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Scientists Adapt DNA Test to Sugarbeet Fungal Pathogens

By Ben Hardin
August 31, 1999

Sugarbeet growers may soon get a new tool for identifying fungi poised to damage their crop. With the same basic technology used in diagnosing human disease, Agricultural Research Service scientists developed a way to quickly identify any of six major fungi types that attack U.S. sugarbeets. Each disease can cause multimillion-dollar losses.

Developed at ARS' Red River Valley Agricultural Research Center, Fargo, N.D., the diagnostic process can be completed within 8 hours. Researchers designed DNA probes that detect unique DNA segments for each fungal type.

Using polymerase chain reaction (PCR), the scientists reproduce millions of copies of unique segments occurring in a plant tissue sample harboring fungi. From the amplified DNA, they can quickly distinguish pathogens by a “DNA fingerprint” generated when DNA is cut into pieces with an enzyme.

With PCR, scientists don’t have to isolate fungi from diseased roots or leaves and spend days culturing them before they’re identified. Rapid identification of offending microbes by their DNA would tip off growers to the need for applying the most appropriate control measures before diseases seriously curtail yields.

Further research aims at narrowing the fungi's identification by species as well as genus. The scientists have already developed probes to distinguish Aphanomyces cochlioides, which causes black root disease of sugarbeet, from A. euteiches, which causes root rot in peas and other legumes. Other sugarbeet fungi include Pythium ultimum, Cercosporabeticola, Phomabetae, Fusariumoxysporum and Rhizoctonia solani.

Another goal is to use the technology to analyze fungi in field soils as well as plant samples. By knowing soil infestation levels, farmers could better decide when and where to rotate crops.

ARS is USDA's chief research agency.

Scientific contact: John J. Weiland, Sugarbeet and Potato Research, ARS Red River Valley Agricultural Research Center, Fargo, N.D., phone (701) 239-1373; fax (701) 239-1349,