THE INHERITANCE OF PLANT HEIGHT IN HEXAPLOID WHEAT
(Triticum aestivum L.)
Nataša LJUBIČIĆ1*, Sofija PETROVIĆ1, Miodrag DIMITRIJEVIĆ1, Nikola HRISTOV2
1University of Novi Sad, Faculty of Agriculture, Novi Sad, Serbia
2Institute of Field and Vegetable Crops, Novi Sad, Serbia
*Corresponding author:
Abstract
Five winter wheat varieties (Pobeda, Renesansa, Sara, Partizanka and Pesma) have been selected for diallel crossing in order to estimate the mode of inheritance, gene effect and genetic variance components for the plant height in F1 generation. The mode of inheritance was done on the basis of the significance of components of genetic variance and the regression analysis. The combining ability analysis indicated significantdifferences for the general (GCA) and specific (SCA) combining ability in the F1 generation, which means that plant height had resulted from the genes with additive and non-additive impact. The best general combining ability was denoted in varieties Partizanka and Pesma and the best specific combining ability have shown in cross combination Partizanka/Pesma. The genetic components of variance, average degree of dominance and regression line indicated over-dominancein the inheritance of plant height.
Keywords:wheat, plant height, diallel, regression.
Introduction
Wheat is one of the most important crops in the world and itsdemand growing at approximately 2% per year, twice the current rate of gain in genetic yield potential (Reynolds et al., 2001).Since that grain yield is complexcharacterinfluenced by many components,breeders normally use yield components to improve the grain yield,despite the fact that these components compensate each other in practice and increase in one cause a decrease in the other (Foroozanfar and Zeynali, 2013).Therefore, an efficient wheat improvement program requires an understanding of genetic mechanism involved in the expression of yield and yield components of plant material to be used in hybridization program (Shabbir et al., 2011). Plant breeders frequently use diallel analysisfor testing a number ofparental lines in all possible combinations.Diallel analysisis a suitable method for estimating of genetic parameters and provides early information on the genetic behaviour of these traits in the first generation (Farshadfar et al.,2012).Techniques for analyzing genotypes for all possible crossesinclude diallel analysis of variance, calculation of genetic components of variation, Vr/Wr regression analysis, as well as estimationgeneral and specific combining ability effects and have been developed by Griffing (1956), Hayman (1954) and Mather and Jinks (1971, 1982). In the most of the diallel studies of wheat, genetic control of plant height,as one of several yield components of wheat, has been subject of numerous studies. Since that inheritance of plant height has complex nature, this question has been investigated in many its aspects (Zečević, 2005).
Therefore, the aim of this study was to obtain the information about inheritance of plant height in a 5×5 diallel cross of wheat.These results would be additional information in the selection of desirable parents for an effective breeding program to evolve new varieties of economic importance.
Materials and methods
Five winterwheat genotypes, (Triticum aestivum L.), Pobeda, Renesansa, Sara, Partizanka and Pesma, were crossed in all possible combinations following an 5×5 diallel mating system and it was obtained F1 generation of progenies. The experiment was conducted at the trial field of the Institute of Field and Vegetable Crops in Novi Sad, according to random block design with three replications, in three growing seasons (2009/2010, 2010/2011 and 2011/2012). The cultivars were sown in 2 m long rows with 20 cm of inter-row spacing and 10 cm spacing between plants in the row. At the stage of full maturity, ten plants from each replication of hybrids and parents were selected randomly for recording data for plant height.Average values of three years trait analysis were used. Analysis of variance for parents and F1 hybrids for the plant height was done according to Steel and Torrie (1980). General combining ability (GCA) and specific combining ability (SCA) was done following the Method 2 (parents and F1 generation) Mathematical Model 1 of Griffing (1956). The regression analysis was conducted by the method of Mather and Jinks (1971). The components of genetic variance were analyzed following the models of Hayman (1954) and Jinks (1954).
Results and Discussion
The analysis of variance for plant height of wheat revealed highly significant differences among the replications and significant differences among genotypes (Table 1).Significant differences between replication indicated differences between years what was expected, given that the trial was conducted in three different growing seasons. Significant differences between genotypes suggested that the parents differ significantly and could be used efficiently for improvement of this trait.Using divergent genotypes in the crosses is preferable because selecting genetically divergent parents provides a wider genetic variability.These results are in accordance with earlier findings of Jadoon (2011) and Zeeshan et al. (2013).
