4 research outputs found
Modélisation du mouvement des chevreuils dans un paysage bocager simulé : premiers résultats, projets
Les tiques, dont Ixodes ricinus, espĂšce la plus rĂ©pandue en Europe, sont vecteurs de nombreux agents pathogĂšnes, protozoaires, bactĂ©ries ou virus, qui peuvent ĂȘtre responsables de maladies touchant lâHomme (Borreliose de Lyme) ou lâanimal(babĂ©siose bovine). En vue dâidentifier les zones Ă risque vis-Ă -vis de ces maladies, il est important de connaĂźtre la distribution spatiale des tiques. Cette distribution dĂ©pend dâune part des conditions locales de tempĂ©rature et dâhumiditĂ©, dâautre part des mouvements des hĂŽtes des tiques(Estrada-Peña, 2002). Les chevreuils sont notamment reconnus pour influencer fortement la densitĂ© de tiques(Ruiz-Fons et Gilbert 2010) et se dĂ©placer sur de longues distances. Dans le cadre de lâestimation spatiale des risques, il est nĂ©cessaire de disposer dâun modĂšle de dĂ©placement des hĂŽtes en fonction des caractĂ©ristiques du paysage, dont le dĂ©veloppement nâa pas Ă©tĂ© rĂ©alisĂ© Ă ce jour. Dans un premier temps, une approche thĂ©orique a Ă©tĂ© privilĂ©giĂ©e. Un modĂšle du paysage a Ă©tĂ© dĂ©veloppĂ© via une tesselation de VoronoĂŻ et un processus de marquage. Au sein de ce paysage modĂ©lisĂ©, le mouvement du chevreuil est modĂ©lisĂ© par des Ă©quations diffĂ©rentielles stochastiques. Ce mouvement se dĂ©compose donc en deux termes : un de dĂ©rive, qui dĂ©pend dâune fonction de potentiel reliĂ©e aux diffĂ©rents habitats qui composent le paysage, et un terme de diffusion. A partir dâune premiĂšre fonction potentielle, il est donc possible de simuler le dĂ©placement dâun individu dans un paysage modĂ©lisĂ©. Les dĂ©veloppements actuels visent dans un premier temps Ă tester diffĂ©rentes fonctions de potentiel en fonction de nos connaissances sur le comportement du chevreuil. LâĂ©tape suivante consistera Ă dĂ©velopper des mĂ©thodes dâinfĂ©rence afin dâestimer les paramĂštres Ă partir de donnĂ©es simulĂ©es ou observĂ©es. Par la suite le prototype obtenu pourra ĂȘtre utilisĂ© pour tester lâinfluence des caractĂ©ristiques du paysage sur le mouvement des chevreuils. Enfin, un couplage avec un modĂšle de dynamique de population de tiques (Hoch et al, 2010) fournira des aires de rĂ©partition simulĂ©es des vecteurs
Automated image processing framework for analysis of the density of fruiting bodies of Leptosphaeria maculans oilseed rape stems
International audienceUnderstanding the transmission of plant pathogen inoculum during the periods when the host plants are not present is crucial for predicting the initiation of epidemics and optimizing mitigation strategies. However, inoculum production at the end of the cropping season, survival during the intercrop period, and the emergence or release of inoculum can be highly variable, difficult to assess, and generally inferred indirectly from symptom data. As a result, a lack of large datasets hampers the study of these epidemiological processes. Here, inoculum production was studied in Leptosphaeria maculans, the cause of phoma stem canker of oilseed rape. The fungus survives on stubble left in the field, from which ascospores are released at the beginning of the next cropping season. An image processing framework was developed to estimate the density of fruiting bodies produced on stem pieces following incubation in field conditions, and a quality assessment of the processing chain was performed. A total of 2540 standardized RGB digital images of stems were then analysed, collected from 27 oilseed rape fields in Brittany over four cropping seasons. Manual post-processing removed 16% of the pictures, e.g. when moisture-induced darkening of the oilseed rape stems caused overestimation of the area covered with fruiting bodies. The potential level of inoculum increased with increasing phoma stem canker severity at harvest, and depended on the source field and the cropping season. This work shows how image-based phenotyping generates high-throughput disease data, opening up the prospect of substantially increased precision in epidemiological studies
Besides stem canker severity, oilseed rape host genotype matters for the production of Leptosphaeria maculans fruit bodies
International audienceFor fungal cyclic epidemics on annual crops, the pathogen carry-over is an important but poorly documented step. Plant resistance affects the pathogen development within the epidemics but we lack data on the interannual transmission of inoculum. For Leptosphaeria maculans on 15 oilseed rape genotypes in field during 4 growing seasons, stem canker severity was visually scored at harvest. The number of fruit bodies produced on incubated stubble was quantified using an automated image analysis framework. Our results confirm that fruit body production increases with disease severity and is significantly affected by host genotype and nitrogen supply. Tracking individual stems through incubation, we confirm for the first time that the oilseed rape genotype has a direct effect on inoculum production, not only disease severity. This major effect of genotype on inoculum carry-over should be taken into account in models of varietal deployment strategies
Identifying fungal leaf spots on oilseed rape: could pictures help?
Abstract From sowing in late summer until harvest in following summer, oilseed rape can be infected by several fungi, which foliar symptoms (leaf spots) coexist on the crop. Training an expert at their identification is quick for the typical symptoms with characteristic appearance. However, in many cases the size, colour and morphology are similar and for the atypical symptoms, there is a risk of confusion or in-decidability. Also, scouting the fields for expert training is not possible at all seasons and all diseases might not be seen in all years and all places. The aim of our study was to produce large sets of pictures annotated by several experts, from which tables illustrating the diversity of symptom appearance were chosen. These tables will enable assistance to diagnostic and expert training