TEST CROSS PERFORMANCE AND COMBINING ABILITY OF QUALITY PROTEIN MAIZE (ZEA MAYS L.) INBRED LINES FOR GRAIN YIELD AND AGRONOMIC TRAITS EVALUATED IN HIGHLAND SUB-HUMID AGRO-ECOLOGY OF ETHIOPIA

TEST CROSS PERFORMANCE AND COMBINING ABILITY OF QUALITY PROTEIN MAIZE (ZEA MAYS L.) INBRED LINES FOR GRAIN YIELD AND AGRONOMIC TRAITS EVALUATED IN
HIGHLAND SUB-HUMID AGRO-ECOLOGY OF ETHIOPIA
TEST CROSS PERFORMANCE AND COMBINING ABILITY OF
QUALITY PROTEIN MAIZE (ZEA MAYS L.) INBRED LINES FOR
GRAIN YIELD AND AGRONOMIC TRAITS EVALUATED IN
Zeleke Keimeso1*
, Dufera Tulu 1
, Demissew Abakemal1
, Tefera Kumsa1
, Abiy Balcha2
and Shimelis Tesfaye2
1EIAR- Ambo Agriculture Research Center, PO Box 37, Ambo, Ethiopia.
2 EIAR- Kulumsa Agricultural Research Center, Ethiopia.
The present study was conducted to assess the performance of test cross hybrids and
estimate the combining ability of highland maize inbred lines for grain yield and yield-related
traits. 40 crosses generated by crossing twenty lines with two testers and two genetic checks
were evaluated using alpha lattice design with two replications at Ambo and Kulumsa
agricultural research centers in 2019 main cropping season. Analyses of variances showed
significant mean squares due to crosses for all studied traits that indicated genetic variation
among the materials. GCA mean square due to lines showed significant differences for all
traits. Similarly, GCA mean square due to testers was significant for all traits except anthesis-
silking interval, while SCA mean squares were significant only for grain yield and number of
ears per plant. Inbred lines viz., L7, L13, L5, L2 and L18 were good general combiners for yield
and yield attributing characters. Tester CML159 was high combiner for grain yield than
CML144. Among the hybrids, L5 x T1, L18 x T1 and L12 x T1 exhibited high mean values over
checks and highest SCA effects for yield and yield attributing traits, thus could be used for
further use in the breeding and cultivar development process.
Keywords: General combining ability, line by tester analyses, quality protein maize, specific combining ability, test crosses
INTRODUCTION
Maize (Zea mays) is believed to have originated in central
Mexico 7000 years ago from a wild grass, and Native
Americans transformed maize into a better source of food
(Eubanks, 1995). Maize contains approximately 72%
starch, 10% protein, and 4% fat, supplying an energy
density of 365 Kcal/100 g and is grown throughout the
world, with the United States, China, and Brazil being the
top three maize-producing countries in the world,
producing approximately 563 of the 717 million metric
tons/year (FAOSTAT, 2018; Ranum et al., 2014). It can be
processed into a variety of food and industrial products,
including starch, sweeteners, oil, beverages, glue,
industrial alcohol, and fuel ethanol. In Ethiopia, maize
grows from moisture deficit semi-arid lowlands, mid-
altitudes and highlands to moisture surplus areas in the
humid lowlands, mid-altitudes and highlands (Legesse et
al., 2012). Based on area of production of major cereals,
maize ranks second following teff. Whereas it ranks first in
total grain production followed by teff, sorghum and wheat
(FAOSTAT, 2018). Maize is one of the most important field
crops cultivated in Ethiopia that provide calorie
requirements in the majority of Ethiopians diet. It
contributes the greatest share of production and
consumption along with other major cereal crops, such as
tef [Eragrostis tef (Zucc.) Trotter], wheat (Triticum
aestivum L.) and sorghum [Sorghum bicolor (L.) Moench]
(CSA, 2018). It has significant importance in the diets of
rural Ethiopia. It has gradually penetrated urban centers,
particularly evidenced by green maize cobs being sold at
road sides throughout the country as a hunger-breaking
food available during May to August annually (Twumasi et
al, 2012)
*Corresponding Author: Zeleke Keimeso, EIAR- Ambo
Agricultural Research Centre, P.O. Box 37, Ambo,
Ethiopia.
Email: zeleke.keimiso@gmail.com
International Journal of Plant Breeding and Crop Science
Vol. 7(4), pp. 963-974, December, 2020. © www.premierpublishers.org, ISSN: 2167-0449
Research Article

Zeleke et al. 964
In spite of its widespread and increased consumption as a
source of carbohydrate, the protein of maize endosperm is
deficient in two amino acids named lysine (C6H14N2O2) and
tryptophan (C11H12N2O2) (Bressani, 1991). Lysine ranges
across genetic backgrounds from 1.6 - 2.6% in normal
maize and 2.7 - 4.5% in their opaque-2 gene converted
counterparts, and tryptophan ranges from 0.2 - 0.5% in
normal maize and 0.5 - 1.1% in QPM counterparts
(CIMMYT, 2002). Protein malnutrition is, therefore, a
serious problem, especially among children where maize
and other cereal crops are the predominant staple foods
(Dufera et al., 2018). Quality protein maize (QPM) is a type
of maize variety with improved quality protein content
developed after the discovery of maize mutant in the mid-
1960’s containing the opaque-2 gene in which its mutation
alters protein composition of the maize endosperm
resulting in increased concentrations of lysine and
tryptophan (Mertz et al., 1964).