Table 1.Analysis of variance for parents and F1 hybrids for the plant height in a 5×5 diallel cross of bread wheat
Source of variance / FtDF / SS / MS / F / 0.05 / 0.01
Replications / 2 / 3743.09 / 1871.54 / 220.19** / 3.32 / 5.39
Genotypes / 14 / 332.06 / 23.72 / 2.79* / 2.60 / 2.84
Error / 28 / 237.99 / 8.50
Total / 44 / 4313.13
+DF: Degree of Freedom, SS: Sum of Squares, MS: Mean Square, F: Level of Significance by the F test; Significant (P < 0.05), Highly significant (P < 0.01), Non-significant (ns)
Significant genotypic variation for this character was further partitioned into variation due to general combining ability (GCA) and specific combining ability (SCA) effects and presented in Table 2.The results of the analysis was indicated highly significant differences for the general (GCA) and significant differences for the specific (SCA) combining ability in the F1 generation,meaning that plant height having resulted from the genes with additive and non-additive, i.e. dominant effects.The GCA/SCA ratio was equaland indicates that both kinds of gene effects were important in controlling the inheritance of the plant height of wheat.The present findings thus supported the results ofJadoon (2011); Farshadfar et al. (2013) and Zeeshan et al. (2013), which also showed the roles of both effects for plant height in wheat.
Table 2.Analysis of variance for combining ability for the plant height in a 5×5 diallel cross of wheat
Source of variance / FtDF / SS / MS / F / 0.05 / 0.01
GCA / 4 / 31.80 / 7.95 / 2.81** / 2.69 / 4.02
SCA / 10 / 78.88 / 7.89 / 2.78* / 2.16 / 2.98
E / 28 / 237.99 / 2.83
GCA/SCA / 1.01
+GCA: General Combining Ability, SCA: Specific Combining Ability, E: Error; DF: Degree of Freedom, SS: Sum of Squares, MS: Mean Square, F: Level of Significance by the F test; Significant (P < 0.05), Highly significant (P < 0.01), Non-significant (ns)
Estimates of general combining ability (GCA) were presented in Table 3. The GCAestimates revealed thatthe tendency of the largest positivevalue of GCA effects were observed in genotypes Partizanka andPesma, suggesting that these genotypes contain more genes with additive effects or additive×additive interaction effects and could be a good parent for this trait. Findings of current studywere similar to findings of Zeehsan et al. (2013).Genotype Renesansa was the poorest general combiner with maximum negative but not significant GCA effects. Negative GCA effects were also observed in genotypesPobeda and Sara.However, if in breeding program short stature behavior is preferred, therefore, negative combining ability effects are preferred for plant height. In that case,the most appropriateare genotypes with the highestnegative values of combining ability.
Table 3.Estimates of GCA effects for the plant height in 5×5 diallel cross of bread wheat
Parents / LSDGCA values / Rank / SE / 0.05 / 0.01
Pobeda / -0.826 ns / 4
Renesansa / -1.216 ns / 5 / 0.900 / 1.82 / 2.43
Sara / -0.127 ns / 3
Partizanka / 1.084 ns / 1
Pesma / 1.083 ns / 2
+GCA: General Combining Ability, SE: Standard Error; LSD: Least Significant Difference test; Significant (P < 0.05), Highly significant (P < 0.01), Non-significant (ns)
Estimates of specific combining ability (SCA) are given in Table 4. Crosses which displayed high SCA effects for the plant height were obtained from parents with various types of GCA effects (high x high, high x low and low x low).The highest positive significant SCA effect was exhibited by the cross Partizanka/Pesma (high x high general combiner). Tendency of higher, but not significantvalues of SCA effects was also observed in crosses Sara/Pesma (low x high), Renesansa/Sara (low x low), Pobeda/Sara (low x low) and Pobeda/Pesma (low x high).The highest negative SCA effects was shown by the cross Renesansa/Pesma, followed by crosses Renesansa/Partizanka, Sara/Partizanka and Pobeda/Partizanka. The SCA effect represents the dominance and epistatic interactions which do not contribute remarkably in the improvement of self-fertilizing crops as wheat, except for the exploitation of hybrid wheat where non-additive genetic variability could be utilized (Javaid et al., 2001). The most important are greater SCA effects in crosses which were involving both parents with high GCA, such as a crossPartizanka/Pesma, because they contain the additive×additive type of interaction which is fixable in later generations and can be used in future plant breeding.Greater SCA effects obtained in this cross, indicated the possibility of genetic improvement for plant height through pedigree selection and may be produce transgressive recombinants for this trait.Greater SCA effects obtained in crosses Sara/Pesma and Pobeda/Pesma which were involving one parent with high and other with low GCA, indicated the involvement of additive×dominance gene interaction in expression of this trait.Greater SCA effects obtained in crosses which were involving one parent with high GCA, was also reported by Ivanovska et al. (2003).Higher positive SCA effects exhibited by the crossesRenesansa/Sara and Pobeda/Sara which involving both parents with low general combiner, indicated the presence of non-allelic interaction at heterozygous loci. This interaction is unfixable,so it is suggested utilizing these crosses through single plant selection in the later generations (Hassan, 2004). Parents with high values of SCA are good combination of filial generation, which uses dominant gene action, but for wheat parents that show a high GCA are more important and are used in cases where the selection is performed in subsequent generations.
