Editor’s Note: Much of this information is from a story by Jan Suszkiw of the Agricultural Research Service that was published in the September 2011 issue of Agricultural Research magazine.
Wireworm feeding damage is easy to spot, says Rich Novy, a USDA-Agricultural Research Service (ARS) plant geneticist seeking to shore up America’s $3.3 billion potato crop. The damage resembles a nail hole that has been punched into the spud, pitting its surface and making it less appealing for use in fresh-pack or processing markets.
Organophosphate- and carbamate-based insecticides are available for use against wireworms on potato, among the most commonly used being ethoprop (Mocap, Bayer CropScience). However, the continued registration of some of these insecticides is uncertain, says Novy, who is in ARS’s Small Grains and Potato Germplasm Research Unit in Aberdeen, ID. Plus, the chemicals don’t always eliminate the slender, brownish-orange pests, which as larvae can survive beneath the soil for as long as five years before emerging as adult click beetles.
“That’s part of what makes them so problematic, they are able to just stay in the soil so long,” he says. “That’s why you can get a buildup of wireworms over time.”
South American Aid
Over the last several years, Novy, ARS plant pathologist Jonathan Whitworth, and former University of Idaho associate professor Juan Alvarez, who is now with DuPont, have looked for a solution to the problem in the form of genetic resistance. In particular, they’ve focused the attention on two wild relatives of cultivated potato obtained from Chile and Bolivia: Solanum berthaultii and S. etuberosum. Taking their cue from previous studies showing that the wild potatoes are resistant to Colorado potato beetles and green peach aphids, two disparate pests, the researchers decided to pit the plants against hungry wireworms as well.
To do this, the team crossed germplasm derived from the wild potatoes with a cultivated variety and then selected 15 top-performing plants from three generations of progeny. The researchers’ next step was to plant the progeny lines, called “breeding clones,” in wireworm-infested field plots in southern Idaho and compare the feeding damage they sustained to that of adjacent rows of susceptible Russet Burbank potatoes.
As the researchers had hoped, the resistant clones fared as well as — and sometimes better than — the insecticide-treated Russet Burbank potatoes. “Wireworms are really tough,” says Novy. “Even with chemicals, there isn’t complete control.”
At this time, the mechanism of resistance to wireworm has not been determined, but it may be related to glycoalkaloids. These naturally occurring chemical compounds in potato tubers are known to deter some insect pests. Total concentrations of glycoalkaloids in many of the resistant clones are at levels suitable for human consumption, which may open the door to their use in the development of wireworm-resistant commercial varieties.
Novy says they do have a clone, a long, typey Russet, that is derived from its wild relatives, but it hasn’t been tested to confirm that it has wireworm resistance. The potato is in the intermediate stages of development — if it is identified as being wireworm resistant and its agronomic characteristics make it acceptable for release as a variety, then that clone could be available to growers in five to six years. “I’m quite excited by this one clone,” he says. “It needs several more years of evaluations, but it looks promising.”
The team has submitted a paper on their research to the Journal of
Economic Entomology. Novy says that besides wireworm, they are working on resistance to other potato pests such as potato psyllid, to mitigate zebra chip disease, and nematodes, specifically potato cyst nematode and Columbia root-knot nematode, in collaboration with Chuck Brown of USDA-ARS at Prosser, WA.
For more information on the potatoes used in this research, please turn the page