Gene Effects and Combining Abilities for Oil Content in Sunflower

Considering the worldwide importance of sunflower oil, objective of this study was to evaluate gene effects and combining abilities of six sunflower open pollinated varieties. Varieties were crossed according to incomplete diallel method and produced fifteen F1 progenies. Comparing the mean values of F1 progenies to parents mean in most cases superdominance was expressed as a mode of inheritance. Nonetheless, dominance of better parent and partial dominance of better parent were also recorded as a mode of inheritance. GCA/SCA ratio indicated greater importance of non-additive genetic component in oil content expression. The genetic variance analysis showed that dominant component was more important and dominant genes prevailed compared to recessive genes for oil content in sunflower.


Introduction
Sunflower (Helianthus annuus L.) is one of the most important oilseed crops in the world and the preferred source of oil for salads and cooking (Hu et al. 2010).Sunflower oil is a valuable source of tocopherols and phytosterols and has positive effect on human health (Bramley et al. 2000, Patel & Thompson 2006, Gotar et al. 2008).It has a relatively high concentration of linoleic acid which is an essential poly-unsaturated fatty acid that is not synthesized by humans and is a precursor of gammalinolenic acid and arachidonic acid (Dorell 1978).Sunflower oil has a wide range of applications and can be used as a supplement in chemical industry in production of varnishes, copolymers, polyester films, modified resin, plasticizer and detergent, as well as in pharmaceutical industry.
Oil content is a quantitative trait and it is very variable depending on the genetic background and environmental conditions.Success in breeding largely depends on genetic variability in the initial material.Thorough knowledge of the mode of inheritance and combining ability in the material which is available has a crucial role in the breeding process with the goal of creating superior genotypes that can bring progress in production.Plant breeders frequently use diallel analysis to evaluate general combining abilities (GCA) of parents and specific combining abilities (SCA) of their crosses for a number of traits.Investigation on gene effect for oil content in sunflower so far provided different results depending on the genetic divergence in studied material.In previous studies Škorić (1976Škorić ( ), Miller et al. (1980) ) and Marinković (1984) reported additive gene effect, while investigations of Marinković (1993) and Škorić et al. (2000) reported that non-additive genes were responsible for oil content in sunflower.
Present investigation was performed to obtain information about gene effects and combining abilities of sunflower open pollinated varieties and their F 1 progeny for oil content.

Materials and Methods
This study included six sunflower varieties crossed according to diallel method, without reciprocals.Parental lines and their fifteen F 1 hybrids were sown in three replicates at the experimental field Rimski Šančevi of the Institute of Field and Vegetable Crops, Novi Sad.Basic plots were 10 m 2 , with four 3.6 m long rows and 70x30 cm plant spacing.The data were recorded on 10 plants in each replicate from middle rows.Oil content was determined by nuclear magnetic resonance (NMR) in pure seed and expressed in percentage.Mode of inheritance was determined by applying test of significance (t-test) of the mean values of F 1 progenies compared to parents' means.General combining abilities (GCA) and specific combining abilities (SCA) were tested using diallel method (Griffing 1956), while analysis of components of genetic variance was performed according to the method suggested by Mather and Jinks (1971).

Results and Discussion
Comparing the mean values of oil content between parents and F 1 progeny it is evident that in most cases superdominance (sd + ), i.e. heterosis, was expressed as a mode of inheritance (Tab.1).Dominance of better parent (d + ) was expressed five times and partial dominance of better parent (pd + ) in one crossing combination as a mode of inheritance for oil content.In earlier study Škorić (1975) reported heterotic effects for the inheritance of sunflower oil content.
As GCA and SCA provide information for additive and non-additive gene actions, respectively (Sprague & Tatum 1942), analysis of variance for combining ability of oil content in sunflower Analysis of GCA and SCA effects showed that there were significant differences among parents and crosses for oil content in sunflower (Tab.3).Significant and positive GCA effect was only recorded for variety S5 which makes it the best general combiner for improving oil content.Positive GCA effect was recorded also for varieties S3 and S4 but without significance.Varieties S1, S2 and S6 had negative GCA effect for oil content.SCA effects for oil content were found positive and significant in crosses S1xS2, S1xS3 and S3xS6, while in crosses S1xS4, S2xS4 and S2xS5 SCA effects were negative (Tab.3).
The analysis of the components of genetic variance indicated that dominant component (H 1 and H 2 ) was larger than additive (D) in oil content expression (Tab.4).According to F value, which is positive, dominant genes prevailed compared to recessive ones in the inheritance of oil content.This is in agreement with the frequency of dominant (u) and recessive (v) genes and K D /K R ratio which is larger than 1 and represent the total number of dominant versus recessive genes.Dominant and recessive genes were not equally distributed among parents as confirmed by the H 2 /4H 1 ratio.Moreover, average degree of dominance (√H 1 /D) indicated that seed oil content exhibited superdominance in the F 1 generation, considering all crossings (Tab.4).

Conclusions
Development of superior synthetics or hybrids involves estimation of gene action in various traits in order to design an efficient breeding plan for further genetic improvement of the initial material.Sunflower oil content is one of the most important traits considering this crop and information about inheritance, gene effects and combining abilities are necessary for improving this valuable trait.
According to results from this study, superdominance prevailed as a mode of inheritance for sunflower oil content.The non-additive genetic component was more important than additive in the expression of oil content.The best general combiner for oil content is variety S5 because of the highest GCA effect, while the highest significant positive SCA effects were recorded in crosses S1xS2, S1xS3 and S3xS6.Dominant genes were predominant compared to recessive ones, which was confirmed with the frequencies of dominant and recessive genes.

Table 1 .
Mean values, mode of inheritance, standard deviation and coefficient of variation for oil content (%) in sunflower Parameswari et al. (2004)rent; pd + -partial dominance of better parent indicated that additive and non-additive genetic components were important in the inheritance of oil content as presented by GCA and SCA values (Tab.2).The GCA/SCA ratio was lower than 1, meaning that non-additive component was more important than additive.In agreement with this studyParameswari et al. (2004)andHladni et al.

Table 2 .
Analysis of variance for combining ability of oil content in sunflower