Combining ability of inbred lines in quality protein maize (QPM) for varietal improvement

Combining ability of inbred lines in quality protein maize (QPM) for varietal improvement
IJPBCS
Combining ability of inbred lines in quality protein
maize (QPM) for varietal improvement
Bullo Neda Tulu1
and Dagne Wegary Gissa2
1
Addis Ababa University, Selale Campus, P.O.Box 245, Fiche, Ethiopia.
2
International Livestock Research Institute, CIMMYT, Ethiopia.
Information on the combining ability of elite germplasm is essential to maximize their use for
variety development. Sixty-six F1 crosses resulted from diallel crosses of 12 QPM inbred lines
and two standard checks BHQP542 and Melkassa6Q were evaluated to determine general
(GCA) and specific (SCA) combining ability for yield and yield related traits using alpha-lattice
design with two replications during the 2013 cropping season at Mechara. Analysis of
variance showed that mean squares due to entries were significant for most traits studied,
indicates existence of variability among the materials. Mean squares due to crosses and
crosses versus checks were also significant for most studied traits. GCA and SCA mean
squares revealed highly significant (p<0.01) differences for grain yield and most yield related
traits. Inbred lines P1, P3 and P12 were good general combiners as the lines showed
significant and positive GCA effects for grain yield. Among the crosses, P2 x P11 and P6 x P8
manifested positive and significant SCA effects for grain yield, indicating high yielding
potential of the cross combinations. In general, this study identified inbred lines and hybrid
combinations that had desirable expression of important traits which will be useful for the
development of high yielding varieties.
Key words: Combining ability, quality protein maize, traits, yield components.
INTRODUCTION
Maize is one of the most important food crops worldwide.
It has the highest average yield per hectare and is the
third after wheat and rice in area and the first in total
production in the world (FAOSTAT, 2010). The global
annual production of maize is about 833 million tons
(FAOSTAT, 2010). Maize is cultivated in all of the major
agro-ecological zones such as high altitude moist (1800-
2400 m.a.s.l), mid-altitude moist (1000-1800m.a.s.l), low
altitude moist (below 1000 m.a.s.l) and moisture stress
areas (500-1800 m.a.s.l) (EARO, 2001) in Ethiopia. The
total annual production and productivity exceed all other
cereal crops, though it is surpassed by teff in area
coverage (CSA, 2013). Therefore, considering its
importance in terms of wide adaptation, total production
and productivity, maize is one of the high priority crops to
feed the increasing population of the country (Mosisa et
al., 2001). In the country, about 2.1 million hectares of
land was covered with maize in 2013 with an estimated
production of about 7 million tons (CSA, 2013). However,
the national average yields is about 3.43t/ha (CSA, 2013)
is still below the world average 5.2t/ha (FAOSTAT, 2010).
Millions of smallholder farmers in the major maize
producing regions of Ethiopia consume maize as
important staple food and derive their protein and calories
requirements from it. But, normal maize varieties are
deficient in two essential amino acids, lysine and
tryptophan; as a result, they cannot provide quality
protein and sustain acceptable growth and adequate
health (Vasal, 2000). For that reason, introducing QPM
varieties with high lysine and tryptophan content would
substantially improve the protein status and greatly
reduce the malnutrition problems of resource poor people
that are dependent on maize as staple food (Leta et al.,
2002).
*Corresponding author: Bullo Neda Tulu, Addis Ababa
University, Selale Campus, P.O.Box 245, Fiche, Ethiopia
Tel.: 251-0913479057, Fax: 251-0111351029, Email:
tulu0913479057@gmail.com
International Journal of Plant Breeding and Crop Science
Vol. 3(1), pp. 079-086, February, 2016. © www.premierpublishers.org. ISSN: 2167-0449
Research Article

Tulu et al. 079
The potential contribution of QPM to improve human
nutritional status has been also accorded worldwide
attention highlighted with the award of the world food
prize of 2000 to scientists (Dr. S.K. Vasal and E.V.
Villages) of the International Maize and Wheat
improvement Center (CIMMYT) who undertook the
research effort on QPM for more than 30 years (Vasal,
2000).
It is understandable that the achievements to minimize or
alleviate protein malnutrition through QPM largely
depends on how efficiently suitable QPM varieties are
developed, made available and accepted by the farmers.
To carry out this task and bridge the nutritional gap of low
income community, it is important to initiate strong QPM
breeding program. To initiate effective hybrid
development program, information on the combining
ability is an essential and critical factor. Combining ability
analysis is one of the powerful tools in identifying better
combining breeding materials which may be hybridized to
exploit heterosis and to select better crosses for direct
use or further breeding work. A suitable means to
achieve this goal is the use of diallel mating system, a
method where by the progeny performance can be
statistically separated into components related to general
combining ability and specific combining ability (Sprague
and Tatum, 1942).
Although such genetic studies have been made widely for
normal maize, in various parts of the country, little effort
has been made on the genetic analysis of quality protein
maize in Ethiopia by Hadji (2004) and Dagne (2008) who
evaluated QPM inbred lines for combining ability effects.
Therefore, in the present study, an attempt was made to
generate information on 12 QPM inbred lines crossed in
half-diallel fashion. Therefore, our objectives were to (i)
estimate general (GCA) combining ability for grain yield
and yield components among QPM inbred lines, and (ii)
estimate specific (SCA) combining ability effects and
identify best hybrid combination among these inbreds.
MATERIALS AND METHODS
Description of the Study Area
The study was conducted at Mechara Agricultural
Research Center during the main cropping season of
2013. The center is located in West Harerge Zone of
Oromia Region at 434 km east of Addis Ababa, the
capital of Ethiopia and 110 km south of Chiro town, the
capital of West Hararghe zone. The center lies at 08036
0
North latitude and 40019
0
East longitudes and at an
altitude of about 1773 meter above sea level (m.a.s.l).
The area receives an annual rainfall of 1294mm. The
annual average minimum and maximum temperatures of
Mechara are 18.1 °C and 33.1 °C, respectively (Mechara
Agricultural Research Center, unpublished).
Experimental Materials
The experimental materials used for the current
experiment consisted of a total of 68 entries which
comprised of 66 F1 crosses obtained from 12 x 12 diallel
crosses (Table 1) (excluding the reciprocal crosses and
parents) of QPM inbred lines, and two standard checks;
namely, BHQP542 and Melkassa6Q. The 66 diallel
crosses were made during the main season (May-
October) of 2012/2013 and off-season (November-April)
of 2012/13 at Melkassa Agricultural Research Center.
