Etude de l’hybridation inter-spécifique entre espèces du genre Coffea en Nouvelle-Calédonie : distribution des niches favorables et structuration de la diversité

Abstract : Coffee trees are originated from inter-tropical forests of Africa and Madagascar and their diversification origin areas are highly threatened. Among the 103 species of the Coffea genus, only three are cultivated: C. arabica, C. canephora and C. liberica. C. canephora has the widest natural distribution in tropical African forests, and its genetic diversity is structured in five distinct groups. The study of the genetic diversity structuring has revealed a particular importance of the Dahomey gap floristic breaking as biogeographic barrier, as well as the past climatic variations on the diversity structuring (model to study the “refuge theory”). A core set of both wild and cultivated (represented in majority by inter-group hybrids) accessions was selected to characterize the introduced diversity in New-Caledonia (since 1856). On introduced New-Caledonian sample, high levels of genetic diversity have been revealed for C. canephora and C. liberica while as expected, low level of diversity has been revealed for C. arabica. These three species (C. liberica to a lesser extent) have been introduced in different regions of New Caledonia for their culture. Because of economical reasons, a lot of traditional coffee plantations have been abandoned during the Second World War, leaving the cultivars to evolve in natural conditions. Inter-specific hybridizations are occurring between coffee species (at a level of 3% according to the study of a tri-specific population) thanks to a removal of reproductive barriers facilitated by particular environmental conditions. An environmental expertise based on the comparisons of environmental conditions between Sarramea region and African origin regions of the three species has underlined the favorable environmental combinations to sympatry and inter-specific hybridizations. Equilibrium between draining and humidity, precipitations sequences and the forest cover are important parameters maintaining a favorable microclimate. The canopy forest study by remote sensing tools has reinforced the predicting distribution model of favorable niches to inter-specific hybridization thanks to the information brought on canopy heterogeneity and large tree crowns and to the spatial resolution improving the detection of micro-habitats. Favorable niches are micro-environments distributed throughout the study area. The question is to underline the preservation of such de novo adapted coffee genetic resources.
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Céline Gomez. Etude de l’hybridation inter-spécifique entre espèces du genre Coffea en Nouvelle-Calédonie : distribution des niches favorables et structuration de la diversité. Biodiversité. Université de la Nouvelle-Calédonie, 2009. Français. ⟨tel-01252685⟩

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