Combining Ability and Heterosis for Yield and its Contributing Characters in Okra ( Abelmoschus esculantus (L.) Moench)

Estimation of combining ability by line x tester analysis and magnitude of heterosis was conducted at Vegetable Research Farm, BHU, Varanasi, in a set of 8 parents (five lines and three testers) received from IIVR Varanasi by making 15 cross combinations evaluated during summer and kharif 2009 in RBD with three replications. The data on nine characters viz. plant height, number of primary branches, days to first flowering, total number of fruit plant -1 , fruit length, fruit girth, fresh fruit weight, internodal length and yield plant -1 were utilized for the present study. On the basis of GCA effects across nine characters, Arka Abhay, VRO-6, Hissar Unnat and Punjab Padmini were identified as most promising parents for improving number of fruits plant -1 , fruit girth and days to 50% flowering. The most promising crosses showing significantly positive SCA effects and standard heterosis for fruit yield were Arka Abhay x Parbhani Kranti, Hissar Unnat x Punjab Padmini, VRO-6 x Parbhani Kranti and VRO-6 x Arka Anamika. These crosses should be exploited for further advancement in breeding programme for HYVs and early maturity, simultaneously.

Okra is a green vegetable with immense nutritive value being grown in tropical, subtropical and warm temperate region around the globe. India has emerged as second largest producer of vegetables after China, contributing about 133.73 mt from 7.98 mha having 16.7 t/ha productivity in -10 (NHB database, 2010. India is the largest producer of okra having productivity 10.6 t/ha (NHB database, 2010). It is commonly known as Lady's finger, 'gumbo' or 'bhindi'. It originated from South Africa near Ethiopia in (De Condolle, 1883;Vavilov, 1951). It is extensively cultivated throughout India mainly in Indo-Gangetic plains during summer and rainy seasons for its large, slender and immature green fruit. Matured pods and stem containing crude fibres are used in paper industry and purifying sugarcane juice in preparation of jaggary in sugar industry (Singh, 1989;Akhtar et al., 2010). It occupies good place in kitchen garden having two crops per year along with additional medicinal attributes e.g. anti-ulcer and relief in gastrointestinal ulcer by neutralizing the digestive acids (Wammanda, 2010). In Mediterranean countries, the oil of okra seeds is used for cooking purpose. Okra is an often cross pollinated crop as the natural crossing occurs in this crop up to a range of 4-19% (Purewal andRandhawa, 1947 andKumar et al.2010). Emasculation and pollination events are easier due to large flower and monoadelphous stamens. It is essential to mitigate the future thrust of higher productivity by estimating the extent of combining *Corresponding author email: karstav@yahoo.com ability in lines and crosses for choosing lines of best general combining ability (GCA) and crosses of specific combining ability (SCA) (Sprague and Tatum 1942). GCA reveals the preponderance of additive gene effects while SCA reveals the intraallelic (dominance) and inter-allelic interactions (epistasis).
For judicious application of heterotic vigour, it is imperative to assess the magnitude of genetic differences among the parents involved in the crosses, because high genetic diversity between parents shows maximum heterotic response (Moll and Stuber, 1976). Through Line x Tester analysis and heterosis estimation, our aim of current study was to identify best combiner genotypes and their crosses on the basis of GCA and SCA variances and effects on standard heterosis.

Materials and Methods
The present investigation was carried out during summer and kharif, 2009 at the Vegetable Research Farm, BHU, Varanasi (U.P.) which is situated at 250152 N latitude and 63003¢ E longitude, having elevation of 129.23 m above mean sea level. The genotypes under current study were procured from the germplasm collection of the Indian Institute of Vegetable Research, Varanasi, India and maintained through selfing. All the genotypes were grown in a crossing block during summer season 2009. Crosses were attempted in line x tester fashion involving five parents as male and three parents as females (Table  1). Seeds were harvested cross wise to raise next crop in kharif season. The seeds of 15 F 1s crosses were sown in Randomized Block Design with three replications. The parents and F 1s were shown in plots having rows of 20 plants with a spacing of 60x45cm. Recommended agronomic package and practices were applied to raise a healthy crop.
Data were recorded for nine yield and its contributing characters in okra viz. plant height (cm), number of primary branches plant-1, days to first flowering, total number of fruits plants-1, fruit length, fruit girth, fresh fruit weight, internodal length and Yield plant -1. Data of ten plants of each genotype and its crosses were averaged replication wise and mean data was used for statistical analysis. The analysis of variance (ANOVA) for RBD was estimated crosswise according to Panse and Sukhtame (1989) and ANOVA for line x tester analysis was done according to Kempthorne (1957) and Singh and Chaudhary (1985).
Heterosis over better parent and standard/check variety (VRO-6) was estimated Heterobeltiosis = F 1 -BP, Standard = F 1 -Check BP Heterosis Check Where, F1= mean performance of cross, BP= mean performance of better parent and Check = mean performance of standard variety and significance of heterosis is tested with the help of standard error using 't' test.

