Gene flow is an important component in evolutionary biology; however, the role of gene flow in dispersal of herbicide-resistant alleles among weed populations is poorly understood. Field experiments were conducted at the University of Nebraska-Lincoln to quantify pollen-mediated gene flow (PMGF) from glyphosate-resistant (GR) to -susceptible (GS) common waterhemp using a concentric donor-receptor design. More than 130,000 common waterhemp plants were screened and 26,199 plants were confirmed resistant to glyphosate. Frequency of gene flow from all distances, directions, and years was estimated with a double exponential decay model using Generalized Nonlinear Model (package gnm) in R. PMGF declined by 50% at <3 m distance from the pollen source, whereas 90% reduction was found at 88 m (maximum) depending on the direction of the pollen-receptor blocks. Amplification of the target site gene, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), was identified as the mechanism of glyphosate resistance in parent biotype. The EPSPS gene amplification was heritable in common waterhemp and can be transferred via PMGF, and also correlated with glyphosate resistance in pseudo-F 2 progeny. This is the first report of PMGF in GR common waterhemp and the results are critical in explaining the rapid dispersal of GR common waterhemp in Midwestern United States.
Bibliographical noteFunding Information:
We thank the Indian Council of Agricultural Research (ICAR), New Delhi, India for partial financial support to Debalin Sarangi for this study. We also appreciate the help of Bradley Meusch, Ian Rogers, Irvin Schleufer, Katy McIntyre, Mason Adams, Parminder Chahal, Simranpreet Kaur, and Zahoor Ganie in field, greenhouse, and laboratory experiments. We appreciate partial financial support of USDA-NIFA Hatch project #NEB 22-365 and USDA-NIFA-Nebraska Extension Implementation Program project #NEBN-09-504.
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