Thus, QPM cultivars with improved quality protein content
have the potential to improve the nutrition and health of
people who are dependent on maize as a staple food and
thus do not have easy access to a rich source of protein,
such as animal products Leta et al. (2003); Tilahun et al.
(2019). Knowing the potential benefits of QPM varieties,
the National Maize Research Program of Ethiopia initiated
a systematic QPM research in collaboration with CIMMYT
in the early 1990s, which led to the subsequent release of
different hybrid varieties Adefris et al. (2015). To enhance
this subsequent identification and release of different
hybrid varieties, Line x tester study is useful in deciding the
relative ability of female and male lines to produce
desirable hybrid combinations (Kempthorne, 1957). The
two types of combining ability estimates, i.e., general
(GCA) and specific combining abilities (SCA), have been
recognized in genetic studies. General combining ability
relates to additive gene effects, while specific combining
ability reflects the non-additive gene actions (Sprague and
Tatum, 1942).
In Ethiopia, Breeding efforts are underway to convert elite
highland conventional maize inbred lines to QPM through
back crossing and to introduce and to adapt QPM inbreds
by the breeding program of Ambo agricultural research
center of the Ethiopian Institute of Agricultural Research
(EIAR). This effort has led to many QPM inbred lines,
including inbred lines used in this study. Thus, this study
was conducted to estimate the combining ability of QPM
inbred lines for grain yield and yield-related traits in line x
tester QPM hybrids.
MATERIALS AND METHODS
Description of experimental sites
The study was conducted at two locations in the high-
altitude sub-humid agro-ecologies of Ethiopia, namely,
Ambo (AARC) and Kulumsa (KARC) Agricultural
Research Centers in the main cropping season of 2019
(Table 1).
Table 1: Description of testing sites
Research center Altitude (masl) RF(mm) Temp (0c) Latitude Longitude Soil type
Min Max
Ambo 2225 1050 10.4 26.3 8o57’N 38o7’E Black vertisol
Kulumsa 2180 830 10 23.2 805'N 39o10'E luvisol/eutric nitosols
*Rainfall and Temperature were taken as averages of many years for each location
Experimental materials
A total of 42 entries composed of 40 test crosses, formed
by crossing 20 QPM inbred lines with two-line testers
(referred to as CML144 and CML159), and two genetic
checks (KIT21/SRSYN20 and FS170Q/SRSYN20Q) were
studied. The QPM lines used in the crosses were originally
obtained from CIMMYT-Zimbabwe. They were locally
selected based on previous field performances for
adaptation, disease reaction, light table selection for kernel
modification, presence of an opaque-2 gene, and lab
(biochemical) analysis for tryptophan and lysine content
confirmation at EIAR quality lab by the highland maize
breeding program at Ambo agricultural research center
(AARC). The list and the pedigrees of the inbred lines and
testers used in the line by tester crosses are given in Table
2. A standard QPM conversion procedure developed by
CIMMYT was used to identify the QPM inbred lines, which
involved light table screening for endosperm modification,
laboratory analysis for tryptophan and lysine contents, as
well as field evaluation for agronomic traits. The testers
used in this study were identified by CIMMYT Zimbabwe
and introduced to Ethiopia by Ambo highland maize
breeding program (AHMBP) breeding program.

Int. J. Plant Breed. Crop Sci. 965
Table 2: List of QPM inbred lines and testers used for cross formation.
S/N Lines
code
Pedigree Origin
(source)
1 L1 ([NAW5867/P49SR(S2#)//NAW5867]F#-48-2-2-B*/CML511)F2)-B-B-42-2-B-B AHMBP*
2 L2 (CLQRCWQ01/CML312SR)-4-2-1-BB-5-B-B-B-B-B >>
3 L3 [(CLQRCWQ50/CML312SR)-2-2-1-BB/CML197]-B*5-1-B-B-B >>
4 L4 [CML144/[CML144/CML395]F2-5sx]-1-3-1-3-B*4-1-1-B-B-B-B >>
5 L5 [CML159/[CML159/[MSRXPOOL9]C1F2-205-1(OSU23i)-5-3-X-X-1-BB]F2-3sx]-8-1-
1-BBB-4-B-B-B-B-B
>>
6 L6 (CML395/(CML395/[NAW5867/P49SR(S2#)//NAW5867]F#-48-2-2-B*4)F2)-B-B-17-
2-B-B-B
>>
7 L7 [[GQL5/[GQL5/[MSRXPOOL9]C1F2-205-1(OSU23i)-5-3-X-X-1-BB]F2-4sx]-11-3-1-
1-B*4/CML511]-1-B-1-BBB-1-B-B-B-B-B-B
>>
8 L8 [CML144/[CML144/CML395]F2-8sx]-1-2-3-2-B*5-1-B-B-B-#-B >>
9 L9 (CLQRCWQ50/CML312SR)-2-2-1-BB-1-B-B-B-#-B >>
10 L10 ([NAW5867/P49SR(S2#)//NAW5867]F#-48-2-2-B*/CML511)F2)-B-B-37-3-B-#-B >>
11 L11 ([NAW5867/P49SR(S2#)//NAW5867]F#-48-2-2-B*/CML511)F2)-B-B-39-1-B-#-B >>
12 L12 (CML197/(CML197/[(CLQRCWQ50/CML312SR)-2-2-1-BB/CML197]-BB)F2)-B-B-9-
1-B-#-B
>>
13 L13 (CML197/(CML197/[(CLQRCWQ50/CML312SR)-2-2-1-BB/CML197]-BB)F2)-B-B-
35-2-B-#-B
>>
14 L14 (CML197/(CML197/(CLQRCWQ50/CML312SR)-2-2-1-BBB)F2)-B-B-18-2-B-#-B >>
17 L17 (CML395/(CML395/[CML144/[CML144/CML395]F2-8sx]-1-2-3-2-B*5)F2)-B-B-46-1-
B-#-B
>>
18 L18 (CML395/(CML395/[CML144/[CML144/CML395]F2-8sx]-1-2-3-2-B*5)F2)-B-B-50-1-
B-#-B
>>
19 L19 (CML395/(CML395/S99TLWQ-B-8-1-B*4-1-B)F2)-B-B-14-1-B-#-B >>
20 L20 (CML395/(CML395/CML511)F2)-B-B-11-2-B-#-B >>
21 T1 CML144 >>
22 T2 CML159 >>
*AHMBP = Ambo Highland Maize Breeding Program
Experimental design trial management and data collection
The 40 F1 crosses plus the two genetic checks adapted to
the highland agroecology of Ethiopia were planted using
alpha lattice design (Patterson and Williams, 1976) with
two replications, each of which has seven blocks with six
entries in each of the blocks. Design and randomization of
the trials were generated using CIMMYT’s Field book
software (Bindiganavile et al., 2007).
