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Heritability and genetic progress of grain yield and its components in Maize

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https://www.eduzhai.net International Journal of Plant Research 2012, 2(5): 138-145 DOI: 10.5923/j.plant.20120205.01 Heritability and Genetic Advance for Grain Yield and its Component Characters in Maize (Zea Mays L.) Bello O. B.1,*, Ige S. A.2, Azeez M. A.3 , Afolabi M. S.4, Abdulmaliq S. Y.5, Mahamood J.6 1Department of Biological Sciences, Fountain University, Osogbo, Osun State, Nigeria 2Department of Agronomy, University of Ilorin, Ilorin, Nigeria 3Department of Pure and Applied Biology, Ladoke Akintola University of Technology, Ogbomoso, Nigeria 4Department of Crop Science, Landmark University, Omuaran, Kwara State, Nigeria 5Department of Agronomy, Ibrahim Badamasi Babangida University, Lapai, Niger State, Nigeria 6Lower Niger River Basin Development Authority, Ilorin, Kwara State, Nigeria Abstract Knowledge of the magnitude of genetic variability, heritability and genetic gains in selection of desirable characters could assist the plant breeder in ascertaining criteria to be used for the breeding programmes. Ten open pollinated maize varieties were evaluated at the Teaching and Research farm, University of Ilorin, Nigeria, during 2005 and 2006 cropping seasons to estimate genetic variability, heritability and genetic advance of grain yield and its component characters. The effect of genotype and genotype by year interaction were significant for ear weight and grain y ield, while the effect of year was highly significant (P< 0.01) for all the characters. High magnitude of phenotypic and genotypic coefficient of variations as well as high heritability along with high genetic advance recorded for grain yield, number of grains ear-1, ear weight, plant and ear heights provides evidence that these parameters were under the control of additive gene effects and effective select ion could be possible for improvement for these characters. Tze Co mp3 C2, Acr 94 Tze Co mp5, Tze Co mp 4-Dmr Srbc2 and Acr 90 Pool 16-Dt were identified as outstanding genotypes for maize grain yield and should be tested at mu ltilocation for their y ield performance. Keywords Maize, Heritability, Genetic Gain, Grain Yield, Open Po llinated Maize Varieties 1. Introduction Maize (Zea mays L.) has high potential for production and productivity in the savanna ecology of sub-Saharan Africa due to high solar radiation and low night temperatures[1,2]. As a result of its co mmercial importance in the Nigerian economy, maize is comp lementing the traditional crops such as guinea corn[Sorghum bicolor (L.) Moench] and millet [Pennisetum glaucum (L.) R. Br.] in parts of the Sudan, Sahel and Gu inea ecologies[3]. Maize p roduction has progressively increased over the years with estimated national outputs reaching 7.68 million tonnes in 1995[4]. The projected production and demand by the year 2010 is 13.4 million tonnes[5]. In view of the importance of maize in Nigeria, researchers are utilizing availab le genetic resources to reconstruct the ideotype of the plant in order to meet the ever increasing requirements of the population through improvement in grain yield, other desirable agronomic and phenological characters as well as quality[6]. The success of any crop imp rovement p rogramme not * Corresponding author: obbello2002@yahoo.com (Bello O. B) Published online at https://www.eduzhai.net Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved only dependent on the amount of genetic variability present in the population but also on the extent to which it is heritable, which sets the limit of progress that can be achieved through selection[7-12]. Genetic variab ility for agronomic characters therefore is a key co mponent of breeding programmes for b roadening the gene pool of crops[13]. Heritability is a measure of the phenotypic variance attributable to genetic causes and has predictive function in plant breeding. It provides information on the