Four sugar beet lines with resistance to a key root disease have been found in the U.S. National Plant Germplasm System collection by an Agricultural Research Service scientist.

The lines are resistant to Rhizoctonia root rot, the most common and serious fungal root disease of sugar beets in the United States. Sugar beets account for more than half the sugar produced in the United States.

ARS plant pathologist Linda E. Hanson, based at the Sugar Beet Research Unit in Fort Collins, Colo., tested 36 plant introductions, including wild and garden beets, from the plant germplasm system. She inoculated the beets with Rhizoctonia fungi and later compared them to more susceptible varieties during hot, Colorado summer weather that helped the disease to flourish. She found four lines that had healthy roots, compared to the susceptible varieties that were infected.

While there are already some disease-resistant sugar beets, researchers want to develop new lines in case current varieties become susceptible.

In addition to causing yield losses of up to 50 percent in the field, Rhizoctonia root rot can reduce storage and processing qualities in harvested beets.

Most of the lines Hanson studied are not available yet commercially. But ARS geneticist and research leader Leonard W. Panella will use some of the successful plant introductions in breeding new lines. The new germplasm, if proven successful at resisting the disease and producing high yields, will be used for a future release.

Hanson and Panella are also hoping to figure out why certain lines are resistant to diseases; they want to see the genetics behind the disease response. They may be able to apply that knowledge to other crops that suffer from Rhizoctonia root rot, such as soybeans. Their research is part of a national program to screen plant introductions for resistance to 10 important disease and insect pests.

ARS is the U.S. Department of Agriculture's chief scientific research agency.