The trials were hand planted with two seeds per hill, which
later thinned to one plant per hill at the 2-4 leaf stage to get
a total plant population of 53,333 per hectare. Each entry
was placed in a one-row plot of 5.25 m long and 0.75 m x
0.25 m apart between and within rows spacing. The
recommended rate of inorganic fertilizers, i.e., 150 and
200 kg ha-1 of DAP and urea, respectively, were used.
Other standard cultural and agronomic practices were
followed in trial management as per recommendations for
the areas.
The procedure of data collection followed CIMMYT’s
manual for managing trials and reporting data (CIMMYT,
1985). Data on grain yield and other important agronomic
traits were collected on a plot and sampled plant base.
Data collected on a plot basis include days to 50%
anthesis (DA), days to 50% silking (DS), anthesis-silking
interval (ASI), grain yield (GY) (t -ha-1). Data collected on
plant base include ear height (EH) (cm), plant height (PH)
(cm) and the number of ears per plant (EPP).
Statistical analyses
Analysis of variance (ANOVA) per individual and across
locations was carried out using the PROC MIXED method
= type3 procedure in SAS (2013) by considering
genotypes as fixed effects and replications and blocks
within replications as random effects for individual site
analyses. In the combined analyses, environments,
replications within environments and blocks within

Zeleke et al. 966
replications and environments were considered as random
while genotypes remained as fixed effects following the
same procedure of Moore and Dixon (2015). Combined
analyses were done for the traits which had a significant
and positive correlation between the two environments
that also did not significantly affect the rank difference of
genotypes across environments. In the combined
analyses, entry and location main effects were tested
using entry x location interaction mean squares as an error
term, while entry x location interaction mean squares were
tested against pooled error.
Combining ability analyses
Line x tester analysis was done for traits that showed
statistically significant differences among the crosses
using the adjusted means based on the method described
by Kempthorne (1957) .General combining ability (GCA)
and specific combining ability (SCA) effects for grain yield
and other agronomic traits were calculated using the line x
tester model. The F-test of mean square due to lines,
testers and their interactions were computed against mean
square due to error for individual location analysis (Singh
and chaudary, 1985). For across locations ANOVA, the F-
test for the main effects such as crosses, lines and lines x
tester interaction mean square was tested against their
respective interaction with the locations. The mean
squares attributable to all the interactions with the
locations were tested against pooled error mean square.
Significances of GCA and SCA effects of the lines and
hybrids were determined by F - test using the standard
errors of GCA and SCA effects, respectively.
RESULTS AND DISCUSSION
Analyses of variance (ANOVA)
Analyses of variances across the two locations were
computed and presented in table 3. The combined
analysis of variance across environments and combining
ability analysis were performed only for the traits
significantly different among the genotypes at each of the
two locations. Significant differences were observed
among the genotypes and crosses for all traits except EH
and PH (which showed significant differences for only
among crosses). Significant differences observed among
the genotypes for most of the traits studied indicated the
presence of genetic variation among the materials, making
the possibility for the improvement of the traits. In
consistence with this finding, Tolera et al. (2017); Dufera
et al. (2018); Tilahun et al. (2019); Tesfaye et al. (2019)
and Keimeso et al. (2020) reported the presence of
significant differences among genotypes for grain yield
and other traits in different sets of maize parental inbred
lines. Mean squares due to locations were significantly
different for all traits indicating the presence of variation
among locations resulting in performance variation across
locations. The GCA mean square due to lines showed
significant differences for all traits (Table 3).