extent to which a part icular mo rphogenetic character can be transmitted to successive generations. Knowledge of heritability influences the choice of selection procedures used by the plant breeder to decide which selection methods would be most useful to improve the character, to predict gain fro m selection and to determine the relat ive importance of genetic effects[14-16]. The most impo rtant function of heritability in genetic studies of quantitative characters is its predictive ro le to indicate the reliab ility of phenotypic value as a guide to breeding value[17]. Characters with high heritability can easily be fixed with simple selection resulting in qu ick progress. However, it has been accentuated that heritability alone has no practical importance without genetic advance[8]. Genetic advance shows the degree of gain obtained in a character under a part icular selection pressure. High genetic advance coupled with high 139 International Journal of Plant Research 2012, 2(5): 138-145 heritability estimates offers the most suitable condition for selection. Reference[18] reported the limitation of estimating heritability in narrow sense, as it included both additive and epistatic gene effects, and thereby suggested that heritability estimates in the broad sense will be reliable if acco mpanied by a high genetic advancement. Different researchers[19-22] have reported high heritability and high genetic advance for different yield controlling traits in maize. Therefore, availability of good knowledge of these genetic parameters existing in different yield contributing characters and the relative proportion of this genetic informat ion in various quantitative traits is a pre-requisite for effective crop improvement. The present study was conducted to assess genetic variability, heritability and genetic advance for grain yield and its component characters in ten open pollinated maize varieties to provide necessary information that could be useful in maize improvement programmes aimed at improving grain yield. 2. Materials and Methods Ten open pollinated maize variet ies (OPVs) were evaluated at the Teaching and Research (T and R) farm of University of Ilorin (Lat itude 8°29’N, Longitude 4°35’E) with an annual average rainfall of 945 mm, located in the southern Gu inea savanna ecological zone of Nigeria. The OPVs were selected for grain yield and adaptation to abiotic (drought) and biotic (Stalk rot, Striga and Downy mildew) stress factors. They were early to med iu m maturing wh ite cultivars with maturity period of 90 to 100 days. The cultivars were obtained fro m the International Institute of Tropical Agriculture (IITA ), Ibadan. The orig in, genetic background, breeding emphasis and ecological adaptation of the maize parents are presented in Table 1. Soil samples collected fro m the trial site before cropping in 2005 and 2006 were analyzed in the So il Science Laboratory of the University of Ilorin, Ilo rin, Nigeria for selected physical and chemical properties and presented in Table 2. The co llected samples were air-dried and passed through 2mm sieve to remove large particles, debris and stones. The sieved samples were analyzed for pH in 1:1 soil to water ratio using the Coleman pH meter. Organic carbon was determined by Walkley and Black procedure[23]. Total Nitrogen was determined by the micro Kjeldahl method[24], while available phosphorus was extracted by Bray’s P1 method[25] and read fro m the atomic absorption spectrometer. Exchangeable Ca, Mg, K, Na and effective cation exchangeable capacity (ECEC) were analyzed using Atomic Absorption Spectrophotometery[26], wh ile textural analysis was done by hydrometer method. The soil textu re was loamy and the other soil properties were not significantly different in both years at 0-15cm and 15-30cm depth. At 0-15cm depth, the appro ximate amounts of silt, sand and clay were 8%, 84% and 8%, respectively, with soil pH = 7.30 and ECEC = 2.83 (Cmo l kg-1). However, rainfall distribution data for the year 2005 and 2006 were also collected (Fig. 