Bean pod mottle virus (BPMV) causes a disease of soybeans. The disease cycle in Virginia is still under investigation to find the primary source of the virus; however we do know that the virus is spread by the bean leaf beetle (Fig. 1). BPMV causes reduction in yields as well as reduced seed quality.
The visible symptoms of BPMV in soybeans are crinkled leaves with a mosaic of light and dark green regions (Fig.2). Seeds produced on infected plants often show a dark streaking, or “mottle” of the hilum. In areas where BPMV incidence is high, yield reductions between 10% and 40% have been reported. Earlier plant infection results in greater chance of yield loss.
The Midwest has a higher prevalence of BPMV than the Eastern US. This virus, however, seems to be reemerging in Virginia, Maryland and Delaware. In Virginia the disease is found mostly in the eastern part of the state (Fig. 3) with a high prevalence on the Eastern Shore and Northern Neck (Table 1). By investigating the possible sources of the virus, the disease may be managed to minimize impact on Virginia soybeans.
|Table 1. 2009 BPVM Surveyed Counties|
BPMV Prevalence on the Eastern Shore
Bean leaf beetles collected in 2008 and 2009 on the Eastern Shore of Virginia were tested for BPMV by ELISA (enzyme-linked immunosorbent assay). Assays in 2008 determined that over 80% of the beetles from the Eastern Shore AREC carried the virus on their mouthparts. In 2009 a total of 544 beetles from Accomack and Northampton counties were tested individually for BPMV by ELISA. Of these, 222 (41%) were positive for BPMV. Of 38 soybean fields tested in 2009, 24 fields had BPMV positive beetles and 14 had positive leaf tissue by TBIA (Fig.4) (Table 1). Accomack County had a higher percentage of infected leaf tissue and beetles than did Northampton County. In addition, fields from the Eastern Shore of Maryland as well as the Northern Neck of Virginia also had BPMV positive fields. Limited sampling in the Tidewater area of Virginia did not detect virus infected beetles and soybeans.
Beetle Processing for ELISA
|1. Locate suspicious plant|
Possible Sources of the Virus
It is unlikely that the seed stage is responsible for being the viral source due to low disease prevelance in fields early in season. It is possible that winter annual, weedy legumes are the source. In the Midwest, the weed tick trefoil, or Tickerfoil has been shown to be an overwintering source for BPMV. The weed is not found in high abundance in Virginia. Tissue blot immunoassays (TBIA) have shown red sorrel and yellow wood sorrel to be positive for virus on the Eastern Shore of Virginia. Other legumes such as clover and vetch have not tested positive for virus, but need further evaluation.
Breeding virus-resistant soybean varieties will likely be the best control tactic in the future. Other strategies that may reduce virus incidence include:
- Controlling beetle-vector populations in the spring by using nicotinoid insecticide seed treatments or targeted sprays. (Our research has shown that bean seeds coated with nicotinoid insecticides can protect seedlings from beetle feeding until 3rd trifoliolate);
- Adjusting planting date to avoid peak beetle populations when soybeans are young should decrease severity of disease (Fig. 5);
- Eliminating virus-reservoir host plants (weeds) on the farm; and
- Decreasing the incidence of seed-borne BPMV by only using clean seed, although incidence of transmission is quite low (< 1 in 1000 seeds). (Select varieties of soybeans that have less mottling).
Funding for the production of this factsheet was provided by a grant from the Virginia Soybean Board.
Virginia Cooperative Extension materials are available for public use, reprint, or citation without further permission, provided the use includes credit to the author and to Virginia Cooperative Extension, Virginia Tech, and Virginia State University.
Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg.
September 9, 2010