Similarly, the mean square due to tester GCA was
significant for all traits except for the anthesis-silking
interval, which indicated the traits were controlled by
additive gene action. The SCA effects (line × tester
interaction) were significant for grain yield and number of
ears per plant, indicating these traits were controlled by
non-additive gene action. But as already indicated above,
these traits also showed significant GCA mean square for
both line and tester, indicating both additive and non-
additive gene actions controlled the traits. Similar results
were reported by Tesfaye et al. (2019) in line × tester
mating of highland maize inbred lines, whereby mean
squares attributable to GCA and SCA effects were
significant for most traits studied. Keimeso et al. (2020)
also stated that both GCA and SCA mean squares were
significant for most traits studied. The percentage sum-of-
squares of GCA was greater than the percentage sum-of-
squares of SCA in all studied traits except grain yield.
Thus, the ratio of GCA/SCA was greater than unity (Table
3), suggesting that the traits were conditioned mainly by
additive gene effects. In line with these results, several
authors reported the predominance of additive gene action
in the inheritance of most agronomic traits in maize. Amare
et al., 2016; Beyene (2016); Bitew et al., 2017; Tolera et
al., 2017; Dufera et al., 2018 and Tesfaye et al., 2019
reported the predominance of additive gene effects in the
inheritance of most traits. Similar findings were also
reported by Keimeso et al. (2020) for the predominance of
non-additive gene effects in the inheritance of grain yield
in diallel crosses of highland maize inbred lines.
Significant mean squares due to genotype × location and
cross x location was observed for grain yield and number
of ears per plant, indicating that the genotypes performed
differently across locations, which means that the relative
performances of the genotypes were influenced by the
varying environmental conditions for these traits. On the
other hand, the rest studied traits showed a non-significant
difference for genotype by location and cross x location
interaction (Table 3), indicating that the varying
environmental conditions did not influence the relative
performance of the genotypes for these traits. Inconsistent
with the present finding, Tilahun et al. (2018) reported
significant Cr x Loc interaction for all studied traits except
ear position and grey leaf spot. Significant mean squares
due to GCA × location for lines was observed for grain yield
and number of ears per plant, but for testers, significant
GCA x location was observed for anthesis silking interval,
indicating that GCA effects for these traits were
inconsistent across locations. The rest traits showed non-
significant mean square for GCA x location interaction for
both lines and testers, indicating that GCA effects
associated with both lines and testers were consistent over
the two environments.

Similarly, Nepir et al. (2015) reported significant GCA ×
location interaction in QPM inbred lines for grain yield and
some agronomic traits. Except for grain yield, all other
traits showed non-significant SCA × location interaction
effects, indicating that most traits were consistent across
locations. Similar findings were reported by Keimeso et al.
(2020) in diallel crosses of highland maize inbred lines
evaluated across locations.
Table 3: Combined analysis of variance for line by tester crosses involving 20 lines and two testers evaluated at
Ambo and Kulumsa, 2019.
Source of variation DF Mean squares
GY DA DS ASI PH EH EPP
Location (Loc) 1 529.93** 7088.91** 6162.81** 32.4* 23426.33** 15431.54** 1.53**
Rep (Loc) 2 4.56 77.11** 76.46** 3.7 836.55 414.86 0.079
Block (Rep x Loc) 24 1.29 5.96 6.048 3.81 444.74* 224.67 0.04
Genotype (G) 41 6.4** 28.96** 23.23** 13.05* 387.86 213.86 0.17**
Cross (Cr) 39 7.33** 31.96** 25.81** 13.25** 456.85* 217.47 0.19**
GCA line (L) 19 7.36** 52.12** 40.03** 17.03** 611.15** 274.60* 0.14**
GCA testers (T) 1 0.39 146.31** 68.91* 14.4 1591.86* 650.34* 3.26**
SCA (Lx T) 19 7.68** 5.79 9.31 9.41 243.09 137.36 0.09*
G x Loc 41 3.44* 7.37 6.69 7.82 265.77 152.61 0.11**
Cr x Loc 39 3.82* 7.23 5.43 8.49 273.97 151.67 0.12**
L x Loc 19 3.64* 8.99 3.98 7.57 383.11 162.68 0.17**
T x Loc 1 2.64 20.31 0.76 28.9* 680.96 20.55 0.15
L x T x Loc 19 4.06* 4.77 7.14 8.33 143.41 147.57 0.06
Polled Error G 58 1.92 6.79 7.76 7.6 266.61 144.91 0.06
Polled Error Cr 54 1.78 6.79 7.58 6.75 272.24 149.67 0.05
GCA (L)% 48.86 79.43 75.57 62.61 65.17 61.52 34.12
GCA (T)% 0.14 11.74 6.85 2.79 8.93 7.67 42.95
SCA% 50.99 8.83 17.59 34.6 25.92 30.77 22.66
** Significant at 0.01 level of probability, * = significant at 0.05 level of probability, Loc= location, Rep= replication, Blk=
block, DF= degrees of freedom, GY= grain yield, DA= number of days to anthesis, DS= number of days to silking, ASI=
anthesis silking interval, PH= plant height, EH= ear height, EPP= number of ears per plant.