1). Rainfall (mm) 300 250 200 150 100 2005 50 2006 0 Months Source: Lower Niger River Basin Development Authority, Ilorin, Nigeria Figure 1. Monthly rainfall distribution pattern for Ilorin in 2005 and 2006 Plantings were carried out during the gro wing seasons on 28th July, 2005 in the first year and 22nd July, 2006 in the second year using a randomized co mplete b lock design with four replications. Each plot consisted of four ro ws of five-met re length with row spacing and plant spacing of 75 and 50 cm respectively. Three seeds were planted per h ill, drilled 3-4cm deep in the ridges and thinned to two plants per hill to give an approximate plant density of 53,333 plants per hectare. Fertilizer was applied in split-dosage at three and seven weeks after planting (WAP) at the rate of 80 kg/ha N, 60kg/ha P and 60kg/ha K respectively fro m co mpound NPK fertilizer (20-10-10). Weed control was carried out by use of pre-emergence herbicides (a.i. 3kg/l Metolachlor and 170g/l Atrazine) at a rate of 5 lit res per hectare. This was supplemented by a regime of hand weeding at 6 weeks after planting. Data on seedling emergence, days to 50% tasselling, pollen shed and silking, anthesis-silking interval, plant and ear height (cm), nu mber o f grains ear-1, ear weight and grain yield were collected fro m the two middle ro ws of each plot in both the years. Plant and ear heights were measured fro m soil level to the node of the flag leaf and to the highest ear-bearing node respectively at harvest stage. Days to 50% tasselling, pollen shed and silking were calculated as the number of days fro m planting to when 50% of the population have tasselled, shed pollen and silked respectively. Anthesis-silking interval was estimated as the d ifference between days to pollen shed and silking, and grain yield (t/ha) measured after adjusting to 12.5% mo isture content. Three hundred grain samples were collected fro m each plot at harvest for determination of harvest moisture. The samples were first weighed to obtain in itial weight followed by drying to a constant weight in the oven at 800 C in the laboratory. The difference between the two weighs recorded as moisture at harvest. 2.1. Statistical Analysis Co mbined analysis of variance and means over years were computed using PROC GLM model of SAS[27] fo r the OPVs with respect to grain y ield and other agronomic characters The mean values were co mpared using least significant difference (LSD) p rocedure as laid down according to[28]. Bello O. B. et al.: Heritability and Genetic Advance for Grain Yield and its 140 Component Characters in M aize (Zea Mays L.) The linear statistical model was used as described by[29] as Yijk = µ + βj + ʎk + (GE)ij + Ԑijk Where: Yijk = the observation made in the ith genotypes on the jth replication, in the kth year; µ = the overall mean of the character; βj = the effect of the jth replicat ion; ʎk = the effect of the kth year; (GE)ij = sum of interaction terms of the genotypes and year, and iԐjk = the residual effects. The form of the analysis of variance indicat ing sources of variation, mean squares and their expected values are shown in Table 3. Co mponents of variance were estimated using the method described by[29]. The form of the estimation of the variance components obtained by equating the mean square for a source of variation to its expectation and solving for the unknown is presented in Table 4. Where: δ2g, δ2gy and δ2e are co mponents of genotype, genotype by environment interaction and variance for error respectively. M1, M2, and M3 are the observed values of the mean squares for the error, interaction and genotype res p ectiv ely [30 ]. Table 1. Origin, genetic background, breeding emphasis and ecological adaptation of the maize parents Genotypes Origin and genetic background Breeding emphasis Early white dent CIMMYT cult ivar, derived from crosses among large numbers of Acr 90 Pool 1. early late whit e flint mat erials from Mexico, the Caribbean area, Central and South 16-Dt America. Selected for drought tolerance. Tze Comp 2. 