The parental lines were originally obtained from CIMMYT
and selected for their per se performance across drought
stressed environments in Ethiopia such as; Melkassa,
Ziwai and Dhera. From the standard checks, BHQP542 is
QPM hybrid released in 2002 by Bako National Maize
Research Project and is a medium maturing three-way
cross hybrid released for mid-altitude (1000-1800
m.a.s.l.) high potential maize growing agro-ecologies of
Ethiopia. Whilst Melkassa6Q is a QPM open pollinated
variety (OPV) released in 2008 by Melkassa Agricultural
Research Center and is an early maturing variety
released for moisture stressed areas of the country.
Experimental Design and Field Management
The seeds of 68 entries (66 F1s and 2 standard checks)
were obtained from Melkassa Agricultural Research
Center and planted at Mechara Agricultural Research
Center of the Oromia Agricultural Research Institute
(OARI). The experiment was laid out in 4 x 17 (4
incomplete blocks in a replication and 17 plots in an
incomplete block) alpha-lattice designs (Patterson and
Williams, 1976) with two replications. Planting was done
manually by placing two seeds per hill, which were later
thinned to one plant per hill. Each plot consisted of two
rows of 4 m length with spacing of 0.75 m between rows
and 0.25 m between plants. Both the rows were used to
collect data on yield and other traits. At planting, 46 kg
P2O5 per ha and 18 kg N per ha were applied in the form
of DAP and an additional of 46 kg N per ha was applied
35 days after planting in a form of urea. Weed control and
other crop management practices were applied done
following research recommendations.
Data Collected
Days to emergence was recorded as the number of
days from planting to when 50% of the seedlings
emerged above ground in each plot. The information was
used to calculate days to anthesis, days to silking and
days to maturity.
Stand count after thinning is the number of well
established plants per plot after thinning.
Leaf rolling was recorded on 1-3 scale, where 1 = not
rolled, 2 = moderately rolled and 3 = highly rolled.
Days to anthesis was recorded as the number of days
from emergence to when 50% of the plants in the plot
shed pollen.
Days to silking was recorded as the number of days
from emergence to when 50% of the plants in the plot
showed up 2-3cm long silk protrusion.
Anthesis-silking interval was recorded as the difference
between number of days to anthesis and silking.

Int. J. Plant Breeding Crop Sci. 080
Table 1. Code and pedigree of QPM inbred lines used in diallel cross analysis
Serial
No. Code Pedigree
1 P1 [CML312/GQL5]-B-B-4-1-1-1
2 P2 [BO155W/CML395]-B-B-2-2-2-1
3 P3 [CML202/CML181]-B-B-10-2-1-1
4 P4 [CML216/CML182]-B-B-5-3-1-1
5 P5 [CML202/CML175]-B-B-1-4-2-3
6 P6 [CML141/[MSRXPOOL9]CIF2-205-1(OSU23i)-5-3-X-X-1-B-B]-B-B-1-5-1-3
7 P7 [CML387/CML182]-B-B-1-3-1-3
8 P8 [CML395/CML182]-B-B-3-1-1-1-1
9 P9 [CML395/CML175]-B-B-5-1-1-1
10 P10 [CML182/[EV7992#EV8449-SR]CIF2-334-1(OSU8i)-1-1-X-X-3-B-B-B]-B-B-10-1-2-1
11 P11 CML144
12 P12 CML159
Days to maturity was recorded as the number of days
from emergence to when 50% of the plants in a plot form
black layer at the tip of the kernels on the ears.
Number of ears per plant was recorded as the total
number of ears harvested from a plot divided by the
number of plants at harvest in that particular plot.
Disease scores were recorded by visual observation of
the diseased plant parts using 1-5 scale, where 1 =
Resistance or no infection, 2 = moderately resistance or
light infection, 3 = moderately susceptible or moderate
infection, 4 = heavy or susceptible infection, 5 = very
heavy or highly susceptible infection.
Plant aspect is overall phenotypic appearance of the
plant recorded on 1-5 scale; where, 1 = very good, 2 =
good, 3 = fair, 4 = poor and 5 = very poor.
Stand count at harvest is the number of plants per plot
at harvest.
Ear aspect is overall phenotypic appearance of all the
ears harvested from a plot and expressed on 1-5 scale;
where, 1 = very good, 2 = good, 3 = fair, 4 = poor and 5 =
very poor.
Shelling percentage was recorded as the ratio of
shelled grain weight to unshelled cob weight (field weight)
expressed in percent for each plot.
Thousand kernel weight was taken at 12.5% moisture.
Grain yield (kg/ha) is the total grain yield of each
experimental plot adjusted to 12.5% moisture level was
converted to ha basis.
Plant height (cm) was measured as distance in cm from
the soil surface to the base of tassel branching taken
from 10 randomly selected plants and the measurement
was made two weeks after pollen shedding was ceased.
Ear height (cm) was measured as the distance in cm
from the ground level to the upper most ears bearing
node taken from 10 randomly selected plants. The
measurement was made two weeks after pollen shedding
was ceased.
Ear length (cm) is the length from the base to the tip of
the ear. Mean of 10 representative ears were used to
represent a plot and measurements were taken just after
harvest.
Number of kernel rows per ear was recorded as the
average number of kernel rows per ear of 10 randomly
selected ears from each plot.
Number of kernels per row was recorded as the
average number of kernels per row of 10 randomly
selected ears from each plot.
Ear diameter (cm) was measured as the average
diameter of 10 randomly selected ears from each
experimental plot.
Leaf area index is the average area in cm
2
of five
sampled leaves per plant in the plot calculated as the
product of its length and width taken from each of the five
sampled plants per plot then multiplied by the correction
factor k ( k = 0.75).
Number of nodes per plant is the average number of
nodes per plant taken from five sampled plants per plot.
Internode length (cm) is the average length of the
internode that is immediately below the upper most ears
taken from the five randomly sampled plants per plot.
Internode length (cm) is the average length of the
internode that is immediately below the upper most ears
taken from the five randomly sampled plants per plot.
