Studies on heterosis in genetically diverse lines of cultivated sesame ( Sesamum indicum L.)

: A study was made in sesame (Sesamum indicum L.) to assess the extent of heterosis in 36 F 1 hybrids derived from Line x Tester fashion. The 36 F 1 hybrids and their parents were used to estimate the heterosis for 9 traits including seed yield. The parent VRI 1 used as a standard parent. Based on standard heterosis and per se performance the superior crosses were identified for each trait. Heterosis for yield was generally accompanied by heterosis for component traits. The crosses CO 1 x ORM 14, TMV 4 x ORM 17, TMV 5 x ORM 17, Paiyur 1 x ORM 14 and TNAU 2030-35 x ORM 14 could be used for pedigree breeding method due to additive x additive nature of epistatic gene action.


Introduction
Sesame (Sesamum indicum L.) is an important oilseed crops of India.The exploitation of heterosis has been a practical proposition in many allogamous crops and a few autogamous crops.Sesame, an autogamous crop, has not so far been amenable for heterosis breeding due to lack of economic methods for largescale seed production.However, considerable cross-pollination has been recorded in the crop (Paramanantham, 1992).Heterosis is defined as the deviation of F 1 hybrid over its mid parent (Relative heterosis), better parent (Heterobeltiosis) and standard parent (Standard heterosis), as the consequence of hybridization.Heterosis breeding studies in sesame were initiated in India from 1935 onwards (Pal, 1945) and its varying degree for seed yield and other traits had been reported by Sarathe and Dabral (1969).
Many seeds in single pollination and availability of male sterility (Rangasamy andRathinam, 1982 andPrabakaran et al., 1995) offer scope for exploitation of hybrid vigour and heterosis breeding is gaining momentum to achieve quantum jump in yield of sesame.

Materials and Methods
The materials consisted of twelve lines viz., CO 1, TMV 3, TMV 4, TMV 5, TMV 6, Paiyur 1, SVPR 1, VRI 1, Uma, TNAU 2030-35, TNAU 2030-70 andVarasampatty Local 1 (VL 1) and three testers viz., ORM 7, ORM 14 and ORM 17 and the resulting thirty six hybrids were raised in randomized block design with two replication during 2003-04 at College Farm, Tamil Nadu Agricultural University, Coimbatore.Each treatment comprised a row of 6m length with a spacing of 30 x 30cm.Observations for morphological, reproductive and yield contributing characters were recorded on five random plants from each treatment.The mean values were used for estimation of heterosis over mid parent, better parent and standard parent (VRI 1).

Results and Discussion
The analyses of variances for various economic traits are presented in table 1. Analysis of variance showed significant differences among parents for all the nine traits studied.This revealed the presence of significant variability in the experimental material.The crosses showed significant differences for all traits, which indicated the existence of variability among the crosses.The interaction between the parents and crosses recorded significant differences.This revealed that the choice of the exploitation of heterosis for all the metric traits studied.Sumathi and Kalaimani (2000) reported significant differences among parents and crosses for days to 50 per cent flowering, plant height, number of primary branches per plant, number of capsules per plant and seed yield per plant.Significant differences for days to maturity and oil content were reported by Karuppaiyan et al. (2000).Ramesh et al. (2000) reported significant difference for 100 seed weight.
The data on range of three types of heterosis, number of hybrids having significant heterosis and best crosses are presented in table 2. The extent of heterosis for days to 50 per cent flowering varied from -15.31 to 8.42% where five crosses exceeded the standard heterosis, while 21 crosses surpassed the standard parent for days to maturity in which heterosis was ranging from -13.09 to 13.53%.These findings are in consonance with Krishnaiah et al. (2002).In general, heterosis for days to 50 per cent flowering and days to maturity were required in negative direction, hence the crosses Uma x ORM 17 (-15.31)and SVPR 1 x ORM 17 (-13.09)could be used in future crop improvement programmes for development of early maturing varieties.The characters that contributed to vegetative growth such as plant height and number of primary branches exhibited heterosis upto 69.83 and 38.57% respectively, which was in concurrence with the findings of Santha et al. (2001).A desirable degree of vegetative growth is essential for realizing high yield as total dry  Saravanan and Nadarajan (2002).Two hybrids for 100-seed weight, one hybrid for oil content, seven hybrid for seed yield per plant and five hybrids for oil yield per plant showed significant positive standard heterosis.
The hybrid vigour for seed yield and oil yield varied from -51.60 to 46.85 and -54.09 to 63.11 respectively.The highest value of heterosis was being observed in the cross CO 1 x ORM 14. Heterosis for yield was also reported earlier by Deepa Sankar and Ananda Kumar ( 2001) and Saravanan and Nadarajan (2002).Grafius (1959) suggested that there could not be any one gene system for yield per se and that the yield was an end product of multiplicative interaction between yield components.Sasikumar and Sardana (1990) also opined that hybrid vigour of small magnitude for individual yield component might have additive or synergistic effects on yield.From the above said discussion, the hybrids having higher non-additive component could be utilized for exploitation of hybrid vigour and other hybrids having additive component could be used for further improvement through selection.
Kadambavana Sundaram (1980) suggested that heterotic expression over standard variety should be given due importance for exploitation of commercial hybrids.The mean and standard heterosis for selected hybrids are presented in table 3. Based on per se performance and heterosis for seed yield, oil yield and its component characters and earliness, the hybrids CO 1 x ORM 14, TMV 4 x ORM 17, TMV 5 x ORM 17, Paiyur 1 x ORM 14 and TNAU 2030-35 x ORM 14 could be used for pedigree breeding method due to additive x additive nature of epistatic gene action.However, the selection should be postponed to later generation for improvement of yield and yield related traits.