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Arriola, P.E. Résumé Les problemes potenciels lies a la diffusion des cultures transgeniques sont varies. Parmi ces problemes il y a la menace de la dispersion de genes par le transfert de pollen de la culture genetiquement alteree aux parents sauvages ou herbaces qui poussent dans les environs. Comme certains genes peuvent conrefer une adaptation plus avantageuse, les mauvaises herbes qui les acquierent peuvent devenir plus problematiques. Bien que le taux de dispersion de genes de culture vers les mauvaises herbes a ete mesure dans le cas de quelques systemes, la comprehension de ce phenomene n'est pas encore totale. Le papier decrit le passage de gene d'une culture telle que le sorgho vers une mauvaise herbe, S. halepense, au nord de l'Amerique. En examinant les progenitures, il etait possible de mesurer le taux et l'incidence de l'hybridation. L'hybridation spontanee en conditions de champ etait detectee a 100 metres de distance. Les mesures de plusieurs correlations etaient faites sur les mauvaises herbes hybrides et comparees aux non-hybrides en vue de determiner la persistance de genes transferes dans cet environnement. Il n'y avait pas de differences significatives entre hybrides et non-hybrides de mauvaises herbes; ceci indique que les genes benefiques introduits dans les populations de mauvaises herbes pourraient persister. Le papier discute aussi les implications dues a la dissemination des sorgho transgeniques en Afrique. Mots Clés Transfer de pollen, Sorghum bicolor, S. halepense, transgenes, mauvaises herbes

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Crop to Weed Gene Flow in Sorghum: Implications for Transgenic Release in Africa Arriola, P.E. Abstract Potential problems with the release of transgenic crops are varied. Among these problems is the threat of gene flow via pollen transfer from the genetically altered crop to wild or weedy plant relatives growing nearby. Because some engineered genes may confer an adaptive advantage, troublesome weeds may become more problematic if they bear such transgenes. Although the rate of crop to weed gene flow has been measured for a few systems, large gaps in our understanding of this phenomenon remain. The likelihood of crop to weed gene flow in a crop/weed system involving the crop, Sorghum bicolor, and a related weed, S. halepense, in North America is described. Measurements of the rate and incidence of hybridization were made using progeny analysis. Spontaneous hybridization under field conditions was detected at distances of 100 metres. Measurements of several fitness correlates were taken on hybrid weeds and compared to non-hybrid weeds in order to address the potential for persistence of transgenes in the environment. No significant differences were recorded between hybrid and non-hybrid weeds, suggesting that beneficial genes introduced into weed populations may persist. The implications for the release of transgenic sorghums in Africa are discussed. Keywords Pollen transfer, Sorghum bicolor, S. halepense,transgenes, weeds

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