Performance of genotypes
The mean performance of the 40 crosses and two genetic
checks evaluated for grain yield and agronomic traits
across locations is presented in Table 4. The overall mean
grain yield was 6.55 t ha−1 and ranged from 3.53 to 9.15 t
ha−1. Among the 40 crosses, L5 × T1 (Trt 9) (9.15 t ha−1)
(fig. 1) expressed significantly higher grain yield (34.16%)
compared with the two checks (6.82 t ha−1). In addition to
this hybrid, the hybrids L18 × T1, L12 × T1, L10 × T2, L7 ×
T1, L20 × T2, L14 × T2 and L13× T1 showed greater grain
yield compared to non-QPM(KIT21/SRSYN20) and QPM
(FS170Q/SRSYN20Q) genetic checks (Table 4). The
presence of crosses having mean values better than the
checks indicated the possibility of obtaining a good hybrid
(s) for future use in the breeding program. In line with this,
Dufera et al. (2018) and Tesfaye et al. (2019) identified
genotypes performing better than check for grain yield.

Zeleke et al. 968
Figure 1: Mean distribution of grain yield of the 42 genotypes across the two locations
Days to anthesis (DA) and days to silking (DS) ranged from
97.5 to 112.75 and 101.25 to 113 days, with overall means
of 104.79 and 107.4 days respectively. The highest mean
values for both DA and DS were observed from the
crosses L16 x T1, L10 x T1 and L11 x T1, while the lowest
mean values for both DA and DS were observed in cross
L1 x T2, L2 x T1 and L2 x T1 (Table 4). As compared to
the checks, Most of the crosses showed a long number of
days to anthesis and silking. This shows that those crosses
could be grouped as late maturing types. Late maturing
crosses are important in the breeding programs for the
development of high yielding hybrids in areas that receive
sufficient rainfall. The anthesis–silking interval ranged from
0.25 days (L16 x T1 and L16 x T2) to 7.75 days (L1 x T2)
with a mean of 2.61 days. Most of the crosses exhibited
short gaps between anthesis and silking days, which is the
desired character for a good seed setting. Mean plant
height ranged from 162 to 223 cm with mean value of
202.9. The lowest mean values were observed from the
crosses L8 x T1 and L15 x T1, while the highest mean
values were observed from the crosses L19 x T1 and L11
x T2. Genotypes with shorter plant heights could be used
as sources of genes to develop shorter statured varieties.
Ear position is one of the traits that determine lodging
tolerance as well as the vulnerability of ears to wild
animals’ attack in the field. Maize varieties with too high
ear placement and height are prone to lodging, while those
with too short ear placement are prone to wild animals
attack. In line with this result, Tolera et al. (2017) also
identified genotypes with short and long plant and ear
heights. The maximum and minimum number of ears per
plant (EPP) was 1.9 and 0.88, respectively, and the overall
mean was 1.44 ears per plant. Twenty two crosses
exhibited a higher number of ears per plant than the two
checks (Table 4). The high yielding crosses also had a
higher number of ears per plant (EPP), indicating that a
high number of ears per plant contributes to having high
grain yield. The desirability of a higher number of ears for
grain yield improvement was suggested by authors such
as Demissew et al. (2011); Amare et al. (2016); Bullo and
Dagne (2016) and Bitew et al. (2017).

Table 4. Mean values of yield and yield-related traits of 40 test crosses and two genetic checks evaluated at
Ambo and Kulumsa in 2019.
Crosses Grain yield (t/ha) DA DS ASI PH EPP
Ambo Kulumsa Across (days) (days) (days) (cm) No
L1 x T1 5.05 8.69 6.87 101.25 102.75 1.5 197.5 1.45
L1 xT2 3.57 6.35 4.96 97.5 105.25 7.75 189.25 1.31
L2 x T1 5.55 9.32 7.43 99.5 103.5 4 203 1.81
L2 x T2 5.41 9.76 7.59 98.5 102.25 3.75 216.25 1.38
L3 x T1 4.74 6.38 5.56 105.75 107.5 1.75 198.25 1.64
L3 x T2 3.93 7.88 5.91 100 106.5 6.5 191.25 1.36
L4 x T1 4.06 4.5 4.28 106 112 6 203 1.45
L4 x T2 6.23 9.14 7.68 102.25 107.75 5.5 217.5 1.37
L5 x T1 5.17 13.12 9.15 104.5 106.5 2 198 1.9
L5 x T2 4.49 7.73 6.11 104 105 1 197.25 1.22
L6 x T1 6.04 7.47 6.75 106.75 107.5 0.75 203 1.72
L6 x T2 5.68 6.93 6.31 104.5 106.25 1.75 208.25 1.64
L7 x T1 5.99 10.86 8.42 105.25 106.5 1.25 205.5 1.77
L7 x T2 5.2 8.95 7.08 103 105.75 2.75 204 1.28
L8 x T1 2.54 5.22 3.88 107 109 2 162 1.52
L8 x T2 5.69 9.13 7.41 106 107 1 198.25 1.15
L9 x T1 5.08 6.03 5.55 107.25 109.5 2.25 195 1.48
L9 x T2 4.35 7.34 5.85 107.25 108.75 1.5 193.75 1.59
L10 x T1 3.79 8.45 6.12 108.25 112 3.75 191.25 1.47
L10 x T2 5.66 11.35 8.51 106.25 108 1.75 208 1.28
L11 x T1 5.05 7.9 6.48 107.5 111 3.5 211 1.44
L11 x T2 5.45 8.14 6.79 106.5 111.25 4.75 221 1.27
L12 x T1 5.07 12.11 8.59 105.75 106.25 0.5 197.25 1.62
L12 x T2 5.5 6.06 5.78 106.5 109.25 2.75 202.25 1.3
L13 x T1 4.88 10.51 7.69 105.75 106.5 0.75 206.25 1.74
