The beet necrotic yellow vein virus has long been thought to act alone in inflicting rhizomania, one of the costliest diseases of sugarbeets. But it may actually have a partner in crime, Agricultural Research Service scientists now suspect.
Rhizomania, also known as "crazy root," causes a thick "beard" of feathery hairs to sprout from the taproot of infected sugarbeets. Severe outbreaks can diminish sucrose yields by as much as 40 percent.
In October 2005, ARS plant pathologist John Weiland noticed something odd while examining diseased specimens that colleague and ARS scientist Rebecca Larson had collected from a commercial beet field near Greeley, Colo. Although most of the plants sported the telltale beard, the BNYVV was nowhere to be found--at least, not according to the antibody-based tests Weiland used.
In follow-up studies at the ARS Red River Valley Agricultural Research Center in Fargo, N.D., Weiland inoculated a common weed and a sugarbeet hybrid with extracts from the infected root specimens. Yellow lesions appeared on the leaves in five days--sooner than would have occurred if rhizomania were the culprit. Hexagonal particles within the cytoplasm of the plant cells revealed a mystery virus. By teasing out the virus' genome and sequencing it, Weiland and colleagues were able to conduct a search of published viral genomes--and their identifying coat proteins--for a match.
Surprisingly, their match was the beet black scorch virus, known previously to occur only in China, according to Weiland. In northern China, BBSV reportedly inflicts black, scorch-like marks on sugarbeet leaves. However, the rhizomania-like symptoms that Weiland's group observed in U.S. beet specimens may reflect genomic changes in the U.S. isolates of BBSV.
Besides determining where, when and how the virus entered the United States, the team is trying to figure out whether BBSV is, by itself, a danger to American beets or only in the presence of other diseases such as rhizomania.
Read more about the research in the March 2007 issue of Agricultural Research magazine, available online at www.ars.usda.gov/is/AR/archive/mar07/plant0307.htm.
ARS is the U.S. Department of Agriculture's chief scientific research agency.