Résumé
Information about the potential for crop-wild hybridization is needed to understand how crop genes, including transgenes, affect the population genetics and ecology of sexually compatible relatives. Transgenic sorghum is under development for use by traditional farmers in Africa, the center of origin for sorghum [Sorghum bicolor (L.) Moench], but systematic surveys of the current extent of contact with wild and weedy relatives are lacking. We studied wild and weedy sorghums that are interfertile with the crop and constitute a crop-wild-weed complex. The survey was conducted in 2005 in areas of traditional sorghum cultivation in three regions of Ethiopia and two regions of Niger. Within each region, we examined eight representative sorghum fields at each of 10 locations during peak flowering of the crop. In all regions, wild and weedy sorghum occurred intermixed with and adjacent to cultivated sorghum. Wild and weedy sorghums were detected at 56, 44, and 13% of the Ethiopian sites (Amhara, Tigray, and Hararghe regions, respectively), and 74 and 63% of sites in Niger (Maradi-Tahoua and Tillabery-Dosso regions, respectively). Flowering periods of wild and weedy sorghum populations overlapped with those of cultivated sorghum at most sites where the two co-occurred, especially in Ethiopia, and many putative crop-wild hybrids were observed. Therefore, current gene transfer from cultivated sorghum to wild and weedy sorghum populations in Ethiopia and Niger is likely to be widespread.