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Potato varieties show resistance to early blight (Research Brief #3)

Posted October 1992

Growers, processors and consumers alike may reap the benefits from a recent study that has identified several potato varieties with improved resistance to early blight. Castile, a relatively high-yielding variety (cultivar) from the U.S. Department of Agriculture breeding program, shows particular promise for growing potatoes with less fungicide.

Most common potato varieties in the state are susceptible to early blight, a foliar disease which occurs every year in Wisconsin. Left untreated, early blight can reduce yields by 10 percent or more. This amounts to a potential annual production loss worth about $12 million to state growers.

Growers stand to increase profits by planting varieties such as Castile that need fewer purchased inputs and mature before many standard varieties are ready for harvest. Reduced fungicide use also will mean greater environmental and food safety for consumers.

“This study shows that there are varieties of potatoes that can be grown with substantially reduced fungicide inputs and have commercial acceptability,” says UW-Madison Plant Pathologist Walt Stevenson. “It’s the first step to utilizing even better varieties in terms of breeding in blight resistance.” These varieties could fit in well with integrated pest management (IPM) programs to reduce chemical use, he adds.

In recent years, potato growers have reduced fungicide use through IPM practices, such as monitoring disease development, rotating crops, and planting disease-free stock. However, growers still must make 6 to 10 fungicide applications a year to control early blight.

While fungicides effectively control the disease, health and environmental concerns over the use of chemicals have grown. In addition, the U.S. Environmental Protection Agency recently limited the amount of EBDC fungicide that potato growers can apply during a season. EBDCs have been the cheapest and one of the most effective fungicides used to control early blight.

Stevenson and UW-Madison Plant Pathologist Vaughan James led an interdisciplinary research team that tested Castile and about 60 other breeding lines for early blight resistance in 1990 and 1991. Several other university scientists, four state potato growers, and the Ore-Ida company also participated in the project.

The researchers conducted the study at the Hancock Agricultural Research Station and the Langlade County Research Project Area, two sites that represent loamy sand and silt loam soil types typical of Wisconsin potato growing areas, respectively. They also established trials on growers’ fields in 1991 to determine the number of fungicide applications needed to grow Castile profitably.

At each location, early blight appeared on all varieties at approximately the same time and progressed at varying rates afterward. In general, potato varieties harvested early or mid-season were more susceptible to early blight than late maturity varieties. While several varieties better resisted the disease than the standard cultivars grown in Wisconsin, Stevenson says, Castile stood “head and shoulders over the other varieties tested.”

Castile required fewer fungicide applications than growers normally use to control early blight, he notes. There were no yield differences between fungicide-treated and untreated Castile plots when moisture and nutrient levels met crop demands and the potential for other crop stress was minimized. Limited fungicide applications were needed when the crop suffered from stresses such as insect damage, potato early dying, or moisture shortages.

In addition to producing yields equal to Russet Burbank with fewer fungicide applications, Castile is generally ready to harvest in mid-August. This is before many other varieties are harvested, and could improve Castile’s potential for processing and marketing. A late-season variety, Russet Burbank currently makes up more than one-half of Wisconsin’s total potato production.

“The beauty of the Castile,” Stevenson says, “is that it matures at a time when storage is normally empty and can fill a niche for growers and processors.” Stevenson adds, however, that a surplus of potatoes remaining in storage during certain years — such as 1992 — wipes out any advantage of growing an early-season variety.

Several UW-Madison researchers have breeding programs that provided potato varieties for this research. More than 200 varieties of wild and domestic potatoes grow throughout the world. In the future, Stevenson plans to continue testing potato cultivars and breeding selections for early blight resistance.

“There is potential for finding other varieties that are disease-resistant and even better than Castile in terms of storability and processing,” he says.

For more information on this research, contact:

Walt Stevenson
Department of Plant Pathology
University of Wisconsin-Madison
Madison, WI 53706
(608) 262-6291

Published as Research Brief #3
October, 1992