URBANA, Ill. — The presence of tiny seeds from Palmer amaranth in mixed bags of seed distributed to participants in the Conservation Reserve Program (CRP) last summer led a molecular weed scientist and graduate student partner to develop an effective, low-cost test that can sniff out even a single Palmer seed in a large mixed sample of seeds.

 

Pat Tranel of the University of Illinois Crop Sciences Department and grad student Brent Murphy developed a way around past stumbling blocks in identifying young Palmer seeds, which are speck-tiny, without having to grow an entire plant in order for seeds to be large enough to identify.

Through a method known as quantitative PCR, the pair found a way to detect genetic variations unique to Palmer – an invasive, destructive species of pigweed that turned up in Illinois and other corn-producing Midwest states in recent years – even when presented with numerous other samples from closely related species, including waterhemp.

The technology is available to seed growers and companies that purchase and sell seed used in USDA’s CRP from specialty farmers who grow purple coneflower, little and big bluestem and other beneficial plants and pollinators distributed to program participants. The new test developed by Tranel and Murphy calls for a thorough grounding of all seed samples, where old tests examined only single seeds.

Unlike the old tests that could cost up to $100 per seed, the University of Illinois Extension Plant Clinic is now offering the technology for $50 per mixed seed sample.

“We have developed a quantitative test to identify Palmer amaranth contamination in a much larger pool,” Tranel said of the new technology. “We wanted farmers to be able to identify Palmer amaranth when it shows up on their fields. Even if you are trained, in the seedling stage before the plants start flowering, it’s very difficult to tell them apart from other amaranth species.”

The problem has led Ohio and Minnesota to prohibit the sale and transport of Palmer-contaminated seed mixes, designating the aggressive and hard-to-kill weed as a “noxious” plant.

 

“If you want to sell seed in those states, you have got to make sure there is no contamination in the seed you are selling,” said Tranel, who has received several inquiries about the test from those in Palmer- banning states and the Midwest. “I have heard a lot of interest, but most inquiries are now going through the Plant Clinic.”

Palmer has been the object of much study and scrutiny by U of I crop scientists, led by Dr. Aaron Hager, for much ofthe 2010s. Its increasing presence in corn and soybean acreage has been documented by researchers year after year, leading to improvements in testing mechanisms for the detection of Palmer.

“Palmer amaranth was entering into our state looking like a lot of other amaranth or pigweed species that were already here, but Palmer has additional challenges associated with it. It’s a very fast-growing weed and a more problematic pigweed than we here in Illinois are used to dealing with,” Tranel explained. “What we have done is to take advantage of previous work to identify species as Palmer amaranth, but expanded on the work to ID the seedlings. Previous tests of one seed at a time were not economically viable.

“Palmer, redroot pigweed, waterhemp – they all have tiny black seeds that basically look the same. We needed a way to efficiently extract DNA from pooled seed samples, and, if it’s present, identify Palmer,” he explained.

Diagnostic outreach extension specialist Diane Plewa and Plant Clinic technician Elizabeth Phillippi contributed to the project by examining different methods of extracting DNA from seed in mixed samples.

“The trick is to make sure every seed is ground up during the extraction process,” said Plewa.

For more information on the Palmer amaranth test, call 217-649-3941 or visit the U of I Extension Plant Clinic websiteat http://web.extension.illinois.edu/plantclinic