North Dakota-based Laboratory Develops a DNA Test for Growers to Confirm Palmer Amaranth, Waterhemp, and Related Pigweed Species
By Dr. Zack Bateson, Research Scientist, National Agricultural Genotyping Center
Palmer amaranth (Amaranthus palmeri) has invaded the fields of North Dakota. Recognized as one of the most yield-robbing weeds in agriculture, the North Dakota Department of Agriculture wasted little time adding Palmer amaranth to the noxious weed list. Concern over its devastating effects has made the weed a popular topic at recent North Dakota expos and conferences. One common theme during these discussions was to inform growers on how to differentiate Palmer amaranth from other pigweeds, specifically Waterhemp (A. tuberculatus). The window of opportunity for effective herbicide treatments is often limited to shortly after emergence, and before the weeds reach approximately three inches. Early detection can mean the difference between effectively shutting down a recent Palmer amaranth infestation and a permanent increase in annual herbicide to curtail a well-established population of this highly productive weed. Unfortunately, visual identification at the most vulnerable and early stages are challenging for even the most experienced weed scientists. Additionally, nature is not always textbook. It is difficult to fully document the overwhelming variation among individual Palmer amaranth plants, which can arise from field or regional differences in soil types, nutrient loads, and water availability. As a result, photographs that are used to help growers tell the difference among pigweed species can sometimes fall short, potentially causing confusion and lead to inadequate control recommendations. Thus, the most reliable way to confirm Palmer amaranth and other pigweed species is to supplement the visual diagnosis with a DNA test.
Since identification is difficult and effective control can be time-dependent, the National Agricultural Genotyping Center (NAGC) partnered with weed scientist, Dr. Michael Christoffers, at North Dakota State University to develop a rapid DNA test for the agricultural community. Co-funded by the North Dakota Corn Utilization Council and North Dakota Soybean Council, the DNA test was developed in just under six months to identify five amaranth species found in the state. Specifically, the DNA test can detect the presence of Palmer amaranth, Waterhemp, Powell amaranth (A. powellii), Redroot Pigweed (A. retroflexus), and Smooth Pigweed (A. hybridus) from both fresh and dried plant material. Importantly, the one-step test can directly differentiate both Palmer amaranth and Waterhemp from each other as well as from the three other pigweed species. The test has the potential to detect hybrid plants that include either Palmer amaranth or Waterhemp parents. In fact, during test development, seeds collected from a North Dakota field and grown in the greenhouse contained a Waterhemp-Redroot hybrid. The hybrid plant was not visibly obvious, and was only uncovered using the DNA test.
The next objective is to integrate this test into a surveillance program to help limit the spread of Palmer amaranth. The DNA test developed by NAGC is available to all growers, county agents, and researchers. It can identify the pigweed species by using any plant tissue, including newly emerged weeds picked from the field. Only a single leaf is necessary for testing larger plants pulled from the field. If growers want to submit multiple plants from different areas or fields, each leaf should be placed into individually labeled zipper bags (wrapped in a paper towel) or brown paper bags. Easy sample submission guidelines, including the required submission form, can be found on NAGC’s website (https://www.genotypingcenter.com/services/testing/). Samples can be hand-delivered or mailed directly to NAGC in Fargo, ND. Our normal business hours are 8am to 4pm, Monday through Friday. Normal testing will result in an official report within 7 business days. Clients can elect for a rush diagnosis within 48 hours after NAGC receives samples Monday through Wednesday for an additional fee (call NAGC for more details). Reported results are only provided to the original submitter and other requested parties on the submission form. Please call the scientists at NAGC with any questions regarding submission at (701) 239-1451.
NAGC is also in the process of finalizing a DNA test to identify Palmer amaranth and Waterhemp in seed lots for certification purposes. This seed test should be available by the end of summer 2019.
Photo credit: Photos from a power point located at link below, from authors below:
Michael Horak, Dallas Peterson, Dennis Chessman & Lloyd Wax