Cédric Loi

Comparison of three approaches to model grapevine organogenesis in conditions of fluctuating temperature, solar radiation and soil water content.

BACKGROUND AND AIMS There is increasing interest in the development of plant growth models representing the complex system of interactions between the different determinants of plant development. These approaches are particularly relevant for grapevine organogenesis, which is a highly plastic process dependent on temperature, solar radiation, soil water deficit and trophic competition. METHODS The extent to which three plant growth models were able to deal with the observed plasticity of axis organogenesis was assessed. In the first model, axis organogenesis was dependent solely on temperature, through thermal time. In the second model, axis organogenesis was modelled through functional relationships linking meristem activity and trophic competition. In the last model, the rate of phytomer appearence on each axis was modelled as a function of both the trophic status of the plant and the direct effect of soil water content on potential meristem activity. KEY RESULTS The model including relationships between trophic competition and meristem behaviour involved a decrease in the root mean squared error (RMSE) for the simulations of organogenesis by a factor nine compared with the thermal time-based model. Compared with the model in which axis organogenesis was driven only by trophic competition, the implementation of relationships between water deficit and meristem behaviour improved organogenesis simulation results, resulting in a three times divided RMSE. The resulting model can be seen as a first attempt to build a comprehensive complete plant growth model simulating the development of the whole plant in fluctuating conditions of temperature, solar radiation and soil water content. CONCLUSIONS We propose a new hypothesis concerning the effects of the different determinants of axis organogenesis. The rate of phytomer appearance according to thermal time was strongly affected by the plant trophic status and soil water deficit. Furthermore, the decrease in meristem activity when soil water is depleted does not result from source/sink imbalances.

A Stochastic Growth Model of Grapevine with Full Interaction Between Environment, Trophic Competition and Plant Development

Grapevine development is mainly determined by environmental factors whose effects are modulated by its complex topological structure. The trophic relationships between all the organs of the different axes appear to be the main underlying process which drive axis organogenesis in fluctuating environment. A new modelling approach is proposed based on GreenLab formalism in which axis organogenesis is controlled by stochastic processes according to trophic competition between the different axes. In this model, a water budget was also implemented to account for the effects of water depletion. The model was validated at organ and axis scales on a large range of environmental conditions in terms of photosynthetic active radiation, temperature and soil water supply. The efficiency of the model to simulate plant development at a detailed scale proved its ability to further analyse of the retroactions between plant development and the different environmental variables in order to improve crop management.

Plants as Combinatorial Structures and Applications

In this article, we introduce a new method allowing the computation of the distribution associated to the number of complex structures in plants deriving from GreenLab type growth model. In order to use this method, we set a new mathematical framework based on combinatorics. We show how plants can be seen as plane rooted trees and how their topology can be described by Dyck words. Moreover, we integrate plant growth in the formalism by adapting stochastic F0L-systems to the framework. This new representation enables not only the computation of the distribution associated to all types of organ but also the analysis of particular patterns thanks to a symbolic method. This approach gives new kinds of applications such as estimating the age of a plant from a set of botanical data.

A Symbolic Method to Analyse Patterns in Plant Structure

Formal grammars like L-systems have long been used to describe plant growth dynamics. In this article, they are used for a new purpose. The aim is to build a symbolic method derived from computer science that enables the computation of the distribution associated to the number of complex structures in plants whose organogenesis is driven by a multitype branching process. To that purpose, a new combinatorial framework is set in which plant structure is coded by a Dyck word. Moreover, the organogenesis is represented by stochastic F0L-systems. By doing so, the problem is equivalent to determining the distribution of patterns in random words generated by stochastic F0L-system. This method leads directly to numerous applications like parametric identication for plant growth model.