I wish to comment on the recent SciDev.Net opinion articles about whether GM crops are compatible with sustainable agriculture (see Do genetically modified crops have a role in the responsible control of pests?).
The scientific literature suggests that such crops pose potential ecological risks, making them incompatible with sustainable or organic farming.
GM agriculture limits farmers' ability to manage their land because of the increased need for herbicides. Moreover, pollen could carry transferred genes beyond their intended destination and into weedy relatives. 
It is not enough to say that GM crops cannot be grown in areas where there are sexually compatible wild relatives. Corporate pressure, a lack of biosafety regulations and human error could all contribute to such gene flow.
Added to this is the danger that GM crops could produce environmental toxins that enter the food chain or end up in the soil affecting bacteria that play a role in nutrient cycles. 
Farmers in poor countries need to continue producing food keeping their local agricultural biodiversity intact. 
 Marvier, M. Ecology of transgenic crops. American Scientist 89, 160 (2001) Alteir, M. A. The ecological impacts of transgenic crops on agroecosystem health. Ecosystem Health 6,13 (2000)