France
November 24, 2009

Node canker is one of the principal leaf diseases affecting wheat in France and many other European countries. Two parasitic fungi are responsible for this disease: currently the most widespread is Mycosphaerella graminocola. It can cause major yield losses and its strains can sometimes rapidly develop fungicide resistance. INRA researchers, working in partnership with INRIA*, have developed epidemic models that take account of the structure of the plant canopy on which these epidemics develop; they have explored how the canopy architecture of wheat plays a role in disseminating the disease. This work has also been able to identify some of the parameters of canopy architecture involved in curbing epidemics

In a field of wheat, the leaf surface area can reach up to four times that of the soil surface area.  How does node canker propagate within this architectural structure?  This virtual approach to simulating plants and pathogens differs from the other epidemic models available at present in that it integrates explicitly the development of wheat canopy architecture associated with the proliferation of one of its pathogens.  Indeed, canopy architecture may define the substrate on which the pathogens develop. For example, it will determine the distances that spores need to travel in order to infect new tissues.  The plant and pathogen models are dynamic and combined to simulate the spread of the epidemic.  This approach has also been applied to vines by INRA scientists at the Bordeaux-Aquitaine Research Centre.   The epidemic spreads as the canopy develops.  The epidemic results from a succession of infective cycles during which spores are produced and then dispersed by splashing (adapted from: Robert et al. 2008) How does the canopy architecture of wheat affect the dissemination of disease? In the context of the INRA-INRIA Virtual Plant project, INRA researchers in Versailles-Grignon have developed a virtual simulation model.  Under different climatic scenarios, they can simulate the dissemination of node canker within the wheat canopy and explore the role of canopy architecture in development of the epidemic.  Their work aims to identify components in the canopy architecture that could curb the spread of epidemics.  At each time step, the model simulates canopy development (3D wheat development module), the development of lesions on leaves leading to the production of spores (Infective cycle module) and the dispersion of spores by splashing when raindrops reach spore-producing lesions (Dispersion module).   Three principal canopy characteristics are involved in the development of an epidemic: - the distance between leaves, because this limits the flow of droplets loaded with spores from infected leaves to healthy leaves at the top of the canopy, - the quantity of leaf tissue available, because this determines the surfaces where lesions develop and the "umbrella" effect of leaves at the top of the canopy over infective surfaces at the base, - the density and orientation of leaves that modify the penetration pathway of rainwater and hence the probability of leaf-to-leaf spore transmission. Such a model thus makes it possible to identify the architectural parameters involved in the development of epidemics.  These favourable architectural parameters could then be prevented, while those that contribute to curbing an epidemic would be encouraged. At the crop level, a susceptibility analysis performed for three contrasting climate types suggested that a node canker epidemic could be curbed: - significantly when the rate of plant development is rapid, - less rapidly when the leaf surface area is reduced and the rates of leaf extension and plant height are increased. Development of this model opens the way to taking account of other interactions between the development of wheat and that of its pathogen, such as the age of plant organs, their physiological status (e.g. carbon or nitrogen content) or the light and moisture induced by modifications to canopy architecture.  Indeed, all these variables affect the biological cycles of the fungus responsible for node canker. Applications for these findings could include, firstly, an aid to defining cultivation practices adapted to climatic conditions that will reduce the need for treatments with plant health products, and secondly, the design of optimised wheat ideotypes.   * INRIA Virtual Plant project team (INRIA: French National Institute for Research in Computer Science and Control) References: Robert C. Fournier C. Andrieu B. Ney B. 2008. Coupling a 3D virtual wheat (Triticum aestivum) plant model with a Septoria tritici epidemic model (Septo3D) : a new approach to investigate plant-pathogen interactions linked to canopy architecture, Functional Plant Biology, 2008, 35, 997-1013

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Published: November 24, 2009