Pollinator-mediated gene flow in and among fields of alfalfa produced for seed
Boyle, Natalie Kira
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Cross-pollination by bees is necessary for commercial alfalfa seed production. To maintain varietal purity in alfalfa, seed producers adhere to spatial isolation standards to minimize or prevent bee flight and subsequent pollen flow between fields. The increased use of genetically-engineered (GE) crops in agriculture has raised concerns over pollinator-mediated gene flow between transgenic and conventional agricultural varieties. The 2011 deregulation of genetically engineered glyphosate-resistant alfalfa by the USDA has generated public concern and scientific debate over current recommended bee management practices and their ability to maintain varietal purity of alfalfa grown for seed production. The primary objective of this research is to determine the roles that pollinators play in contributing to undesired gene flow between alfalfa fields.We evaluated the impact of migratory beekeeping practices on transgenic pollen flow between spatially isolated alfalfa fields by permitting honey bees, Apis mellifera, to openly forage upon transgenic alfalfa blossoms, and transporting them 112 km to forage on caged conventional alfalfa following either 8 or 32 hours of isolation from the transgenic source. Cross-pollination between transgenic and conventional alfalfa was nearly eliminated (0.00008%) following eight hours of isolation from the transgenic source. The alfalfa leafcutting bee, Megachile rotundata (ALCB), is another commercially managed pollinator used extensively in alfalfa pollination. We evaluated the influence of the ALCB on gene flow between GE and conventional alfalfa seed fields by testing for the presence of the GE trait in pollen provisions collected from domiciles located in conventional alfalfa seed fields planted directly adjacent to GE alfalfa fields. Pollen samples collected from domiciles in conventional seed fields were at variable distances from the adjacent GE fields. Alfalfa seed in the vicinity of each domicile was harvested and tested for the transgene. We found that the ALCB frequently forages at distances which exceed current estimates for ALCB foraging range. Additionally, GE trait expression in harvested conventional seed was detected at rates that surpass established thresholds for varietal purity. Measurable impacts of ALCB-mediated pollen flow were confirmed and can be used to inform science policy regarding the development of best management practices mitigating undesired gene flow between genetically distinct alfalfa varieties.