Combining Ability Analysis and Estimates of Heterosis for Grain Yield and Nutritional traits in Finger millet ( Eleusine coracana (L.) Geartn)

Finger millet ( Eleusine coracana (L.) Gaertn.) is an important subsistence cereal in parts of Africa and South Asia. Finger millet is commonly called as “nutritious millet” as the grains are superior to many cereals providing fair amount of protein, minerals and vitamins in abundance to the people. The parental values of different traits in different crosses depend on their potential and their combining ability in different combinations. The concept of general and specific combining abilities is useful to characterize the hybrids in the breeding programme and also elucidate the nature and magnitude of gene actions involved in the trait of interest. Two hybrids namely CO (Ra) 14 x PR 202 and GPU 28 x K 7 were found to be superior for grain yield and other major yield components along with the protein content based on per se performance, sca effect and standard heterosis.

Finger millet is the primary food for millions in dry lands of eastern and central Africa and southern Asia. The most important development in plant breeding in recent years has been the use of heterosis or hybrid vigour in many self pollinated species and has been the object of considerable study as a mean of increasing productivity of wheat and other cereals (Malik et al., 1986). Ragi being a self pollinated crop, exploitation of heterosis is the best option to further improve the grain yield and nutritional characters. Evidences are available to confirm the potential use of heterosis and in self pollinated crops (Parashuram et al., 2011). Exploitation of variability created by hybridization through recombination breeding is the next major approach adopted in finger millet improvement programme (Kadam et al., 2008). Among the several biometrical methods developed to identify superior parents for heterosis breeding, the line x tester analysis has received considerable attention. It is a technique employed to gain information on hybrid vigour, combining ability and nature of gene action from the study of first generation itself. Combining ability analysis of cultivars is thus important to exploit the relevant type of gene action for a breeding programme. Combining ability estimates can be used to evaluate the number of promising lines in F1 and F 2 generations, which is quite helpful in selecting the potential parents for hybridization (Hennawy, 1996;Iqbal and Chowdary, 2000). It also helps in identifying the parents suitable for hybridization programme and deciding suitable the easiest ways of commercial exploitation of genetic *Corresponding author email: saviagri @ gmail.com potential breeding methodology (Senthil et al., 2005). Though per se performance of parental lines provides clues, reliable information on the magnitude of heterosis for yield and yield attributing traits are of more helpful in selecting appropriate parents and desirable cross combinations for the exploitation of hybrid vigour (Shailaja et al., 2010). Therefore, the present study was, undertaken to determine the combining ability, the extent of relative heterosis, heterobeltiosis and standard heterosis in fingermillet and to identify the most heterotic hybrids.

Materials and Methods
The experiment was conducted in the Department of Millet, Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural University, Coimbatore, during 2009 -2011. The experimental material consisted of ten parents and twenty one hybrid combinations obtained by crossing seven lines (female) viz., CO (Ra) 14, RAU 8, PES 110, VR 708, GPU 28, GPU 48 and OEB 259 and with a set of three testers (male) viz., PR 202, KM 252 and K 7 in line x tester mating design (Kempthorne,1957). The F1's were raised in a randomised complete block design (RCBD) with three replications along with the parents during kharif, 2010. The observations on three randomly selected competitive plants for parents and hybrids were recorded for days to 50 per cent flowering, plant height (cm), number of productive tillers per plant, number of fingers per ear head, longest finger length (cm), thousand grain weight (g), grain protein (%), iron and zinc contents (mg/100g), harvest index (%), single plant dry fodder yield (g) and single plant grain yield (g). Heterosis value was calculated by using the overall mean of each parent and hybrid in all three replications for each character. Relative heterosis was estimated as the percent deviation of the F1 hybrid from its mid parental value. Heterobeltiosis for each character in each hybrid combination was expressed as per cent increase or decrease of F1 value over better parental value. Standard heterosis was estimated as difference between the mean of the F1 and that of the standard check CO (Ra) 14.

Results and Discussion
The results revealed that among the lines, CO(Ra)14 was superior for two important yield  (Table 1). Similar results were reported in finger millet by Ganapathy et al. (2011). The line, GPU 28 showed high per se performance along with high gca effects for days to 50 per cent flowering, plant  (Table 3). Similar results were also given by Priyadharshini et al. (2011).
The early maturing varieties are desirable in finger millet under rainfed condition. The cross, VR 708 x K 7 was the most promising combination for early duration since it showed highly significant negative heterosis of all the three types of heterosis (Table 2). Dwarf varieties are highly favourable as they confer resistance to lodging and also preferred for mechanization. Hence, negative heterosis for plant height is utilized in finger millet. The hybrid, OEB 259 x PR 202 and RAU 8 x PR 202 showed highly significant negative heterosis for all the three types of heterosis for plant height. The hybrid, OEB 259 x KM 252 showed highly significant negative relative heterosis and standard heterosis for plant height.
For number of productive tillers per plant, the hybrids VR 708 x K 7 and GPU 28 x K 7 showed highly significant positive heterosis of all the three types of heterosis. The hybrid, CO (Ra) 14 x PR 202 recorded highly significant standard heterosis for productive tillers per plant. Regarding number of fingers per ear head, none of the hybrids showed significant heterosis for any of the three types of heterosis by which it is inferred that heterosis could not be exploited for improving the finger number per ear head. Similar results were reported by Priyadharshini et al. (2010). Alternatively, number of productive tillers per plant and test weight of the grains had to be chosen for productivity enhancement (Parashuram et al. 2011).
In case of thousand grain weight, the hybrid, GPU 28 x KM 252 showed highly significant positive heterosis for all the three types of heterosis (Table 3). The hybrid, OEB 259 x PR 202 recorded highly significant positive heterobeltiosis and standard heterosis. For grain protein content, three hybrids viz., CO(Ra)14 x PR 202, CO(Ra)14 x KM 252 and CO(Ra)14 x KM 252 were found to be significant for all the three types of heterosis. These results confirmed the findings of Priyadershini et al. (2010) and Ganapathy et al. (2011). In case of iron content, the hybrid, VR 708 x KM 252 recorded significant positive heterosis for all the three types of heterosis.
For harvest index, none of the hybrids showed significant heterosis for any of the three types. For single plant dry fodder yield, two hybrids viz., GPU 28 x K 7 and VR 708 x PR 202 were found to be significant for all the three types of heterosis. In case of single plant grain yield, GPU 28 x K 7 recorded significant positive heterosis in all three types of heterosis. Similar observation has been reported by Sumathi et al. (2005).
Selection of hybrids combining superior per se performance, sca effect and heterosis is desirable for breeding programmes to get satisfactory results (Sumathi et al., 2007). In the present investigation, CO(Ra)14 x PR 202 was identified as the superior hybrid as it recorded high magnitude of standard heterosis for single plant grain yield, number of productive tillers per plant, seed protein content and single plant dry fodder yield with high sca effect and per se performance for many of the traits studied. The hybrid, GPU 28 x K 7 also recorded high standard heterosis, sca effect and high per se for number of productive tillers per plant, fodder yield and single plant grain yield. This was in agreement with the findings of Priyadharshini et al. (2010). Similar results of per se performance, sca effect and standard heterosis were used to identify as the best hybrids for grain yield by Shailaja et al. (2010). Gupta and Kumar et al. (2009) reported higher heterosis for grain yield for finger millet. Increasing the yield potential is an ultimate objective for plant breeders. In the present study, two hybrids viz., CO (Ra) 14 x PR 202 and GPU 28 x K 7 showed favorable heterosis of all the three types for grain yield and hence may be utilized in future finger millet yield improvement.