Stalk diameter (cm) is the average diameter in cm of the

Tulu et al. 081
stalk immediately below the ear bearing nodes of five
sampled plants per plot measured by a caliper.
Statistical Analysis
Analysis of variance (ANOVA) was carried out following
the PROC MIXED procedure in SAS (SAS, 2003) to
determine the differences among the genotypes.
Genotypes were considered as a fixed effects while
replications and blocks within replications where
considered random. Further analyses were carried out for
traits that showed statistically significant differences
among the genotypes to estimate combining ability using
a modification of the DIALLEL-SAS program (Zhang and
Kang, 1997). Griffing‟s (1956) Method IV and model I
(fixed) diallel analysis, which involves F1 hybrids only was
used to estimate components of variance due to general
combining ability (GCA) and specific combining ability
(SCA).
RESULTS AND DISCUSSION
Analysis of Variance (ANOVA)
The analysis of variance revealed that mean squares due
to entries were significant (P< 0.05) for internode length
and ear diameter, and highly significant (P<0.01) for grain
yield, days to silking, days to anthesis, plant height, ear
height, number of nodes per plant, ear length, number of
kernels per row, stalk diameter, days to maturity,
thousand kernel weight and leaf area index (Table 3). On
the other hand non-significant differences were observed
for anthesis-silking interval, stand count after thinning,
leaf rolling, number of kernel rows per ear, stand count at
harvest, ear aspect, plant aspect, shelling and shelling
percentage, number of ears per plant and disease score.
The significant mean squares due to entries indicated the
existence of variability among the materials evaluated,
which could be exploited for the improvement of
respective traits. Further partitioning of the sum of
squares due to entries into that of crosses, checks and
crosses versus checks indicated that mean squares due
to crosses were either highly significant (P< 0.01) or
significant (P<0.05) for most traits studied except for
stand count after thinning, internode length, leaf rolling,
number of kernel rows per ear, stand count at harvest,
ear aspect, plant aspect, shelling percentage, number of
ears per plant and disease score. In line with the current
study, Vasal et al. (1993a, 1993b) also found significant
mean squares due to crosses for days to silking, plant
height and grain yield in CIMMYT‟s QPM germplasm.
Checks showed non-significant effects for all traits
studied except for number of nodes per plant and days to
maturity that exhibited highly significant (P< 0.01) mean
squares. Significant differences (P<0.01 or P<0.05) were
observed for crosses versus checks for most studied
traits.
Combining Ability Analysis
Analysis of variance for combining ability showed that
mean squares due to GCA and SCA were highly
significant (p<0.01) for most traits studied (Table 4).
These suggest the importance of both GCA and SCA
effects in determining the inheritance of most characters
studied. The significant difference due to GCA and SCA
effects for ear length and diameter in this study is in
agreement with the findings of Dagne (2002, 2008),
Jemal (1999), Dagne et al. (2007) and Birhanu (2009).
Results of this study also confirmed the finding of Yoseph
(1998) who also reported significant GCA and SCA mean
squares for most characters in diallel cross analysis of
maize inbred lines. In line with the current study, Hadji
(2004) found highly significant mean squares due to GCA
and SCA for grain yield, plant height, ear height, days to
silking, ear diameter, days to maturity, number of kernels
per row and thousand kernel weight. In contrast, he found
highly significant mean squares due to GCA and SCA for
ear length that showed highly significant mean squares
only due to GCA in the current study. Mosisa et al.
(2008) also reported the importance of both GCA and
SCA effects in controlling most of the traits although
higher proportion of sum of squares were observed for
GCA than for that of SCA in days to anthesis, ear height
and plant height. Gelana (2000) also reported similar
result that high GCA to SCA ratio which imply greater
contribution of additive gene action than non-additive
gene action. When additive gene effects are dominant
any recurrent selection method can be employed to
improve the traits under study. The importance of both
GCA and SCA effects observed in the current study for
most traits are in line with the findings of Mandefro
(1998), Leta et al. (1999), Mandefro and Habtamu (2001),
Dagne (2002) and Birhanu (2009) who also reported the
importance of both additive and non-additive type of gene
actions for the same traits. In diallel crosses of QPM
germplasm, Vasal et al. (1993b), Glover et al. (2005) and
Dagne (2008) observed both significant GCA and SCA
effects for days to silking. In contrast to the present study,
Vasal et al. (1993a) reported highly significant GCA
effects and non-significant SCA effects for days to silking.
Jemal (1999) and Bello and Olaoye (2009) also observed
non-significant SCA effects for days to silking. The
current study is in agreement with the work of Habtamu
(2000), Dagne (2002) and Dagne et al. (2008) who
reported significant mean squares due to GCA and SCA
for days to maturity. However, Mandefro (1998) and
Jemal (1999) reported non-significant SCA effects for
days to maturity in diallel crosses of drought tolerant
populations. For plant height and ear height, both additive
and non-additive gene actions were important in the
current study. Similar results were reported by Vasal et
al. (1993b), Mandefro (1998), Jemal (1999) and Dagne
(2002).