L13 x T2 5.29 10.08 7.68 104 105.5 1.5 213.25 1.58
L14 x T1 3.37 8.36 5.86 106 107.5 1.5 201.75 1.62
L14 x T2 5.15 10.29 7.72 104.25 106 1.75 206.25 1.26
L15 x T1 1.85 5.22 3.53 104.75 106.75 2 180.5 1.63
L15 x T2 4.69 6.31 5.49 103.25 105.5 2.25 199 1.31
L16 x T1 3.75 8.59 6.17 112.75 113 0.25 194 1.47
L16 x T2 4.18 7.32 5.75 107.5 107.75 0.25 210.75 1.02
L17 x T1 2.69 6.19 4.44 106.5 109.5 3 212.5 1.29
L17 x T2 5.2 5.67 5.44 103.25 105.25 2 204 1.33
L18 x T1 6.43 10.96 8.69 104.75 107.5 2.75 208.25 1.47
L18 x T2 4.58 7.96 6.27 103.75 106.5 2.75 217.5 1.04
L19 x T1 4 10.76 7.38 107.25 108.5 1.25 223 1.54
L19 x T2 3.95 6.63 5.29 106 110.25 4.25 207.75 1.31
L20 x T1 5.55 7.95 6.75 106 112.25 6.25 192.25 1.58
L20 x T2 3.56 12.42 7.99 106 109.5 3.5 214.5 0.88
KIT21(W)/SRSYN20 5.75 7.89 6.82 102 105 3 214 1.42
FS170Q/SRSYN20Q 4.58 9.06 6.82 100.5 101.25 0.75 199.75 1.44
Mean 4.73 8.36 6.55 104.79 107.4 2.61 202.9 1.44
LSD (0.05) 1.9 3.53 1.96 3.69 3.94 3.9 23.11 0.33
CV (%) 19.66 20.63 21.17 2.49 2.59 105.53 8.05 16.4
Max 6.43 13.12 9.15 112.75 113 7.75 223 1.9
Min 1.85 4.5 3.53 97.5 101.25 0.25 162 0.88
GY= grain yield, DA= number of days to anthesis, DS= number of days to silking, ASI= anthesis silking interval, PH= plant
height, EH= ear height, EPP= number of ears per plant, CV= coefficient of variation, LSD = least significant difference,
Min= minimum, Max= maximum.

Zeleke et al. 970
Estimates of general combining ability effects
The general combining ability effects of parental inbred
lines and testers were computed for the traits that exhibited
significant general combining ability (GCA) mean squares
in combining ability analyses of variance (Table 3) and are
presented in Table 5. Estimation of GCA effect revealed
that none of the QPM inbred lines and testers were
observed to be good general combiners for all traits.
However, ten inbred lines (L2, L5, L7, L10, L11, L12, L13,
L14, L18 and L20) showed positive GCA effects for grain
yield, indicating the potential advantage of these inbred
lines for the development of high-yielding hybrids and/or
synthetic varieties, as the lines can contribute desirable
alleles in the synthesis of new varieties. Out of the 10
inbred lines that showed negative GCA effects, only one
inbred line (L15) showed a negative significant GCA effect
for GY. Inbred lines with negative GCA effects are poor
general combiners for the improvement of GY. Results of
the current study are similar to the findings of several
authors such as Dagne et al. (2010); Demissew et al.
(2011); Girma et al. (2015); Seyoum et al. (2016) and
Tesfaye et al. (2019), who reported significant positive and
negative GCA effects for grain yield in maize germplasm.
Inbred lines L1 and L2 showed negative and significant
GCA effects for both days to anthesis and silking,
indicating that these lines were good general combiners
for early maturity and ten lines for days to anthesis and
nine lines for silking showed positive GCA, indicating that
these lines tend to increase late maturity. The desirability
of negative GCA for days to anthesis and silking for
earliness and desirability of positive GCA for these traits
for lateness was suggested by various authors such as
(Umar et al., 2014; Girma et al., 2015 and Beyene, 2016).
Even though nine inbred lines showed negative GCA
effects for plant height (Table 5), only one inbred line L8 (-
19.97), showed a significant GCA effect, implying the
tendency of this line to reduce plant height, which is very
important for the development of genotypes resistant to
lodging. The rest eleven inbred lines that showed positive
GCA (L2, L4, L6, L7, L11, L12, L13, L17, L18, L19 and
L20) were poor general combiners for short plant height/
can induce tallness in crosses/ as they showed positive
GCA effects. The testers showed non-significant GCA
effects for all of the traits. T1 showed a positive GCA effect
for days to anthesis (DA), days to silking (DS) and number
of ears per plant (EPP). But it showed a negative GCA
effect for grain yield (GY), anthesis silking interval (ASI)
and plant height (PH). While T2 showed a positive GCA
effect for GY in the desired direction and showed positive
GCA for ASI and PH. In line with the present study,
Demissew et al. (2011) and Tilahun et al. (2019) found
significant positive and negative GCA effects for plant
height.
Five lines viz., L2, L5, L7, L13 and L18 were identified as
overall high general combiners and these lines could be
utilized for the development of either the synthetic varieties
or an elite breeding population by allowing thorough mixing
among them to achieve new genetic recombination and
then subjecting the resultant population to recurrent
selection.
Table 5: General combining ability effects (GCA) of inbred lines and testers over the two locations in 2019.
