Crop-to-wild geneflow: environmental risk assessment for the release of genetically modified sorghum in Kenya

[摘要] English: The important socio-economic position enjoyed by sorghum has made it a target for genetic modification to enhance productivity and/or nutritional quality. However, there are growing environmental concerns that through geneflow, transgenes might escape from genetically modified (GM) sorghum to its sexually compatible wild and/or weedy relatives, with possible negative effects. Characterising the levels and dynamics of geneflow in the wild-weedy-domesticate complex of sorghum in traditionalgroecosystems of Africa, including Kenya, is of interest to biosafety regulators. This study used approaches based on population genetics theory to (i) characterise the genetic structure of the wild-weedy-domesticate complex of S. bicolor at a country scale in Kenya and (ii) to estimate the extent and direction of geneflow between cultivated and wild-weedy populations at a local scale in the country. The structure and dynamics of diversity was first estimated and compared at country scale by genotyping 329 cultivated and 110 wild sorghum individuals using 24 microsatellite markers. Subsequently, the magnitude and direction of geneflow between the two congeners was estimated at a local scale by analysing 483 individuals comprising of 15 wild-weedy and 12 cultivated sorghum populations using 10 microsatellite markers. Overall, cultivated sorghum harboured lower diversity than its wild counterpart. Levels of genetic diversity in cultivated and wild sorghum differed significantly among regions, with most of the diversity being partitioned more within than among the crop's growing regions. There were generally low levels of differentiation within and between cultivated and wild sorghum at country scale, but the extent of crop-to-wild genetic proximity varied among sorghum growing regions. These findings may reflect important historical geneflow between cultivated sorghum and its progenitor, with the level of crop-to-wild genetic exchange varying among regions. At local scale, the extent of geneflow was approximately nine times higher from cultivated sorghum to its wild-weedy relatives than vice versa. Additionally, the extent of crop-to-wild geneflow varied significantly among farms. Overall, this study suggests that deployment of GM sorghum in Kenya's agroecosystems will most likely lead to movement of transgenes into sympatric populations of its wild-weedy relatives.

[发布机构] University of the Free State