Abstract
Gene flow in agricultural crops is important for risk assessment of genetically modified (GM) crops, particularly in countries with a large informal agricultural sector of subsistence cultivation. We present a pollen flow model for maize (Zea mays), a major staple crop in Africa. We use spatial properties of fields (size, position) in three small-scale maize farming communities in Zambia and estimate rates of cross-fertilisation between fields sown with different maize varieties (e.g. conventional and transgene). As an additional factor contributing to gene flow, we present data on seed saving and sharing among farmers that live in the same communities. Our results show that: i) maize fields were small and located in immediate vicinity of neighboring fields; ii) a majority of farmers saved and shared seed; iii) modeled rates of pollen-mediated gene flow showed extensive mixing of germplasm between fields and farms and iv) as a result, segregation of GM and non-GM varieties is not likely to be an option in these systems. We conclude that the overall genetic composition of maize, in this and similar agricultural contexts, will be strongly influenced both by self-organised ecological factors (pollen flow), and by socially mediated intervention (seed recycling and sharing).
Highlights
Gene flow in agricultural crops is important for risk assessment of genetically modified (GM) crops, in countries with a large informal agricultural sector of subsistence cultivation
In this study we present detailed maps generated from GPS data on sizes and spatial arrangement of maize fields in three Zambian communities
The cultivation conditions differ considerably from those for which biosafety investigations of genetically modified maize were done in North America and Europe
Summary
Gene flow in agricultural crops is important for risk assessment of genetically modified (GM) crops, in countries with a large informal agricultural sector of subsistence cultivation. Maize gene flow occurs through cultivator determined seed selection and mixing as well as through pollen transfer between individual plants and fields. From its center of origin, farmers have for thousands of years experimented, spread, mixed and selected favorable maize plants for different environmental conditions, which provide the crop biodiversity that currently exists[5,6,7]. This diversification process is based on a long history of informal systems for seed exchange.
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