By Tyler J. Baum, Editor
Since pale cyst nematodes were first detected in Bingham and Bonneville Counties in southeastern Idaho in 2006, potato researchers have been looking for new ways to eradicate the quarantine-inducing pests. Some solutions, such as using mustard seed meal, are possible but not very economically viable.
One of the most viable options to their eradication may very well lie with a distant cousin of the potato—sticky nightshade.
Nematode eggs, which are protected by cysts, survive a very long time in the soil—sometimes up to 30 years—waiting for the presence of hatching factors. There are chemicals in potato roots, which are still somewhat unknown to researchers, which exidate from the roots and stimulate the eggs to hatch. The nematodes emerge as second-stage larvae, or J2. The J2 then mold and become J3, establish a feeding site and then become either a female or male adult.
A key to their survival is to not hatch unless a host is present.
“Not only do the eggs in the cysts hatch in the presence of potato roots, but the potato also hosts the nematode,” says Dr. Pamela Hutchinson, University of Idaho potato cropping systems weed scientist. “That’s why it’s devastating to the potato crop.”
However, researchers are finding the potato’s distant cousin of sticky nightshade (<<<Solanum sisymbriifolium>>>) exidates the same chemical that induces hatching, but is not a host for the nematode.
“The eggs hatch in the presence of sticky nightshade roots, but once the nematodes hatch there’s no place for them really to survive, and so they die.”
Researchers have been calling this a “suicide hatch.” A handful of researchers are determining how economically viable sticky nightshade will be as a “trap crop.”
Chuck Brown, USDA-ARS breeder out of Prosser, Wash., obtained sticky nightshade seed from the Netherlands. After growing it in a greenhouse facility, the nightshade is then sent to University of Idaho campus in Moscow, Idaho, to Louise-Marie Dandurand, director of the PCN Project. In a sterile quarantine lab, researchers observe nematodes hatching in the presence of PCN.
Dandurand stated at the UI Potato Conference in January that they’ve seen nematode reductions of up to 70 percent in populations in a lab environment.
At the UI Parma R&E Center, Southwest Idaho Research and Extension Centers Superintendent Mike Thornton is studying the agronomics of sticky nightshade as a trap crop—the best time to plant, length of growing season, how much bio-mass it should have above ground, etc. Meanwhile, Hutchinson at the Aberdeen R&E Center is looking at a few weed-related objectives. One of them is to make sure that if sticky nightshade is planted as a trap crop, it doesn’t become a volunteer weed the following year.
Perhaps her biggest challenge is controlling the pesky distant relative of both potatoes and sticky nightshade—hairy nightshade (<<<Solanum sarrachoides>>>)—which induces hatching and is also a host for nematodes. The challenge is to control one nightshade but not the other.
“It wouldn’t be any good if you had that weed out there or other nightshade weeds that will host the nematodes, because then it wouldn’t be worth planting the trap crop,” she says.
Another challenge Hutchinson faces is the short-growing season in southeastern Idaho—two weeks shorter than Parma—along with the painfully slow growing process for sticky nightshade.
“With the sticky nightshade, you need the soil to be at least 50 degrees F before it will even germinate. Once you plant it, it takes about a month before it emerges. And then it still takes two or three weeks before it even starts growing to any height,” she says. “We’re concerned our season is too short,” she says, but then adds, “But it seems like from what Mike Thornton is doing and what I’ve been able to do over here in southeastern Idaho…we have roots that go fairly deep.”
The Idaho State Department of Agriculture is involved in the process to help regulate the research.
“They’re helping us do that in a cooperative manner, to be in on the regulation of how the trap crop is brought in and how it’s grown,” she says.
Hutchinson says that once they get seed production going for sticky nightshade in Idaho, it will be “very economical,” but she points out that it must be grown the entire growing season.
“It isn’t like some of the green manures that we plant after wheat harvest and then plow it down right before we get a hard frost in the fall. It needs to grow a whole summer so we make sure we have the roots out to get the eggs to hatch,” she says. “So that would be the economic or challenge for the grower.
“However,” she says, “you can’t grow potatoes in a quarantined field anyway, and so [the grower is] already faced with not being able to produce potatoes [in infested ground].”
One thing that makes sticky nightshade a pain to work with—literally—is the painful briars, or spines. Brown is seeking to develop a spineless sticky nightshade, because the plant is so painful to work around.
“We have to wear double gloves,” Hutchinson says. “It can be somewhat painful to walk around in the crop unless you have long pants and boots and that kind of thing.”
Brown is also seeking to develop a sticky nightshade variety that is sterile so it doesn’t produce berries that can go to seed. Those will, in turn, be handed over to Dandurand to test with nematode cysts.
Hutchinson is very optimistic. She says Dandurand has found they can get at least 60 percent of nematode eggs in a given field to hatch out.
“We’re hoping that, in conjunction with other control methods—such as fumigation, which would maybe get 40 percent hatch—we could get nearly 100 percent of those eggs to hatch. And then the grower could take those fields out of quarantine. So, it’s really looking good to have sticky nightshade.”