Project Details:

Quantifying the temporal and spatial spread of bean pod mottle virus and to identify site risk factors to improve BPMV management and soybean yield

Parent Project: This is the first year of this project.
Checkoff Organization:Iowa Soybean Association
Categories:Soybean diseases
Organization Project Code:
Project Year:2009
Lead Principal Investigator:Forrest W Nutter Jr (Iowa State University)
Co-Principal Investigators:
Alison Robertson (Iowa State University)

Contributing Organizations

Funding Institutions

Information and Results

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Project Summary

The overall objectives of this project are to identify the seasonal and site-specific disease risk factors to predict (pre-season) the risk of bean pod mottle virus (BPMV); to quantify BPMV-risk in terms of the rate of spread in soybean fields and determine the relationship between time of BPMV detection in soybean and the reduction in soybean grain yield and quantity. A bean pod mottle virus (BPMV) prevalence and incidence database for 2007 has been completed and verified, and GIS maps for both BPMV prevalence and incidence have been made.

Project Objectives

Project Deliverables

Progress of Work

Final Project Results

Other findings included:
~ Bean pod mottle virus occurred in 75 of Iowa's 99 counties. Bean pod mottle virus incidence at the county scale was low to moderate. Only two Iowa counties had BPMV incidence greater than 60%. In 2007, Iowa counties with higher levels of BPMV incidence tended to be neighbored by counties that also had high levels of BPMV incidence. Clustering of Iowa counties with high BPMV incidence was noted in 2005 and 2006.
~ In all three years of the study (2005, 2006 and 2007), we detected the presence of a disease gradient for BPMV within the state of Iowa. Average latitudes for each of the nine tiers of counties were treated as a causal variable (x), and regression analysis was performed to examine the relationship between county-level BPMV incidence levels (y) and latitude (x). Mean latitude explained 57.8 to 95.5% of the variation in mean BPMV incidence in tiers (Appendix IV). Slope values ranged from -0.03 to -0.20 % per km, indicating that for every 10 km increase in latitude (going south to north), the risk of BPMV incidence decreased between 0.3 and 2.0%. For example, in 2006 the incidence of BPMV decreased by 1.0% for every 5 km change in latitude, progressing from Iowa?s southern tier of counties to the northern tier of counties. A significant relationship between risk of BPMV incidence and longitude (west to east) positions of Iowa counties was not found.
~ We found that soybean fields with row spacing 15? and narrower were associated with high BPMV prevalence. This may be due to the fact that narrow-spaced soybean rows close earlier in the season, enabling bean leaf beetle movement from one row to another, and thereby increasing the spread of BPMV infection.
~ The 2008 soybean growing season was planted rather late (on 6/20/2008) due to flooded fields. Soybean quadrats were sampled 6 times. Only one quadrat from the 6th (last) sampling date tested positive for BPMV. Very few bean leaf beetles were observed in plots in 2008, hence there was low BPMV incidence.
~ We monitored infectious overwintering bean leaf beetle populations in grassy areas adjacent to woodlots and alfalfa. Very few overwintering bean leaf beetles were collected from April 14 to June 15; these were transferred individually to healthy plants to determine if the overwintering population was infectious. None of the beetles or test plants tested positive for BPMV. The low number of bean leaf beetles observed during the spring of 2008 may be attributed to a long winter period and a late soybean planting date.
~ A greenhouse experiment was conducted to quantify the infectious period of bean leaf beetles. We found that a bean leaf beetle can remain infectious for 5 to 9 days. After 12 days, only 2 of 24 bean leaf beetles were capable of transmitting BPMV to healthy plants. This experiment will be repeated in the greenhouse to confirm the results.
~ BPMV was found in the topmost growing point of each soybean plant within five days after inoculation. Thus, it is likely that bean leaf beetles can acquire virus in the uppermost leaves within five days after inoculation. At one month after inoculation, BPMV was found in nearly all leaves and lateral branches (V1 to V10), indicating that all above ground plant parts could serve as an inoculum source for the acquisition of BPMV by bean leaf beetles.
~ Time of BPMV detection (related to infection) explained 57.9% of the variation in soybean yield. In 2007, the regression-line slope value of 0.12 bushels/day indicated that for every 8.5 days BPMV detection was delayed, a soybean farmer would harvest an additional bushel of soybeans per acre.
~ In both 2006 and 2007, time of BPMV detection was significantly related to the percentage of mottled seeds. The earlier BPMV was detected in developing soybean plants, the higher the percentage of mottled seed. Late infection (after the R2 reproductive stage) had minimal or no impact on the percentage of mottled seed.
~ In both 2006 and 2007, we measured soybean seed protein and oil content and regressed these values against the date that BPMV was detected. We did not find a significant linear relationship between time of BPMV detection and protein or oil content.
~ Row spacing had an impact on BPMV risk; with narrow spacing (15 and 7.5 inches) having a greater risk than 30-inch row spacing.
~ We are now investigating whether the presence or absence of alfalfa fields next to soybean fields influences virus risk. We are also evaluating other predictive factors such as county elevation, snow depth, and snow duration, and the influence of these factors on BPMV gradients.

Benefit to Soybean Farmers

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