Fixing Hairy Vetch’s Bad Reputation
Noble scientists are using the gene editing technique CRISPR to improve legume cover crops.
Like a professional sports team, what producers do in the offseason can make a big difference when it comes to their bottom line. And one of the most important decisions a producer makes is which crop to use as a cover.
Cover crops protect the soil from erosion due to wind and water and help suppress weeds. They should have deep roots and cover the ground completely, and many double as a forage crop for cattle. Different regions may also have specific requirements, such as cold tolerance in the North or drought and heat tolerance in the South.
“If Suresh is successful in producing a softseeded hairy vetch, the potential for crop farmers could be huge. All of the corn and soybean acreage in the U.S. needs a cover crop of some sort. Producers typically use a rye or a wheat, but they understand the legume’s potential benefit because of its ability to fix nitrogen. If this works, the sky’s the limit.”
— Twain Butler, Ph.D.
Small grains such as rye, oats and wheat are the most common type of cover crop and are used in more than half the acreage. However, scientists at the Noble Research Institute think that legumes, which currently constitute less than 20 percent of cover crops, could be a viable — and valuable — alternative.
Legumes add nitrogen back into the soil through a symbiotic relationship with certain species of bacteria. The bacteria live in the roots of the legumes and convert nitrogen from the air into a form that’s beneficial for plants. When the legume is decomposed back into the soil, the nitrogen is released, providing nutrients for the commodity crop. This “green manure” can reduce growers’ nitrogen fertilizer needs and may be a cheaper alternative to traditional fertilizers.
Suresh Bhamidimari, Ph.D., who leads the Noble Research Institute Forage and Cover Crop Legume Breeding Laboratory, collects leaf tissue from hairy vetch plants.
“The advantage of using legumes as a cover crop is they are kind of a protein punch, like those power bars that we eat, because they fix nitrogen in the soil,” says Suresh Bhamidimarri, Ph.D., who leads Noble’s Forage and Cover Crop Legume Breeding Laboratory. “In comparison, other plants used as cover crops are nitrogen hogs.”
One legume in particular stands out for its regional versatility. Hairy vetch has good cold tolerance and can be used as a winter cover crop in northern latitudes to protect the ground from ice and snow. It can also be grown in southern states, where it is used as a dual forage and cover crop.
Suresh and his team exit a selection nursery after collecting data on hairy vetch growing in Knox City, Texas.
Despite its potential advantages, many producers see hairy vetch as a liability. The plant’s bad reputation is rooted in its hardseededness, which is present in roughly 25 percent of the crop. Hard seeds lie dormant in the ground for years. In a forage environment, this can be an advantage because growers don’t have to worry about replanting every year. But producers consider hairy vetch to be a weed because if the plant grows at the wrong time, it can interfere with their commodity crop.
“Many farmers frown upon using hairy vetch because it’s perceived as a noxious weed,” says Twain Butler, Ph.D., a research agronomist at Noble and project manager for the national cover crop research initiative funded by Noble and the Foundation for Food and Agriculture Research (FFAR). “Due to this perception, many producers won’t even try to plant it. If we could solve the seed problem, it would allow it to be more widely adopted.”
Suresh and his team are also experimenting to propagate hairy vetch through stem cuttings in the laboratory as part of the breeding program.
A Better Cover Crop
Bhamidimarri is trying to fix this seed problem using CRISPR/Cas9 to edit the plant’s genome. He hopes to produce a new variety of hairy vetch that only has soft seed by deleting the hardseededness genes.
“We want to provide farmers and ranchers with more options,” he says. “This way, they could choose an exclusively hardseeded or softseeded variety depending on their needs for a forage or a cover crop.”
The CRISPR/Cas9 system acts like a pair of genomic scissors. The CRISPR part of the package is designed to exactly match a section of DNA so it can home in on a specific gene. Once the section is located, the Cas9 protein snips the DNA, inactivating the target gene.
One benefit of using genome editing in hairy vetch is that it eliminates the chance of the hardseededness trait being reintroduced when the plant reproduces. Hairy vetch is an outcrossing plant, which means it needs pollen from a different plant to reproduce. With traditional breeding methods, there is no guarantee that a bee that’s been pollinating a wild variety of hairy vetch won’t fertilize the bred variety. The next generation of plants could be contaminated with a new copy of the hardseededness gene and potentially carry that trait. With CRISPR, you edit out both copies of the hardseededness gene, removing this possibility.
The process is easier said than done, however. Because hairy vetch is not a popular plant like wheat or corn, its genome hasn’t been sequenced. So the first step for Bhamidimarri’s team is to find the genes responsible for hardseededness. Fortunately, they have a template in soybean, a related legume in which two hardseededness genes have already been identified.
Once they confirm the relevant genes, the researchers will get to work knocking them out. Amr Ibrahim, Ph.D., a postdoctoral fellow in Bhamidimarri’s lab, is currently perfecting the process to introduce the CRISPR/Cas9 package into the plant’s cells. Eventually, they will help the edited cells grow into a new variety of hairy vetch, one that hopefully only produces soft seeds.
“If Suresh is successful in producing a softseeded hairy vetch, the potential for crop farmers could be huge,” Butler says. “All of the corn and soybean acreage in the U.S. needs a cover crop of some sort. Producers typically use a rye or a wheat, but they understand the legume’s potential benefit because of its ability to fix nitrogen. If this works, the sky’s the limit.”