1. SCREENING OF GENERATED PARTIAL INBREDS FOR
RESISTANCE TO CASSAVA BROWN STREAK DISEASE
IN UGANDA
By
Kaweesi1T, Kawuki1 R, Baguma1 Y, Kyaligonza1 V,
Ferguson2 M
1
National Crops Resources Research Institute
2
International Institute for Tropical Agriculture

2. Introduction
• The search for durable resistance to CBSD in cassava through
conventional means is still a challenge in all CBSD affected areas
• This can be attributed to the high heterozygosity due to its
outcrossing nature.
• As a result, the crop has accumulated a high genetic load that limits
some of its traits from full expression especially traits controlled by
recessive traits and quantitative trait loci.
• According to Kulembeka (2010), resistance to CBSD is quantitative
and therefore is more controlled by additive genetic effects than
dominant effects.

3. Introduction Cont’ns
• According to Walsh (2005), inbreeding allows “concentration” of
desirable genes originally present in the elite clone.
• Inbreeding forces an average of half of the loci to become
homozygous, the additive value in a generated inbeds is thus
increased
• Against this premise, this study was initiated to generate new
sources of resistance to both CBSV and UCBSV through inbreeding

4. Generation of partial inbreds at NaCRRI
• Eight cassava genotypes ( 0040, I00142, 130040 and 182/00661 from
IITA and Namikonga, TZ/140, TZ/130 and kigoma Red from Tanzania)
were selected as S0
• Seeds generated (table 1) were planted and seedlings were
evaluated for 9 months then cloned for final evaluation
• Field evaluation of S1 for CBSD was done using a severity score of
1-5 (Gondwe et al., 2002)
• Foliar data was take at 3, 5,7 and 9 month while root data taken
at harvest (9 MAP)
• Wilcoxon ranking, ranksum and AUDPC were used in analysis
of both foliar and roots data

5. Generation of S1 at NaCRRI Generation of seedling at NaCRRI
Field establishment of seedling at NaCRRI

6. Data analysis
Analysis of root data
DI – Ratio of diseased to total number of roots
Rank-sum = Rank of DI + Rank of ISS
Analysis of foliar data
-3 -2 -1 Grand mean 1 2 3
HR R MR MS S HS
Resistance Categorization
Fig 1: Resistance categories of partial inbreds as determined by deviation (d) from the grand mean

7. Results
Table 1: Number of S1 seeds generated, seedling established and clones generated
S0 Seeds generated Seedling Planted clones generated clones established
182/00661 79 40 24 7
Kigoma 60 40 20 11
TZ/130 123 90 79 67
I00142 396 280 160 22
130040 353 200 104 56
Namikonga 123 60 46 29
TZ/140 25 17 11 8
0040 418 200 100 46
According to table 1, family 100142, 182/00661 and 0040 were greatly affected by CMD
and inbreeding depression causing a loss of 94.4%, 91.1% and 88.9% (Personal observation)

8. Determination of resistance levels of generated partial inbreds
using rank sum and AUDPC
Table 2: Relative resistance of generated cassava partial inbreds to cassava brown
streak disease as determined by rank sum method and AUDPC
S1 DI Rdi ISS RISS RS d RC AUDPC d2 RC
182/00661 5 8 1.87 7 15 1.63 MS 284.3 1.34 MS
Kigoma 0.36 7 2.14 8 15 0.99 MS 243 0.54 MS
TZ/130 0.19 6 1.48 6 12 0.30 MS 237.6 0.27 MS
I00142 0.17 4.5 1.4 5 9.5 0.06 MS 205.4 0.26 MS
130040 0.17 4.5 1.22 3 7.5 0.01 MS 202.4 -0.12 MR
Namikonga 0.08 2 1.23 4 6 -0.34 MR 196.7 -0.81 MR
TZ/140 0.1 3 1.1 2 5 -0.72 MR 180 -97 HR
0040 0.03 1 1.09 1 2 -1.1 R 186.5 -1.14 R
DI – Disease incidence ISS – Index of symptom severity d – Deviation from grand mean of the rank sum RC –
Resistance category MS – Moderately susceptible MR – Moderately resistant R – Resistant HR – Highly
resistant d 2 – Deviation from the grand mean of the rank score for AUDPC RS -Rank sum Rdi - Rank score of
disease incidence R ISS - Rank score of index for symptom severity

9. Frequency distribution within each family
Frequency distribution of CBSD root necrosis reaction among family OO40,
Tz/140, Namikonga and 130040

10. Frequency distribution within each family
Frequency distribution of CBSD root necrosis reaction among family
100142, Tz/130, Kigoma Red and 182/00661.

11. Number of genotypes per family generated with
root necrosis score 1
• According to the graphs, the distribution among 0040, TZ/140,
Namikonga and 130040 was more skewed on the left
• There was segregation among Kigoma Red and 182/00661
• Family 0040, Tz/140 and Namikonga had the highest number of
genotypes with root necrosis score 1 (92.8%, 90% and 82%)
• Family 182/00661 and Kigoma Red had the lowest number of
genotypes with root necrosis sev score 1 (33.3% and 56.3%)

12. Comparison of frequency distribution based on root score 1
and Wilcoxon ranking
Table 3: Comparison between frequency distribution based on the number of genotypes with root
necrosis score 1 and Wilcoxon ranking
S0 No* No of S1 with score 1(%) Ranking Wilcoxon Ranking* RC
0040 83 92.8 1 1 R
TZ/140 10 90 2 2 MR
Namikonga 34 82 3 3 MR
130040 101 78.2 4 4 MS
I00142 111 77.5 5 5 MS
TZ/130 80 61.3 6 6 MS
Kigoma 16 56.3 7 7 MS
182/00661 9 33.3 8 8 MS
*Wilcoxon ranking and RC- Resistance category as obtained from table 2, *No – number of S1 that had
roots to evaluate

13. Challenges
• Male sterility among some genotypes
Male sterility in Nachinyaya and kiroba limited generation of partial inbreds
among these genotypes

14. Conclusions
• This study has demonstrated that inbreeding can be used in the
generation of new sources of resistance to CBSD.
• The S1 generated have been screened in a “hotspot” for both
UCBSD and CBSD therefore can be used as parental genotypes in
different breeding programs.
• This study has also demonstrated that Wilcoxon ranking, rank
sum and AUDPC can be used together to combine foliar, root
necrosis and disease incidence in assessment of resistance to
CBSD
• Comparison of S1 and S0 in a Clonal evaluation trial is ongoing to
evaluate the impact of inbreeding on CBSD resistance