Researchers attempt to turn weed into a crop

Date:10-17-2022

Early adopters might want to take a little time to explain to the neighbours why their entire field is covered by what looks like, and from a genetic standpoint, is mostly stinkweed.

What may resemble the worst weed infestation ever may be just a new cover crop and oilseed called domestic pennycress, or formally, Thlaspi arvense.

John Sedbrook is a professor of genetics at Illinois State University and one of the researchers working to turn this weed into a crop. In some ways it echoes the development of its plant relative, canola.

Sedbrook and his colleagues have been using plant-breeding tools such as CRISPR gene editing to modify pennycress.

″We’ve gotten to the point where this crop can be economical,″ he said.

Like canola’s rapeseed ancestors, pennycress suffers from two problems: high levels of antinutritional erucic acid in the oil and high levels of glucosinalates, particularly one called sinigrin, in the meal. If you’ve experienced the sinus-clearing effects of a good horseradish sauce, you are familiar with sinigrin.

This limits pennycress’s value as animal feed. Raw glucosinalate-containing plants contain enzymes that break them down into toxic products in the body. While heating deactivates this enzyme, the glucosinalates can add an off taste to products such as milk, for example, if dairy cattle are fed rapeseed meal.

″It’s been challenging to reduce glucosinalate content,″ Sedbrook said. ″(Pennycress) produces so much glucosinalate, so that is hardwired metabolically. It’s been a challenge to lower that without making the plant partially unhappy.″

Despite the challenges, the researchers brought the plant from weed to domesticated crop in about 10 years, remarkably fast, Sedbrook said, crediting tools such as gene editing.

″We’ve got the erucic acid reduced, we’ve got reduced fibre which substantially improves the quality of the meal, the oil quality has been improved as well and we’re working on the glucosinalate.″

This field of pennycress is in full flower. The domesticated version is planted in the fall and establishes itself to the rosette stage, where it can endure freeze-thaw cycles all winter until spring arrives and it continues its growth cycle. | Steve Cermak photo

The domesticated pennycress is being marketed as Covercress, a trademarked name that Sedbrook hopes may eventually catch on as the generic term for the crop, much as canola is now the name for edible oilseed rape.

Covercress is a cold-tolerant, short-season oilseed that yields about 32 percent oil content and 20 percent protein in the meal, similar to camelina. Its seeds are a golden colour, easily distinguishing it from the black of wild pennycress, and are about the same size as camelina. Test fields in Illinois have delivered 2,500 to 3,000 pounds per acre, which beats camelina’s 1,800 to 2,200 lb. per acre.

While development is so far limited, researchers from Montana, Ohio, Minnesota and Indiana are taking a look. In a presentation at a canola conference last year, Sedbrook said they continue to welcome collaborators to develop the crop further.

While Sedbrook and his colleagues work on a genetic solution for the glucosinate problem, there are chemical means to make domestic pennycress meal suitable for animal feed.

Research chemist Roque Evangelista is processing lead for a pennycress project at the Bio-oils Research Unit at the U.S. Department of Agriculture’s National Center for Agricultural Utilization Research in Peoria, Illinois. He is exploring the characteristics of the new crop and how its meal stacks up.

″The first target of course will be to use it in feed,″ he said. ″We have some processes we have looked at to reduce sinigrin in the processed meal, but the end product still has higher glucosinalates than canola but at least we can cut it significantly.″

Pennycress does have another thing going for it — in Illinois, it can be planted after the corn crop comes off in September and is ready to harvest by about the end of May, offering a third income source for farmers.

″So that’s another advantage,″ Evangelista said. ″You have this land that could produce a good amount of oil, really, compared to soybeans, and it’s something that will not restrict the corn-soybean rotation.″

It also anchors idle soil over the winter season. As a cover crop, domestic pennycress can reduce soil erosion and use up excess nitrogen in the soil, reducing spring runoff and the nitrogen that is carried with it, which can pollute the Mississippi watershed and cause dead zones in the Gulf of Mexico. The cover crop may also help reduce emissions of nitrous oxide, a greenhouse gas.

While it may eventually yield an edible oil, the main focus for domestic pennycress is biofuel, particularly for areas such as aviation where there are no viable alternatives to liquid fuels.

Sedbrook said commercial aviation in the United States alone uses 20 billion gallons of jet fuel a year; the world uses five times that amount.

″To get to carbon neutral by 2050, we need to have alternatives to burning fossil fuels,″ he said.

As to whether domestic pennycress will spread north, some indications may be found in its origins.

A mature domestic pennycress crop’s seed is about the same size as camelina and can be harvested with similar equipment. | John Sedbrook photo

In 2002, USDA researchers Terry Isbell and Steve Cermak were scouting fields in Illinois, looking for some land to plant the specialty oilseed crop cuphia, used in chemical and personal care products.

Isbell noticed there seemed to be a good stand of stinkweed pretty much everywhere they went.

″It’s common throughout the Midwest. It seems it just grows. It’s a better-known weed here in Illinois,″ said Cermak, now research leader working in the same unit as Evangelista.

Pennycress is an invasive import, native to Eurasia. Able to handle harsh conditions including multiple freeze-thaw cycles, over the years it has spread from the U.S. Midwest through Canada and all the way to Alaska.

Isbell picked a bunch of the distinctive notched-disc seedpods and brought them back to the lab to look for interesting fatty acid profiles. Analysis showed nothing special: the oil and meal were similar to rapeseed.

″Soybean oil, I think at the time was nine cents a pound,″ Cermak said. ″So it was, ‘what do you do with something like this?’″

Although the researchers mostly set the pennycress project aside, Isbell continued to tinker with it, working on such traits as getting it to set all its seed at once. Then, in 2008-09, fuel prices spiked and with them, interest in sources of biofuel. New plant breeding techniques came online, making the task of turning a weed into a crop, if not easy, at least feasible. Universities, government researchers and industry all took an interest.

Start-up companies formed to commercialize the new crop. These eventually morphed into Covercress, which was bought this year by Bayer, Bunge and Chevron, putting it on firm financial footing.