Genetic Variability and Association Studies in RIL Population of Sunflower (Helianthus annuus L.)

Sunflower (Helianthus annuus. L) is one of the important oilseed crops in the world. It is native to North America and belongs to the family Asteraceae (Compositae). The genus name Helianthus is derived from two Greek words, namely Helios, which means “sun,” and anthos, which means “flower.” It is successfully grown over a widely scattered geographical area and is considered a crop adapted to a wide range of environmental conditions (Ekin et al. 2005).

Sunflower is the third major source of vegetable oil in the world after soybean and groundnut. Seeds of the oilseed varieties are a rich source of edible oil (40 to 45%). It is considered good from a health point of view due to a high concentration of polyunsaturated fatty acids (PUFA), 55 to 60 percent linoleic, and 25 to 30 percent oleic acid. They are known to reduce the risk of coronary disease by regulating the cholesterol content in blood plasma. It also acts as a good source of vitamin E, lecithin, and carotenoids.

Sunflower production is lagging behind in terms of supply because of the increasing population and lack of high-yielding cultivars. To meet the demand, there is a need to increase production without increasing the acreage. The best way to meet the increasing demand is to develop high-yielding cultivars.

Variability helps in better understanding the breeding behavior of various traits and in assessing the character of importance for choosing the best cultivars. It is also essential to know the type and magnitude of the association between yield and yield-contributing traits. Correlation studies help in understanding the type of association between characters. Path analysis helps in understanding the magnitude of association and divides the effects of various traits into direct and indirect effects (Wright, 1921).

The present investigation was carried out with 129 recombinant inbred lines (RIL) in F₁, generation of a cross 17B x 7-1B. The parent 17B has low oil content (30-33%) with medium brown seed color and prominent stripes on both the seed surfaces. The parent 7-1B has high oil content (35 - 38%) with black seed color and non striped seed surface. The hybrids viz., Sunbred 275, Hybrid CO 2, DRSH 1 and a variety COSFV 5 were used as checks. These RILs were evaluated along with checks in augumented block design 1. The field experiment was carried out at the Department of Oilseeds, Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural University, Coimbatore during kharif 2016. Observations were recorded for plant height(cm), head diameter(cm), volume weight(g/100m), 100 seed weight(g), seed yield per plant(g), oil content(%), oleic acid content(%), linoleic acid content(%) and oil yield per plant(g). The oil content was estimated using BRUKER MATRIX-I NIR spectrometer.

Genetic Variability

Analysis of variance (Table 1) revealed a high significant difference among all genotypes for all characters. This indicated the presence of high variability among all genotypes for all traits. Variability helps to choose a potential cross since it indicates the extent of recombination for initiating effective selection procedures.

The genetic parameters were presented in Table 2. High PCV was observed for plant height (23.23), head diameter (22.33), 100 seed weight (31.24), seed yield per plant (58.38), oleic acid content (24.33), and linoleic acid content (35.26).

Table 1. Analysis of variance of RIL population of 17B x 7-1B for various characters

Oil yield per plant (58.68). These results were in agreement with Sridhar et al. (2006), Mijic et al. (2009), and Dhillon et al. (2011). Moderate and low PCV was observed for volume weight (12.42) and oil content (7.37). This result was in agreement with the report of Mijic et al. (2009) and Dhillon et al. (2011).

Table 2. Variability parameters of various traits for RIL population of 17B x 7-1B

High GCV values were observed for plant height (21.87), 100 seed weight (29.39), seed yield per plant (56.38), oleic acid content (20.81), linoleic acid content (30.09), and oil yield per plant (35.6). These results are in agreement with Makane et al. (2011).
Moderate GCV values were observed for head diameter (16.37) and volume weight (12.16).
Low GCV was observed for oil content (7.37). These results are also in agreement with Tyagi and Tyagi (2011).
These results indicated that a sufficient level of variability was observed for most of the traits in this population. Hence, selection can be carried out for those traits with high and moderate GCV.

The heritability and genetic advance provide the proportion of heritable variation and the genetic gain to be obtained in subsequent generations.
High heritability was recorded for plant height (88.63), volume weight (95.78), 100 seed weight (88.5), oil content (86.9), seed yield per plant (93.28), oleic acid content (73.16), linoleic acid content (72.86), and oil yield per plant (88.51).
Moderate heritability was observed for head diameter (53.76). These results are also in agreement with Jagadeesan et al. (2008). No trait showed low heritability.

