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Inoculating scab in an apple orchard would facilitate the control of V. inaequalis pressure on experimental plots to enhance experiments of management methods. The technique presented here consists of the application of a conidial suspension made with conidia from a unique strain of V.inaequalis on growing shoots of apple trees. The creation of an optimal infection context consists of a good positioning of the inoculation and a use of the irrigation system to spray the foliage of apple trees. This methodology has been tested in a try in an orchard of twenty-year-old trees. Three factors known to influence the development and the dispersal of the disease were studied: the quantity of inoculum, the stage of development of the shoots and the number of shoots to inoculate. The inoculations did not produce any significant scab development. The technical is simple and easily reproducible but its implementation needs to be reconsidered to lead to a reliable service.; L’établissent d’une méthode d’inoculation de tavelure dans un verger de pommiers doit permettre à l’expérimentateur de maîtriser la pression du pathogène en vue d’optimiser les conditions d’expérimentation de méthodes de gestion. La méthode présentée ici repose sur l’application d’une suspension de conidies d’une souche unique de V. inaequalis sur des pousses de pommiers en croissance. La création d’un contexte favorable à l’infection fait aussi partie de la méthode, et repose sur le positionnement de l’inoculation et l’irrigation par aspersion sur frondaison de la parcelle. Cette méthodologie a fait l’objet d’un essai en verger. Afin de l’optimiser, trois facteurs pouvant influencer le développement et la dispersion de la maladie ont été étudiés : la quantité d’inoculum, le stade de développement des pousses et le nombre de pousses inoculées. Les inoculations n’ont pas conduit à un développement significatif de symptômes de tavelure. La technique adoptée est simple et reproductible, et n’est globalement pas remise en question, mais sa mise en oeuvre doit être retravaillée afin d’espérer aboutir à un service fiable à proposer.

La physique et la tavelure : édition 2015. 23. Journées Annuelles sur la Recherche et l'Innovation Technologique (JARIT 2015)

Modéliser la mouillure du feuillage : une approche réaliste et sans station météo. Journée Technique Agropomme

National audience; Water yam (Dioscorea alata), an important root tuber crop in the tropics, is affected by anthracnose caused by Colletotrichum gloeosporioides. In order to reduce the impact of epidemics while reducing fungicide applications, the use of a combination of resistant yam cultivars and cultural practices is required. Among cultural practices, staking is traditionally used to grow yam vines in small fields, but is not in larger fields where mechanization is more widespread. In the literature, contradictory results have been obtained in the eighties by researchers when trying to assess the effect of staking on the dynamics of anthracnose. We compared the disease dynamics in both staked and unstaked plots under natural infestation in humid pedoclimatic conditions, by measuring weekly severity indices across a 12x8 grid made of 1 m² units spaced by 1.5 m. Additionally, leaf wetness sensors were placed at several locations in both plots, and leaf wetness duration (LWD) as well as other climatic and microclimatic variables (e.g. relative humidity, air and canopy temperatures, wind speed and direction) were monitored every 15 minutes for 41 days. Disease incidence (percentage of diseased units) could not be measured as all the units were diseased at the time of the first measurements; however severity indices suggest that the incidence was higher in the staked plot at a given time, and that the disease may have appeared earlier than in the unstaked plot. After fitting a 3-parameter logistic model to the data, we found that both the rate of increase of the disease and the time at the inflexion point were significantly different in both plots: the point of inflexion (time when 50% severity level is reached) occured on average at 154 ±1.9 and 165 ± 1.6 days after plantation for staked and unstaked plants, respectively), but the rate of increase was higher for unstaked than staked plots (11.22 ± 0.97 and 9.28 ± 0.76 dimensionless, respectively). Comparing the microclimate in staked and unstaked plots, cumulated LWDs were significantly longer in unstaked (491 ± 37 hours) than in staked plot (371 ± 70 hours). We observed that in the tropical conditions of the experiment, the high relative humidity of the air led to significant dew deposition during every clear night, and that dew was the main contributor to leaf wetness duration overall. Disease dynamics differences observed between staked and unstaked plots could not be readily explained by LWD differences only, since one would have expected faster disease development in the unstaked plot than in the staked plot whereas the opposite was observed. It is likely that in the humid pedoclimatic conditions of the experiment, leaf wetness duration was not a limiting factor for disease development, and that other factors at disease onset (such as the source and density of primary inoculum) play a critical role.

