This document summarizes research on cassava brown streak disease (CBSD) in East Africa. It finds that CBSD incidence and yield losses are higher in the Coast Zone compared to the Lake Zone. Varieties can be categorized based on their resistance and tolerance to CBSD. Estimated financial losses from CBSD are over $50 million annually across the two zones. Ongoing research is working to develop new virus-resistant varieties and management strategies like community phytosanitation to reduce the impact of CBSD.

1. www.iita.orgA member of CGIAR consortium
Analysis of Interactions between Cassava Brown Streak
Disease Symptom Types Facilitates the Determination
of Varietal Responses and Yield Losses
23 November 2015
(R4D Week 2015)
Ndyetabula, S. Merumba, S. Jeremiah, S. Kasele, G. Mkamilo,
F. Kagimbo, C. Chuwa and J. Legg

2. Analysis of Interactions between Cassava
Brown Streak Disease Symptom Types
Facilitates the Determination of Varietal
Responses and Yield Losses
Ndyetabula, S. Merumba, S. Jeremiah, S. Kasele, G. Mkamilo,
F. Kagimbo, C. Chuwa and J. Legg
R4D Week, IITA-Ibadan, Nigeria: November 23-27, 2015

3. A member of the CGIAR consorum
Cassava: A Globally Important Food Staple

4. A member of the CGIAR consorum
Cassava in Africa: Sharing the Cake…………….
Cassava
Mealybug
Cassava
Green Mite
Cassava
Mosaic Disease
Cassava Brown
Streak Disease

5. …………….with some World-Class Viruses
Cassava
Mosaic Geminiviruses
• ACMV – No. 7 virus in
world. Sholthof et al. 2011
• CMGs – Global top 10
Rybicki - 2015
Cassava Brown
Streak Viruses
• CBSD – Top 7 global disease
threat. Pennisi 2010
• CBSVs – Top 3 trans-boundary
emergency threats. FAO

6. CBSD: Key Features
Transmission Symptomatology

7. 1930s
Distribution of CBSD
1930s - 2004

8. 2004: The Re-emergence of CBSD in Uganda

9. www.iita.orgA member of the CGIAR consortium
Cassava Virus Surveillance
http://www.keiththompsonart.com
 Context
 Great Lakes Cassava Initiative (2007-2011)
 Annual surveys of cassava pests & diseases
 6 countries of East and Central Africa
 Approach
 Surveys of young and old cassava fields in major
cassava-growing districts
 Ten plants assessed in old fields and harvested:
 Roots cut five time cross-sectionally
 Each cut scored: 1 (no symptoms) – 5 (severest symptoms)

10. www.iita.orgA member of the CGIAR consortium
CBSD Incidence Variables
http://www.keiththompsonart.com
Factor Description
Plant Total Incidence Percent of plants with any symptom of CBSD
Plant Shoot Incidence Percent of plants with foliar symptoms
Plant Root Incidence Percent of plants with root symptoms
Root Incidence Percent of roots with root symptoms
Unusable Root Incidence Percent of roots with symptoms of score ≥ 3
Factor Description
‘Tolerance’ Ratio between shoot infection (plant shoot
incidence) and unusable root incidence
‘Resistance’ Mean plant total incidence for District
minus mean plant total incidence for field

11. Surveyed
Districts

12. CBSD Total
Plant Incidence

13. CBSD Incidences: Coast and Lake Zones, Tanzania
Region
Field
no.
Plant total
incidence
Plant shoot
incidence
Plant root
incidence
Root
incidence
Unusable
root
incidence
Root
severity
Coast Zone 128 49.5 45.0 20.9 12.2 8.6 3.05
Lake Zone 213 32.7 26.2 18.3 9.3 3.4 2.57
District
Number
of fields
Plant total
incidence
Plant shoot
incidence
Plant root
incidence
Root
incidence
Unusable root
incidence
Root
severity
Muheza 8 50.0 41.3 38.8 28.0 15.6 2.66
Pangani 10 91.0 85.0 47.0 24.8 15.3 2.92
Kibaha 10 92.0 90.0 33.0 22.5 14.8 2.89
Bagamoyo 10 60.0 59.0 4.0 2.2 1.1 2.58
Kisarawe 10 57.0 55.0 15.0 8.5 6. 2.95
Mkuranga 10 73.0 71.0 4.0 1.0 0.5 2.58
Lindi 10 69.0 59.0 29.0 14.6 9.4 3.14
Nachingwea 10 7.0 1.0 6.0 2.3 0.3 2.12
Masasi 10 51.0 33.0 45.0 25.8 16.9 2.66
Newala 10 0 0 0 0 0 -
Mtwara 10 12.0 9.0 12.0 9.3 7.4 3.80
Rufiji 10 36.0 36.0 2.0 1.1 0.2 2.04
Zanzibar 10 45.0 45.0 40.0 30.0 29.3 3.45
Mean(Total) 128 49.5 45.0 20.9 12.2 8.6 3.05
Overall Mean(Total) 341 39.1 33.4 19.3 10.5 5.4 2.85
CBSD Incidence Values – Coast Zone Districts
CBSD Incidence Values – Lake Zone and Coast Zone Means

