille des populations

National audienc

An easy, rapid and accurate method to quantify plant disease severity: application to phoma stem canker leaf spots

International audienceAssessing plant disease severity and pathogen population size is central to epidemiological studies that help to devise disease control practices for crop protection. Among current methods, there is a trade-off between accuracy, defined as the closeness of the estimated value to the true value, and cost, defined as the consumption of resources that have to be spent in order to achieve the appropriate measurement. On the one hand, accurate methods based on counting lesion numbers per plant are time consuming. On the other hand, quick methods based on evaluations of diseased area, are adequate for varietal evaluation, but not sufficient for a quantitative ranking of numerous observations such as those required for an estimation of spore dispersal. A new method based on counting of leaf spots observed during 1 min in a delimitated one square meter area (lesions counted/m(2)/min, Mac.m2) was tested, using phoma stem canker as a case study in experimental plots and farmers' fields of oilseed rape. We showed that direct sampling of disease symptoms is feasible, reduces observation time and yields a continuous quantitative variable. We confirmed that: (i) lesions counted/m(2)/min (Mac.m2) values were correlated with mean number of leaf spots per plant (lesions/plant, Mac.pl); (ii) repeat phoma leaf spot counts of the same sample area by the two methods (Mac.m2 and Mac.pl) were correlated when assessed either by the same or different observers; and (iii) ranking of field plots with different disease severity was coherent among observers. We conclude that the lesions counted/m(2)/min (Mac.m2) method is equal in performance to the lesions/plant (Mac.pl) method, and was faster. Used with care, this method will facilitate studies requiring disease severity estimates, which were previously hampered by cost and/or tim

Connected populations for detecting quantitative resistance factors to phoma stem canker in oilseed rape [i](Brassica napus[/i] L.)

International audienceImprovement of effectiveness and durability of disease resistance in crops most often relies on the use of quantitative resistance, with the hypothesis that a wide range of quantitative resistance factors (QTL) makes the overcoming of the resistance by the pathogen more difficult. For an optimum use of these QTL in effective and durable strategies of resistance deployment, there is a need to precisely know their localization but also their stability/specificity and their allelic effects in various genetic backgrounds. Stem canker caused by the fungus Leptosphaeria maculans is one of the most important diseases in oilseed rape. In this Brassica napus-L. maculans pathosystem, QTL were previously identified by linkage analysis using populations derived from biparental crosses that were analyzed separately. In this study, we explored new quantitative resistance factors using a multi-cross connected design derived from four resistant lines crossed with a single susceptible line. Independent and connected mapping analyses revealed to be complementary to get an overview of QTL organization. We validated different QTL across different years and genetic backgrounds and identified novel QTL which had not yet been mapped. Population-common and population-specific QTL were identified. Knowledge of QTL organization and effects should help in the rational choice of relevant factors in breeding resistant genotypes to be integrated with other control means such as cultural practices and rotations for durable management of the diseas

New insights into the genetic basis of premature ovarian insufficiency: Novel causative variants and candidate genes revealed by genomic sequencing

International audienceOvarian deficiency, including premature ovarian insufficiency (POI) and diminished ovarian reserve (DOR), represents one of the main causes of female infertility. POI is a genetically heterogeneous condition but current understanding of its genetic basis is far from complete, with the cause remaining unknown in the majority of patients. The genes that regulate DOR have been reported but the genetic basis of DOR has not been explored in depth. Both conditions are likely to lie along a continuum of degrees of decrease in ovarian reserve. We performed genomic analysis via whole exome sequencing (WES) followed by in silico analyses and functional experiments to investigate the genetic cause of ovarian deficiency in ten affected women. We achieved diagnoses for three of them, including the identification of novel variants in STAG3, GDF9, and FANCM. We identified potentially causative FSHR variants in another patient. This is the second report of biallelic GDF9 and FANCM variants, and, combined with functional support, validates these genes as bone fide autosomal recessive “POI genes”. We also identified new candidate genes, NRIP1, XPO1, and MACF1. These genes have been linked to ovarian function in mouse, pig, and zebrafish respectively, but never in humans. In the case of NRIP1, we provide functional support for the deleterious nature of the variant via SUMOylation and luciferase/β-galactosidase reporter assays. Our study provides multiple insights into the genetic basis of POI/DOR. We have further elucidated the involvement of GDF9, FANCM, STAG3 and FSHR in POI pathogenesis, and propose new candidate genes, NRIP1, XPO1, and MACF1, which should be the focus of future studies