Combining ability assessment in Helianthus annuus L. through line × tester analysis for quantitative traits and quality parameters

The cross combinations of different lines and testers (L×T) for high yielding sunflower (Helianthus annuus) hybrids were evaluated. Plant materials were utilized by L×T mating design of 7 lines and 3 testers and their 21 hybrids were sown in the field during 2015 autumn season in RCBD design with 3 replications. Genetic variability, general combing ability (GCA) and specific combining ability (SCA) among genotypes were assessed. Lines A-12, A-2.2 and tester G-53 were found to be good general combiners for days to flowering, plant height, number of leaves per plant, stem diameter, achene yield per head, 100-seed weight, oil content, and protein content. Among the crosses, A-12 × B-3.16 and B12.10 × C-3.3 were reported as good specific combiners for yield-related traits. For protein content, the cross B-3.1 × B-3.16 showed the maximum SCA effects.


INTRODUCTION
Sunflower (Helianthus annuus) is an important oil producing crop after soya bean. Sunflower oil is the best due to its mild taste, low amount of saturated fatty acid and light color. Sunflower oil plays an important role in the economy of Pakistan (Imran et al., 2015). The national average yield of sunflower crop is about 1520 kg/ha (Shah et al., 2013). Sunflower plays an important role in increasing the local production of vegetable oil.
There is a huge gap between production and consumption of vegetable oil and it is increasing day by day. Pakistan is spending a huge amount of foreign exchange every year to import edible oil. Due to changing habit of people and increasing population in the country, it has the ability to decrease the gap between local production and consumption. Thus, the local production of hybrids seed with high oil contents is one of the best *Corresponding author. E-mail: aurkhalid75@yahoo.com. Tel: 092 333 6367206.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License goals (Habib et al., 2006). Sunflower Oil is light in taste, appearance and contains more essential vitamin E than other vegetable oils. The oil consists of monounsaturated and polyunsaturated fats. It is used in foods, cosmetics, industries, and for the treatment of cholesterol and atherosclerosis (Madhavi et al., 2010). Oil contents in cultivated sunflower show considerable variation. In wild species, oil contents are much less than cultivated sunflower (Seiler, 1992). Sunflower oil has greater percentage of unsaturated fatty acids such as oleic acid (90%) and linoleic acid (10%). It can be utilized directly for cooking and as salad oil. Sunflower oil is considered as the second best after olive oil for edible purposes due to high proportion of unsaturated fatty acids. It is also very suitable for making vegetable ghee and margarine and its pulp is utilized for paper production. The seed cake meal is a rich protein source as its seed protein components range from 20 to 30% (Arshad et al., 2010).
In plant breeding, general combining ability (GCA) and specific combing ability (SCA) are important techniques to identify the best lines for hybrid production. Sunflower hybrids exhibit superior performance as compared to open pollinated populations due to expression of hybrid vigor. The hybrid plant seeds also have uniform moisture contents that make them fit for storage (Nasreen et al., 2011). The hybrids also show better response to high inputs usage of fertilizers and water which results in increased production potential. Therefore, estimating the GCA and SCA effects is helpful to select the best parent inbreeds for desired hybrids in seed yield and oil contents.
The line × tester analysis is an efficient method to assess the large number of inbreeds and it provides information on the relative importance of general and specific combining ability effects to understand the genetic basis of important plant characters, namely, plant height, head diameter, stem diameter, achene weight, achene yield and oil contents, etc. The GCA of a line means the average value of its performance in hybrids when crossed with other lines (Ahsan et al., 2013;Saeed et al., 2014;Naseem et al., 2015a, b). The line × tester analysis by Kempthorne (1957) may be the simplest and efficient method for evaluation of inbreeds for their combining abilities. GCA was defined by Sprague and Tatum (1942). The objective of this study was to evaluate the cross combinations of different lines and testers for high yielding hybrids.

