COMBINING ABILITY AND MODE OF GENE
ACTION IN CASSAVA FOR RESISTANCE
TO CASSAVA GREEN MITE AND CASSAVA
MEALY BUG.
Michael M. Chipeta, J.M. Bokosi, V.W. Saka & I.R.M. Benesi
(University of Malawi, Bunda Collge of Agriculture)
PRESENTATION OUTLINE
 Introduction
• importance of cassava
• production constraints
 Objectives
 Materials and Methods
 Results and Discussion
 Conclusions and Recommendation
Introduction
 Cassava (Manihot esculanta Crantz) is a primary
staple food crop for more than 800 million people in
the world (Lebot, 2009)
 In Malawi- a staple food crop for almost 30-40% of
the population (Moyo et al., 1998)
 Contains 25 to 35 % starch; leaves used as
vegetables (Nweke et al., 2002; Moyo et al., 1998; FAO, 1993;
Hahn, 1988)
 Pellets from cassava are used in manufacturing
animal feed
 Industrial crop-its starch used in food industries and
in the textile paper industry (Githunguri, 1991; Silvestre, 1989)
Introduction
 Cassava production is constrained with a number
of factors which include insect pests.
 Among the arthropod pests reportedly causing crop
losses in Africa are cassava green mite (CGM) &
cassava mealy bug (CMB) (Bellotti, 2002; IITA, 1990).
 Fresh root yields reductions due to CGM attack
ranges from 15% (resistant cultivars) to 73%
(susceptible cultivars ) (Bellotti, 2002).
 Yield loss due to CMB on susceptible cultivars can
reach as high as 88% (Bellotti et al., 1987).
Introduction
 Cassava being predominantly grown in traditional
farming systems, pest control is often a low priority.
 Continual use of pesticides is not feasible for low
income small scale farmers & adverse effects on
environment
 Therefore, host plant resistance has been
advocated for the control of pests and reduce their
populations below economic injury levels
Objectives
 In Malawi, virtually no genetic studies on cassava
have been done to determine CA & the mode of
gene action controlling the expression of CGM and
CMB traits
 The objective of this study was to estimate CA and
mode of gene action controlling the expression of
CGM and CMB traits in cassava.
Materials and Methods
Plant materials
 A total of 21 F1 crosses and 21 reciprocals derived
from a 7×7 diallel mating design were the genetic
material used in the study.
Seedling nursery
 Seeds sown in Nov. 2010 & seedlings transplanted
in Jan. 2011 @ Chitedze Research Station (Malawi)
 spacing of 90 cm × 50 cm. Using RCBD & 2 reps.
 Parents (Mature stems 25 cm long) were also
planted at the same spacing but 20 plants per
genotype of each parent.
 No irrigation and fertiliser were applied at this stage.
Materials and Methods
 Individual plants in each F1 cross and seven
parental stands were assessed for their reaction to
CGM and CMB due to natural infection at 3, 6, 9
and 12 MAP.
 The assessment was based on the standard 5
point scoring scale for CGM and CMB.
•
where 1 indicates no obvious symptom and 5 indicates severe
symptoms (IITA, 1990).
 At harvest, 12 MAP, the individual plants were
assessed for their number of storage roots per
plant and root weight (Kg/plant)
Materials and Methods
 Data was analysed for combining ability variances,
estimates of genetic parameters and heritability and
phenotypic correlations using Agrobase 2000.
 CMB severity indices were transformed [square
root (x+3/8)] before performing the analysis.
 GCA effects and SCA effects were estimated using
Griffing (1956) model 1 of method 3
Results and Discussion
Table 1. Mean square values and estimates of genetic
components in cassava for CGM, CMB, ARN and FRW
Source
Genotype
GCA
SCA
Reciprocal
Error
DF
41
6
14
21
41
CGM
0.484***
0.329***
0.169***
0.269***
0.008
CMB
0.077***
0.037***
0.050***
0.031***
0.007
ARN
3.044***
3.513***
1.538***
0.942***
0.239
FRW
0.337***
0.239***
0.240***
0.101***
0.018
δ2gca
0.0006
0.0006
0.0205
0.0015
δ2sca
0.0025
0.0023
0.0796
0.0059
δ2gca/ δ2sca
0.24
0.26
0.26
0.25
δ2 A
0.0012
0.0012
0.041
0.003
δ2 D
0.0025
0.0023
0.0796
0.0059
(σ2D/σ2A)1/2
1.44
1.38
1.39
1.40
H2 (%)
56.6
57.1
57.4
57.1
h2 (%)
18.0
19.6
19.5
19.2
***P<0.001, CGM=Cassava Green Mite, CMB= Cassava Mealy bug, ARN=Average root number
plant-1, FRW=Fresh root weight (Kg plant-1), DF = Degrees of freedom, GCA=General combining
ability, SCA=Specific combining ability, H2 =broad sense heritability, h2=narrow sense heritability
Table 2. Mean and GCA effects of genotypes
for CGM, CMB, root number and root weight.
