Genetic studies lead to ways to reduce damage from potato blight diseases
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NC State University

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Genetic studies lead to ways
to reduce damage from
potato blight diseases

Cubeta (left) now works with the College's Integrated Center for Fungal Research in Raleigh.  (Photo by Herman Lankford)


Each year North Carolina growers generate $20 million in farm income by growing potatoes, most of which become potato chips. But two little-understood problems — Rhizoctonia disease and internal heat necrosis (IHN) — consistently chip away at farmers’ yields and profits.

College of Agriculture and Life Sciences’ scientists are out to change that. While Dr. Marc Cubeta works to find a novel solution to Rhizoctonia disease of potato, Dr. Craig Yencho is making strides in developing new potato varieties that withstand IHN.

North Carolina growers produce about 17,500 acres of potatoes, mostly in the coastal plain counties of Beaufort, Camden, Carteret, Currituck, Hyde, Pamlico, Pasquotank, Tyrrell and Washington.

Cubeta, a plant pathologist, was assigned to the Vernon G. James Research and Extension Center in Plymouth shortly after a late blight epidemic decimated the potato crop in 1994. Working from northeastern North Carolina, at the heart of the state’s potato-growing region, he implemented a disease forecasting system that allows him to alert growers when conditions are favorable for late blight and to advise them on ways to manage the disease.

With that system now well developed, Cubeta has turned his attention to the chronic, but less devastating, Rhizoctonia disease. This disease commonly causes annual yield losses of 10 to 15 percent in eastern North Carolina.

The fungus initially infects and kills developing sprouts and produces sunken lesions called cankers on stems and stolons that restrict the movement of nutrients from the plant’s leaves to the potato.

“It’s a hidden enemy, because a lot of the damage occurs underground, where growers can’t see it,” he says. “It’s quite prevalent, and there are no potato varieties that we know of that have resistance. Crop rotation is not an effective option for managing Rhizoctonia disease of potato because the fungus can survive for many years in soil.”

Cubeta, now with the College’s Center for Integrated Fungal Research in Raleigh, is collaborating with University of Maine researchers to learn more about the ecology, genetics and population dynamics of the Rhizoctonia fungus.

Dr. Stellos Tavantzis, a leading expert in the area of mycoviruses in Rhizoctonia, is on sabbatical leave from the University of Maine to work with Cubeta and Dr. Ralph Dean, a fungal genomics researcher. While at N.C. State, Tavantzis is learning genomics-based techniques to better understand the interaction of nuclear encoded genes and double-stranded RNA mycoviruses in Rhizoctonia.

With such an understanding, Cubeta says, scientists might have a chance of finding ways to use the Rhizoctonia fungi already present in North Carolina soils to reduce the damage associated with Rhizoctonia disease.

As Cubeta explains, scientists already know that certain genetic individuals of the Rhizoctonia fungi in North Carolina contain unique double-stranded RNA virus particles, called mycoviruses. These mycovi-ruses can reduce the fungus’ ability to cause disease.

Cubeta and his colleagues are conducting laboratory, greenhouse and field experiments to determine how mycoviruses are transmitted among different genetic individuals of the Rhizoctonia fungus. This information, Cubeta says, could provide the foundation to explore further the possibility of developing and deploying naturally occurring mycoviruses to manage Rhizoctonia disease.

Like Rhizoctonia disease, IHN is a chronic problem found in North Carolina-grown potatoes, especially the variety Atlantic. Chipmakers prefer potatoes that have a high specific gravity (i.e., dry matter content), and Atlantic is the highest specific gravity variety available to the state’s producers.

But the variety is susceptible to IHN, which a relatively warm climate brings out. In some years, and late in the season, this condition affects about 40 percent of the crop, creating undesirable brown patches on the inside of the potato.

Craig Yencho, a plant breeder, hopes to develop a potato variety better than Atlantic, which makes up 60 percent of the state’s potato crop.

Yencho says it’s not uncommon for a chipmaker to turn away trucks loaded with too many potatoes that have these patches. “There are even times when entire fields are never harvested because of heat necrosis,” he says.

With scientists at N.C. State’s Genome Research Laboratory, Yencho is hoping to learn more about what makes particular types of potatoes susceptible to heat necrosis. Meanwhile, he’s also helping carry out trials of a promising variety developed by U.S. Department of Agriculture-Agriculture Research Service that is resistant to IHN.

“It’s a little lower in dry matter, but it out-yields Atlantic, has a good appearance and you see very little heat necrosis,” he says. “What we need to do next is to test it on a large scale to see if there are any disease, storage, sprouting or harvesting issues,” Yencho adds. “Based on results we get here, we expect that a company in Maine will be increasing production of seed potatoes for our growers.”

Such a variety, coupled with new strategies for managing such chronic diseases as Rhizoctonia, could be key to strengthening North Carolina’s position at the center of a rolling cycle of East Coast potato harvesting. That cycle starts each spring in Florida, then moves up the coast, bringing jobs and income to northeastern North Carolina each summer and making potatoes the state’s third-leading vegetable crop.

—Dee Shore


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