Heterosis and Combining Ability in Sesame ( Sesamum indicum L.)

The present study on heterosis and combining ability for seed yield and its components was carried out in a set of 15 F 1 hybrids of sesame involving five lines and three testers diverse parents at Agricultural college, Bapatla. The ratio of the genetic variance was less than the unity, which indicated the predominance of the non-additive gene action in all the characters studied. The analysis revealed that none of the parents was found as good general combiners for all the traits consistently, however two lines YLM 95, IS 355 and a tester Gowri were found to be good combiners for seed yield and its contributing traits. The hybrids IS 355 x Gowri followed by KMR x Madhavi, YLM 95 x Gowri and IS 355 x Madhavi have exhibited higher heterosis (Average heterosis and Heterobeltiosis) for seed yield. These crosses involved good x poor and poor x poor combiner parents. Further improvement in seed yield could be possible through the hybridization and selection of transgressive segregants.

Sesame (Sesamum indicum L.) is one of the most important and popular oil seed crop.The breeding method to be adopted for improvement of any crop depends primarily on the nature of gene action involved in the expression of quantitative traits of economic importance.Line x Tester design was followed by crossing each line with all the testers for studying the combining ability and the gene action involved.This approach has practical utility in breeding programme aimed at genetic improvement of yield.

Materials and Methods
An experiment was conducted during Kharif 2011 and rabi 2011-12 at Agricultural College Farm, Bapatla.The experimental materials comprised of five lines (females) namely; YLM 94, YLM 95, YLM 96, IS 355 and KMR 42 and three testers (males) namely; Madhavi, Gowri and RT 54.The complete set of 15 F1 s and eight parents were grown in Randomized Complete Block Design (RCBD) with three replications.Row to row and plant to plant spacing were maintained at 30cm and 10cm, respectively.In each replication, randomly selected 10 plants in each parent and F 1 s were used for observation.Observations were recorded on nine important characters, viz., days to 50 per cent flowering, days to maturity, plant height (cm), number of primary branches per plant, number of capsules per plant, number of seeds per capsule, 1000-seed weight (g), oil content (%) and seed yield per plant (g).Combining ability analysis of parents and *Corresponding author email : didlaratnababu@gmail.com crosses was done by using the Line x Tester fashion as given by Kempthorne (1957).Heterosis was measured as deviation of F1 mean from mid parent (average heterosis) and better parent (heterobeltiosis) mean.

Results and Discussion
The mean sum of square due to gca and sca were highly significant for all the nine characters except days to 50 per cent flowering, days to maturity, 1000-seed weight and oil content for GCA variance (Table 1).It indicated that both additive and non-additive gene action were involved in the expression of these traits.Similar results have been reported by Banerjee and Kole (2009) for plant height, number of capsules per plant, number of seeds per capsule and Gangadhar Rao (2006) for number of primary branches per plant and Gaikwad et al. (2009) for seed yield per plant.The estimates of SCA variance were higher than GCA variance.The ratio of GCA to total variance being lesser than unity for all the traits revealed preponderance of non additive gene effects in the inheritance of seed yield and its component traits.
The estimates of gca effects (Table 2) revealed that none of the parents exhibited significant gca for all the characters so it was difficult to pick good combiners for all the characters considered together.This shows that genes for different desirable characters would have to be combined from different sources.Among the five lines tested, YLM 95 and IS 355 were good general combiners for seed yield per plant.These lines also showed The estimates of specific combining ability effects were found negatively significant in cross combinations YLM 94 x RT 54, YLM 95 x Madhavi and YLM 96 x Gowri for days to 50 per cent flowering, YLM 94 x Madhavi for days to maturity.Significant and positive specific combining ability effects were observed in the cross YLM 95 x Gowri for plant height, IS 355 x RT 54 for number of primary branches per plant, IS 355 x RT 54 for number of capsules per plant, KMR 42 x Madhavi for number of seeds per capsule and YLM 96 x Gowri for 1000-seed weight.The only hybrid KMR 42 x Madhavi exhibited significant sca effect for the seed yield per plant (Table 3).This suggests that high sca effect of any cross combination does not necessarily depend on the gca effects of the parental lines involved.This superiority of sca effects may be due to complementary type of gene action or involvement of non allelic interaction of fixable and non fixable genetic variance.
The hybrids varied in magnitude and direction of heterosis for most of the characters (Table 4).The significant average heterosis and heterobeltiosis observed for days to 50% flowering in cross combinations viz., YLM 94 x RT 54, YLM 95 x Madhavi and YLM 94 x Madhavi, days to maturity in IS 355 x RT 54, YLM 94 x RT 54 and KMR 42 x RT 54.In general, heterosis for days to 50% flowering and days to maturity should be in negative direction, in order to develop early cultivars therefore, YLM 94 x RT 54 can be used in future crop improvement programme for development of early maturing types.These findings are in consonance with Gaikwad et al. (2009).The character that contribute to vegetative growth such as number of primary branches per plant expressed highest magnitude of heterosis (both average heterosis and heterobeltiosis) in cross combinations viz., IS 355 x RT 54 and IS 355 x Gowri.Above findings are in accordance with the results of Mothilal and Ganesan (2005).Cross combinations viz., YLM 95 x Gowri, IS 355 x RT 54 and IS 355 x Madhavi expressed positively significant heterosis for plant height.Similar results were reported by Mothilal and Ganesan (2005) Kar et al. (2002), Mothilal and Ganesan (2005) for average heterosis and Senthil Kumar and Ganesan (2004) for heterobeltiosis respectively.Number of capsules per plant as well as number of seeds per capsule had direct correlation with seed yield per plant.The highest value of heterosis for seed yield per plant was observed in IS 355 x Gowri, YLM 95 x Gowri and KMR 42 x Madhavi.These crosses showing desirable heterosis for seed yield per plant in addition to most of the yield contributing characters studied.Similar results were reported by Mothilal and Ganesan (2005), Prajapati et al. (2006) and Gaikwad et al. (2009).
The cross combinations viz., YLM 96 x Gowri and IS 355 x Madhavi exhibited the highest heterosis for 1000-seed weight.This is similar with the findings of Mothilal and Ganesan (2005) for average heterosis and Shekhat et al. (2008) for heterobeltiosis.For oil content two crosses viz., YLM 96 x Madhavi and IS 355 x Madhavi showed higher heterosis which are in accordance with the results reported by Bhuyan and Sarma (2003) and Shekhat et al. (2008) for average heterosis and heterobeltiosis respectively.
Considering the overall performance in respect of seed yield per plant these promising hybrids viz., IS 355 x Gowri, YLM 95 x Gowri and KMR 42 x Madhavi exhibited high heterotic effects.The cross KMR 42 x Madhavi have higher sca effect even though poor x poor parents are involved.The higher sca effect observed in poor x poor general combiners cross might be due to non-additive gene effects and such could be exploited through the hybridization.The crosses, IS 355 x Gowri, YLM 95 x Gowri also have positive sca effects for seed yield per plant, which involved good x poor parents.The cross involved good x poor general combiners can produce transgressive segregants in later generation.
in case of average heterosis and Shekhat et al. (2008) for heterobeltiosis.A desirable degree of vegetative growth is essential for realizing high capsule yield.