4-Dmr Srbc2 Early maturing white and semi dent cultivar, derived from diverse sources of early mid-altitude germplasm, intermatted with T ZESR-W and DMR-ESRW. Tze Comp4 3. C2 Early maturing white and semi dent cultivar, derived from diverse sources of early mid-altitude germplasm, intermatted with EV 8430-SR and IK 8149 SR. It has synchronous male and female flowering, lower plant height and small tassel size. Acr 97 Tze 4. Comp3 C4 Early white flint dent cultivar, derived from early mid-altitude germplasm with EV 8430-SR, DMR-ESRW, TZESR-W and IK 8149 SR intermatted. Hei 97 T ze Early white flint dent cultivar, derived from early mid-altitude germplasm with EV 5. Comp3 C4 8430-SR, DMR-ESRW, TZESR-W and IK 8149 SR intermatted. Acr 94 Tze Early white flint dent cultivar, derived from early mid-altitude germplasm with Striga 6. Comp5 intermatted with TZE-WC3. Early white flint dent cult ivar, derived from diverse sources of early mid-alt it ude 7. Tze Comp3 Dt germplasm with drought tolerant cultivars, intermatted with TZESR-W and DMR-ESRW. Tze Comp3 Early white and flint dent cult ivar, derived from diverse sources of early mid-alt it ude 8. C2 germplasm, produced by intermating TZESR-W and DMR-ESRW. Early mat uring and flint dent cult ivar, developed from intermat ing diverse sources of Ak 95 9. early mid-alt it ude germplasm, produced by intermat ing DMR sources from Dmr-Esrw Philippines with TZB, TZBP, TZSR and tropical late. Selected for earliness. Early white semi dent cultivar, derived from early mid-altitude germplasm, developed 10. Tze Msr-W from intermating local and early cultivars with TZSR. Source: IITA Archival Report 1988-1992 Stalk rot, Striga and drought tolerance. Yield and Striga tolerance. Yield and Striga tolerance. Yield, downy mildew and Striga tolerance. Yield, downy mildew and Striga tolerance. Striga tolerance. Drought tolerance. Downy mildew and Striga tolerance. Downy mildew and Striga tolerance. Yield and Striga tolerance. Ecological adapt at ion Forest and savannah. Forest and savannah. Forest and savannah. Forest and savannah. Forest and savannah. Savannah. Forest and savannah Forest and savannah. Forest. Forest and savannah. Table 2. Selected physical and chemical characteristics of the soil before cropping of maize Soil properties Text ure Soil PH (water) Sand % Clay % Silt % Exchangeable Ca2+ (Cmol kg -1) Exchangeable Mg2+ (Cmol kg -1) Exchangeable Na+ (Cmol kg -1) Exchangeable K+ (Cmol kg -1) Total acidity H+ (Cmol kg -1) Cation exchange capacity (Cmol kg -1) Organic Carbon % Total Nitrogen % Available Phosphorus (mg kg-1) Value of 0-15cm depth 2005 2006 Loamy sand Loamy sand 7.30 7.34 84.00 84.50 8.00 8.10 8.00 8.20 1.10 1.12 1.60 1.65 0.18 0.19 0.01 0.01 0.04 0.04 2.83 2.83 0.26 0.28 1.30 1.32 4.10 4.10 Value of 0-30cm depth 2005 2006 Loamy sand Loamy sand 6.30 6.31 88.00 88.20 8.00 8.20 7.90 7.92 1.10 1.15 1.50 1.52 0.19 0.19 0.01 0.01 0.04 0.04 2.84 2.83 0.33 0.33 0.90 0.90 3.80 3.80 141 International Journal of Plant Research 2012, 2(5): 138-145 Table 3. Form of combined analysis of variance with mean squares and their expected values Source of Variation Year Rep (Year) Genotypes Genotypes x Year Pool Error Degrees of freedom y-1 r-1 (y) g-1 (g-1) (y-1) (r-1) )(g-1)y Mean squares (MS) M5 M4 M3 M2 M1 Expected Mean squares (EMS) δ2e + rδ2gy + ryδ2g δ2e + rδ2gy δ2e Table 4. Estimation of variance components and method of determination Variance components Genotype (δ2g) Genotype x Year (δ2gy ) Pool Error (δ2e ) Method of determination M3-M2/yr M2-M1/yr M1 Table 5. Mean squares from combined analysis of variance for grain yield and other related characters among 10 open pollinated maize varieties evaluated in 2005 and 2006 at Ilorin (Nigeria) Sources Of v ariat ion Year Rep/Year Genotypes Genotypes x Year Pool Error Degree Of freedom 1 6 9 9 54 Seedling emergen ce 23.45** 31.45 12.68 10.59 33.45 Days to 50% t assellin g 34.55** 7.38 1.43 1.54 2.78 Days to 50% pollen shed 12.68* * 5.43 3,58 4.76 7.39 Days to 50% silking 26.54* * 8.54 4.83 1.28 3.48 Anthesis