1. Soybean mosaic virus and bean pod mottle virus in Iowa: Occurrence, interactions, impact and identification of preplant risk factors
A.E. Robertson, F.W. Nutter, Jr., E. Byamukama, X. Lu and J. Stedman
Department of Plant Pathology, Iowa State University
2007 ICM Conference, Ames, IA

2. Bean pod mottle virus
Losses up to 52% reported

3. The Vector BPMV is disseminated by insect vectors
The major insect vector is the bean leaf beetle (Cerotoma trifurcata Forster)
There are three populations in a year:
Overwintering generation
1st summer generation
2nd summer generation which will overwinter

4. Source: Dr. Marlin Rice

5. Soybean mosaic virus Losses up to 35% reported
Coinfection of two viruses = can decrease yields up to 75%
Photos by Laura Sweets, University of Missouri
Losses up to 35% reported

6. The Vector SMV is disseminated by over 30 spp. of aphid
Introduction of soybean aphid (Aphis glycines) is cause for concern
David Voegtlin 6

7. Justification
Visual assessment of plants to quantify BPMV and SMV prevalence and incidence unreliable
No quantitative information on the spatial patterns of BPMV or SMV over time in soybean
No quantitative information on the impact of soybean aphid on prevalence, incidence and spatial patterns of SMV in Iowa soybean

8. Prevalence and incidence of Bean pod mottle virus and Soybean mosaic virus at county and field scales

9. Objectives
To produce county and field-level BPMV and SMV prevalence and incidence (risk) maps
To test for spatial dependence of BPMV and SMV in Iowa fields and counties during the soybean growing season
To assess interactions between SMV and BPMV, and SMV and soybean aphid
To develop a pre-plant risk model for BPMV

10. Materials and Methods
A state-wide Soybean Disease Survey was carried out in 2005 and 2006
For each Iowa county, 3-5 soybean fields were selected at each sampling time
30 plants were selected from each field using a systematic sampling design
GPS coordinates were recorded for each soybean field sampled

11. Testing for BPMV
The uppermost leaf from each of the 30 plants was removed and divided into five, leaf sub-samples
Leaf sap was extracted from each sub- sample using a leaf press (Ravenel Specialties Corp.)
Leaf sap was tested for the presence of BPMV using ELISA (AGDIA, Elkhart, IN)

12. Data Recorded Prevalence data (%) was calculated as follows:
Field basis - No. of soybean fields testing positive for BPMV or SMV, divided by total fields tested x 100
County basis – No. of counties testing positive for BPMV or SMV divided total counties sampled x 100
Virus incidence: percentage of sub-samples testing positive in a county/field

13. Spatial Dependence Analysis
ArcGIS software was used to map field and county data
Moran’s Index was used
Ranges from -1 to 1
Dependent on neighborhood structure

14. Results

15. Prevalence and incidence maps15

16. Prevalence of BPMV for each month of the growing season, by field

17. Prevalence of BPMV by counties, 2005

18. Prevalence of BPMV by field, 2005

19. Prevalence of BPMV by counties, 2006

20. Prevalence of BPMV by field, 2006

21. BPMV Prevalence BPMV prevalence at the county scale was
42% in (n = 96) and
91% in 2006 (n = 99)
BPMV prevalence at the field scale was
9.5% in 2005 (n=902) and
35.5% (n=1058) in 2006

22. Prevalence of SMV for each month of the growing season, by field

23. Prevalence of SMV by counties, 2005
Prevalence of SMV at the county level in (32.3%)

24. Prevalence of SMV by field, 2005

25. Prevalence of SMV by counties, 2006
Prevalence at of SMV at the county level in (27.3%)

26. Prevalence of SMV by field, 2005

27. SMV Prevalence SMV prevalence at the county scale was
32.3% in (n = 96) and
27.3% in 2006 (n = 99)
SMV prevalence at the field scale was
4.6% in 2005 (n=902) and
3.5% (n=1058) in 2006 29