However, Vasal et al. (1993a) observed highly significant
GCA effects for ear height and non-significant GCA
effects for plant height. Leta et al. (1999) in his study
observed highly significant GCA effects and non-
significant SCA effects of plant height and ear height,
respectively. In contrast, Bayisa et al. (2008) reported
significant GCA effects for ear height only. The existence
of significant differences for both GCA and SCA effects in
controlling number of kernels per row in this study is also
in agreement with the findings of Dagne (2002) and

Table 2. Mean squares for grain yield and yield related traits in 12 x 12 diallel crosses of QPM inbred lines and the two standard checks evaluated at Mechara in 2013
Genotype df GY DS DA ASI PH EH SCAT NNPP IL EL ED LR
Rep 1 9298826.2 188.3 51.89 42.48 693.28 440.27 399.02 3.56 0.21 3.39 0.22 0.013
IB (rep) 32 1467270.4 19.34 6.58 5.66 110 55.57 6.21 0.69 0.93 2.61 0.04 0.007
Entry 67 2081689.9** 30.06** 14.81** 6.9
ns
475.0** 123.17** 8.65
ns
0.96** 2.12* 3.95** 0.09* 0.09
ns
Crosses 65 1898566.5* 27.65** 12.94** 7.02* 409.9** 99.49** 8.13
ns
0.93** 1.83
ns
4.04** 0.09** 0.078
ns
Checks 1 979308.2
ns
72.25
ns
100
ns
2.25
ns
1225
ns
156.3
ns
10.24
ns
1** 7.84
ns
0.06
ns
0.16
ns
0.291
ns
Crosses vs Checks 1 15087098.8** 144.12** 51.57** 2.04
ns
3958.0** 1629.5** 40.86
ns
2.6* 15.12** 2.02
ns
0.12
ns
0.669
ns
Error 35 917044 11.65 5.14 4.35 56.41 28.65 7.04 0.42 1.24 1.63 0.04 0.001
Grand mean 6303.3 74.56 71.04 3.52 178.62 64.64 29.22 11.03 18.15 17.16 4.87 1.02
CV (%) 15.19 4.58 3.19 59.36 4.2 8.28 6.03 5.85 6.13 7.44 3.84 5.02
Genotypes df RPE SDIA SCAH KPR EA DM PA TKW
SHP
EPP LAI DSCORE
Rep 1 4.6 0.47 395.8 73.53 2.13 1.65 0 10817.7
8.21
0.031 46330.03 0.93
IB(rep) 32 0.78 0.32 5.67 11.83 0.29 0.39 0.02 1175.99
1.04
0.014 3358.56 0.564
Entry 67 1.73
ns
0.54** 8.33
ns
19.26** 0.34
ns
6.00** 0.02
ns
2351.99**
71.05
ns
0.105
ns
9767.07** 0.366
ns
Crosses 65 1.77
ns
0.54** 7.94
ns
17.83** 0.33
ns
2.67** 0.02
ns
2381.43**
59.29
ns
0.102
ns
7.02* 0.321
ns
Checks 1 0.25
ns
0.44
ns
6.25
ns
64
ns
0.25
ns
169** 0
ns
238.39
ns
226.25
ns
0.145
ns
8527.60
ns
1.78
ns
Crosses vs Check 1 0.29
ns
0.54* 36.15* 67.43** 1.28* 59.46** 0.002
ns
2551.78
ns
679.88
ns
0.26
ns
645409.47** 1.873
ns
Error 35 1.11 0.12 6.83 5.5 0.23 0.9 0.01 708.43
35.62
0.01 1815.44 0.24
Grand mean 13.7 6.28 28.65 33.84 2.76 135.39 1.98 292.78
73.93
1.10 509.6 1.21
CV (%) 7.71 5.54 9.12 6.93 17.4 0.7 5.75 9.09
12.32
5.08 8.36 8.02
*, **, ns, significant at 0.05 and 0.01 level of probability and non-significant, respectively, ASI = anthesis-silking interval; DA = days to anthesis; df = degree of freedom; DM = days to
maturity; DS = days to silking; ED = ear diameter; EH = ear height; EL = ear length; GY = grain yield; KPR = number of kernels per row; IL = internode length; NNPP = number of nodes per
plant; PH = plant height; SDIA = stalk diameter; TKW = thousand kernel weight

Tulu et al. 083
Table 3. Mean squares due to general (GCA) and specific (SCA) combining ability and error in 12 x 12 diallel crosses of QPM inbred lines
GCA SCA Error
Traits df (11) (54) (35)
GY 3729508** 1288119** 458522
DS 78.12** 13.42** 5.82
DA 35.25** 5.63** 2.57
ASI 12.56** 5.14** 2.18
PH 1319.45** 68.89** 28.21
EH 281.78** 29.38* 14.32
NNPP 2.05** 0.51** 0.21
IL 3.03** 1.02ns 0.62
EL 11.73** 1.3* 0.82
ED 0.14** 0.05** 0.02
SDIA 1.80** 0.10ns 0.06
KPR 43.56** 9.68** 2.75
DM 2.49** 1.98** 0.45
TKW 6583.95** 928.61** 354.22
Table 4. Estimates of general combining ability (GCA) effects for grain yield and related traits of 12 QPM parental lines used in diallel cross
GCA GY DS DA ASI PH EH NNPP IL EL ED SDIA KPR DM TKW
P1 643.4* -0.86ns -1.10ns 0.23ns 3.73ns -2.99ns -0.30ns 0.47ns 0.55ns -0.04ns 0.11ns 2.25* -0.61* -26.38**
P2 -751.8* -4.45** -2.99** -1.42* -20.57** -7.10* -0.22ns -0.95** -2.35** -0.02ns -0.68** -3.80** 0.37ns 53.41**
P3 915.5** 2.81* 1.43* 1.38* 23.30** 14.21** 0.95** 0.89* 1.79** 0.16** 0.65** 2.24** -0.02ns 16.29ns
P4 -590.8* 2.85** 0.82ns 2.03** -4.27ns 2.41ns -0.86** 0.57ns -0.34ns -0.02ns 0.33** -2.54** 0.29ns -9.02ns
P5 225.6ns 1.74ns 1.51* 0.20ns -8.56* -2.60ns 0.04ns -0.57ns 0.30ns 0.02ns 0.14ns -0.98ns 0.79** 16.83*
P6 -375.1ns 0.86ns 0.94ns -0.11ns -4.36ns 2.75ns -0.26ns 0.08ns -0.53ns -0.03ns -0.20ns -1.23ns 0.01ns -6.35ns
P7 -215.1ns -2.35* -0.69ns -1.69* -5.92* 0.26ns 0.67** -0.73* 0.90* -0.15* -0.08ns 0.75ns 0.14ns -6.88ns
P8 453.7ns 1.89ns 1.30ns 0.60ns 16.59** 0.58ns 0.25ns 0.03ns -
0.668ns
0.21** 0.74** 0.41ns 0.09ns 6.8ns
P9 -228.8ns -5.23** -3.72** -1.52* -5.90* -4.84ns -0.68** -0.16ns 1.04* -0.17** -0.35** 2.06** -1.16** -23.88**
P10 -728.6* -0.15ns -0.13ns -0.03ns 0.76ns -0.22ns 0.14ns -0.13ns -0.98* -0.02ns -0.40** -2.11** 0.26ns 0.65ns
P11 -264.3ns 3.02** 2.58** 0.47ns 1.66ns -0.35ns 0.26ns 0.41ns -0.02ns -0.11ns -0.28* 2.14** 0.10ns -43.36**
P12 916.2** -0.13ns 0.04ns -0.14ns 3.54ns -2.12ns -0.03ns 0.11ns 0.29ns 0.13* 0.002ns 0.82ns -0.27ns 21.89*
SE(gi) 290 1.03 0.69 0.63 2.27 2.63 0.2 0.34 0.39 0.06 0.11 0.71 0.29 8.06
SE(gi-gj) 428.3 1.53 1.01 0.93 3.36 2.39 0.29 0.5 0.57 0.08 0.16 1.05 0.42 11.9
*, **, ns, significant at 0.05 and 0.01 level of probability and non-significant, respectively, ASI = anthesis-silking interval; DA = days to anthesis; DF = degree of freedom; DM = days to maturity; DS = days to silking; ED = ear
diameter; EH = ear height; EL = ear length; GY = grain yield; KPR = number of kernels per row; IL = internode length; NNPP = number of nodes per plant; PH = plant height; SDIA = stalk diameter; SE = standard error;
TKW = thousand kernel weight

Table 5. Estimates of specific combining ability (SCA) effects for grain yield and related traits of 12 x 12, diallel crosses of QPM inbred lines evaluated at Mechara in 2013.
