Résumé
Sorghum is the Duupa 'cultural supercrop' : it is a main subject of concern for the people and the backbone of the reproduction, on a material and a symbolic way, of the community. More than forty landraces are named and recognized, and widely exchanged between all cultivators in the community. Each year, every cultivator selects panicles from his own previous crop but often mix it with exchanged seeds. Fluxes of seeds follow the lines of kinship or affinal relations, but they can also come from commercial transactions outside the community. An outstanding feature of the Duupa seed system is the institution of free access to sorghum seeds during the collective threshing work parties. Anyone attending these parties can pick a few panicles for his own seeds on the bulk of the crop to be threshed. Strong moral values underline this safety net, which makes the diversity of landraces, seeds a common property. However, these institutionalized exchanged do not account for all the gene flux and people also rely on non-institutionalized, transfers sometimes including grains for current food use rather than properly selectionized panicles. All these transfers, public as well as private, even if difficult to quantify, should be taken into account for a proper understanding of the shaping of sorghum varietal and genetic diversity. (Résumé d'auteur)