Taking into account the diversity of environment and practices to each agroecological system needs decentralized approaches, which means taking into account genotype environment interactions, and associate empirical knowledge from practitioners to scientific knowledge from researchers.The objectives of this PhD is to develop a participatory plant breeding methodology on bread wheat, based on decentralization and co-construction between farmers, NGOs and reasearch team DEAP from INRA Le Moulon.This approach aims to create population-varieties adapted to environments and farmers' practices, to develop methods and tools for breeding and cultivated biodiversity management and to reinforce learning and autonomy of farmers for breeding.This work contributed to reach these objectives, especially the last two, based on an interdisciplinary approach in statistics, quantitative genetic, populations genetic, bio-informatic and sociology.Objectives were partly reach with creation of methods and tools : monitoring sheet of the crop, data base which manage relation between seed lots in a large network of actors, experimental design on farm and statistical methods that take into account the disequilibrium of trials on farm, taking advantage of the large network, in order to make mean comparisons on farm and analyse genotype x environments interactions in the network of farms, software which create a folder with personalised results for each farmer, technical booklet on participatory plan t breeding.A phenotypic and molecular analysis shows that the programme takes part in in-situ management of genetic resources by creating new population-varieties and their management in a broad network of farms.Moreover, farmers reinforce their learning and their autonomy. They were actors of the programme and their practices evolved with, for example, an increasing number of populations evaluated on the network, of selection, of seed exchange between farmers as the project go on.Two innovations emerged from this project : organisational and genetic. The organisational innovation correspond to the way the project worked, based on decentralisation of the selection directly on farms and co-construction between actors and their networked. Genetic innovations are the consequence of this organisation : a brad genetic and phenotypic diversity has been created, and maintain and evaluated on farms and new population-varieties, coming from the project, are used by farmers on their farms.The methodology that we developed is evolutive, flexible and adaptable. It put farmers in the heart of selection and biodiversity management. This project contribute to a transition toward a new seed system adapted to agroecology.