CGM
CMB
Root number
FRW (Kg plant-1)
Genotype
Mean GCA
Mean GCA
Mean GCA
Mean GCA
4.00 -0.24*** 2.65 -0.08*** 4.12
0.76*** 1.39
0.30***
Mulola
3.92
0.29*** 1.26 -0.01
4.09 -0.42**
0.98 -0.09*
01/1313
3.71
0.12*** 2.22
0.07**
4.10 -0.69*** 1.21
0.09*
Depwete
4.53 -0.10**
1.24
0.04
2.99
0.73*** 0.83
0.01
01/1316
4.00
0.12*** 1.82 -0.09*** 3.23 -0.47**
0.88 -0.17***
Silira
1.00
0.04
2.34
0.28
0.68 -0.09*
TMS4(2)1425 3.29 -0.10**
3.43 -0.09**
1.00
0.02
4.05 -0.19
1.01 -0.06
Maunjiri
0.03
0.18
0.61
0.053
LSD (0.05)
0.03
0.02
0.14
0.04
SE (Gi)
SE (Gi-Gj)
0.04
0.04
0.22
0.09
CGM=Cassava Green Mite, CMB= Cassava Mealybug, FRW= Fresh root weight, SE (Gi) = standard
error for any GCA effect; SE (Gi -Gj) =standard error of the difference between any two effects,
*P<0.05, **P<0.01, ***P<0.001
Table 3. Mean and SCA effects of the crosses for CGM,
CMB, Root number and Root weight (Kg plant-1)
CGM
CROSSES
Mulola × 01/1313
CMB
Root number
Root Weight
Mulola × Depwete
Mulola × 01/1316
Mean
3.13
4.39
4.12
SCA
-0.43***
0.29***
0.03
Mean
1.10
3.20
1.18
SCA
-0.06
0.31***
-0.06
Mean
6.06
3.75
5.88
SCA
1.17***
-0.16
0.38
Mean
1.91
1.13
1.28
SCA
0.61***
-0.20*
0.25**
Mulola × Silira
Mulola × TMS4(2)1425
2.88
4.42
-0.26***
0.53***
1.42
1.00
0.06
-0.15**
5.18
4.90
0.34
-0.50
2.13
0.93
0.36***
-0.53***
Mulola × Maunjiri
01/1313 × Depwete
01/1313 × 01/1316
01/1313 × Silira
3.87
4.38
4.16
4.54
-0.16**
0.01
0.17**
0.26***
1.13
1.23
2.70
1.09
-0.10*
-0.18***
0.18***
-0.05
3.67
2.30
4.63
2.39
-1.22***
-0.98**
-0.65*
-0.42
0.93
1.24
0.95
0.74
-0.50***
0.09
-0.36***
-0.31***
01/1313×TMS4(2)1425
01/1313 × Maunjiri
Depwete × 01/1316
Depwete × Silira
Depwete×TMS4(2)1425
Depwete × Maunjiri
4.43
4.50
3.71
4.05
3.64
4.59
-0.08
0.07
-0.27***
-0.04
0.16**
-0.15**
1.85
1.60
2.55
1.38
1.64
1.40
0.10*
0.00
0.07
-0.10*
0.10*
-0.20***
2.90
3.71
3.865
4.90
3.67
4.40
-0.52
1.40***
-0.52
0.61*
0.33
0.73*
0.86
1.14
1.50
1.31
1.33
1.30
-0.07
0.03
0.11
-0.09
0.05
0.04
01/1316 × Silira
01/1316× TMS4(2)1425
4.25
3.83
0.01
-0.11*
1.48
1.00
-0.05
-0.15**
4.60
5.50
-0.37
0.62*
0.89
1.15
-0.11
-0.09
01/1316 × Maunjiri
Silira × TMS4(2)1425
4.64
3.61
0.16**
-0.29***
2.55
1.30
0.01
-0.02
7.30
4.59
0.54
0.67*
1.40
1.71
0.21*
0.30***
Silira × Maunjiri
TMS4(2)1425×Maunjiri
4.50
3.43
0.31***
-0.23***
1.00
1.44
2.50
3.55
-0.83**
-0.60*
0.50
1.36
-0.14
0.34***
LSD (0.05)
SE (Sij)
SE (Sij-Skl)
0.25
0.16**
0.13*
0.24
0.05
0.07
1.40
0.05
0.06
CGM=Cassava Green Mite, CMB= Cassava Mealybug,
SE=standard error, *P<0.05, **P< 0.01, ***P<0.001
0.38
0.28
0.39
SCA=Specific
0.08
0.10
combining
ability,
Table 3. Continued
CGM
CMB
RECIPROCALS
Mean
SCA
Mean
01/1313 × Mulola
