Gene flow in commercial alfalfa (Medicago sativa subsp. sativa L.) seed production fields: Distance is the primary but not the sole influence on adventitious presence

Authors: KESOJU, SANDYA - Columbia Basin College; Kramer, Matthew; Brunet, Johanne; Greene, Stephanie; JORDAN, AMELIA - Washington State University; Martin, Ruth

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2021
Publication Date: 3/25/2021
Citation: Kesoju, S., Kramer, M.H., Brunet, J., Greene, S.L., Jordan, A., Martin, R.C. 2021. Gene flow in commercial alfalfa (Medicago sativa subsp. sativa L.) seed production fields: Distance is the primary but not the sole influence on adventitious presence. PLoS ONE. 16(3). Article e0248746. https://doi.org/10.1371/journal.pone.0248746.
DOI: https://doi.org/10.1371/journal.pone.0248746

Interpretive Summary: In insect-pollinated crops, gene flow is affected not only by a crop’s characteristics, its mating system, life history and its pollinators, but also by pollinator and planting management practices. These factors are important in genetically engineered crops, where coexistence strategies are needed to ensure conventional cultivars are not contaminated by the genetically engineered trait. To identify variables that influence contamination in conventional alfalfa fields, we performed a variable selection regression analyses at two levels, a sample-level and field-level analysis. The two approaches gave broadly similar results. Distance from the genetically engineered field explained 66% of variation in contamination, confirming its importance in mitigating gene flow of genetically engineered traits. The relative area of fields of genetically engineered cultivars, within pollinator foraging range explained an additional 30% of the variation. The density of alfalfa leafcutting bee domiciles was also significant. This study suggested that management procedures to minimize contamination in conventional seed should focus on managing isolation distances, while taking into account the size of the genetically engineered pollen pool within pollinator foraging range, and the unique foraging behavior of pollinators.

Technical Abstract: In insect-pollinated crops, gene flow is affected not only by a crop’s characteristics, its mating system, life history and its pollinators, but also by pollinator and planting management practices. Previous studies have concentrated on the impact of distance to genetically engineered (GE) fields on adventitious presence (AP), the unwanted presence of a GE trait in non-GE material. However, other variables, including pollinators and different aspects of their management, field size, proximity to riparian and rangeland areas and various environmental and topographical factors may affect AP. In addition, AP may be present in the parent seed lots used to establish conventional fields. To identify the explanatory variables that influence the proportion of AP in conventional alfalfa fields, we performed a variable selection regression analyses at two levels, a sample-level and field-level analysis. The two approaches gave broadly similar, though not identical results. For the sample-level model, distance from the GE field explained 66% of the variance in AP, confirming its importance in affecting AP. The relative area of GE fields within pollinator foraging range explained an additional 30% of the variation in AP in the model. The density of alfalfa leafcutting bee domiciles was also significant in both models. This study suggested that management procedures to minimize AP in conventional seed should focus on managing isolation distances, while taking into account the size of the GE pollen pool within pollinator foraging range, and the unique foraging behavior of pollinators.