Silking int erv al (days) 23.58** 9.78 10.58 13.73 5.73 P lant Height (cm) 32.45** 7.35 1.38 3.47 3.77 Ear Height (cm) 66.58** 11.97 20.54 13.45 8.42 Number Of grains/ ear 68.25** 3.57 15.75 23.54 13.68 Ear Weight (t/ha) 92.48** 9.86 82.58** 93.58** 17.54 Maize grain yield (t/ha) 202.48** 4.54 166.32** 111.54** 93.48 **,si **, significant at P< 0.01 Mean performance of the open pollinated maize varieties Table 6. Combined mean performance of 10 open pollinated varieties for maize grain yield and related traits evaluated in 2005 and 2006 at Ilorin (Nigeria) Variet ies Degree Of freedom Acr 90 Pool 16-Dt Tze Comp 4-Dmr Srbc2 Tze Comp4 C2 Acr 97 Tze Comp 3 C4 Hei 97 T ze Comp 3 C4 Acr 94 Tze Comp5 Tze Comp3 Dt Tze Comp3 C2 Ak 95 Dmr-Esrw Tze Msr-W Mean CV % LSD (0.05) 39 35 41 37 34 35 34 36 34 35 39 10.23 NS Significant F test at 0.05 level of probability Days to 50% t assellin g 52 55 54 53 53 55 55 52 52 55 54 19.04 NS Days to 50% pollen shed 53 56 56 55 55 56 56 54 54 56 53 6.46 NS Days to 50% silking 54 57 57 56 56 57 57 55 55 57 56 11.09 NS Anthesis Silking int erv al (days) 2 2 3 3 3 2 2 3 3 1 3 10.47 NS P lant Height (cm) 123 129 129 122 116 120 111 129 115 116 124 1.47 NS Ear Height (cm) 37 38 39 36 35 35 30 38 34 35 36 2.67 NS Number Of grains/ ear 58 58 54 56 53 59 57 60 52 53 56 3.09 NS Ear Weight (t/ha) 4.96 7.00 5.24 6.64 4.95 7.01 6.94 7.50 5.00 4.80 6.55 6.93 91.39 Maize grain yield (t/ha) 3.67 3.75 2.87 3.16 3.28 3.96 3.25 3.99 2.75 2.75 3.15 1.45 0.45 Table 7. Ranges, Means, and values of ‘F’ from estimates for grain yield and other related characters among 10 open pollinated maize varieties evaluated in 2005 and 2006 at Ilorin (Nigeria) Ch aract ers Seedling emergence Days to 50% t asselling Days to 50% pollen shed Days to 50% silking Anthesis silking interval Plant height (cm) Ear height (cm) Number of grain ear-1 Ear weight (t/ha) Maize grain yield (t/ha) **, significant at P< 0.01 Range of Variation 34-41 52-55 51-58 54-59 1-4 119-133 30-39 53-58 4.8-7.5 2.75-3.99 Means 39 54 53 56 3 124 36 56 6.55 3.15 Standard Deviation 0.4 2.3 0.34 5.48 0.32 0.87 0.12 0.72 0.63 0.35 Error variance 0.54 7.25 3.52 2.35 7.75 0.53 3.78 1.58 3.72 0.58 F observed 45.28 26.72 35.98 10.63 40.73 22.53 33.54 78.93 131.52** 167.97** Bello O. B. et al.: Heritability and Genetic Advance for Grain Yield and its 142 Component Characters in M aize (Zea Mays L.) Table 8. Estimate of genetic variance (δ2g ) genotype × year interaction (δ2gy) variance, phenotypic variance (δ2p ), genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) and environmental coefficient of variation (ECV) for grain yield and other related characters among 10 open pollinated maize varieties evaluated in 2005 and 2006 at Ilorin (Nigeria) Ch aract ers Seedling emergence Days to 50% t asselling Days to 50% pollen shed Days to 50% silking Anthesis silking interval Plant height (cm) Ear height (cm) Number of grain ear-1 Ear weight (t/ha) Maize grain yield (t/ha) δ2p 7.32 9.45 7.58 11.63 9.54 632.58 129.45 2348.42 149.45 181.48 P CV 6.78 5.95 12.98 8.93 10.28 112.34 111.65 123.45 127.11 112.58 δ2g 7.32 8.54 6.32 10.52 8.69 472.54 102.64 2245.32 136.32 114.52 GCV 6.25 6.45 13.72 12.15 11.35 114.58 110.43 108.54 120.45 110.79 δ2gy 15.48 14.79 13.58 15.63 12.54 8.28 4.76 3.48 4.58 210.28 ECV 16.94 13.74 24.73 27.96 23.71 7.43 5.67 7.54 6.93 13.73 Table 9. Estimate of heritability (H2) and genetic advance for grain yield and other related characters among 10 open pollinated maize varieties evaluated in 2005 and 2006 at Ilorin (Nigeria) Sources Of v ariat ion Heritability (%) Genetic Advance Genet ic advance (% of mean) **, si Seedling emergence 75.28 6.45 8.23 Days to 50% t assellin g 77.54 7.23 Days to 50% pollen shed 8.54 7.48 Days to 50% silking 84.32 8.14 Anthesis int erv al 61.79 8.54 Plant Height (cm) 98.64 63.45 Ear Height (cm) 92.54 32.72 6.71 7.25 5.23 11.32 32.48 31.65 Number Of grains/ ear 96.45 151.28 59.87 Ear Weight (t/ha) 89.54 29.45 28.37 Maize grain yield (t/ha) 98.16 29.58 26.54 The phenotypic variance (δ 2 p ) was calculated