CSIRO PUBLISHING
Australian Journal of Experimental Agriculture, 2006, 46, 387–394
www.publish.csiro.au/journals/ajea
Heterosis and combining ability in diallel crosses involving maize (Zea mays) S1 lines M. M. MurayaA,B , C. M. NdiranguA and E. O. OmoloA A Department
of Agronomy, Egerton University, P.O. Box 536, Njoro, Kenya. author. Email:
[email protected]
B Corresponding
Abstract. This study was conducted at Egerton University, Njoro, Kenya for 2 growing seasons, 2001 and 2002. A diallel cross, without reciprocal crossings, involving 7 maize S1 lines: KSTP001, KSTP003, KSTP004, KSTP005, KSTP008, E2 and E3 was used to study the heterosis and inheritance of days to 50% flowering, plant height, ear height, leaf angle, number of leaves per plant, leaf area index, cob length, cob diameter, number of lines per cob, number of seeds per line, 100-grain weight and grain yield. A randomised complete block design with 3 replicates was used. Analysis of variance was conducted on the data generated at 0.05 significant level using MSTAT. The results showed that general combining ability (GCA) and specific combining ability (SCA) was significant (P1 for all traits except cob diameter and 100 seed weight, indicating preponderance of additive gene effects for inheritance of these traits. The study identified KSTP003 as the best combiner for most of the traits, while KSTP001 and E3 was the best combination for most traits. KSTP004 and E3 was good combiner for grain yield. Hybrid KSTP005 × E3 was the best cross for grain yield. KSTP003 × E2 was the best cross for reduction of leaf angle thus good source for erectophile canopies in a hybridisation program. Heterosis estimates showed that heterosis was more important in grain yield, yield components, plant height, number of leaves per plant and, leaf area index than other traits studied. Most of traits studied had a positive and significant (P≤0.01), while all traits studied except days to 50% flowering had a positive and significant (P≤0.01) genotypic correlations. It is recommended that based on their combining ability the lines be recombined to form synthetic maize varieties which can be released both as a variety or used for further improvement using recurrent selection. The lines which combine well for reduction in leaf angle from vertical should be utilised to develop erective maize varieties. Additional keyword: inheritance.
Introduction For the last 2–3 decades, maize breeders have based their selection criteria on the parameters such as days to flowering, root and stalk lodging, susceptibility to diseases and pests, plant and ear height and other yield variables which are not directly related to dry matter accumulation and partitioning. Consequently, slow progress in yield improvement has been realised. For effective yield improvement in maize genotypes, selection criteria should be broadened and sharpened to include variables affecting photosynthetic apparatus (e.g. height, leaf area index and leaf angle, efficient partitioning and chlorophyll fluorescence during pre- and post-anthesis periods) in addition to the usual yield and yield component parameters. Variables which are not directly related to dry matter accumulation such as root and stalk lodging, diseases and pests attack (environment stabilisers) should not be emphasised. Highly productive canopies have the characteristics of erective leaves © CSIRO 2006
(Loomis and Connor 1992). Maize grain yield can be greatly improved by breeding for varieties with erectophile leaves. In addition, cultivars with erectophile leaves will allow for intercropping, a system that is widespread in subsistence farming in tropics and sub tropics. Therefore, there is need to study the inheritance of leaf angle. However, heritability of leaf angle on maize is an aspect that is lacking in literature. The importance of estimating combining abilities is that, the predominant component of genetic variation determines the choice of an efficient breeding method for incorporation of concerned genes into new materials (Dhabholkar et al. 1989). Combining ability has 2 components, general combining ability (GCA) and specific combining ability (SCA) (Sprague and Tatum 1942). In terms of genetic variances, GCA represents additive gene action and additive × additive type of epistatic interaction. SCA is made up of non-additive types of variances, comprising mainly dominance and epistasis (Griffing 1956b). Selection is likely
10.1071/EA03278
0816-1089/06/030387
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Australian Journal of Experimental Agriculture
to be more effective for traits with higher additive genetic variance than those with higher dominance genetic variance. This is because dominance is a result of intralocus gene interaction. Therefore, in advance generations provided it is conducted under random mating, the interactions are interrupted and the next generations have reshuffling and recombination of genes. In terms of selection, if genes with additive effect control a character, there is always a good chance of improving that character by accumulation of the favourable genes. GCA and SCA effects can be evaluated by various analyses, but the diallel cross techniques are the commonly used methods. Griffing (1956a) provided detailed methodology for the estimation of effects and variances in diallel cross analysis. Several studies have shown that for selected maize inbred lines, non-additive genetic variances are of importance in the inheritance of yield and other quantitative traits of economic importance (Darrah and Hallauer 1972; Gamble 1962; Rojas and Sprague 1952). However, for relatively unselected materials the additive genetic variance assume greater role than non-additive types. In studies by Robinson et al. (1949), little or no dominance for genes that control plant and ear height in maize (Zea mays L.) was found. Grafius (1960) and Moll et al. (1962) reported that in maize, non-additive gene effects were more preponderant than additive gene effect on the inheritance of grain yield. Lonnquist and Gardner (1961) estimated general combining ability effect for grain yield and observed that the additive gene effects were more important than non-additive gene effects. Data presented by Mason and Zuber (1976) and Nienhuis and Singh (1986) also suggested the preponderance of additive gene effects for yield and yield component traits of maize and common beans (Phaseolous vulgaris L.), respectively. Ayiecho (1990) indicated that the magnitude of additive genetic variance was greater than that of dominance genetic variance in the inheritance of grain yield in barley (Hordeum vulgare L.), and noted that 100-grain weight was mainly controlled by non-additive genes. The objective of this study was to determine the heterosis and inheritance of 7 S1 maize lines for plant height, ear height, leaf angle, number of leaves per plant, leaf area index, cob length, cob diameter, number of lines per cob, 100-grain weight and grain yield. The findings of this study will be an asset to scientist in Kenya, Australia and elsewhere where maize is grown. It will provide an indication of the possibility for development of cultivars with more erective canopies.
