1. GENETIC DIVERSITY OF COMMON BEANS AS IMPACTED ON
BY FARMER VARIETY SELECTION FOR THE MANAGEMENT
OF BEAN ROOT ROTS IN SOUTH WESTERN UGANDA
STEPHEN BUAH
MSc. Student
CIAT-Uganda
Gines-Mera Memorial Workshop, Cali 13 – 14 May 2010

2. Background
• Common bean is a major source of proteins and calories in
human and li
h d livestock di t worldwide
t k diets ld id
• In Eastern Africa average consumption is 66 Kg/person per
Africa,
year
• Smallholder farmers, especially women, depend on Common
bean as a cash crop for sustaining their livelihoods
• In 2007 Uganda produced about 545, 000 metric tonnes of
beans worth over US $ 237 million thus p y g a vital role in
playing
the country’s economy

3. Background cont’d
• Despite its importance, common bean production in African is
curtailed by several biotic and abiotic constrains
• In SW Uganda, bean root rot, caused by a complex of Pythium
species, is the most devastating disease —100% yield loses
• Traditionally farmers in this area cultivate mixed varieties for
various reasons including disease management
• The practice has resulted in a vast array of seed and plant types
• However, the impact of root rots on the genetic diversity of these
mixtures is not known.
known

5. Objectives
• The roles of cropping system and practice on bean root rot
management and diversity of beans in SW Uganda.
• The specific objectives of the study were:
1. To study farmer practices of using bean mixtures in bean root
rot management.
2. To analyze genetic diversity associated with bean mixtures in
South-western U
S th t Uganda.
d

6. Materials and Methods
Seed collection from farmers
Mixtures and stockists, Questionnaire
Separation by seed phenotype
Morpho-agronomic
M h i
characterization
Clustering
3 2 3 3 Sub-sampling from each
cluster, 20%
l t
Morpho-agronomic
characterization
Pythium screening
Single plants randomly
chosen
Microsatellite Molecular analysis
Analysis

7. Results
• Why do farmers mix bean varieties?
100
80
ponses (%)
60
Resp
40
20
0
Differential Land Differential Culture High yield High Better taste
survival shortage maturity demand
Reasons for mixing varieties

8. How do farmers select planting materials?
100
80
Response (%)
60
es
40
20
0
Healthy Highy yield Early Adapted High Taste Fast Resistance
seeds maturity seeds demand cooking
Local knowledge

9. Does selection vary from seasonal to season?
120
100
Respo nse (% )
80
es
First season
60
Second season
40
20
0
Rain Large seeds Drought Climbing
resistance resistance varieties
Attributes used

10. Survey conclusion
• Small scale farmers have capacity to utilise available g
p y genetic
resources to manage disease and maintain bean production.
• Farmers are aware of the benefits of applying integrated
management approaches for root rot management.

11. Genetic Diversity
1. Selectable markers
• Seed phenotypes
• Morpho-agronomic characterization
2. Neutral Markers
• SS
SSRs
• Phaseolin

12. Relationships based on Selectable traits
3
44
33
65
57
51
23
67
42
46
29
98
35
5
19
60
77
8
26
Mesoamerican
55
RWR 719
11
84
69
92
15
58
52
41
61
95
50
74
94
4
7
6
96
20
28
27
80
16
17
85
83
CAL 96
48
53
21
24
99
Andean
56
18
34
78
47
43
49
68
31
73
72
79
0.33 0.50 0.67 0.83 1.00
Similarity coefficient

13. Group characteristics
• Mesoamerican group were largely more tolerant to Pythium with 56%
moderately resistant and 22% purely resistant. Overall disease score for
this group was 4 7
4.7
• Andean Group had 40% of the genotypes susceptible to Pythium root
rots and another 50% were only moderately resistant.
t d th l d t l i t t
• Overall, this study found
, y
• 16 Pythium resistant lines (mostly from Kisoro district),
• 26 susceptible and
• 58 intermediates with disease scores of 4-to-6.

14. Molecular characterisation
District
Kabale Kisoro
Populations*/indices Bub Buf Ham Rub Kya Muk Nya Nyz Nyu Kan Mean
No. of samples 14 12 9 11 10 8 6 5 14 5 9.4
Polymorphism (%) 82.9 82.9 85.4 80.5 73.2 58.5 70.7 48.8 69.4 65.1 71.7
Mean pairwise 13.5 14.8 16.1 12.7 12.8 8.3 10.7 10.4 11.1 10.6 12.1
differences
Average gene 32.9 36.2 39.2 31.0 31.2 20.2 26.2 25.4 30.8 25.9 29.9
diversity over loci (%)
*Bub = Bubare, Buf = Bufundi, Ham = Hamurwa, Rub = Rubaya, Kya = Kyanamira, Muk =
Muko, Nya = Nyakabande, Nyz = Nyarusiza, Nyu = Nyundo, Kan = Kanaba.

15. Relationships based on SSR analysis
Distance 0.1
20
6
44
66 Clone I
42
83
52
89
8
93
76 79
94
78
Clone II
27
68
63
73
69
99
erican
92 Clone III
26
71 23
4
esoam
m
1
RWR_719
7
76
68 53
M
96
18
5
71 28
3
73 60
17
58
65
13
93 57
100
16
61
51
48
35
29 Clone IV
21
77 74
77 55
56
19
37
69 15
80 41
77 11
dean
46
43
And
38
74 99 24
84 Clone V
80
CAL_96
31
64 50
49
47
MAIZE

16. AMOVA
Source of variation % of Variance Fixation indices P-value
Among districts 0.00 0.000 (FCT) >0.05
Among sub counties 0.00 0.000 (FSC) >0.001
within districts
Within sub counties 100.00 0.000 (FST) <0.001
•No significant differentiation between the districts of Kabale and
Kisoro (FCT = 0.000, P > 0.05)
•No significant genetic variability among sub counties within
each of the two districts (FSC = 0.000, P > 0.001)
•Overall proportion of variation (100%) was due to differences
within populations at the sub county level

17. General Conclusions
• Farmers’ knowledge on bean production was good and variety mixtures are
used as broad insurance against total crop loss including disease
loss,
management.
• As farmers select for higher y
g yields, they invariably select for root rot
, y y
resistance as well and this could aid breeding
• Resistance to PRR was highest in Kisoro district & decreases towards
Kabale district probably due to more fertile volcanic soils and adoption of
climbing beans
• Root rot intermediate genotypes (
g yp (58%) highest compared to susceptible
) g p p
(26%) and resistant (16%) beans
• The maintenance of the susceptible and moderately resistant genotypes in
bean mixtures could be attributed to market demand and other cooking
qualities

18. Acknowledgements
• We thank GINES-MERA Fellowship Fund for generously providing the
financial support
fi i l
• Supervisors: Dr. Robin Buruchara and Dr. Patrick Okori
• CIAT-Uganda provided the research facilities and administered the
funds

19. Many thanks for your Attention!!