1. Progression of Cassava Brown Streak Disease in Infected Cassava Roots in Uganda
Alex Abaca
Robert S. Kawuki
Phenehas Tukamuhabwa
Yona Baguma
Anthony Pariyo
Joseph Orone
Christopher A. Omongo
Titus Alicai
Anton Bua
GCP21-II, June 19th, 2012.

2. Outline Introduction Problem Statement Research questions
Materials and methods
Data collection and analysis
Results
Implications
Conclusion
Acknowledgements

3. Introduction
Cassava brown streak disease (CBSD) is caused by two +ssRNA viruses: Cassava brown streak virus (CBSV) and Uganda cassava brown streak disease virus (UCBSV) (Ipomovirus: Potyviridae)
It affects the yield and quality of cassava storage roots.
Affected roots show necrosis in the starchy tissues, malformations and constrictions
CBSD produces characteristic symptoms on the leaves, stems and roots

4. Introduction: CBSD Symptoms

5. Problem statement
CBSD is endemic in the lowland coastal areas of Kenya, Tanzania, Mozambique and Lake shores of Malawi
CBSD has appeared in mid altitude areas including Uganda
CBSD affects both the local and elite genotypes
The most damaging symptom occurs in the storage roots
Most CBSD root evaluations is done once at harvest

6. Research Questions
At what age does root necrosis begin to develop in the storage roots?
Is necrotic progression trend similar for susceptible and tolerant genotypes?
Is there a relation between CBSD foliar symptom with root necrosis?

7. Materials and methods Location: NaCRRI, Namulonge
Duration: March 2010 to March2011
Genotypes: 4 CBSD susceptible and 5 CBSD tolerant genotypes
Experimental Design: Split plot Factorial design of single row plot of 15 plants per genotypes
Replication: 3 replications
Spreader row: Diseased TME 204

8. Data collection and analysis
Commenced at 4 months after planting (MAP) till 12 MAP
Plant health data; Incidence & Severity for roots and foliar was done by scoring using a scale of 1-5
Root necrosis assessed by destructive sampling of one plant per genotypes at every data point
generated and summarized data was subjected to Genstat 13th Edition for Statistical analysis

9. Data collection: scoring scale3 4 2 5 1
CBSD Foliar evaluation

10. Data collection: scoring scale

11. Results
Significant differences (P<0.001) were recorded for the reaction grade, genotypes and sampling times.
CBSD root necrosis progression varied among genotypes and between reaction grades (P<0.001)
Susceptible genotypes begins to show root necrosis at 4 MAP, high severity scores of 3 or more at 7MAP
NASE 3 and TME 14 (tolerant genotypes), their root necrosis severity scores of 3 appeared at 10 and 8 MAP respectively

12. Results: Root Severity Months After Planting (MAP)
Reaction Grade
Genotypes
Months After Planting (MAP) 4 5 6 7 8 9 10 11 12
TME 204 1 3
TMS I92/0067
Susceptible
MH96/2961 2
Bamunanika
TME 14
NASE 1 NR
Tolerant
NASE 3
28-TME 14
MM96/0686
Severity Scores: 1= No apparent necrotic tissue, 2 = Less than 5% necrotic tissue, 3 = 5-10% necrotic tissue, 4 = 10-25% of necrotic tissue with mild root constriction and 5 = >25% necrotic tissue and severe root constriction. NR = No roots were found at that sampling time.

13. Results Cont
Most susceptible genotypes had their incidence of 50% or more at 7 MAP whereas TME 14 and NASE 3 (Tolerant genotypes) had their incidences of < 20% and 63 respectively at 10 MAP.
A positive correlation between CBSD foliar symptom severity and root necrosis for both susceptible and tolerant genotypes.
A linear regression coefficient between CBSD foliar severity and CBSD root severity with the coefficient of determination (R2) of 65.8 percent.

14. Results: CBSD Progression Trend in Susceptible genotypes
Figure 1A: Progression of CBSD root necrosis in susceptible varieties over a 12 month growth period. Evaluation was based on one random plant harvested at each sampling occasion

15. Results: CBSD Progression Trend in Tolerant genotypes
Figure 1B: Progression of CBSD root necrosis in tolerant varieties over a 12 month growth period. Evaluation was based on one random plant harvested at each sampling occasion

16. Implications Fine-tuning CBSD root evaluation methods
Preliminary evaluations of CBSD root symptoms in segregating progeny at seedling stage
Use of early maturing varieties and host plant resistance as another option for CBSD management.

17. Conclusion
This being first study to examine the progression of CBSD root necrosis symptoms at different months after planting, it has provided useful insights on the progression of CBSD in cassava roots for some selected varieties in Uganda.

18. Acknowledgements

19. Thank you