1. A Combining Ability Analysis of Cassava Genotypes to Yield and Cassava Mosaic Disease
E.Y. Parkes, M. Fregene, A.G.O. Dixon, H. Ceballos, B.B. Peprah, P. Illona, P.A. Kulakow and M.T. Labuschagne
presented at the
GCP 21-!! Meeting, Speke Hotel Kampala at Uganda from 18th -22nd June 2012

2. Introduction
Cassava supports over 800 million people in sub-Saharan Africa. Grown in 39 countries
80% of the production is from West Africa
Ghana is the 3rd highest producer
10 million tons/year, thrives in adverse conditions
Ranks first in area under cultivation and utilization .Over 70% of the resource poor farmers produce cassava
Uses
Food (‘gari’, ‘fufu’ etc) ,Feed for animals
emerging industrial uses (starch for plywood, textiles, pharmaceuticals and ethanol production)

3. Materials and method Objective
To determine the relative importance of general (GCA) and specific (SCA) combining ability among cassava genotypes
diallel mating scheme of 7 (non-reciprocal) cassava genotypes
Design: Randomised Complete Block (7 progenitors and 21 F1 progenies) ,3 replications
Locations: (Ejura and Fumesua) for two seasons

4. Soil and climatic conditions of locations
Research site
Soil series
Soil type
Fumesua
Bomso-Asuansi series
(ferric acrisol)
Sandy loam top soil over sandy clay
Ejura
Amantin series
Sandy loam top soil
Research site
Eco-zone
Rainfall (mm)
Months of rainfall
Temperature (oC)
Fumesua
Forest zone
Bimodal April-July Sep-Nov
20-34
Ejura
Forest-transition zone
21-34

5. Source of parents for the study
Accra
Kumasi
Wenchi
80Km
UPPER EAST REGION
UPPER WEST REGION
NORTHERN REGION
BRONG AHAFO REGION
ASANTE
REGION
GREATER ACCRA
CENTRAL
WESTERN
VOLTA
EASTERN
320 landraces were collected from 73 villages in Ghana
Each farmer contributed 2-5 cassava varieties
DNA extraction done for all samples
36 SSR markers were used to analyze the 320 samples on PAGE

6. Crosses of 7 parents Dabodabo Debor Agric Lagos Tuaka Afebankye Kwasea
Fig.8

7. Why diallel?
The diallel mating design has been specifically designed to investigate the combining ability of parents and to identify superior parents for use in hybrid and cultivar development
Diallel mating designs permit the estimation of the magnitude of additive and non additive components of the heritable variance (Griffing 1956; Mather and Jinks 1977).

8. Why diallel? Obtain information on the value of the progenitors
assess the gene action involved in the various characters thereby develop appropriate selection procedures
understand heterotic patterns of progenies at an early stage of hybridisation programmes (Dikerson 1969; Le Gouis et al. 2002; Egesel et al. 2003)

9. SCA is where certain hybrid combinations do relatively better or worse than would be expected on the basis of the average of the performance of the lines involved.
It is the deviation to a greater or lesser extent from the sum of GCA of the parents.
SCA consist of dominance and all types of epistatic variances and is regarded as estimates of effects of non-additive gene actions (Falconer and Mackay 1996).

10. Table1. Estimates of SCA effects for yield and CMD resistance of cassava progenies in the forest zone
Crosses/F1 progenies
Fryld
Rootno
Dryld DM
CMD
Dabodabo x Debor
0.33
-1.73**
0.06
-0.58
-0.11
Dabodabo x Agric
-0.80*
-0.26
-2.26
-0.46
0.08
Dabodabo x Lagos
-0.21
-0.06
-0.04
0.28
Dabodabo x Tuaka
0.47
-0.02
0.07
-0.63
-0.12
Dabodabo x Afebankye
-0.22
1.38*
0.46
-0.07
Dabodabo x Kwasea
0.43
0.68
0.16
0.93*
0.26
Debor x Agric
0.09
Debor x Lagos
0.11
0.04
-0.05
Debor x Tuaka
-0.49
1.08
-0.08
1.08*
Debor x Afebankye
-0.17
-0.31
-0.29
Debor x Kwasea
0.97
-0.32