High heritability and high genetic advance as a percentage of the mean were recorded for the traits plant height (42.42), volume weight (24.51), 100 seed weight (56.96), seed yield per plant (28.32), oleic acid content (36.66), and linoleic acid content (52.91).
High heritability and high genetic advance as a percentage of the mean indicate the presence of additive gene action. Directional selection for these traits would be more effective for desired genetic improvement. These results are also in agreement with Sridhar et al. (2006), Sujatha and Vishnuvardhan Reddy (2009), Janamma et al. (2009), Makane et al. (2011), Sudrik et al. (2014), and Amin et al. (2016).

High heritability and low genetic advance as a percentage of gain were observed for oil yield per plant.
Among the traits, all traits showed positive skewness except linoleic acid, which showed no skewness, indicating a normal distribution of population for linoleic acid content.
In kurtosis, the characters volume weight (1.94), seed yield per plant (2.80), and oil yield per plant (2.73) showed a leptokurtic nature, indicating wider variability for these traits.
Thus, directional selection may improve per se performance of these traits.

Table 3. Simple Correlation Coefficients between Oil Yield and Yield Component Characters in RIL Population of 17B x 7-1B

Oil yield per plant showed positive and significant correlation with plant height, head diameter, volume weight, 100 seed weight, oil content, and seed yield per plant. These results were confirmed with earlier findings of Sridhar et al. (2005), Vidhyavathi et al. (2005), Ravi et al. (2006), Sowmya et al. (2010), and Muthupriya et al. (2016).

Seed yield per plant had a significant and positive correlation with plant height, head diameter, volume weight, and 100 seed weight. These results were confirmed with the earlier findings of Manivannan et al. (2007), Kalukhe et al. (2010), and Neelima et al. (2012).

Plant height had positive and significant correlation with head diameter, volume weight, 100 seed weight, and oleic acid content. These results were similar to the findings of Binodh et al. (2008) and Dan et al. (2012).

Head diameter had positive and significant correlation with 100 seed weight and oleic acid content but had negative significant correlation with oil content and linoleic acid content. Similar results were reported by Rehman et al. (2012), Zia Ullah et al. (2013), and Sincik et al. (2014).

Volume weight had positive significant correlation with 100 seed weight, oil content, and oleic acid content. These results were confirmed with the findings of Vidhyavathi et al. (2005) and Anandhan (2010).

The traits 100 seed weight and oil content had significant and positive correlation with oleic acid content and linoleic acid content, respectively. These results were confirmed with findings of Anandhan (2010) and Tyagi & Khan (2013).

Thus, the traits plant height, head diameter, volume weight, 100 seed weight, and oil content were important selection indices for both oil and seed yield improvement.

Table 4. Path Coefficients of Oil Yield with Various Traits in RIL Population of 17B x 7-1B

Content and seed yield per plant. These results were confirmed with the earlier findings of Sridhar et al. (2005), Vidhyavathi et al. (2005), Ravi et al. (2006), Sowmya et al. (2010), and Muthupriya et al. (2016).

Seed yield per plant had significant and positive correlation with plant height, head diameter, volume weight, and 100 seed weight. These results were confirmed with the earlier findings of Manivannan et al. (2007), Kalukhe et al. (2010), Neelima et al. (2012).

Plant height had positive and significant correlation with head diameter, volume weight, 100 seed weight, and oleic acid content. These results were similar to the findings of Binodh et al. (2008) and Dan et al. (2012).

Head diameter had positive and significant correlation with 100 seed weight and oleic acid content, and it had negative significant correlation with oil content and linoleic acid content. Similar results were reported by Rehman et al. (2012), Zia Ullah et al. (2013), and Sincik et al. (2014).

Volume weight had positive significant correlation with 100 seed weight, oil content, and oleic acid content. These results were confirmed with the findings of Vidhyavathi et al. (2005) and Anandhan (2010).

The traits 100 seed weight and oil content had significant and positive correlation with oleic acid content and linoleic acid content, respectively. These results were confirmed with findings of Anandhan (2010) and Tyagi and Khan (2013).

From the foregoing discussion on character analysis, it might be concluded that the traits viz., plant height, head diameter, volume weight, 100 seed weight, and oil content were important selection indices for both oil and seed yield improvement.

Path Analysis

Path coefficient analysis permits the separation of direct and indirect effects by partitioning the simple correlation coefficients. It provides a clear picture of the characters that can be relied upon in a selection programme for improvement. The direct and indirect effects of various traits on oil yield per plant are tabulated in Table 4.

Seed yield per plant recorded the highest positive direct effect on oil yield per plant. Oil content had a low direct effect as reported by Binodh et al. (2008). Head diameter, plant height, and 100 seed weight had high indirect effect via seed yield per plant on oil yield per plant. Remaining traits had negligible effects.

From the foregoing discussion on correlation and path analysis, it can be concluded that the traits plant height, head diameter, 100 seed weight, and seed yield are important selection indices for oil yield improvement programme.