as δ 2 p = δ2g+(δ2gy/y) + (δ2e/ry). Where y, g and r are number of years, genotypes and replicat ions res p ectiv ely . δ 2 g and δ 2 e are components of variance for genotypes and error respectively[30]. Broad sense heritability (H2 ) for pooled data across years was estimated as described by[31]. H2 (%) = (δ 2 g / δ 2 p ) x100 Genetic Advance (GA) and Genetic Gain (GG) values were determined as described by[32] GA =(K)(δA)(H). Where, K = 2.063 (selection differential at 5%), δA = phenotypic standard deviation of the mean yield of the n original lines and H = Broad sense heritability. Genetic gain (GG) was determined fro m genetic advance (GA) expressed as a percentage of the population mean (x) Genotypic and phenotypic coefficients of variations were estimated by the formula suggested by[33] g iven as: GCV = (√ δ 2 g /Ū) x100 and PCV = (√ δ 2 p h/Ū) x100 Where Ū = mean value of the particular character. 3. Results and Discussion 3.1. Analysis of Variance Co mbined analysis of variance ind icated that the effect of year was highly significant (P< 0.01) for all the characters (Table 5). Rainfall amount and distribution that was higher and favourable in the year 2006 co mpared to 2005 might have contributed significantly to the differences observed between the years for these traits as differences in environmental conditions varied fro m year to year. (Fig. 1). Mean squares due to genotypes and genotype x year interaction were significant for ear weight and grain yield indicating presence of genetic variability for these two traits in the germplas m material studied and they were h ighly infuenced by environmental factors. Th is also indicated that there was significant amount of phenotypic variability, and that all the genotypes differed fro m one another with regard to ear weight and grain yield offers way for further improvement through simple selection. However, the interaction of the year with genotypes is very important in this study. The effect of genotype by year interaction was highly significant for ear weight and grain yield. This indicates the diversity of the genotypes and their differences in environ mental responses across the two years for these traits. This invariab ly suggests that maize grain yield could be genetically manipulated fo r its improvement. The mean performances across the two years for grain yield and related characters of the OPVs is presented in Table 6. The results showed significant differences among the genotypes for growth, yield and yield co mponents. The most outstanding genotypes for grain y ield are Tze Co mp3 C2, Acr 94 Tze Co mp 5, Tze Co mp 4-Dmr Srbc2 and Acr 90 Pool 16-Dt in descending order with yield ranging fro m 3.67-3.99 t/ha, wh ile Ak 95 Dmr-Esrw had the lowest value of grain y ield (2.75 t/ha) over the two years. Seedling emergence varied fro m 34-41 with a mean of 39 (Tables 5 and 6) and Tze Co mp4 C2 having the highest. The range observed for days to anthesis was 52-55 days with overall mean of 54 days. Acr 90 Pool 16-Dt, Tze Co mp 3 C2 and Ak 95 Dmr- were the earliest to tassel. Days to silking varied fro m 54-59 with overall mean of 56 days. Half of the number of genotypes under study took the longest time to silk by silking at 57 days after sowing. The mean plant and ear heights of the genotypes ranged from 119-133cm and 30-39cm respectively. Highest number of grains ear-1 (60) was recorded for Tze Co mp3 C2, wh ile Tze Msr-W had the lowest ear weight (4.8 t/ha). The erro r of variance of the 143 International Journal of Plant Research 2012, 2(5): 138-145 mean for all the traits was small. Th is might be as a result of optimu m nu mber of replications (four) and data fro m t wo growing seasons used in estimat ing the components of variance for the traits. The wide variability observed for grain yield as a quantitatively inherent character among the genotypes means that there is ample opportunity for selection in the genotypes for improvement of this important economic character. Th is variability could be heritable and exploited in the process of selection in the breeding programmes. However, non-significant F observed values were recorded for the agronomic traits except ear weight and grain yield (Tab le 7). 