11. Table1. Estimates of SCA effects for yield and CMD resistance of cassava progenies in the forest zone (cont)
Crosses/F1 progenies
Fyld
Rootno
Dyld DM
CMD
Agric x Lagos
0.39
1.03
0.14
0.52
0.09
Agric x Tuaka
0.32
0.04
0.10
-0.18
-0.09
Agric x Afebankye
-0.19
-0.48
-0.04
-0.77
0.15
Agric x Kwase
-0.001
-0.27
-0.13
Lagos x Tuaka
-0.23
-0.95
-0.10
Lagos x Afebankye
0.37
0.12
0.08
-0.03
Lagos x Kwasea
-0.44
-0.12
Tuaka x Afebankye
0.17
0.008
0.31
-0.14
Tuaka x Kwasea
-0.11
-0.33
-0.009
Afebankye x Kwasea
0.18
-0.88
0.05
-0.26
0.16
Rootno=average root number per plant, Fyld=fresh root yield, Dyld=Dry yield, DM=Dry matter content, SCA=specific combining ability
* P≤0.05, ** P≤0.01

12. Table2. Estimates of GCA effects for yield and CMD resistance of cassava progenies in the forest zone
Parents
Fyld
Rootno
Dyld DM
CMD
Dabodabo
-0.11
0.27
-0.02
0.51*
-0.12
Debor
-0.06
-0.60*
-0.04
-0.34
0.16*
Agric
-0.26
-0.92**
-0.09
-0.10
0.18**
Lagos
-0.07
-0.20
-0.01
Tuaka
0.35
0.52
0.08
-0.40
-0.15*
Afebankye
0.29
0.004
0.20
-0.03
Kwasea
-0.16
0.63
0.07
-0.36*

13. Table 3. Mean squares for GCA and SCA for CMD, yield and yield components of cassava genotypes for the forest ecological zone 2008/2009
Source Df
Rootno
Fyld
Dyld Dm
CMD
GCA 6
22.53**
2.02
0.21
6.77*
0.87**
SCA 21
9.48**
4.31**
0.32**
4.30**
0.50**
Error
108
2.52
0.22
0.023
0.973
0.099
GCA:SCA
2.38
0.47
0.66
1.57
1.74
Rootno=average root number per plant, Fyld=fresh root yield,
Dyld=Dry yield, Dm=Dry matter content, GCA=general combining ability,
SCA=specific combining ability, DF –degree of freedom
* P ≤ 0.05, ** P ≤ 0.01

14. Table 3. Mean squares for GCA and SCA for CMD, yield and yield components of cassava genotypes for forest ecological zone (2009/2010)
Source Df
Rootno
Fryld
Dyld Dm
CMD
GCA 6
30.29**
3.08*
0.25*
2.85*
0.64**
SCA 21
11.97**
7.47**
0.65**
4.36**
0.54**
Error
108
2.72
0.27
0.02
0.89
0.11
GCA:SCA
2.53
0.41
0.38
0.65
1.19
Rootno=average root number per plant, Fyld=fresh root yield,
Dyld=Dry yield, Dm=Dry matter content, GCA=general combining ability,
SCA=specific combining ability, DF –degree of freedom
* P ≤ 0.05, ** P ≤ 0.01

15. Results and discussion
The ratio between GCA and SCA mean squares for yield, CMD and number of roots was greater than 1.0 indicating the predominance of additive gene action
The predictability ratio was 0.83 and 0.74 for root number and CMD respectively, indicating the importance of GCA and additive gene action
GCA:SCA ratio indicated that the SCA was larger than GCA for fresh root yield indicating environmental effects on the trait and confirms the non-additive effects mainly determining expression of root yield

16. Conclusions
Progenies from crosses Dabodabo x Kwasea, Debor x Lagos and Lagos x Kwasea were the best combinations for CMD resistance
Dabodabo for DM 0.51
Kwasea and Tuaka for CMD
Narrow-sense heritability was 0.61 for root number and 0.52 for CMD

17. Acknowledgement Cornell University, New York, USA
University of the Free State, South Africa
IPICS, Uppsala University, Sweden
GCP (Generation Challenge Programme),Mexico
CIAT (Centro International de Agricultura Tropical) Colombia
IITA (International Institute of Tropical Agriculture), Ibadan, Nigeria
Government of Ghana and CSIR- CRI
WAAPP
LEGON,UCC
CSIR Institutes
CSIR-CRI PARTNERS

18. Thank You!
Welcome for collaboration