Ascochyta blight (Mycosphaerella pinodes) development on pea is affected by leaf wetness duration (LWD) and temperature (1). The aim of this study was to investigate the effects of canopy architecture and development on microclimate and on ascochyta blight development in pea canopies with contrasting architectures under field conditions.A split-plot experiment was conducted at Le Rheu, France, in the spring of 2009 and 2010 with three pea cultivars (Athos, Antares and Gregor), each sown at two densities (80 and 40 seeds/m²) plus a third density in 2010 (30 seeds/m²). LWD and air temperature (Ta) were estimated respectively with leaf wetness sensors and thermocouples at the bottom and middle height of each canopy. Two mesoclimate parameters (LWD and Ta) were recorded with sensors placed at 1.50 m above the soil level. For each cropping season, microclimatic conditions prevailing during wetness episodes were compared according to the presence or absence of rainfall (rainfall and dry periods respectively).Differences were observed between meso- and microclimate parameters only on LWD but not on Ta. During rainfall periods, LWD was longer inside the canopy than outside (more than 3 to 10h daily). Conversely, during dry periods, LWD became shorter inside the canopy after canopy closure (decreased of 1 to 7h daily). In the denser canopies, these differences appeared first at the bottom. During dry periods, LWD due to dew was longer in the middle than at the base of the canopy, with an average daily LWD of around 4h that decreased during canopy development. When the canopy was completely closed, no LWD was recorded at the base of the plants. Moreover, cultivar Gregor with the greatest leaf area index (LAI) provided lower LWD than the two other cultivars. A plant density effect was also observed in 2010 with longer LWD (more than 2 to 6h daily) in the canopies with the lowest density for each cultivar as soon as canopy was closed. During rainfall periods, no leaf wetness distribution patterns were observed inside the canopy whatever the cultivar or the plant density with an average daily LWD of around 15h. In 2009, longer LWD were observed at the base level for each cultivar sown at the greatest density from two weeks before canopy closure (more than 2 to 5h daily). Regarding the effect of microclimate on disease development, we observed that during dry periods, temperatures were too low during wetness periods to favour disease development and correspondingly, a prediction model adapted from Magarey et al. (2) showed that infection periods occurred only during rainfall periods.Denser canopies limit water evaporation and prevent dew formation on leaves while the lowest canopy densities favour dew formation. Therefore the microclimates of denser canopies are the more favourable to disease development and led to greatest disease severities.

Many cultivars of water yam (Dioscorea alata) are affected by anthracnose epidemics due to Colletotrichum gloeosporioides. While there is neither authorized nor advisable pesticide treatment, the only way to limit disease impact is to use combination of partial plant resistances and cultural practices limiting fungi dispersion and development. Staking was traditionally used to grow yam on small plots but was no longer used in larger mechanized yam plots.In order to evaluate the role of staking in anthracnose epidemiology, we designed in 2011 an experiment to compare the disease dynamics and the microclimate within staked and unstaked yam plots. We recorded microclimatic variables (Radiation budget, wind speed, air temperature and relative humidity) 2 m above ground outside the plots and 1 m above ground into the plots between rows of 2m high stakes. Leaf temperature (LT) and leaf wetness duration (LWD) were recorded by appropriate sensors placed in vegetation at the bottom and the top of the stakes near the ground in unstaked plants.LWD was always recorded by all sensors when rainfall was greater than 1mm in a 15 minute time step. For a given rainfall, LWDs were longer in unstaked that in staked crop (up to 8 h LWD in unstaked plot, for 2 h LWD in staked plot). During clear nights with no rain, dew was deposited and measured LWDs were longer at the bottom than at the top of the stakes. Consistent differences of LT in the three canopy conditions were observed and confirmed by latent heat fluxes calculated from microclimatic data. The data recorded along the experiment were used to calibrate LWD models for the three canopy conditions. Simulations of LWD with data from two weather stations in contrasted climatic conditions of Guadeloupe, showed that staking may be efficient to limit periods favourable for disease development in drier climate, but not in regions where rainfalls are more frequent and intense.While traditional staking provides dense vegetation mound, trellising is increasingly used for yam. This practice leading to new vegetation spatial distribution may exhibit antagonist effect on fungi development and dispersion and should be investigated.

