The extent of variability present in the bush cowpea genotypes was measured in terms genetic parameters viz., genotypic and phenotypic coefficients of variation, heritability in broad sense and genetic advance along with mean and range of different characters are presented in Table 2.

In the present investigation, for majority of the characters, magnitude of GCV and PCV were closer, suggesting greater contribution of genotype rather than environment.  So, the selection can be very well based on the phenotypic values. Such a closer PCV and GCV for different characters were earlier reported by Girish et al (2006). High values of PCV with corresponding high values of GCV for plant height, pod weight, pod length, pods per plant and yield per plant which indicates that there exist high genetic variability and better scope for improvement of these characters through selection. Similar results were obtained for pod weight and yield per plant by Vidya et al (2002), and Sobha and Vahab (1998), pods per plant by Selvam et al (2000), Narayankutty et al (2003), plant height by Malarvizhi et al (2005), Girish et al (2006) and pod length by Mathura Rai et al (2004), Sobha and Vahab (1998). From the foregoing discussions, it is clear that the characters viz., pod weight, pods per plant, pod length and yield per plant offer good scope for selection in bush cowpea.

The variability existing in a population is the sum total of heritable and non-heritable components.  A high value of heritability indicates that the phenoltype of that trait strongly reflects its genotype. In the present investigation, the heritability estimates were high for all characters studied except primary branches per plant. High heritability for yield and yield attributes in bush cowpea were reported by many workers (Tyagi et al., 2000; Venkatesan et al., 2003; Suganthi and Murugan, 2008). 

Heritability estimates were high for all the characters studied. The values were especially high for plant height, Days to first harvest, pod length, pod girth, pod weight, yield of vegetable pods per plant and number of pods per plant. High heritability for vegetable pod yield and pod weight reported by Sobha and Vahab (1994) and Vidya et al (2002) supports the present findings. Further, similar to the present results, high heritability for number of pods per plant and pod length was reported by Anbumalarmathi et al (2005), Suganthi and Murugan (2007). High values of genetic advance as percentage of mean (> 20 %) were obtained in the present study for all the biometric characters studied except days to days to first flowering and first harvest.

In present study yield per plant, plant height, primary branches, pod length, pod girth pod weight and pods per plant recorded high heritability coupled with high genetic advance.  These results confirms the findings of Sobha and Vahab (1998) and Anbumalarmathi et al (2005) who reported high heritability coupled with high genetic advance for plant height, primary branches,  pod length, pods per plant and yield per plant. Johnson et al (1955) suggested that high heritability combined with high genetic advance is indicative of additive gene action and selection based on these parameters would be more reliable.

Materials and Methods
The experiment was carried out at Department of Olericulture, College of Agriculture, Vellayani (8°5' N latitude and 77°1' E longitude at an altitude of 29 m above mean sea level) during 2011-2012 with 22 bush cowpea genotypes. Soil type is a red loam belonging to Vellayani series, texturally classified as sandy clay loam. The trial was laid out in a randomized block design with three replications. Seeds were sowed at a spacing of 45 cm×30 cm. The crop received timely management practices as per the recommended package of practices to maintain a good population stand in the field.

The crop was maintained properly till last harvest and observations on growth, yield as well as yield contributing characters viz., plant height (cm), number of primary branches per plant, days to first flowering, days to first harvest, pod length (cm), pod girth (cm), pod weight (g), number of pods per plant and yield per plant (g) were recorded on five randomly selected plants in each plot at different stages of the crop. The analysis of variance was carried out and was used for calculating other genetic parameters. Genotypic coefficients of variation (GCV) and phenotypic coefficients of variation (PCV) were calculated as per the formula suggested by Comstock and Robinson (1952). Heritability in broad sense and expected genetic advance were calculated as per formula given by Allard (1960) and Johnson et al (1955) respectively.

Acknowledgements
The authors are highly grateful to the Department of Olericulture, College of Agriculture, Kerala Agricultural University, Vellayani, Thiruvananthapuram, Kerala for providing all necessary materials to carry out the present study.

Conflict of Interest
The authors declare that they have no conflict of interest.

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