MATERIALS AND METHODS
The present research was conducted in the experimental area of Plant Breeding and Genetics Department, University of Agriculture, Faisalabad, Pakistan during autumn 2014 and spring seasons in 2015. The experimental material consisted of 3 lines; G-53, B-3.16 and C-3.3 as male parents and 7 lines; B-3.1, A-16.1, A-12, A-14.13, A-2.2, A-22 and B-12.10 as female which were obtained from the Plant Breeding and Genetics Department, University of Agriculture. These lines were planted during the 2014 autumn season. The hybrid combinations were obtained by crossing the male with female lines in line × tester mating design. The plants in the female line were hand emasculated and crossed by their male parents. Male parents were used as a source of pollen only.
Seeds of these hybrid combinations and the parents along with 2 commercial hybrids were sown in the field during spring season following a randomized complete block design (RCBD) with 3 replications, maintaining row-to-row and plant-to-plant distance of 75 and 25 cm, respectively. Cultural and agronomic practices were applied during the crop growing season. The data were recorded on 10 plants per entry of each replication for the following traits: days taken to first flowering; days taken to 50% flowering; days taken to complete flowering; plant height (cm); internode length (cm); leaf area (cm); head diameter (cm); dry head diameter (cm); stem diameter (cm); number of leaves/plant; achene yield per head (g); 100 achene weight per head (g); oil content (%); and protein contents (%).
Oil and protein contents of all genotypes were analyzed at the National Institute of Food and Agriculture (NIFA) Peshawar, Pakistan.

RESULTS AND DISCUSSION
Mean squares of all characters exposed significant differences among sunflower genotypes (Table 1a and b). High significant differences among crosses were observed for all traits. High significant differences were also present for all traits except plant height, internode length and oil content among parents. There was no significant difference for all characters except stem diameter among lines and testers. These results were similar to the findings of earlier researchers (Jayalakshmi et al., 2000;Kannababu and Karivaratharaju, 2000;Monotti et al., 2000;Sharma et al., 2000). However, L × T interaction was highly significant for all traits except flower initiation and complete flowering. Parents vs. crosses showed significant differences for all traits under study. Significant difference inside different components showed the presence of genetic variability in the breeding material. This genetic variability may be used in the breeding programs for improvement of sunflower achene yield and its related traits. Significant differences among parents vs. crosses showed the presence of heterosis in crosses that may be used for the development of high yielding sunflower hybrids. These findings were similar to the results of Alone et al. (1996), Shekar et al. (1998), Ashoke et al. (2000), Habib et al. (2007) and Khan et al. (2008). The analysis of variance of all crosses showed significant variability (Tables 2 and 3).
The concept of general and specific combining ability has gained great importance for plant breeders because of the wide use of hybrid in many crops. In general, the minimum GCA effects were observed in the line A-12 and the tester G53 which were also significant in negative direction and were desirable for days to flowering and for the development of short stature hybrids. Tester G-53 and C-3.3 had positive and significant GCA effects for 100 achene weights per head and number of leaves per plant, respectively, which were desirable high yielding. Significance at 0.05% probability level; **Significance at 0.01% probability level.      Table 2a and b shows that line A-12 and tester G-53 displayed positive and significant GCA effects for fresh, dry head diameter, 100 seed weight, achene yield per head, and protein content. The line A-2.2 and tester G-53 were identified as proper general combiners because these lines revealed the highest GCA effects for oil content which was significant in positive direction and it was desirable. The line A-12, A-2.2 and tester G-53 were identified as proper general combiners that may be used in the improvement of the most yield related traits. The proper combinations of lines and testers may be recommended for hybrid development and breeding program in the future. These findings were similar with the results of Imran et al. (2015), Naik et al. (1999) and Skoric et al. (2000). Table 3a and b shows that the crosses A-12 × B-3.16 and B-12.10 × C-3.3 performed as proper specific combiners for yield related traits. Especially for protein content, the cross B-3.1 × B-3.16 showed the maximum SCA effects. So the crosses A-12 × B-3.16 and B-12.10 × C-3.3 were exhibited to the best specific combiner followed by the hybrid G-65×A-85. These crosses may be recommended for high yielding in the future. Lande et al. (1997), Shekar et al. (1998) and Kumar et al. (1998) reported similar results.

Conclusion
It was concluded that the evaluation of breeding materials had sufficient genetic variability that may be used in further breeding programs. GCA and SCA ANOVAs proposed these traits under control of non-additive gene action. Further analysis showed over-dominant gene action controlling the plant traits. Therefore, estimation of combining ability was suggested to improve yield and yield related traits in short duration using these sunflower breeding materials. Among the proposed genotypes, that is, A-12, A-2.2, and G-53 indicated the highest GCA effects and considered to be good general combiner for almost 85% traits. The cross combinations A-12 × B-3.16, B-12.10 × C-3.3 and B-3.1 × B-3.16 showed best specific combining ability whereas these genotypes can be used for further hybrid development breeding programs for seed yield and oil contents improvement.