Soils represent a large source of the N2O greenhouse gas. N2O emissions peaks by soils are due to denitrification in anoxic conditions, for water contents close to saturation. The objective of the study was to continuously measure the N2O emissions by soil under controlled water content conditions. Measurements on undisturbed soil samples showed that initial N2O fluxes were about 0,5 mgN/m²/j at field capacity and reached a maximum value of 100 mgN/m²/j after wetting up to a water filled pore space equal to 0.8. The largest peaks, larger than 1000 mgN/m²/j, were recorded during desiccation but remained fleeting. For a second wetting/drying cycle, the same dynamics was observed, but absolute values of fluxes were lower. These phenomena demonstrated the role of i) wetting/drying dynamics evolution and ii) dynamics history in the understanding of N2O emissions by soils.; Les sols représentent une part importante des sources du gaz à effet de serre N2O. Les pics d’émissions de N2O par les sols sont attribués à la dénitrification qui se produit en condition anoxique, quand la teneur du sol est proche de la saturation. Le but de cette étude est de mesurer, en continu et en conditions contrôlées, la dynamique de réponse des émissions de N2O par le sol, à des teneurs en eau élevées. Nos résultats sur des échantillons de sol non perturbés montrent que les flux, de l’ordre de 0,5 mgN/m²/j lorsque les échantillons sont à la capacité au champ atteignent, lors de l’humectation, un maximum de l’ordre de 100 mgN/m²/j pour un indice d’eau de 0,8. Les flux les plus élevés (supérieurs à 1000 mgN/m²/j) se produisent lors de la dessiccation mais restent fugitifs. Lors d’un second cycle d’humectation/dessiccation, la même dynamique est observée, mais les flux sont légèrement plus faibles. Ces phénomènes déjà observés par certains auteurs mais peu expliqués montrent l’importance i) de la dynamique d’évolution de la teneur en eau (humectation vs dessiccation) et ii) de l’historique de cette dynamique, dans le déterminisme des émissions de N2O par les sols.

2 annexes, 2 p. Diplôme : Master Professionnel; In arboriculture, the use of pesticides is a key factor of production. But this implies a negative impact on the environment and human health. The combination of various methods or practices can be a partial alternative to chemical control being used against pests and diseases of apple. Compared to driving Solax the centrifuge one showed some interest by increasing the lighting in the foliage, the colour, improving the eating quality of apples and limiting the spread of certain pests and diseases. That’s why we conducted a study comparing the influence of centrifuge training on the development of scab and powdery mildew to another conduct, fusetto, which showed a lower incidence of powdery mildew and scab on fruit. On the whole, the wetness periods were shorter in fusetto than in centrifuge training. The results suggest that the training system can influence outbreaks of major diseases of apple in changing trees microclimate.; En arboriculture, l’utilisation des pesticides est un facteur clef de la production. Seulement cela implique des effets néfastes sur l’environnement ainsi que sur la santé humaine. La combinaison de diverses méthodes ou pratiques à effet partiel peut être une solution alternative à la lutte chimique actuellement utilisée contre les bioagresseurs du pommier. Par rapport à la conduite dite Solaxe, la centrifuge a montré un intérêt certain en augmentant l’éclairement au sein du feuillage, améliorant la coloration et la qualité gustative des pommes et en limitant la propagation de certains ravageurs et maladies. C’est pour cela que nous avons réalisé une étude comparant l’influence de la conduite centrifuge sur le développement de la tavelure et de l’oïdium à celle d’une autre conduite, la fusetto. Cette étude a montré une réduction de la tavelure sur fruit ainsi que de l’oïdium par rapport à la conduite centrifuge. Les durées d’humectation au niveau de la conduite fusetto étaient moins importantes, globalement, que celles enregistrées sur la conduite centrifuge. Les résultats obtenus révèlent que la conduite influence les épidémies des principales maladies du pommier en modifiant le microclimat au sein des arbres.