M. M. Muraya et al.
long enough to acquire good level of striga tolerance. Embu population was developed from 2 populations, Embu I and Embu II. Embu I was developed by pooling together medium maturing Kenya local landraces, while Embu II was developed by pooling together medium maturing materials from Central America. Lines used in this study were extracted from KSTP and Embu population in 1999 and 2000 using S1 selection methods. This study was conducted at Egerton University, Njoro, Kenya for 2 growing seasons (2001 and 2002). Seven S1 lines: KSTP001, KSTP003, KSTP004, KSTP005, KSTP008, E2, and E3 were used as parents in this study. KSTP001, KSTP003, KSTP004, KSTP005 and KSTP008 were derived from KSTP. E2 and E3 were derived from Embu population. The 7 lines were selected on bases of their suitability for intercropping system. They had more erect leaf orientation with mean leaf angle less than 30◦ . Diallel crosses without reciprocal crossings were made. The 7 parents and the 21 F1 s were grown in a randomised complete block design with 3 replicates. The inter block distance was 90 cm. Each plot had 5 rows of 11 plants spaced at 75 cm between the rows and 30 cm within the rows. At planting diammonium phosphate (DAP) fertiliser was applied at the rate of 70 kg P2 O5 /ha. Topdressing was done 6 weeks from planting using calcium ammonium nitrate (CAN) at the rate of 60 kg N/ha. Data was recorded on 12 randomly selected plants from the middle 2 rows from each plot for the plant height, ear height, mean leaf angle at 50% flowering, number of leaves per plant, leaf area index, 50% maturity, cob length, cob diameter, number of grains per line, number of lines per cob, 100-seed weight, and grain weight. Days to flowering was recorded when 50% of plants had flowered. Leaf angle per plant was determined physically using a protractor. Leaf angle was taken as the vertical distance between the stalk and leaf. The leaf area index (LAI) was determined using the formula: leaf area = leaf length × leaf diameter at the mid of the leaf LAI =
[(0.75 × leaf area/spacing)]
(1)
i=l
where n is number of leaves/plant. A diallel analysis was performed for the crosses according to model I of Griffing (1956a). Method II which involves parents and one set of F1 s, without reciprocal crosses, was used. The error mean squares were used in the statistical F-test. Data were analysed by the MSTAT package. All statistical analysis was conducted on plot means across 2 seasons. For data analysis the parental lines are regarded as exactly the same as their selfing progenies. Griffing (1956a) statistical model I The Griffing (1956a) statistical model states that Yij = µ + gi + gj + sij + eij ,
(2)
where Yij is the mean performance of the ith parental line mated to the jth parental line, µ is the population mean effect common to all observations, gi and gj are the general combining ability effects of ith and jth parents, respectively, sij is the interaction of the ith and jth parents, and eij is the random error. Linear model for the ANOVA The linear model for the ANOVA states that
Materials and methods Plant materials and experimental design The original populations comprised of Kakamega Striga Tolerance Population (KSTP) and Embu population. KSTP is an open pollinated medium maturing variety developed by Kenya Agricultural Research Institute (KARI) from a collection of Kenya local landraces which have been grown in striga [Striga hermonthica (Del.) Benth.] infested fields
n
Yijk = µ + cij + bk + εijk
(3)
cij = gi + gj + sij ,
(4)
where
and Yijk are estimates of performance of the genotype, µ is the population mean effect common to all observations, gi and gj are the general
Heterosis and combining ability in maize
Australian Journal of Experimental Agriculture
combining ability effects of ith and jth parents, respectively, sij is the interaction of the ith and jth parents, and eij is the random error. Heterosis was estimated with equation 5. H = [(F1 − Mp )/Mp ] × 100,
(5)
where H is heterosis, F1 is the mean performance of the F1 hybrid, Mp is the mean performance of mid-parent. The phenotypic correlations (rp) between character X and Y was calculated as: (6) rp = Cov(Px , Py )/σ2Px × σ2Py . Genotypic correlations were calculated from the derived equivalent covariance and variance estimates (Hallauer and Miranda 1988). Significance of the genotypic correlations values were obtained following procedures outlined by H´ebert et al. (1994).
Results and discussion Estimates of 11 morphological and agronomic traits were used to evaluate GCA through a diallel scheme and significant genotypic effects (P
