1Kansas State University and ²USDA/ARS Agronomy Department, 2004 Throckmorton Hall, Manhattan KS 66506, and ³USDA/ARS, Irrigated Agricultural Research Center, Prosser WA 99350.

Pollen can function as a vehicle to disseminate introduced, genetically-engineered genes throughout a plant population or into a related species. The measurement of the risk of inadvertent dispersal of engineered genes must include an assessment of accidental dispersion of pollen. Factors to be considered include the rate of pollen spread, the maximal dispersion distance of pollen, and the spatial dynamics of pollen movement within seed production fields; none of which are known for alfalfa (Medicago sativa L.), an insect-pollinated crop species. Using a rare, naturally-occurring molecular marker, pollen dispersal can be tracked without introducing engineered genes into the environment. In this study, a suitable marker was found, using PCR-based methods, in an intron of the alfalfa glutamine synthetase gene. This marker system was used to track pollen movement within and away from seed-production fields; random amplified polymorphic DNA (RAPD) fragments were used to detect cross-pollination events in widely-dispersed alfalfa plants escaped from cultivation. Results indicated that leafcutter bees (Megachile spp.) used in commercial seed production show a bi-directional bias when pollinating, primarily resulting in the movement of pollen from marker plants directly toward and away from the bee domicile. Within-field pollen movement was detected only over distances of 4 m or less. Long-range dispersal of pollen from alfalfa hay and seed production fields has been confirmed for distances up to 1000 m using small trap plantings of alfalfa (Fig. 1). Individual plants grown within urban areas at least 800 m from known alfalfa plants failed to produce seeds. An assessment of scale dependencies is lacking from most risk assessment studies. A novel field design and marker system was developed to allow an accurate investigation of scale dependencies on gene movement by comparing dispersal from research scale plots with that of commercial scale fields. In this study, pollen moved from commercial scale fields three times farther than from small, research scale fields. Data suggest that complete containment of transgenes within alfalfa seed or hay production fields would be highly unlikely using current production practices.