14. Relationship between Shoot & Root Incidence

15. CBSD ‘’Resistance” and “Tolerance”
CATEGORIES
I
IV
III
II

16. CBSD ‘’Resistance” and “Tolerance”
Variety Zone
Field
no.
Plt shoot
inc.
Plt root
inc.
Root
inc.
Root
Sev.
Unusable
root inc.
Tolerance Resistance
CATEGORY I
Lumala Coast 11 71.9 71.9 11.8 2.0 0.0 98.8 -19.7
Mkombozi Lake 3 66.7 66.7 30.0 2.0 0.6 68.7 -4.0
Bintindope Coast 5 100 100 10.0 2.7 0.7 84.4 -20.8
CATEGORY II
Kiroba Coast 16 60.0 60.0 5.6 2.7 0.6 60.0 -4.6
Kirati Lake 8 26.0 20.0 26.0 2.1 5.4 45.3 5.6
Kiguzo Coast 6 99.7 91.7 45.0 2.5 12.3 36.8 -5.7
CATEGORY III
Liongo Lake 21 6.7 2.9 5.7 2.0 0.0 23.3 2.9
Lwakitangaza Lake 15 76.0 76.0 46.7 2.5 3.2 27.6 -6.4
Tandika Lake 6 25.0 0 25.0 2.0 0.4 25.0 -10.0
CATEGORY IV
Sheria Coast 6 36.7 31.7 26.7 3.1 11.8 5.0 -9.0
Mreteta Coast 6 41.6 38.3 40.0 2.6 20 2.4 -12.7
Agriculture Coast 4 75.0 75.0 75.0 3.4 73.3 1.01 -30.0

17. www.iita.orgA member of the CGIAR consortium
Estimating Yield Loss - 1
http://www.keiththompsonart.com
 Assumptions and Data Sources
 Tuberous root weight loss is proportional to the
reduction in tuberous root number
 Losses are uniform throughout the two main Zones
 Production estimates (2007-2008 – latest available)
 Coast Zone: 1,944,052 t
 Lake Zone: 2,432,729 t
 Fresh market value of cassava: 125 Tsh/kg
equivalent to US$ 60/t (Sewando, 2013)
 Loss = sum of proportion of root number reduction
and the proportion of unusable roots

18. www.iita.orgA member of the CGIAR consortium
Estimating Yield Loss - 2
http://www.keiththompsonart.com
Zone Root
number
reduction
Unusable
root
incidence
Total loss Recorded
Production
(t)
Production
loss due to
CBSD
Financial loss
(US$)
Lake 5.5 % 3.4 % 8.9 % 2,432,729 237,665 14,259,900
Coast 15.7 % 8.6 % 24.3 % 1,944,052 624,048 37,442,880
TOTAL 4,376,781 861,713 51,702,780
Comments
 CBSD causes additional losses, yet to be estimated
 Loss of planting material due to early harvesting
 Opportunity cost of extra labour required for peeling
 Nutritional cost of consumption of mildly diseased roots

19. www.iita.orgA member of the CGIAR consortium
New Cassava Virus/Vectors Research
http://www.keiththompsonart.com
Topic Funding
Absolute quantification of CBSVs BMGF/5CP
Seed degeneration associated with cassava virus infection BMGF/5CP, RTB comp
Conventional host plant resistance BMGF/5CP, RTB, USAID
Clean seed systems BMGF/5CP
Community phytosanitation as a control approach BMGF/Comm. Phyt.
Transmission mechanisms for CBSVs by B. tabaci RTB
Climate change impacts of CBSVs and their whitefly vector Agtrain (EU)
Genomics-based approaches to managing whiteflies USAID
Whitefly chemical ecology Lund University

20. The Fruits of Effective Management
Improved Local
Virus-free cv. Mkombozi: ChatoCommunity phytosanitation yield data: Mkuranga
Chato
Mkuranga
Introduction of virus-free CBSD-tolerant
varieties to communities in Lake and Coast Zones
Chato
• CBSD incidence < 10% after 3 seasons
• 110% yield increase cw local material

21. www.iita.orgA member of the CGIAR consortium
Acknowledgements
http://www.keiththompsonart.com
 BMGF – funding the GLCI project
 CRS – GLCI co-ordination
 Lava Kumar – IITA co-ordination
 Hein Bouwmeester & Tunrayo Alabi
– maps
 Regina Kapinga – Production data
 Farmers – permission to sample
fields