3.2. Phenotypic and Genotypic Coefficients of Variati on Since most of the economic characters (grain yield) are complex in inheritance and are greatly influenced by several genes interacting with various environmental conditions, the study of phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV) is not only useful for co mparing the relat ive amount of phenotypic and genotypic variations among different traits but also very useful to estimate the scope for improvement by selection. The reliab ility of a parameter to be selected for breeding programme among other factors is dependent on the magnitude of its coefficient of variat ions (CV) especially the GCV. However, the d ifferences between genotypic and phenotypic coefficient of variability indicate the environmental influence. While a lo wer value of CV generally depicts lo w variability among the tested sample; a high proportion GCV to the PCV is desirable in breeding works. The results given in Table 8 depicted that phenotypic variances (σ2p) and PCVs were slightly higher than genetic variances (σ2g) and GCVs for all the characters, suggesting the least influence of environ ment in the exp ression of these characters Similar res u lts h av e also b een rep o rt ed b y [22]. A lso, estimates of genotype x year interaction variance (σ2gy) for the traits in most instances were low. This result tends to support the notion that greater heterozygousity confers a buffering effect or stability over a wide range of environments, whereas inbreeding leads to increased homozygousity of the OPVs and less buffering capacity[34]. High genetic variab ility for grain yield in the genotypes over years recorded in the test materials suggested that it could be further exp loited through improvement and selection programmes[8,9,35,36]. High values of PCV and GCV observed in grain yield fo llo wed by number of grain ear -1, ear weight, plant height and ear height not only show that the selection can be effective for these traits but also indicated the existence of substantial variability, ensuring ample scope for their imp rovement through selection. These observations are in confirmation with the findings of[19,21,22]. On the other hand, very low values of PCV and GCV recorded for seedling emergence, anthesis silking interval days to anthesis, days to pollen shed and silking revealed that low variab ility among the genotypes was very low for these characters. 3.3. Heritability and Genetic Advance High magnitude of broad sense heritability estimated in all the characters except days to pollen shed (Table 9). This implied the possibility of effect ive selection for genetic improvement of these traits. High heritability estimates for maize grain yield[9,19,22,35], days to silking and plant height[37] and number of grains ear-1[8,9,20,38,39], observed in the present study were in agreement with the findings of earlier workers. Values of genetic advance as percentage of mean ranged fro m 59.87 for nu mber of grains ear-1 to 5.23 for days to silk ext rusion. High heritability estimates coupled with high estimates of genetic advance expected in the next generation in grain yield, nu mber of grains ear-1, ear weight, plant and ear heights indicate the preponderance of additive gene action for the expression of these traits which is fixab le in subsequent generations. This also provides the evidence that larger proportion of phenotypic variance has been attributed to genotypic variance, and reliab le selection could be made for these traits on the basis of phenotypic expression. These results find support from the earlier studies by[9,20] that there was greater magnitude of broad sense heritability and high genetic advance in grain yield plant-1, plant height, days to anthesis and silking. The authors suggested that these parameters were under the control of additive genetic effects. Reference[7] also