Cross GY DS DA ASI PH EH NNPP EL ED KPR DM TKW
P1 x P2 57.9 -1.33 -0.13 -1.12 -1.62 4.77 0.18 1.03 -0.11 2.48 1.45 32.05
P1 x P3 854.9 0.00 -2.56 2.50 1.51 -0.24 0.01 -0.02 0.01 -3.85 -0.46 3.67
P1 x P4 717.3 -3.13 -0.95 -2.26 2.98 0.06 1.02 -0.19 -0.21 2.02 -1.57 -17.42
P1 x P5 99.5 2.18 2.16 0.08 -6.13 -1.03 -0.88 -0.63 -0.15 -2.44 -1.97* -43.07
P1 x P6 -1845.2* 2.36 2.23 0.18 3.77 -0.28 0.12 2.31 0.1 2.21 -0.58 44.81
P1 x P7 192.4 0.27 -0.44 0.76 -10.67 -7.89 -0.01 -0.73 0.22 -0.16 1.48 -9.96
P1 x P8 1542.5 -4.47 -4.13 -0.43 3.82 0.39 0.01 -0.18 -0.04 4.08 -0.27 19.66
P1 x P9 -1516.3 3.65 3.39 0.29 1.81 -5.99 0.14 -2.77* -0.06 -1.27 -0.12 -22.06
P1 x P10 -286.2 5.27 2.00 3.20 -2.75 -4.11 -0.48 -1.25 -0.01 -4.51* 1.36 11.61
P1 x P11 373.9 -0.9 0.69 -1.60 -1.95 5.02 -1.1 0.7 0.18 1.45 2.12* 10.02
P1 x P12 -190.7 -3.85 -2.27 -1.60 9.27 9.29 0.99 1.69 0.04 -0.03 -1.41 -29.33
P2 x P3 168.4 -1.8 -1.36 -0.47 8.61 4.86 0.63 0.29 0.39* 1.09 -0.44 1.68
P2 x P4 449.3 -0.64 -1.05 0.39 2.18 -6.74 -0.46 0.02 0.27 -4.14 0.75 9.69
P2 x P5 -1276.7 0.37 0.56 -0.19 -6.53 -3.23 -0.36 -1.93 -0.17 -2.1 0.05 11.34
P2 x P6 479.4 -5.45 -3.07 -2.39 0.67 1.62 1.14 0.51 -0.12 2.05 0.54 17.02
P2 x P7 -985 4.26 2.66 1.50 -13.77 -2.89 -0.69 -0.83 -0.2 -3.12 -0.1 -41.75
P2 x P8 839.2 0.92 -0.53 1.42 9.92 -2.01 0.23 -0.86 0.24 -1.38 0.45 3.57
P2 x P9 -1192.8 3.94 2.79 1.13 -1.09 -2.69 -0.54 -0.47 0.02 1.07 1.4 4.85
P2 x P10 -1032.6 2.96 3.3 -0.27 -1.05 0.09 -0.26 1.06 0.17 0.23 -1.02 -10.88
P2 x P11 2762.5** -3.21 -3.11 -0.06 5.85 7.12 0.82 1.2 -0.04 4.39* -3.96** 34.83
P2 x P12 -269.6 -0.06 -0.07 0.05 -3.13 -0.91 -0.69 -0.02 -0.48** -0.59 0.91 -62.42*
P3 x P4 1036.2 -8.70** -4.58* -4.11* 4.31 6.75 -0.03 -0.13 -0.01 3.73 -0.36 15.61
P3 x P5 -387 1.01 1.23 -0.18 0.8 0.26 0.67 -0.37 0.05 -1.63 -2.36** 12.86
P3 x P6 1046.9 -1.41 -0.3 -1.18 5.6 4.71 0.67 -0.14 -0.1 1.72 0.83 5.24
P3 x P7 -581.1 1.5 0.73 0.91 -3.04 -8.7 -0.01 0.31 -0.77 -3.35 0.89 10.67
P3 x P8 -2650.7** -3.84 0.04 -3.88* -20.45** -4.72 0.04 -2.66* -0.1 0.99 -0.96 -42.21
P3 x P9 90.9 3.48 1.66 1.86 -7.86 4.001 0.03 -0.07 0.9 -2.76 0.59 -32.13
P3 x P10 911.6 2.4 0.07 2.25 0.58 -3.72 -0.08 -0.2 0.32 3.4 1.07 -3.46
P3 x P11 -712.1 5.23 3.66 1.56 6.28 -1.69 0.003 1.47 -0.55 1.16 0.63 -5.95
P3 x P12 222.1 2.18 1.4 0.76 3.7 -1.52 0.05 1.17 0.55 -0.52 0.6 34
P4 x P5 -901.9 4.87 2.34 2.48 -3.23 1.26 0.02 -0.34 -0.64 -2.06 -0.27 8.27
P4 x P6 1458.6 -0.85 0.11 -0.93 6.97 -1.39 -0.01 -0.99 0.6 1.19 -1.78* 23.45
P4 x P7 10.6 -1.34 1.34 -2.55 1.43 -3.4 -0.01 -0.78 0.97 4.12 -0.82 -16.62
P4 x P8 -1438.1 2.02 3.15 -1.13 -9.48 2.98 0.04 -0.54 -2.07 -4.24 1.73 -52.99*
P4 x P9 286.7 -1.16 1.07 -2.22 -1.59 -0.4 0.03 0.96 0.43 3.31 1.18 12.08
P4 x P10 -204.1 -0.04 -0.22 0.2 -8.45 -8.12 -0.08 0.83 0.35 -3.53 0.66 -37.85
P4 x P11 -743.7 4.29 -2.93 7.21** -4.45 2.01 0.003 -0.52 1.49 1.73 -0.28 14.56
P4 x P12 -671 4.64 1.71 2.91 9.37 6.98 0.05 1.49 -0.83 -2.15 0.79 41.21
P5 x P6 -880.5 3.56 -0.88 4.41* 8.56 0.52 0.02 0.06 0.86 2.33 0.32 22.6
P5 x P7 -1508.3 -1.83 -1.45 -0.32 2.02 8.11 0.02 -0.54 0.73 0.16 0.68 -10.17
P5 x P8 477.7 -0.37 1.46 -1.9 5.31 -1.11 -0.03 1.21 0.9 -0.3 0.33 -14.25
P5 x P9 1607.9 -1.05 -0.82 -0.19 -0.7 -5.99 -0.04 0.7 0.49 1.95 2.38** -7.17
P5 x P10 1304.6 -0.83 0.69 -1.48 -0.76 -2.11 -0.05 0.57 0.11 2.21 -0.34 21.1

Tulu et al. 085
Table 5. Cont.