28. Incidence of BPMV by counties, 2005

29. Incidence of BPMV by field, 2005

30. Incidence of BPMV by counties, 2006

31. Incidence of BPMV by field, 2006

32. Incidence of SMV by counties, 2005

33. Incidence of SMV by field, 2005

34. Incidence of SMV by counties, 2006

35. Incidence of SMV by field, 2006

36. Virus Incidence BPMV incidence ranged from 0 - 31% in 2005 and
SMV incidence ranged from
% in 2005 and
% in 2006 38

37. Spatial dependence
Moran’s Index values vary between -1 and +1: if the index is >0, there is a spatial dependence showing similar neighbourhood areas; if the value is negative, the neighbourhood areas are discordant; if the index has a value near zero, there is no spatial dependence. 39

38. Spatial analysis of BPMV
Prevalence data (county level)
Year
Moran's I
Pattern
2005
0.26
Clustered
2006
0.53

39. Spatial analysis of BPMV
Incidence data (county level)
Year
Moran's I
Pattern
2005
0.35
Clustered
2006
0.58

40. Spatial analysis of SMV
Prevalence data (county level)
Year
Moran's I
Pattern
2005
0.27
Clustered
2006
0.04
Random
Weak spatial dependence in 2005 only

41. Spatial analysis of SMV
Incidence data (county level)
Year
Moran's I
Pattern
2005
0.28
Clustered
2006
0.21

42. Summary of spatial analysis
Counties in Iowa in which BPMV was detected were clustered in both 2005 and 2006
A weak spatial dependence for SMV in Iowa was detected in 2005

43. Interaction of SMV with BPMV

44. Interaction of SMV with BPMV
- County level, 2006
BPMV
SMV + -
Total 22 68 90 5 4 9 27 72 99
Chi-square value: 3.99
Probability: 0.045

45. Interaction of SMV with BPMV
- Field level, 2006
BPMV
SMV + -
Total 11
362
375 26
659
683 37
1021
1058
Within the 11 fields that tested both positive, 7 fields had one or more sub-samples tested both positive.
Chi-square value: 0.51
Probability: 0.47

46. Interaction of SMV with BPMV
The probability of SMV/BPMV co-infection was low in 2005 and 2006
Within the 11 fields that tested both positive, 7 fields had one or more sub-samples tested both positive.

47. Interaction of SMV with the soybean aphid (Aphis glycines)

48. Interaction of SMV with soybean aphid
- County level, 2006
Aphis glycines
SMV + -
Total 27 69 96 3 72 99
Chi-square value: 1.16
Probability: 0.28

49. Interaction of SMV with soybean aphid
- Field level, 2006
Aphis glycines
SMV + -
Total 15
514
529 20
436
456 35
950
985
Chi-square value: 1.72
Probability: 0.19

50. Interaction of SMV with soybean aphid
In 2005 and 2006, the presence of Aphis glycines did not increase the risk of SMV infection in Iowa
Within the 11 fields that tested both positive, 7 fields had one or more sub-samples tested both positive.

51. Development of a Pre-plant BPMV Risk Model Based upon Climatological and Biological Disease Risk Factors

52. Pedigo’s Model

54. Actual BPMV INCIDENCE, 2006

55. NUMBER OF DAYS MEAN TEMPERATURE WAS < 32 F (0 C)

57. Future Research on BPMV Risk Factors
Duration, depth of snow cover
Soil temperature
BPMV incidence the previous year
/cont.

58. Future Research on BPMV Risk Factors
Site risk factors:
Alternative hosts nearby
Planting infected seed
Planting date 65

59. CONCLUSIONS
BPMV prevalence and incidence was low to moderate in 2005 and low to high in 2006 in Iowa
There was significant spatial dependence for BPMV in Iowa
The southern half of Iowa had a higher risk for BPMV in both years

60. CONCLUSIONS
SMV prevalence and incidence was low in 2005 and in 2006 in Iowa
There was weak spatial dependence for SMV in Iowa in 2005 67

61. CONCLUSIONS
The probability of SMV/BPMV co-infection was low in 2005 and 2006
In 2005 and 2006, the presence of Aphis glycines did not increase the risk of SMV infection in Iowa 68

62. CONCLUSIONS The best single predictor of BPMV at the county level is
# days mean temperature <32F 69

63. Acknowledgments Lu Liu Carlos Rodriguez
PWISE interns (Young-Eun Choi, Sheryl Bottjen, Quyen Nguyen)
GWC Intern (Katherine Schuessler)
ISUE Field Agronomists & CEEDS
USDA-NASS enumerators
The Soybean Disease Survey Assessment Team
Mark Gleason’s Lab

64. Thank you