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.

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

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

Introduction: CBSD Symptoms

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

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?

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

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

Data collection: scoring scale 3 4 2 5 1 CBSD Foliar evaluation

Data collection: scoring scale

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

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.

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.

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

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

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.

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.

Acknowledgements

Thank you