P5 x P11 1430.7 -6.1 -3.72 -2.47 3.84 5.02 0.03 -0.18 -0.26 -2.73 1.32 -2.69
P5 x P12 34.1 -1.85 -1.58 -0.27 -3.14 -1.71 -0.02 0.13 0.74 4.59* -0.11 1.16
P6 x P7 62.5 2.95 0.62 2.29 8.72 4.26 -0.01 0.82 -1.05 -1.79 0.77 -17.99
P6 x P8 1902.7* -2.79 -3.07 0.31 1.91 2.74 -0.13 0.43 0.15 0.25 0.82 69.13**
P6 x P9 -322.5 2.53 1.45 1.12 -1.7 0.86 -0.4 0.02 -0.07 1.7 -0.53 -52.59*
P6 x P10 292.2 -2.35 -1.24 -1.08 -2.66 1.84 1.18 -0.87 -0.02 2.36 -0.05 -37.02
P6 x P11 -1634.7 -1.22 1.65 -2.87 -25.36** -16.63** -0.54 -2.93* 0.17 -8.08** -0.09 -58.41*
P6 x P12 -559.5 2.63 2.49 0.14 -6.44 1.74 0.25 0.27 0.03 -3.96 -0.22 -16.26
P7 x P8 566.2 3.82 2.56 1.29 4.67 0.13 0.24 0.7 0.27 2.58 0.08 -29.94
P7 x P9 1375.8 -5.26 -4.22* -1.11 9.46 8.05 1.17 0.99 0.15 2.83 -1.67 64.14*
P7 x P10 -705.5 -2.14 -1.01 -1.2 -5.8 -0.87 -0.15 0.01 -0.1 -2.91 -2.29* -5.09
P7 x P11 130.3 -2.01 -1.12 -0.99 0.7 1.86 0.73 0.75 -0.01 0.55 1.27 24.92
P7 x P12 1442 -0.26 0.32 -0.59 6.32 1.33 -0.48 -0.77 0.35* 1.07 -0.26 31.77
P8 x P9 1342.8 -5.6 -3.81 -1.79 7.95 6.93 1.39 2.16 -0.11 2.27 0.48 9.06
P8 x P10 -851.2 0.62 -0.5 1.13 6.99 7.31 -0.23 0.68 -0.26 1.63 -1.34 30.13
P8 x P11 -1817.3* 10.55** 5.79** 4.84* -12.11 -7.76 -1.25 -1.69 0.03 -4.91* -0.88 0.34
P8 x P12 86.2 -0.9 -0.97 0.14 1.51 -4.89 -0.16 0.01 -0.01 -0.99 -0.41 7.49
P9 x P10 -160.7 -1.96 -1.68 -0.27 -3.32 0.93 0 -1.24 0.52** -4.82* 1.71 37.91
P9 x P11 -766.8 0.57 -0.89 1.45 7.28 -0.24 1.18 -0.3 -0.59** -1.96 -2.73** -13.08
P9 x P12 -745.1 0.82 1.05 -0.26 -10.2 -5.47 -0.73 -0.21 -0.33 -2.34 -2.66** -1.03
P10 x P11 528.6 -3.91 0.32 -4.15* 22.22** 9.44 0.76 1.93 -0.04 4.70* 0.05 -2.21
P10 x P12 203.2 -0.06 -1.74 1.66 -4.96 -0.69 -0.45 -1.09 -0.08 1.22 0.22 -4.26
P11 x P12 448.5 -3.33 -0.35 -2.94 -2.26 -4.16 -0.17 -0.35 0.21 3.68 2.58** -2.35
SE(Sij) 866.2 3.09 2.05 1.89 6.79 4.84 0.58 1.16 0.17 2.12 0.86 24.08
SE(sij-sik) 1284.8 4.58 3.04 2.8 10.08 7.18 0.87 1.71 0.25 3.15 1.27 35.71
SE(sij-skl) 1211.3 4.32 2.87 2.64 9.5 6.77 0.82 1.62 0.24 2.97 1.2 33.67
*, **, ns, significant at 0.05 and 0.01 level of probability and non-significant, respectively, ASI = anthesis-silking interval; DA = days to anthesis; DF = degree of freedom; DM = days to maturity; DS = days to silking; ED = ear
diameter; EH = ear height; EL = ear length; GY = grain yield; KPR = number of kernels per row; IL = internode length; NNPP = number of nodes per plant; PH = plant height; SDIA = stalk diameter; SE = standard error;
TKW = thousand kernel weight
Birhanu (2009). However, Mandefro (1998) reported
the absence of non additive type of gene action for this
particular trait. The additive and non-additive gene
actions observed for thousand kernel weight in this
study was also apparent in the studies conducted by
(Habtamu, 2000; Dagne, 2002, 2008). In agreement
with the current study, several workers reported the
importance of both additive and non-additive gene
actions in determining the inheritance of grain yield.
