Employing a Composite Gene Flow Index to Numerically Quantify a Crop’s Potential for Gene Flow

Guidelines to ensure the efficient coexistence of genetically modified (GM) and non-GM crops are currently being considered across the European Union. Curtailing pollen/seed-mediated gene flow between GM and non-GM crops is central to effective coexistence. While models have been designed for specific crops,1 traditional commentary associated with a crop’s potential for gene flow would typically rank the crop as a high, medium, or low risk. By its qualitative nature, this approach does not provide the detail required to highlight those aspects of a crop’s biology that will serve to challenge coexistence management. The substitution of this classification system with a numerical gene flow index would permit a background level of gene flow, specific for a particular crop, to be calculated. In turn, this would underscore those crops that require additional measures when genetically modified, in order to minimize gene flow in accordance with anticipated coexistence guidelines. The concept of a gene flow index or botanical file is not new2 and their potential as tools to assist risk assessment strategies has already been suggested.3 However, present systems fall short by not encompassing all modes of gene flow that are of relevance to coexistence. Here we present a gene flow index (GFI)4 model that we have applied to seven conventional crops in Ireland. By combining four strands of gene flow—crop pollen-to-wild relative (CPW); crop pollen-to-crop (CPC); crop seed-to-volunteer (CSV); and crop seed-to-feral (CSF)—we have established a baseline data set that describes the potential of Ireland’s primary arable crops for both pollen- and seed-mediated gene flow