Résumé
The population genetic theory of isolation by distance was applied to infer seed exchange between farmers of two very different crop species, barley and pearl millet, in semi-arid regions of Syria and Rajhastan, India, respectively. Gene flow data between populations of landraces were obtained from genetic markers and plotted against geographic distance. It was anticipated that restricted seed exchange would be reflected by exponentially decreasing gene flow with increasing geographic distance. While seed management of barley landraces in Northern Syria seems to be characterised by locally restricted seed exchange, a significant seed exchange over long distances was observed for pearl millet landraces in Rajhastan. It appears that these contrasting results can not only be explained by different mating systems of the crop species, but by different strategies to maintain local landraces. (Résumé d'auteur)