Crossa et al. (1990), Vasal et al. (1994), Mandefro
(1998), Jemal (1999), Leta et al. (1999), Habtamu
(2000), Dagne (2002), Saad et al. (2004), Bayisa et al.
(2008), Glover et al. (2005), Dagne et al. (2007, 2008),
Birhanu (2009) and Bello and Olaoye (2009) found the
importance of both additive and non-additive gene
actions in controlling grain yield. However, Vasal et al.
(1993a, 1993b) reported that grain yield is mainly
controlled by additive gene action. In contrast to this
study, Bhatnagar et al. (2004) reported non-significant
mean square due to GCA for grain yield.
Estimates of general combining ability (GCA)
effects
Estimates of GCA effects of each of the parental inbred
lines for various traits with their respective standard
errors are presented in Table 5. Positive and significant
GCA effects for grain yield were exhibited by P1, P3
and P12 inbred lines. In contrary, P2, P4 and P10
inbred lines showed negative and significant GCA
effects for grain yield. Hence, P1, P3 and P12 inbred
lines were the best general combiners and could be
used in hybrid and synthetic variety development more
effectively. However, lines P2, P4 and P10 inbred lines
were the poor general combiners for grain yield. In
similar fashion the highest mean grain yield was
produced by crosses of P3 and P1 while the lowest
mean grain yield was obtained by crosses having line
P2 as one parent (Table 4). Parental inbred lines P5
and P8 contributed positively to yield but showed non-
significant GCA effects for grain yield. On the other
hand, P6, P7, P9 and P11 inbred lines

contributed negatively to grain yield as the parents
showed non-significant GCA effects for grain yield.
Parents P3, P4 and P11 showed positive and highly
significant GCA effects for days to silking, indicating the
tendency for lateness hybrid progenies, whereas P2, P7
and P9 showed negative and significant GCA effects for
the trait and were found to be the most suitable parents
for reduced days to silking. Positive and significant GCA
effects for days to anthesis were exhibited by P3, P5 and
P11 while P2 and P9 showed negative and significant
GCA effects. Positive and significant GCA effects for
anthesis-silking interval were exhibited by P3 and P4,
whereas P2, P7 and P9 showed negative and significant
GCA effects. Days to anthesis and anthesis-silking
interval follow the same trends with days to silking, in
which parents with GCA positive and significant GCA
effects are considered as poor general combiners while
those with negative and significant GCA effects are
considered good general combiners in breeding for early
type of variety for short rainy season. Parents P2, P5, P7
and P9 showed negative and significant GCA effects for
plant height, out of which P2 was the best general
combiner and the most suitable parent in breeding for
short plant stature followed by P5, P7 and P9. On the
other hand parents P3 and P8 showed positive and
highly significant GCA effects and were poor combiners
as they showed the tendency to increase plant height.
nbred lines P2 and P3 also showed negative and positive
significant GCA effects for ear height, respectively. Those
parents having negative general combining ability effects
for plant and ear height appeared to be good general
combiners in reducing lodging problem. Hence, parents
such as P2, P5, P7 and P9 could serve the purpose of
breeding for lodging tolerance. Positive and significant
GCA effects for number of nodes per plant were exhibited
by P3 and P7 while P4 showed negative and significant
GCA effects and was good general combiners in
reducing number of nodes per plant. Parent P3 showed
positive and significant GCA effects for internode length
whereas parents P2 and P7 showed negative and
significant GCA effects for internode length. Parents P3,
P7 and P9 exhibited positive and significant GCA effects
for ear length and were found to be good general
combiners for the trait. Conversely, P2 and P10 showed
negative and significant GCA effects, indicating poor
general combining ability of the lines. Inbred lines P3, P8
and P12 showed positive and significant GCA effects and
hence combined best for ear diameter while negative and
significant GCA effects were exhibited by P7 and P9,
indicating that these lines were poor combiners for ear
diameter. Parents P1, P3, P9 and P11 showed positive
and significant GCA effects for number of kernels per row
and were the best general combiners for this trait while
P2, P4 and P10 showed negative and significant GCA
effects and were poor general combiners. Positive and
significant GCA effects for stalk diameter were exhibited
by P3, P4 and P8 while P2, P9, P10 and P11 showed
negative and significant GCA effects for the trait. A
Positive and significant GCA effects for days to maturity
was exhibited by P5, showing the tendency of this inbred
line to enhance lateness. P1 and P9 showed negative
and significant GCA values and were found to be early
types. Hence, line P9 which was relatively early in
anthesis, silking and maturity is desirable in developing
relatively early flowering and maturity hybrid that can best
fit to areas with shorter rainy season. Parent P2 revealed
highly significant GCA effects followed by P12 while P5
showed significant GCA effects in the desirable positive
direction for thousand kernel weight, indicating that they
were the best general combiners for the traits. On the
other hand P11 was the poorest general combiner for this
trait followed by P1 and P9, that all the three parents
attributed to highly significant negative GCA effects for
thousand kernel weight. In this experiment some of the
parents were good combiners and the other parents were
poor combiners for the traits studied. Similar results were
also reported by Vasal et al. (1993a, 1993b), Mandefro
(1998), Mandefro and Habtamu (2001) and Dagne
(2002). Among the parents, P3 showed positive and
significant GCA effects for grain yield, internode length,
ear length, ear diameter, number of kernels per row and
stalk diameter, and it was good general combiner for the
mentioned traits. Line P2 which showed negative and
significant GCA effects for days to silking, days to
anthesis, anthesis-silking interval, plant height and ear
height was also good general combiner for these traits
and can be used to develop relatively early flowering
varieties with shorter plant stature so as to escape
terminal moisture stress and also tolerate lodging.