suggested that these parameters could be man ipulated according to requirements, and worthwhile improvement could be achieved through selection. Reference[7] concluded that the selection at an early segregating generation will prove beneficial for selecting superior variet ies of maize. However, h igh heritability and low genetic advance were observed for seedling emergence, days to anthesis and silking which may be attributed to non-additive gene action governing these traits, and these characters could be improved through the use of hybridizat ion and hybrid vigour. High heritability accompanied with low genetic advance as per cent of mean in days to tasselling and silking had earlier been reported by[7]. Days to pollen shed exhibited low heritability with low genetic advance indicating non-additive genetic effects governing this trait. Moderate heritability along with high genetic advance was recorded for anthesis-silking interval providing little chance for its further improvement. Ho wever, care must be taken while breeding for this co mplex trait as it is considerably influenced by environmental factors. It seems a limited scope of improvement could be achieved for this trait within this group of genotypes. Maize grain yield, number o f grains ear-1, ear weight as well as plant and ear height can be improved by selection, as these characters exhibited moderate genotypic and phenotypic coefficient of variations along with both mediu m to high heritability and genetic advance. Seedling emergence, anthesis-silking interval, days to anthesis and silking had high heritability but the genetic coefficient of variations was low. This indicates that though, the character is highly heritable, its improvement through early generation selection may not give the desired results. Low genetic coefficient of variation and heritability obtained for days to pollen shed is not Bello O. B. et al.: Heritability and Genetic Advance for Grain Yield and its 144 Component Characters in M aize (Zea Mays L.) particularly surprising since yield is a product of many complex characters. Therefore, d irect selection for days to pollen shed improvement may not be possible, but through indirect selection of other secondary traits may be feasible. 4. Conclusions This study revealed that informat ion about the extent of variation, estimates of heritability and expected genetic advance in respect of maize grain yield and yield contributing characters constitutes the basic requirement for a crop improvement programme. Broad sense heritability is useful for measuring the relative importance of additive portion of genetic variance that can be t ransmitted to the offspring. The preponderance of additive gene effects controlling a trait usually resulted to both high heritability and genetic advance, while those governed by non-additive gene actions could give high heritability with lo w genetic advance. However, in the present research, expected genetic advance values were based on broad sense heritability, which integrates additive portion of the total phenotypic variance. Effective selection for superior genotypes is possible considering grain yield, nu mber of grains ear-1, ear weight, plant and ear heights and could be used as target traits to improve maize grain yield. The most outstanding genotypes (Tze Co mp3 C2, Acr 94 Tze Co mp5, Tze Co mp 4-Dmr Srbc 2 and Acr 90 Pool 16-Dt) for grain yie ld could be sources of alleles that can be man ipulated with other promising cultivars for higher grain yield in this southern Gu inea savanna ecology. agronomic characters among open pollinated maize varieties and their F1 hybrids in a diallel cross. Afri. J. Biotech., 9(18): 2633-2639. [7] Sumathi P, Nirmalakumari A and M ohanraj K (2005). Genetic variability and traits interrelationship studies in industrially utilized oil rich CIMM YT lines of maize (Zea mays L). M adras Agric. J. 92 (10-12): 612-617. [8] Najeeb S, Rather AG, Parray GA, Sheikh FA and Razvi SM (2009). 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