New Research Quantifies the Dispersal of Glyphosate Resistance Trait Through Pollen-Mediated Gene Flow

Amit Jhala (left) and Debalin Sarangi
Amit Jhala (left) and Debalin Sarangi (right) along with other scientists detected pollen-mediated gene flow from glyphosate-resistant common waterhemp in Nebraska.

New Research Quantifies the Dispersal of Glyphosate Resistance Trait Through Pollen-Mediated Gene Flow

New multidisciplinary research from the University of Nebraska–Lincoln quantifies the dispersal of the glyphosate resistance trait through pollen-mediated gene flow in the most problematic weed in Nebraska. The research was highlighted in a paper recently published in Nature Scientific Reports.

Commercialization of glyphosate-resistant crops in 1996 changed the pattern of glyphosate use in agriculture. Gradually, glyphosate became the most widely used herbicide in the world. Glyphosate-resistant common waterhemp (Amaranthus rudis Sauer) is the most problematic weed in eastern Nebraska with more than 1.5 million acres of corn and soybean fields infested. As of 2016, glyphosate-resistant common waterhemp has been confirmed in 18 states in the midwestern and southern United States. Common waterehemp is a dioecious (male and female flowers occur on separate plants) and a wind-pollinated species.

For this study, field experiments were conducted at South Central Agricultural Laboratory at Clay Center as part of Debalin Sarangi’s Ph.D. research project with Amit Jhala, assistant professor and Nebraska Extension weed management specialist in the Department of Agronomy and Horticulture.

The pollen-mediated gene flow was detected 38% to 54% at 0.1 meter distance and 5% to 9% at 50 meters, the highest distance tested in this study. Frequency of gene flow declined rapidly within a 3-meter distance from the pollen source; however, the 90% reduction was found at a maximum distance of 88 meters depending on the direction of the pollen-receptor block.

This study also revealed that amplification of the target site gene, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) was the mechanism of glyphosate resistance in common waterhemp population used in this study, and the gene amplification was heritable and transferred via gene flow.

“The results of this study are important to explain the rapid dissemination of glyphosate-resistant common waterhemp in Nebraska corn and soybean fields and in several other states,” said Jhala.

According to Jhala, weed management strategies adopted by growers are mostly focused on preventing or delaying weed resistance evolution over a small area rather than preventing the large-scale movement of herbicide-resistance traits, but the evidence of long-distance pollen dispersal in common waterhemp should now be considered. The modeling approach considered in this study can be used in the future for the risk assessment of transgenic commercial crops as well as from crops to closely related species.

Others involved with the study include Professor Andrew Tyre from the School of Natural Resources, Professor Suat Irmak from the Department of Biological Systems Engineering, and Professors Stevan Knezevic and John Lindquist from the Department of Agronomy and Horticulture. A part of this study was also conducted in the Molecular Weed Science Lab at Colorado State University with input from Todd Gaines and Eric Patterson, who helped the authors to confirm gene flow using a molecular marker. This project was partially funded by a USDA-NIFA Hatch grant.

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