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Hybrid Potatoes Survive Late Blight

Combining the genes of a wild Mexican potato species with those of U.S. commercial potatoes can provide a measure of resistance to the devastation caused by late blight, says John P. Helgeson. He is a plant physiologist in the ARS Plant Disease Resistance Research Unit at Madison, Wisconsin.

Using a genetic engineering technique whereby leaf cells of different potato species are fused together, Helgeson showed that the wild potato, Solanum bulbocastanum, could be crossed with commercially grown potatoes.

The so-called somatic hybrids that were produced proved highly resistant when exposed to the late blight fungus in test plots in Wisconsin in 1994. Then, in 1995, they were planted in Idaho, Maine, New York, North Dakota, Washington, West Virginia, and Mexico. In 1996, the clinching test was done in a Wisconsin field where the plants grew well, even without fungicide spraying. The best line, called J103K7, yielded more than 20 tons per acre.

ARS researchers at Beltsville and Aberdeen are now using this line to further develop new varieties.

In Madison, Helgeson and ARS plant geneticists are using a method known as polymerase chain reaction (PCR) to map resistance to late blight in S. bulbocastanum. They are using DNA fingerprinting to find pieces of DNA that will allow plant breeders to determine before planting if seedlings are likely to be resistant.

In three different crosses between S. bulbocastanum and commercial potatoes, the researchers found a piece of DNA and used it to identify resistance with 95 percent accuracy. This accomplishment should greatly speed development of new resistant varieties because breeders will be able to determine right away whether or not resistance is present in seedlings.

Helgeson presented information about late blight resistance at the January 1997 North American late blight workshop sponsored by USDA's Cooperative State Research, Education, and Extension Service and ARS in Tucson, Arizona -- By Linda Cooke, ARS.

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