Heterosis for Yield Components in Sunflower (Helianthus annuus L.)

MATERIALS AND METHODS

This research was conducted at Agricultural Research Institute, Tarnab, Peshawar, Pakistan during August 2001. All the inbred lines and the hybrids were supplied by Pakistan Oilseed Development Board, Tarnab, Pakistan. The following single cross hybrids and their parents were evaluated in this study:

The inbred lines and hybrids were evaluated in a Randomized complete block design (RCBD) using three replications. Each row was 5 m long with row to row distance of 0.75 m and plant to plant distance of 0.25 m. Fertilizer was applied in the form of urea and DAP at the rate of 120 and 60 kg ha^-1, respectively. Standard cultural practices were carried out from sowing till harvesting. The following parameters were studied during this research work.

The data, after compiling, was statistically analyzed. Least significance difference test (LSD) was also applied to test the significance of treatment differences. Heterosis for each character was determined by using the following formula:

RESULTS AND DISCUSSION

Results pertaining to different morphological characters of ten sunflower inbred lines and their nine hybrids are discussed in the following paragraphs.

Head weight per plant: Analysis of variance revealed highly significant genetic differences (P<0.01) among inbred lines, however, the differences among hybrids were non significant (P>0.05) for this character (Table 1). Head weight per plant for the inbred lines ranged from 56.7 to 280 g (Table 2). Minimum value was recorded for TR-6023, whereas the maximum value for this character was recorded for TR-11. Mean data among the nine hybrids ranged from 220 to 465 g (Table 3), but these differences were statistically non significant. Per cent heterosis over the mid parent value ranged from 11.9 to 184%. Maximum positive heterosis of 184 and 183% was recorded for TS-17xTR-120 and TS-18xTR-120, respectively.

The hybrids showing maximum value for head weight per plant, also generally possess higher values for thousand seed weight and weight of filled seeds per head, which shows the importance of this character for the selection of superior hybrids.

Seed weight per head: Inbred lines and hybrids showed highly significant genetic differences (P<0.01) for this character (Table 1). Mean data for this character among inbred lines varied from 6.2 to 28 g (Table 2). Mean data for the hybrids ranged from 29.4 to 74.4 g (Table 3). TS-17xTR-120 had significantly higher seed weight per head (74.4 g) than all hybrids. Maximum heterosis of 322.3% was observed for TS-17xTR-120 followed by TS-18xTR-120 (292.7%). The least positive heterosis of 10.7% was recorded for TS-17xR-8.

These findings are supported by the work of Goksoy et al.^[3], Rather and Sandha^[4] and Gill et al.^[5] who have reported high positive heterotic effect for this character. Limbore et al.^[6] have reported heterosis as low as -53% and as high as 146.4% for this character.

Weight of filled seeds per head: Non-significant differences were observed among inbred lines, whereas highly significant differences (P<0.01) were observed among hybrids for this character (Table 1). Mean data for this character ranged from 9.1 to 27.9 g for different inbred lines (Table 2). For hybrids mean data varied from 27.3 to 69 g (Table 3). Minimum weight was recorded for TS-17xR-8 (29.9 g), whereas maximum weight was recorded for TS-17xTR-120 (69 g).

Heterosis relative to midparental value ranged from 4.3 (TS-17xTR-120) to 302.7% (TS-17xR-8). In general the hybrids showing high values for the weight of filled seeds per head possess heavy seeds and it has been reported by Hussain et al.^[7] that oil content increases significantly in hybrids possessing heavy seeds. This shows the importance of this character for selection.

Table 1:	Mean squares and Coefficient of Variation (Cv) for Head Weight per plant (Hw), Seed Weight per head (Sw), Weight of Filled Seeds per head (Wfs), Thousand Seed Weight (1000-sw) and Harvest Index (Hi) of ten sunflower inbred lines and nine sunflower hybrids evaluated at Agricultural Research Institute, Tarnab, Peshawar, during August, 2001

Table 2:	Means for Head Weight per plant (HW), Seed Weight per head (SW), Weight of Filled Seeds per head (WFS), Thousand Seed Weight (1000-SW) and Harvest Index (HI) of ten sunflower inbred lines evaluated at Agricultural Research Institute, Tarnab, Peshawar during August, 2001
Means sharing the same letter (s) in a column are not significantly different at 5% probability level

Table 3:	Means and mid parent hetrosis for Head Weight per plant (HW), Seed Weight per head (SW), Weight of Filled Seeds per head (WFS), Thousand Seed Weight (1000-SW) and Harvest Index (HI) of nine sunflower hybrids evaluated at Agricultural Research Institute, Tarnab, Peshawar during August, 2001
Means sharing the same letter(s) in a column are not significantly different at 5% probability level

Thousand seed weight: The analysis of variance for thousand seed weight revealed highly significant differences among the inbred lines and their hybrids (Table 1). Mean data for different inbred lines ranged from 22.6 to 48.2 g (Table 2). Among hybrids, mean data for this character varied from 26.5 to 62.5 g (Table 3). Most of the heterotic effects for this character were positive except for TS-17xR-8 and TS-4xR-8, which showed negative heterosis of -40.3 and -2.4%. Maximum heterosis regarding mid parental value was recorded for TS-4xTR-11 (104.6%) and TS-18xTR-120 (93.8%).

This study is in accordance with the findings of Goksoy et al.^[3], Radhika et al.^[8], Gill and Punia^[9] and Zinovatanya et al.^[10] who have reported positive heterotic effect for this character. Similarly Sassikumar and Gopalan^[11] have reported heterosis of 14.52% for 100-seed weight.

Harvest index: The ANOVA regarding harvest index revealed highly significant differences (P<0.01) among inbred lines and significant differences (P<0.05) among hybrids (Table 1). Mean data for this character ranged from 7.5 to 18% among inbred lines (Table 2). The minimum harvest index was recorded for TR-110, whereas the maximum harvest index was noted for TF-18. Among hybrids, harvest index ranged from 9.8 to 20.7% (Table 3). Mid parent heterosis for this character ranged from -43.2 to 128.6%. This study is supported by the work of Madrap and Makne^[12], who have reported high levels of heterosis for this character.