Lines and testers Traits
GY DA DS ASI PH EPP
1 -0.61 -5.59* -3.62* 1.98 -11.83 -0.06
2 0.979 -5.97* -4.74* 1.23 6.99 0.16
3 -0.79 -2.09 -0.62 1.48 -7.49 0.06
4 -0.55 -0.84 2.26 3.1 9.57 -0.03
5 1.09 -0.72 -1.87 -1.15 -2.38 0.13
6 -0.0015 0.66 -0.74 -1.4 2.1 0.24
7 1.22 -0.84 -1.49 -0.65 2.79 0.09
8 -0.89 1.53 0.38 -1.15 -19.97* -0.1
9 -0.83 2.28 1.51 -0.78 -8.86 0.09
10 0.78 2.28 2.38 0.1 -4.18 -0.07
11 0.1 2.03 3.51 1.48 13.98 -0.09
12 0.65 1.16 0.13 -1.03 1.03 0.02
13 1.16 -0.09 -1.62 -1.53 5.93 0.22
14 0.26 0.16 -0.87 -1.03 -0.6 0.0003
15 -2.02* -0.97 -1.49 -0.53 -12.82 0.029
16 -0.57 5.16* 2.76 -2.4 -0.83 -0.19
17 -1.59 -0.09 -0.24 -0.15 5.98 -0.13
18 0.95 -0.72 -0.62 0.1 7.84 -0.18
19 -0.19 1.66 1.76 0.1 11.71 -0.01
20 0.84 1.03 3.26 2.23 2.98 -0.2
SE(gi) 0.93 2.49 2.18 1.42 8.52 0.13
T1 -0.05 0.96 0.66 -0.3 -3.29 0.14

T2 0.05 -0.96 -0.66 0.3 3.49 -0.14
SE(gi) 0.049 0.96 0.66 0.3 3.15 0.14
** Significant at 0.01 level of probability, * = significant at 0.05 level of probability, SE(gi)= standard error of general
combining ability effects, GY= grain yield, DA= number of days to anthesis, DS= number of days to silking, ASI= anthesis-
silking interval, PH= plant height, EH= ear height, EPP= number of ears per plant.
Specific combining ability (SCA) effects
The maximum and minimum estimated SCA effects of the
40 crosses across the two locations are presented in
Figure 2. The results of specific combining ability effects
showed that none of the cross combinations exhibited
desirable significant SCA effects for all the characters. Out
of the 40 crosses, half of the crosses, viz. L1 × T1, L2 ×
T2, L3 × T2, L4 × T2, L5 × T1, L6 × T1, L7 x T1, L8 x T2,
L9 x T2, L10 x T2, L11 x T2, L12 x T1, L13 x T1, L14 x T2,
L15 x T2, L16 x T1, L17 x T2, L18 x T1, L19 x T1 and L20
× T2 showed positive SCA effects for yield (Table 6),
indicating the importance of non-additive gene action in
these cross combinations. Positive SCA indicates that the
lines and testers are in opposite heterotic groups, which
can be exploited to develop hybrid varieties. While
negative SCA effects indicate, lines are in the same
heterotic group (Hallauer and Miranda, 1988).
Figure 2: Maximum and minimum SCA effects of crosses for grain yield and other related traits combined across
two locations.
Results indicated that crosses having higher positive SCA
effects generally involved high as well as low general
combiners for grain yield. For grain yield, the cross L8×T2
was the best specific combiner, followed by L4×T2 (Table
6). Both of the crosses were resulted from low general
combiner lines and good combiner tester (T2) for the trait.
Other top rankings specific cross combinations such as
L5×T1, L12×T1 and L18×T1 were among the crosses
having the parents with high general combining ability and
low general combiner tester (T1). The results are in
general agreement with the findings of Tolera et al.
(20017). The highest yielding cross L5×T1 also revealed
positive SCA effects but ranked 3rd. Kambe et al. (2013)
also reported high positive specific combining ability
effects along with high per se performance for grain yield.
For the number of ears per plant, positive SCA effects
were found in twenty of the crosses. The crosses L20 x T1
and L9 x T2 were the two best positive cross combinations
with SCA values of 0.21 and 0.2. Thus, these crosses
could be selected for their specific combining ability to
improve the number of ears per plant. The rest other
twenty crosses showed negative SCA effects in undesired
direction for ear per plant. This indicates that these hybrid
combinations are poor for the number of ears per plant.
-15
-10
-5
0
5
10
15
GY DA DS PH EH EPP
1.72 1.92 2.16
14.34
7.48
0.21
-1.72 -1.92 -2.16
-14.54
-7.57
-0.21
SCAeffects
Traits

Zeleke et al. 972
Table 6: Estimates of specific combining ability effects (SCA) of 40 test crosses evaluated at Ambo and
Kulumsa in 2019.