Depwete × Mulola
Depwete × 01/1313
4.13
3.98
4.39
-0.50***
0.20**
-0.05
1.11
1.80
1.11
01/1316 × Mulola
01/1316 × 01/1313
01/1316 × Depwete
Silira × Mulola
Silira × 01/1313
Silira × Depwete
3.27
4.58
3.81
4.39
4.83
4.36
0.43***
-0.21**
-0.05
-0.76***
-0.15*
-0.16*
Silira × 01/1316
TMS4(2)1425× Mulola
TMS4(2)1425×01/1313
TMS4(2)1425×Depwete
TMS4(2)1425× 01/1316
TMS4(2)1425 × Silira
Maunjiri × Mulola
Maunjiri × 01/1313
Maunjiri × Depwete
Maunjiri × 01/1316
3.83
4.00
3.83
4.75
3.58
3.89
3.17
4.05
3.18
3.31
0.21**
0.21**
0.30***
-0.56***
0.12
-0.14*
0.35***
0.23***
0.71***
0.66***
Maunjiri × Silira
Maunjiri×TMS4(2)1425
LSD (0.05)
SE (Rij)
4.20
3.765
0.25
0.15*
0.15*
0.06
SCA
ARN
FRW
Mean
SCA
Mean
SCA
-0.002
0.20**
0.02
5.78
4.88
2.33
0.14
-0.57
-0.02
2.30
1.80
1.50
-0.20*
-0.34***
-0.13
1.30
1.80
1.60
1.00
1.14
1.00
-0.02
0.12
0.15*
0.08
-0.01
0.07
6.68
3.50
4.00
4.89
3.80
2.80
-0.40
0.56
-0.07
0.14
-0.71*
1.05**
2.40
0.75
1.48
1.41
0.70
0.90
-0.56***
0.10
0.01
0.36***
0.02
0.21*
1.00
1.00
1.92
2.65
1.62
1.29
1.00
1.47
1.00
1.03
0.09
0.00
-0.01
-0.16*
-0.11
0.00
0.03
0.02
0.08
0.25***
4.00
5.00
4.60
5.00
6.59
5.19
3.85
6.68
4.11
3.68
0.30
-0.05
-0.85*
-0.67
-0.54
-0.30
-0.09
-1.48***
0.15
1.81***
1.13
1.00
1.22
1.33
1.08
0.93
1.13
1.20
1.40
1.50
-0.12
-0.04
-0.18
0.00
0.04
0.39***
-0.10
-0.03
-0.05
-0.05
2.70
2.79
0.24
-0.28***
-0.21**
3.33
4.25
1.40
-0.42
-0.35
1.32
1.60
0.38
-0.41***
-0.12
0.06
0.35
0.09
CGM=Cassava Green Mite, CMB= Cassava Mealybug, ARN=Average root number/plant,
FRW=Fresh root weight (Kg/plant), SCA=Specific combining ability, SE=standard error, *P<0.05,
**P< 0.01, ***P<0.001
Severity symptoms
Cassava green mite
Cassava mealy bug
Conclusions and Recommendation
 The best rated general combiners based on GCA
effects were Mulola for CGM, CMB, average root
number, fresh root weight; 01/1316 and
TMS4(2)1425 for CGM and average root number.
 Therefore, a multiple crossing programme involving
these parents is recommended to select superior
genotypes with desired traits.
 The best ranking hybrids based on significant mean
performance and SCA effects were Mulola ×
01/1313, Silira × TMS4 (2)1425, Depwete × Silira,
Mulola × Silira, Depwete × Maunjiri and 01/1316 ×
TMS4 (2)1425.
Conclusions and Recommendation
 The results suggest that both additive and nonadditive gene actions should be considered when
designing a breeding program.
 The study has also demonstrated that cytoplasmic
effects are important in the genetic control of the
traits under investigation.
 Therefore, the choice of the female parent to be
included in the breeding program is critical.
THANK YOU VERY MUCH FOR
YOUR ATTENTION