ANOVA of combining ability analysis for yield and its contributing characters
Highly significant variances due to treatment were obtained for all the characters studied, except fruit girth that showed significant deviation (Table  2). Further, treatment variance was partitioned into Table 1. Parents and their crosses involved in Line X Tester analysis. Variances due to line x tester were significant for all the characters. There were no significant variances due to male and female for all the characters except yield plant -

1.
Further, variances due to female x male were significant for all the characters, except fruit girth.

Estimate of GCA effect of Parents
The GCA effect reveals genetic worth of each parent. Negative significant GCA effect for plant height and days to first flowering are well exploited for further increment in yield and earliness (Table 3). The line VRO-5 and among testers Parbhani Kranti and Arka Anamika showed negative significant GCA effects for plant height. Among lines, Arka Abhay showed positive significant GCA effects for number of primary branches. Lines Arka Abhay and VRO-6 showed negative significant GCA effect for days to first flowering whereas among testers Punjab Padmini. Arka Abhay and Hissar Unnat exhibited significant positive GCA effect for total number of fruits plant -1 while among testers, Punjab Padmini.
Fruit length is an important yield trait, which is directly valuable from marketing point of view. Three lines, namely Arka Abhay, VRO-5 and VRO-6 represented significant positive GCA effect while among testers Parbhani Kranti. The line VRO-6 showed significant positive GCA effect for fruit weight and among testers Parbhani Kranti. Three lines Arka Abhay, Hissar Unnat and VRO-6 represented positive significant GCA effect for yield plant-1, however among testers Parbhani Kranti and Punjab Padmini. The lines, Arka Abhay and VRO-6 emerged as good general combiner for yield plant-1, average  (2)

Estimation of SCA effect of crosses
The ideal cross combination to be exploited is one where high magnitude of SCA effect is present in addition to high GCA effect in both or at least one 33 of the parents. The SCA effects of 15 F1s hybrids with respect to nine yield contributing characters are represented in Table 4. Out of fifteen F1 hybrids, seven cross combinations displayed negative   significant SCA effects for plant height, ranging from -13.53 (VRO-6 x Punjab Padmini) to -1.76 (VRO-5 x Punjab Padmini). Five crosses displayed negative significant SCA effect for days to first flowering that was highest for Arka Abhay x Arka Anamika (-4.64) and lowest for Hissar Unnat x Arka Anamika (-1.40). Six cross combinations exhibited positive significant SCA effect for total number of fruits ranging from 0.66 (Pusa Makhamali x Arka Anamika) to 2.40 (Arka Abhay x Punjab Padmini). Hissar Unnat x Punjab Padmini cross (1.36) exhibits highest positive significant SCA effects for fruit length. Only cross combination, Pusa Makhamali x Punjab Padmini (0.14) exhibited positive significant SCA effect for Fruit girth. Highest positive significant SCA effect for fruit weight was displayed by VRO-6 x Punjab Padmini (1.21), followed by VRO-5 x Parbhani Kranti (0.86). Out of fifteen crosses, five showed positive significant SCA effect for Yield plant-1 ranging from 1.73 (Pusa Makhamali x Parbhani Kranti) to 11.60 (Arka Abhay x Punjab Padmini) as similar reported by Dhanker and Dhanker (2001) Kumar et al.(2006) and Weerasekara et al.(2008). For all the nine characters studied, the crosses with significant SCA effects involved parents with high x high, high x low, low x high or low x low GCA effects. The SCA effects are found to be significant for seed yield and yield components. Five cross combinations, Arka Abhay x Punjab Padmini, VRO-6 x Parbhani Kranti, VRO-6 x Arka Anamika, Pusa Makhamali x Parbhani Kranti and Hissar Unnat x Punjab Padmini were recorded as good specific combiner for fresh fruit yield plant-1 due to positive significant SCA effect as well as negative significant SCA effect for days to first flowering and plant height which is desirable for earliness and may be important for yield as well. On the basis of specific combining ability effect across nine characters, Hissar Unnat x Punjab Padmini could be considered as most promising parent, as it was good specific combiner for plant height, yield plant-1, total number of pickings, total number of fruit plant-1 and fruit length. Of the fifteen crosses, Hissar Unnat x Punjab Padmini appeared as specific combiner for six characters, whereas VRO-6 x Parbhani Kranti for five and Arka Abhay x Punjab Padmini for four characters. The specific combining ability of parental combination is most valuable information to a plant breeder to develop a successful hybrid. In present investigation VRO-6 x Parbhani Kranti and Arka Abhay x Punjab Padmini, appeared to be cross combination with better SCA, therefore, these combination could be exploited in hybrid breeding programme.