Crosses GY DA DS PH EH EPP
L1 x T1 1.01 0.92 -1.91 6.98 6.16 -0.07
L1 xT2 -1.006 -0.92 1.91 -7.17 -6.26 0.07
L2 x T1 -0.028 -0.46 -0.03 -3.07 -0.14 0.07
L2 x T2 0.028 0.46 0.03 2.87 0.05 -0.07
L3 x T1 -0.12 1.92 -0.16 3.84 5.67 -0.005
L3 x T2 0.12 -1.92 0.16 -4.04 -5.76 0.005
L4 x T1 -1.65 0.92 1.47 -2.72 3.64 -0.1
L4 x T2 1.65 -0.92 -1.47 2.53 -3.73 0.1
L5 x T1 1.57 -0.71 0.094 3.69 0.94 0.19
L5 x T2 -1.57 0.71 -0.094 -3.88 -1.03 -0.19
L6 x T1 0.27 0.17 -0.031 1.29 -4.85 -0.1
L6 x T2 -0.27 -0.17 0.031 -1.49 4.76 0.1
L7 x T1 0.72 0.17 -0.28 4.3 3.59 0.1
L7 x T2 -0.72 -0.17 0.28 -4.49 -3.68 -0.1
L8 x T1 -1.72 -0.46 0.34 -14.54 -2.53 0.04
L8 x T2 1.72 0.46 -0.34 14.34 2.44 -0.04
L9 x T1 -0.098 -0.96 -0.28 4.89 1.71 -0.2
L9 x T2 0.098 0.96 0.28 -5.09 -1.8 0.2
L10 x T1 -1.15 0.044 1.34 -4.48 -5.46 -0.05
L10 x T2 1.15 -0.044 -1.34 4.28 5.37 0.05
L11 x T1 -0.11 -0.46 -0.78 -2.26 -2.33 -0.06
L11 x T2 0.11 0.46 0.78 2.07 2.24 0.06
L12 x T1 1.45 -1.33 -2.16 2.96 -1.74 0.02
L12 x T2 -1.45 1.33 2.16 -3.16 1.64 -0.02
L13 x T1 0.057 -0.08 -0.16 0.11 -6.17 -0.06
L13 x T2 -0.057 0.08 0.16 -0.31 6.07 0.06
L14 x T1 -0.88 -0.08 0.09 -0.56 -0.93 0.03
L14 x T2 0.88 0.08 -0.09 0.37 0.84 -0.03
L15 x T1 -0.93 -0.21 -0.03 -5.42 -7.57 0.02
L15 x T2 0.93 0.21 0.03 5.22 7.48 -0.02
L16 x T1 0.26 1.67 1.97 -4.18 0.17 0.08
L16 x T2 -0.26 -1.67 -1.97 3.98 -0.26 -0.08
L17 x T1 -0.45 0.67 1.47 7.52 1.54 -0.16
L17 x T2 0.45 -0.67 -1.47 -7.72 -1.64 0.16
L18 x T1 1.26 -0.46 -0.16 -1.52 6.15 0.07
L18 x T2 -1.26 0.46 0.16 1.32 -6.25 -0.07
L19 x T1 1.096 -0.33 -1.53 10.29 5.59 -0.03
L19 x T2 -1.096 0.33 1.53 -10.49 -5.69 0.03
L20 x T1 -0.57 -0.96 0.72 -9.1 -4.38 0.21
L20 x T2 0.57 0.96 -0.72 8.9 4.28 -0.21
SE(sij) 0.95 0.83 1.05 5.37 4.04 0.1
** Significant at 0.01 level of probability, * = significant at 0.05 level of probability, SE(Sij)= standard error of specific
combining ability effects, GY= grain yield, DA= number of days to anthesis, DS= number of days to silking, PH= plant
height, EH= ear height, EPP= number of ears per plant.
CONCLUSIONS
The current study identified cross combinations having
higher grain yield than the best genetic check for the
studied agro-ecologies. The outstanding hybrids identified
in the present study (e.g., L5 x T1, L18 x T1 and L12 x T1)
with high mean yield and positive SCA values would
contribute to productivity and yield stability for small
farmers’ fields in highland agro-ecologies of Ethiopia. On
the other hand, inbred lines L7, L13, L5, L2 and L18
exhibited high GCA effects for grain yield and other
secondary traits. They thus could be crossed to more
testers and evaluated under more testing locations to get

more information for further use in the highland maize
breeding program.
ACKNOWLEDGEMENTS
We are grateful to the maize research staff at Ambo and
Kulumsa agricultural research centers for hosting the trial
and collecting data. We also like to extend our thanks to
the Ethiopian Institute of Agricultural Research (EIAR) for
financial support.
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Accepted 16 November 2020
Citation: Zeleke K, Dufera T, Demissew A, Tefera K, Abiy
B and Shimelis T (2020). Test Cross Performance and
Combining Ability of Quality Protein Maize (Zea Mays L.)
Inbred Lines for Grain Yield and Agronomic Traits
Evaluated in Highland Sub-Humid Agro-Ecology of
Ethiopia. International Journal of Plant Breeding and Crop
Science, 7(4): 963-974.
Copyright: © 2020: Zeleke et al. 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.

TEST CROSS PERFORMANCE AND COMBINING ABILITY OF QUALITY PROTEIN MAIZE (ZEA MAYS L.) INBRED LINES FOR GRAIN YIELD AND AGRONOMIC TRAITS EVALUATED IN HIGHLAND SUB-HUMID AGRO-ECOLOGY OF ETHIOPIA

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TEST CROSS PERFORMANCE AND COMBINING ABILITY OF QUALITY PROTEIN MAIZE (ZEA MAYS L.) INBRED LINES FOR GRAIN YIELD AND AGRONOMIC TRAITS EVALUATED IN HIGHLAND SUB-HUMID AGRO-ECOLOGY OF ETHIOPIA