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


Bullo Neda Tulu1 and Dagne Wegary Gissa2 1Addis Ababa University, Selale Campus, P.O.Box 245, Fiche, Ethiopia.

2International 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: [email protected]

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 400190

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


Int. J. Plant Breeding Crop Sci. 082 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** 6.9ns

475.0** 123.17** 8.65ns

0.96** 2.12* 3.95** 0.09* 0.09ns

Crosses 65 1898566.5* 27.65** 12.94** 7.02* 409.9** 99.49** 8.13ns

0.93** 1.83ns

4.04** 0.09** 0.078ns

Checks 1 979308.2ns

72.25ns

100ns

2.25ns

1225ns

156.3ns

10.24ns

1** 7.84ns

0.06ns

0.16ns

0.291ns

Crosses vs Checks 1 15087098.8** 144.12** 51.57** 2.04ns

3958.0** 1629.5** 40.86ns

2.6* 15.12** 2.02ns

0.12ns

0.669ns

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 1.73ns

0.54** 8.33ns

19.26** 0.34ns

6.00** 0.02ns

2351.99** 71.05

ns

0.105ns

9767.07** 0.366ns

Crosses 65 1.77ns

0.54** 7.94ns

17.83** 0.33ns

2.67** 0.02ns

2381.43** 59.29

ns

0.102ns

7.02* 0.321ns

Checks 1 0.25ns

0.44ns

6.25ns

64ns

0.25ns

169** 0ns

238.39ns

226.25

ns

0.145ns

8527.60ns

1.78ns

Crosses vs Check 1 0.29ns

0.54* 36.15* 67.43** 1.28* 59.46** 0.002ns

2551.78ns

679.88

ns

0.26ns

645409.47** 1.873ns

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

Int. J. Plant Breeding Crop Sci. 084


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


Int. J. Plant Breeding Crop Sci. 086 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. REFERENCE Bayisa A, Hussen M, Habtamu Z (2008). Combining

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