Estimates of specific combining ability (SCA) effects
Crosses evaluated in this study manifested considerable
variation in specific combining (SCA) effects (Table 6) in
all studied yield and yield-related traits, which is in line
with the study of Mandefro and Habtamu (2001) and
Dagne (2002). For grain yield only 7.6% of the crosses
manifested significant SCA effects. The highest
significant SCA effects for grain yield was recorded for P2
x P11 followed by P6 x P8, indicating that the crosses
were best specific combiners for higher grain yield. On
the other hand, negative and significant SCA effects were
exhibited by P3 x P8, P1 x P6 and P8 x P11, indicating
that these crosses were poor specific combiners for grain
yield. The fact that crosses P2 x P11 and P6 x P8
resulted from poor x poor inbred lines combinations
(Table 6) showed that the crosses performed better than
what would be expected from the GCA effects of their
respective parents. Therefore, the crosses could be
selected for their specific combining ability for grain yield
improvement. When high yielding specific combinations
are desired, especially in hybrid maize development,
SCA effects could help in the selection of parental
material for hybridization. For days to anthesis and
silking, only cross P8 x P11 manifested positive and
highly significant SCA effects while P3 x P4 and P7 x P9
showed negative and highly significant SCA effects,
indicating that hybrid P8 x P11 has higher but P3 x P4
and P7 x P9 has lower number of days to anthesis and
silking than what could be expected based on the GCA
effects of the parents. Positive and significant SCA
effects were exhibited for anthesis-silking interval by
crosses P4 x P11, P8 x P11 and P5 x P6 whereas
crosses P3 x P4, P3 x P8 and P10 x P11 showed
negative and significant SCA effects for the same traits.
Cross P10 x P11 exhibited positive and highly significant

Tulu et al. 087
SCA effects for plant height, which is undesirable as
tallness contributes to susceptibility to lodging. On the
other hand crosses P3 x P8 and P6 x P11 showed
negative and highly significant SCA effects for the same
trait, indicating the better specific combining ability of
these crosses for plant height, which is desirable as short
statured plants are mostly lodging tolerant. Cross P6 x
P11 also showed negative and highly significant SCA
effects for ear height. Out of all the crosses evaluated
under this study, P6 x P11, P1 x P9 and P3 x P8 showed
negative and significant SCA effects for ear length
indicating poor specific combination of the crosses for ear
length. Cross P9 x P10 showed positive and highly
significant SCA effects followed by P2 x P3 and P7 x P12
which showed positive and significant SCA effects for ear
diameter whereas crosses P2 x P12 and P9 x P11
showed negative and highly significant SCA effects. Out
of the 66 crosses, only P8 xP9 showed positive and
highly significant SCA effects for number of nodes per
plant.
With respect to number of kernels per row, P2 x P11, P5
x P12 and P10 x P11 showed positive and significant
SCA effects indicating the tendency of the cross to
enhance this trait while crosses P6 x P11, P1 x P10, P8 x
P11 and P9 x P10 showed negative and highly significant
SCA effects indicating the tendency of the cross
combinations to decrease this trait. Significant and
positive SCA effects were obtained in P11 x P12, P5 x P9
and P1 x P11, respectively for days to maturity, indicating
that these hybrids were late in maturity. Crosses P3 x P5,
P7 x P10, P9 x P11 and P9 x P12 exhibited negative and
highly significant SCA effects while P1 x P5, P2 x P11and
P4 x P6 showed negative and significant SCA effects for
days to maturity, indicating early maturity of the latter
groups of crosses. Among the crosses evaluated in this
experiment, P6 x P8 and P7 x P9 showed positive and
significant SCA effects for thousand-kernel weight
whereas P2 x P12, P4 x P8, P6 x P9 and P6 x P11
showed negative and significant SCA effects. The
maximum SCA effects was recorded in P6 x P8 followed
by P7 x P9 while the lowest (negative) SCA effects was
obtained for P2 x P12 followed by P6 x P11, P4 x P8 and
P6 x P9. This indicates that P6 x P8 and P7 x P9 crosses
combined well to give higher thousand kernel weight and
could be selected for their specific combining ability to
improve thousand kernel weight. Significant and positive
SCA effects were recorded for P8 x P11 for days to
silking, P10 x P11 for plant height and P11 x P12, P5 x
P9 and P1 x P11 for days to maturity indicating that the
cross combinations were poor specific combiners for the
respective traits. Crosses with negative and significant
SCA effect such as P3 x P4 for days to silking, P1 x P5,
P2 x P11, P3 x P5, P4 x P6, P7 x P10, P9 x P11 and P9
x P12 for days to maturity and P3 x P8 and P6 x P11 for
plant height were good specific combiners for respective
traits and can be used as good source germplasm to
develop early maturing varieties. It was observed that
some crosses involved good general combining parents
produced crosses with poor specific combining ability for
a given trait, indicating parents with high GCA effects
might not always give crosses with high SCA effects. The
possible explanation is that both line used in the cross
may have the same gene controlling the trait(s) studied
and are not able to take advantage of any additive gene
action. In general smaller (negative direction) SCA was
considered desirable for traits like days to silking, days to
anthesis, ear height, plant height, number of nodes per
plant and days to maturity while positive and significant
SCA was desirable for traits grain yield, ear length, ear
diameter, number of kernels per row, thousand kernel
weight and leaf area index.
CONCLUSIONS
Maize is one of the dominant staple food crops grown in
different parts of Ethiopia. The nutritional value of maize
protein, however, is deficient in the essential amino acids
such as lysine and tryptophan. This has been a major
concern since long ago and necessitated breeders to
develop nutritionally enhanced maize genotypes. Among
12 QPM inbred lines, P1, P2 and P12 have good general
combiners for grain yield since the lines showed positive
GCA effects and P2 has also the best general combiner
for traits such as; days to silking, days to anthesis, plant
height and ear height. Therefore, from this study I
suggest the respective inbred lines for researchers
interested to develop hybrid varieties so as to increase
the production and productivity of the maize yield and
also very crucial to develop early maturing varieties for
drought stressed areas and short statured varieties that
can tolerate lodging.
Regarding the crosses, since P2 x P11 and P6 x P8
manifested positive and significant SCA effects for grain
yield farmers can also use as a variety due to the high
yielding potential of the cross combinations and also
researchers will use for further study in breeding
program. In general, this study identified inbred lines and
hybrid combinations that had desirable expression of
important traits which will be useful for the development
of high yielding hybrids and synthetics.
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Accepted 10 November, 2015.
Citation: Bullo NT, Dagne WG (2016). Combining ability
of inbred lines in quality protein maize (QPM) for varietal
improvement. International Journal of Plant Breeding and
Crop Science, 3(1): 079-089.
Copyright: © 2016 Bullo and Dagne. This is an open-
access article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium,
provided the original author and source are cited.

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