First Report of Rhizomania of Sugar Beet in the Columbia River Basin of Washington and Oregon

Rhizomania, caused by Beet necrotic yellow vein virus (BNYVV) and vectored by the soilborne fungus, Polymyxa betae Keskin, is one of the most economically damaging diseases affecting sugar beet (Beta vulgaris L.) worldwide and has been found in most sugar beet-growing areas of the United States (2). During harvest in October 2000, sugar beet plants exhibiting typical symptoms of rhizomania (1) were found in a field near Paterson, WA. Sugar beet had been planted in the field in 1999 and 2000, but prior to this, the field had not been planted with sugar beet for approximately 20 years. Symptomatic roots from the field exhibited stunting, vascular discoloration, and proliferation of lateral rootlets. Leaves of affected plants were chlorotic. Four soil samples were taken from symptomatic areas of the field and diluted with an equal amount of sterile sand. Seeds of rhizomania-susceptible sugar beet cv. Beta 8422 were planted in the soil and sand mix and maintained in a controlled environment at 24°C and 12 h of daylight at one location and in the greenhouse at another. After 8 weeks, enzyme-linked immunosorbent assay (ELISA) was performed on roots of plants grown at each location. Triple-antibody sandwich (TAS) ELISA (Agdia, Inc., Elkhart, IN) was conducted at the University of Idaho, Twin Falls, ID and double-antibody sandwich (DAS) ELISA was performed at USDA-ARS, Salinas, CA, with antiserum specific for BNYVV (2). Two of four samples were positive for BNYVV in the ELISA tests at both locations based on absorbance values at least three times those of healthy controls. TAS-ELISA tests were conducted on roots collected in July 2001 from a field in Washington, 12.9 km from the first field, as well as from a field across the Columbia River near Boardman, OR. Samples from both fields tested positive for BNYVV. All three fields are within 24 km of one another. Four additional fields have subsequently been confirmed to be infected with BNYVV in this region, based on symptomology and ELISA. There are approximately 3,240 ha of sugar beet grown in the region, and growers have been advised as a result of this confirmation to plant resistant cultivars and increase the sugar beet rotation interval with nonhost crops to a minimum of 4 years. References: (1) J. E. Duffus. Rhizomania. Pages 29–30 in: Compendium of Beet Diseases and Insects. E. D. Whitney and J. E. Duffus, eds. The American Phytopathological Society, St. Paul, MN, 1986. (2) G. C. Wisler et al. Plant Dis. 83:864, 1999.