National audienceWhile on-farm conservation was considered minor in the development of the National Charter on Genetic Resources in 1998, there is increasing recognition of its important role in the conservation of genetic diversity. In addition to amateur gardening associations that save and exchange seeds, farmers in France have formed networks around systems of shared seed conservation and exchanges, with the goal of protecting the diversity of cultivated species. Parallel to this, the contribution of farmers to the dynamic management of agricultural biodiversity has been recognized by many scientific studies and in international treaties. These developments led us to examine the complementary nature of on-farm and gene-bank conservation efforts in terms of the management of genetic resources. This study, which combines ethnobotanical and genetic approaches, was conducted on bread wheat, for which France has a national collection of 10 000 accessions. There is also an active network of farmers who cultivate historic varieties and landraces, including the Rouge de Bordeaux, which was chosen for a detailed study. By conducting individual interviews with farmers, we were able to understand better their management practices, seed exchanges with other farmers and with the national collection, and strategies for maintaining and selecting this variety on their own farms. We characterized the genetic diversity conserved by several farmers and in the samples preserved in the national collection for Rouge de Bordeaux by using a comparative genetic analysis of samples obtained from farmers and from the collection, in light of the management practices and exchange networks that exist among farmers and between farmers and the national collection. Our results demonstrate that the diversity of these populations is far from being redundant. While certain samples are quite homogeneous and similar to samples from the national collection, others are highly heterogeneous. There is also a high degree of genetic differentiation among populations, with clear groupings of populations identified. The structure of the diversity may be explained by the structure of exchanges and the development of local adaptation within the populations to environmental conditions and management practices, and by differing strategies of selection and conservation. Further analysis will help us understand more precisely what defines a variety and what type of genetic diversity or phenotypic traits are conserved with different management strategies. Our results also support a greater degree of seed circulation between farmers' fields and the national collection, to conserve the adaptive potential and a broader range of genetic diversity for each variety.Considérée comme mineure lors de la rédaction de la Charte nationale des ressources génétiques en 1998, la gestion à la ferme a depuis gagné en importance et en reconnaissance. En effet, après les associations de jardiniers amateurs, des réseaux d'agriculteurs se sont fédérés en France autour de systèmes mutualistes de sélection/conservation de la diversité cultivée. Parallèlement, la contribution des paysans à la gestion dynamique de l'agrobiodiversité a été scientifiquement et institutionnellement reconnue. Ces éléments nous ont conduit à examiner les complémentarités dans la gestion des ressources génétiques à la ferme et en collection. Cette étude, qui croise des approches ethnobotanique et génétique, a été menée sur le blé tendre pour lequel il existe en France une collection nationale de 10 000 accessions et un réseau actif d'agriculteurs-collectionneurs de variétés. Pour la variété Rouge de Bordeaux, nous avons tenté de caractériser la diversité dans les champs et en collection, en procédant à une analyse génétique d'échantillons obtenus auprès d'agriculteurs et auprès de la collection. Nos résultats montrent que les ressources génétiques conservées dans les deux compartiments sont loin d'être redondantes. La structuration de la diversité s'explique par les réseaux d'échanges de semences (entre paysans, et entre les paysans et la collection), par l'adaptation locale des populations aux conditions du milieu et aux pratiques de culture, et par les pratiques de sélection/conservation. Ces résultats appellent des analyses complémentaires pour comprendre précisément ce qui est conservé/cultivé sous un nom variétal donné, et plaident en faveur d'une circulation accrue des semences entre champs et collection