Identification of suitable parents for hybridization programme is an important step to meet the objective of breeding programme. Among several methods available for this purpose, combining ability analysis on the basis of line x tester system found to be most appropriate method to identify the best combiner that can be utilized for hybridization. The knowledge of various gene effects for the expression of yield and its component traits is prerequisite for deciding suitable breeding procedure for the development of superior and desirable genotypes. Hence an investigation was done to identify the best combiner and elucidate gene action for the expression of seed yield and other related attributes for improvement in green gram (Vigna radiata (L.)Wilckzek).

Results and Discussion
The analysis of variance for combining ability showed significant variation for parents and hybrids for most of the characters studied except for pod length in parents, indicating the presence of genetic diversity among parents and hybrids. The partitioning of hybrids mean sum of squares revealed that variance due to male, females and their interaction were significant for all traits except for days to 50 % flowering indicating the manifestation of considerable genetic variability among parents and the hybrids. These findings are in accordance with Ayyangouda Patil et al (2003), Singh et al (2007), Khan et al (2007), Gawande et al (2005).

General combinability effect of the parents indicated that none of parents was good different parents found to be good combiner for all traits, among which TARM-1 ranked as top by exhibiting significant gca effects for five traits viz., number of pod bearing clusters per plant, number of pods per cluster, number pods per plant, total dry matter at harvest and seed yield per plot. This was followed by TARM-18 which was a good combiner for four traits viz., number pods per plant, number of pod bearing clusters per plant, total dry matter at harvest and seed yield per plot. The VC-1 was also a good general combiner with good mean performance for four traits viz., hundred seed weight, harvest index, seed yield per plant and seed yield per plot and all the three testers (TARM-18, TARM-1 and VC-1) were also resistant to powdery mildew disease.

Female parent Chinamung was good general combiner for five traits namely number pods per plant, number of pod bearing cluster per plant, total dry matter at harvest and seed yield per plant seed yield per plot with good per se performance than Pusa baisaki.

The study of sca effects across hybrids revealed that none of the hybrids showed significant positive specific combining ability effects for all the characters (Table 1). The cross, Chinamung×VC-1 exhibited significant sca effect for as many as five traits viz., Seed yield per plot (g), seed yield per plant (g), number of pod bearing clusters per plant, number or pods per plant and harvest index (%).

Table 1 Top ranking hybrids which exhibited significant sca effects, with their mean performance for different characters

Table 2 Mean sum of squares for detecting epistatic gene action for 12 characters in greengram (Vigna radiata (L.) Wilczek)

Table 3 Analysis of variance for sums and differences in respect of 12 characters in greengram (Vigna radiata (L.) Wilczek)

Table 4 Estimates of genetic parameters, dominance ratio and correlation co-efficient of sums and differences of 12 characters in greengram Vigna radiata (L.) Wilczek)

On the basis of present study, additive, dominance and epistatic gene effects contributing significantly in the inheritance of the characters, it can be suggested that improvement may be expected by exploiting the additive genetic variance first through pedigree method of selection and at the same time retaining the non-additive genetic variance in population. It is suggested to give enough weightage to individual yield components while selecting by pedigree method. The use of recurrent selection method and diallele selective mating can help in utilizing the all the three type of gene effects (additive, dominant and epistatic).

Material and Methods
Two adopted varieties namely Chinamung and Pusa baisaki were crossed with ten selected diverse testers for powdery mildew viz., Vaibhav,TARM-1,TARM-2 and TARM-18 (resistant to powdery mildew from BARC, Mumbai) DMG-1030 (resistant) and Meha (susceptible from IIPR, Kanpur), KGS-83 (advance breeding line), BPMR-1 (tolerant) and VC-1 (resistant exotic line, AVRDC Taiwan) and BPMR-145  in a line x tester fashion and resulting 20 F₁­s along with their parents were grown in randomised block design with three replications at  Main Agriculture  Research Station, College of Agriculture, University  of Agricu- ltural  Science, Dharwad in 2009. Five competitive plants were randomly selected from each replication for recording the observations for seed yield and its 11 component traits (Table 5). The parents  were also screened for powdery mildew disease by growing them separately without  any protection the data were subjected to analysis of variance (Panse and Sukhateme, 1976) and combining ability analysis (Kempthorne, 1957) and nature of gene action was detected as additive, dominance and epistatic component as method suggested by Kersay and Jinks (1968) and Jinks et al (1969).

Table 5 List of parents which exhibited significant gca effects with their per se performance

References
Barad H.R., Pithia M.S. and Vachhani J.H., 2008, Heterosis and combining ability studies for economic traits in genetically diverse lines of mungbean (Vigna radiata (L.) Wilczeck), Legume Res., 31(1): 68-71

Dethe A.M., Patil J.V., and Misal A.M., 2008, Combining ability analysis in mungbean, J. Food Legumes, 21(3): 200-201

Gawande V.L and Patil J.V., 2005, Gene action for seed yield and its components in mungbean [Vigna radiata (L.) Wilczek], J. Maharastra Agric. Univ., 30(3): 285-288

Jinks J.L., Perkins J.M., and Breese E.L., 1969, A general method of detecting additive, dominance epistatic variation for metrical traits. II. Application to inbred lines, Heredity,24: 45-57
http://dx.doi.org/10.1038/hdy.1969.4

Kearsey M.J., and Jinks J.L., 1968, A general method of detecting additive, dominance and epistatic variation for metric traits I Theroy, Heredity, 23: 403-409
http://dx.doi.org/10.1038/hdy.1968.52

Kempthorne O., 1957, An introduction to genetic statistics, The IOWA State University Press (Eds.), John Wiley and Sons, Inc., New York, pp: 545

Khan M.G., Ahmad W., Khattak G.S., Sirajud Din and Ahmad H., 2007, Studies on detection of epistasis and estimates of gene effects for secondary yield characters in Vigna radiata (L.) Wilczek, Sarhad J. Agric., 23(4): 1013-1017

Mansuria C.A., and Joshi B.C., 1994, Combining ability analysis for polygenic traits in greengram, Gujarat Agric. Univ. Res. J.,19: 78-81

Panse V.G., and Sukhatme P.V., 1967, Statistical methods for agricultural work,Indian Council of Agric.Res., New Delhi, pp.167-174

Patil A., Kajjidoni S.T., and Salimath P.M., 2003, Genetic analysis of morpho-physiological traits in green gram, Karnataka J. Agric.Sci.,16: 542-547

Patil A., and Kajjidoni S.T., 2005, Gene action for morpho – physiological traits in green gram [Vigna radiata (L.) Wilczeck], National J. Pl. Improv., 7(1): 15-17

Singh V.K., Tyagi K.,Tomer A.K., Singh M.N and Nandan R. 2007, Gene action for yield and yield attributing traits in mungbean [Vigna radiata (L.) Wilczek], Legume Res., 30(1): 29-32