Plant architectural and genetic diversities in Coffea native from Madagascar : Towards an architectural-functional plant growth model applied to Coffea biodiversity perservation

The Coffea genus includes 103 species with 53 endemic to Madagascar (namely Mascarocoffea).The three main centres of species diversity for coffee trees are Madagascar (naturally low-caffeine species), Cameroon and Tanzania. However, Madagascar has the higher Coffea diversity in terms of total number of species due to the great variety of forest types including littoral, evergreen, gallery, mixed deciduous, dry, xerophytic and high-altitude. During these last 20 years, deforestation in Madagascar has become dramatic and has drastically reduced the distribution area of Coffea species. The collection maintained at the Kianjavato Research Station is unique since no living material is authorized to be conserved out of Madagascar. Conservation strategies based on scientific data are needed and become urgent in terms of biodiversity preservation and sustainable development. Recent studies in Coffea trees showed that their phenotypic plasticity could be explain the restricted distribution of Coffea species. Our recent preliminary results showed a high architectural diversity (i.e. architectural model, growth process, branching degree, branch location) between Coffea species and an interspecific variability of functional traits (Leaf Area Mass, wood density). The functional-structural model GreenLab is a dynamic model taking into account architectural plasticity of the plants and biomass allocation to organ level. Potentials of GreenLab model to represent environment x genotype interactions, in particular through its stable endogenous parameter as such the organ sink functions have been demonstrated in some species and they will be tested for Coffea species. The present study focuses on 5 species endemic to Madagascar with different phenotypic traits and forest habitats. For each species, architecture and genetic comparative analyses between individuals growing in situ (natural forest) and ex situ (common garden test) will be performed. In addition, we have set up two experimental stands to analyse the site effect. These whole results will be used to introduce genetic factors into the GreenLab model. The global aim of our approach is to analyse the adaptive capacity and phenotypic plasticity at the individual level within Coffea populations. (Texte intégral)