Il s'agit d'un emagazine; absent

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National audience

Due principalement aux précipitations sous forme de pluie ou de rosée, l’humectation des organes végétaux joue un rôle déterminant lors du processus de contamination des plantes par de nombreux agents phytopathogènes fongiques. Au même titre que la température, la durée d’humectation constitue une variable importante des modèles de simulation des épidémies et des systèmes d’avertissements agricoles. Une revue critique des méthodes instrumentales mises en oeuvre pour estimer la durée d’humectation à l’échelle de la feuille ou du couvert végétal est présentée, avec pour objectif de répondre à la demande émanant du secteur de la protection des plantes., Mainly as a result of precipitation in the form of rainfall or dew, moisture on leaves plays a major role during the process of plant infection by a number of fungal pathogens. Leaf wetness duration and temperature must be taken into account in developing plant disease epidemic models or agricultural warning systems. Natural and artificial causes of canopy wetness are described. Leaf wetness duration (a variable that is difficult to define) is governed by both leaf and canopy structural parameters. Several physical principles are used to construct various types of sensors (mechanical instruments, resistance sensors, radiometric methods). A critical review of the instrumentation available for measuring leaf wetness duration is presented. Both leaf and canopy scales are considered in an effort to answer the demand from plant pathology and plant protection specialists.

* INRA Documentation, Domaine St Paul, Site Agroparc, 84914 Avignon cedex 9 Diffusion du document : INRA Documentation, Domaine St Paul, Site Agroparc, 84914 Avignon cedex 9

Diplôme : Fin d'études

Diplôme : Fin d'études

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Diplôme : DAA

La présence d’eau libre à la surface des organes végétaux pendant un temps minimal est un facteur essentiel lors de la contamination de la plante-hôte par un champignon. Afin de prévoir l’occurrence de ce phénomène en terme de durée, un modèle multi-couches de transfert de masse et d’énergie est adapté au cas de la simulation de la durée d’humectation des feuilles après une pluie au sein d’un couvert végétal homogène. Le but est de spatialiser ce paramètre intéressant les phytopathologistes et qui ne fait l’objet actuellement que d’une estimation globale soit à l’aide d’une mesure standardisée au parc météorologique ou au champ, soit à l’aide d’un modèle simple de bilan d’énergie d’une surface. Nous proposons une paramétrisation originale du mode d’évaporation de l’eau sur les feuilles d’une couche divisée en une zone mouillée et une zone sèche. Les paramètres et variables de la modélisation sont classés au moyen d’une analyse de sensibilité : la capacité d’interception du couvert et son indice foliaire sont 2 paramètres fondamentaux, le mode d’évaporation de l’eau intervient dans une moindre mesure ; la plupart des autres paramètres peuvent être fixés à priori. Les variables externes (rayonnement net, température de l’air, humidité relative, vitesse du vent mesurée à une hauteur de référence au-dessus du couvert sur un pas de temps inférieur ou égal à l’heure) sont déterminantes dans les résultats de la simulation. Une application du modèle montre comment interagissent le couvert et le microclimat ; celui-ci permet de prévoir les conditions physiques régnant dans le couvert, caractérisées par de fortes variations verticales éventuelles, en particulier, en ce qui concerne les durées relatives des épisodes secs et mouillés des différentes strates d’un couvert moyennement à très développé., The persistence of free moisture on leaves for a minimal period of time is very important for the infection of plants by most fungi. In order to predict leaf wetness duration, we propose a one-dimensional multi-layer model of heat and mass transfer in a plant canopy after rainfall. Our aim was to describe the vertical variations of this parameter of interest for phytopathologists. Up till now, it has been measured only at a weather station or calculated from an energy balance model for a single surface without considering any vertical variation. An original aspect consisted in modelling water evaporation on leaves distinguishing wet and dry areas in every layer. We give a classification of the parameters and variables involved in the model according to the sensitivity analysis. The water intercepted by the canopy and the leaf area index were 2 important parameters ; water evaporation was less effective and the other parameters could be arbitrarily fixed. The forcing variables (net radiation, air temperature, relative humidity and wind speed measured hourly at a reference height above the canopy) governed the results of the simulation. We stress the value of such a model which takes into account the interactions between canopy and microclimate, and predicts the physical environment in the canopy, with particular regard to interrupted wet periods in different parallel layers of a medium-sized or tall canopy.

Matieres organiques dans les sols. ATP no.1059. CNRS-INRA-MER/MECV. Coordination PIREN/CNRS, document interne *INRA, Science du sol Montfavet (FRA) Diffusion du document : INRA, Science du sol Montfavet (FRA); National audience

Diplôme : Fin d'études

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