Table 4. Estimates of SCAeffects for the plant height in a 5×5 diallel cross of bread wheatParents / LSD
Pobeda / Renesansa / Sara / Partizanka / Pesma / SE / 0.05 / 0.01
Pobeda / 0.462 ns / 1.810 ns / -0.305 ns / 1.357 ns
Renesansa / 2.033 ns / -2.714 ns / -3.752 ns / 2.01 / 4.06 / 5.43
Sara / -0.867 ns / 2.262 ns
Partizanka / 4.781*
+SCA: Specific Combining Ability, SE: Standard Error; LSD: Least Significant Difference test; Significant (P < 0.05), Highly significant (P < 0.01), Non-significant (ns)
The regression analysis graph (Vr/Wr) for F1 generations for plant height is presented in Figure 1. As it is seen in Figure 1, regression line intersected the Wr axis below the origin, indicated over-dominant inheritance of the plant height.Regression analysis (Vr/Wr) showed that regression coefficient in F1 generation was significantly different from unity, suggestingthe presenceof non-allelic interaction for plant height. This result indicatedthe necessary to study effectsof epistasis, as it mayhave a greater significancein some genotypes.Detectionof epistasissuggested that variation for plant height of wheat was higher under polygeniccontrol.The varieties Renesansa, Sara and Pobeda had higher dominant genes, but varieties Partizanka and Pesma, which were far away from the origin, had higher recessive genes.The arrays that correspond to parents were similarly distributed along the regression line and indicate that the parents were genetically divergent for the analysed trait(Fig. 1).These results suggest that selection would be difficult in the early generations for plant height due to over-dominance type of gene action.Similar results, which indicated over-dominance type of gene action, have been reported bySaleem et al. (2005)and Petrović et al. (2012).
b: Coefficient of Regression, Wr: Covariance, Vr: Variance
Figure 1.Vr/Wr regression analysis for the plant height of bread wheat
Genetics of the plant height, evaluated by calculation of the genetic components of variation is shown in Table 5.The analysis of the components of genetic variance indicated that dominant component (H1 and H2) was larger than additive (D).Unequal values of H1 and H2 suggested that positive and negative alleles were unequal among parent cultivars. The frequency of the dominant allele (u = 0.72) was greater than the frequency of recessive allele (v =0.28), which is in agreement with the calculated F value (interaction additive×dominant effect), which is positive, as well as the value of H2/4H1. The average degree of dominance (√(H1/D) = 4.19) had greater values than 1, which indicated over-dominance type of gene action in the inheritance of the plant height, which was in accordance with the results obtained by regression analysis. The ratio of the total number of dominant against recessive alleles (KD/KR) was greater than 1, indicating the presence of more dominant alleles in inheritance of this trait. Preponderance of dominance effects suggested that selection for the trait in early generations may not be useful and it had to be delayed till late segregating generations. These results are in agreement with earlierfindings of Zečević et al. (2005) and Jadoon (2011), while Minhas (2012)reportedthe predominant role of additive effects in affecting genetic mechanism of plant height and the involvement of partial dominance in the inheritance of this character.
Table 5. Genetic components of variation for the plant height of bread wheat
Components Values / Components ValuesD / 1.48 / H2/4H1 0.20
H1 / 25.88 / u = p 0.72
H2 / 20.72 / v = q 0.28
F / 1.17 / √(H1/D) 4.19
E / 2.83 / KD/KR 1.21
+D: Measures additive effect, H1 and H2: Measures dominance effect, F: Determines frequencies of dominant to recessive alleles in parents, E: Shows environment effect, H2/4H1: Determines proportion of genes with positive and negative effects in the parents, u: The values of dominant alleles, v: The value of recessive alleles, √(H1/D): The average degree of dominance, (KD/KR): Ratio of the total number of dominant against recessive alleles
Conclusion
The results revealed that there was significant genetic variation for the plant height of wheat among the genotypes and among the years. Significant GCA and SCA effects imply the role of both additive and non-additive gene actions in the genetic control of the trait. The largest value of positive GCA effects were observed in genotypes Partizanka and Pesma, suggesting that these genotypes contain more genes with additive effects or additive×additive interaction effects and could be a good parent for this trait. The highest positive significant SCA effect exhibited by the cross Partizanka/Pesma (high x high general combiner)indicated the possibility of genetic improvement for this trait through pedigree selection. The regression analysis in F1 generations indicated over-dominant inheritance of the plant height, which was confirmed using the analysis of the components of the genetic variance.Regression coefficient was significantly different from unity, suggesting the presenceof non-allelic interaction andindicatedthat variation for plant height of wheat is under polygenic control.
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