Extent of Genetic Variability for Quantitative Traits in Indian Clusterbean Germplasm [Cyamopsis tetragonoloba (L.) Taub]

Clusterbean [Cyamopsis tetragonoloba (L.) Taub.] (2n=2x=14) is an under exploited legume belonging to family Fabaceae. It is short day self-pollinated crop (Undersander et al., 1991), commonly known as guar, chavli kayi, guari, khutti etc. The word “guar” has  derivation from the Sanskrit word “Gau-ahaar” which means cow food (Bhosle and Kothekar, 2010). Clusterbean is a versatile legume crop cultivated mostly as animal feed, green manure (Chudzikowski, 1971 and Siddaraju et al., 2010), green leaves as fodder, vegetable and cover crop (Arora and Pahuja, 2008). Clusterbean is a drought resistant, hardy, deep rooted annual arid legume. The powder made from husked clusterbean seeds is known as guar gum which finds use in drilling companies for making high viscosity water to extract shale oil and natural gas. Presently the Shale gas extracting companies are buying large quantity of guar gum from Rajasthan, Gujarat, Haryana and Punjab and it is grown as industrial crop for its endospermic gum (30-35%). Tender pods are nutritionally rich in energy (16 kcal), moisture (81 g), protein (3.2 g), fat (1.4 g), carbohydrate (10.8 g), Vitamin A (65.3 IU), Vitamin ‘C’ (49 mg), calcium (57 mg) and iron (4.5 mg) for every 100 g of edible portion (Kumar and Singh, 2002).
       
Vavilov (1951) considered India as the center of diversity for guar, although no wild species was reported in India. A fairly-large number of landforms and cultivars are available in India. The knowledge of genetic variability in the available germplasm is a pre-requisite for effective selection of superior genotypes (Chatale, 2015). It is also necessary to partition the observed phenotypic variability into its heritable and non-heritable components to understand the extent of influence on economically important traits and accordingly apply suitable selection method.

The experimental material consisted of 40 clusterbean genotypes were obtained from Pulses Research Station, S.D. Agricultural University, Sardarkrushinagar, Gujarat, India (Table 1).
 

       
These germplasm were evaluated in randomized complete block design with four replication at the Agronomy Instructional Farm, Chimanbhai Patel College of Agriculture, Sardarkrushinagar Dantiwada Agricultural University, Sardarkrushinagar, Gujarat during Kharif 2019. The sowing was done on 5^thJuly, 2019. Each genotype was accommodated in a single row of 4 m length with a spacing 45 cm between rows and 15 cm between plants. All the recommended production and protection practices were followed to raise the good crop of clusterbean. The observations on twelve quantitative traits viz., days to 50 % flowering, days to maturity, plant height (cm), number of branches per plant, number of clusters per plant, number of pods per plant, number of seeds per pod, pod length (cm), test weight (g), protein content (%), gum content (%) and seed yield per plant(g) were recorded at appropriate crop growth stage as suggested by Curtis et al., (2020). Five plants from each genotype were selected at random for recording observations except days to 50% flowering and days to maturity which were recorded on plot basis. After the harvest, 1000 matured and dried seeds were drawn from each germplasm and its test weight was recorded. Protein content (%) was estimated by Instalab 600 NIR analyzer and expressed in percentage whereas, gum estimation involves the extraction and purification of galactomannan, which is then alcohol precipitated, dried and weighted. A rapid and accurate method developed by Pablyana et al., (2009) was used. The data recorded for all the characters were subjected to analysis of variance as suggested by Panse and Sukhatme (1978). The coefficient of phenotypic and genotypic variation was calculated using the formula suggested by Burton (1952). Heritability in broad sense (h²BS) was calculated as per Allard (1961). The expected genetic advance as expressed in per centage of mean was calculated by the method suggested by Johnson et al., (1955).

The experimental material consisted of 40 clusterbean genotypes were obtained from Pulses Research Station, S.D. Agricultural University, Sardarkrushinagar, Gujarat, India. Among them some are indigenous collection, local collection and released varieties (Table 1).
       
The analysis of variance (Table 2) revealed highly significant mean square due to genotypes for all the characters studied, suggesting the presence of a sufficient amount of variability in the material used.
 

       
The estimates of GCV, PCV, h²BS, GAM are given in Table 2. The GCV % and PCV % were the highest for number of branches per plant followed by seed yield per plant, days to 50 % flowering and number of clusters per plant and plant height. That was indicating the presence of high variability in the population and therefore more scope for selection. Simple selection based on the phenotypes of these traits would be effective for bringing further improvement. These results are in accordance with the findings of Rishitha et al., (2019), Choyal et al., (2018) and Meghana et al., (2019) for the number of branches per plant, number of clusters per plant, seed yield per plant and Meghana et al., (2019) for days to flowering.
       
Moderate estimates of genotypic and phenotypic coefficient of variation were observed for days to maturity, test weight and number of pods per plant. While the lowest estimates of genotypic and phenotypic coefficient variation were observed for gum content, protein content, pod length and number of seeds per pod, thus indicating lesser variability in the population and lesser scope of selection. These results is in conformity with the findings of Santhosha et al., (2017) for test weight, Patel et al., (2018) for the number of pods per plant, Rishitha et al., (2019) for the number of seeds per pod and Panchta and Khatri (2017) for pod length.
       
In the present study, the differences between PCV and GCV were relatively low for all the traits indicating the lesser environmental influence on these characters.
 
In a general sense, heritability specifies the proportion of the total variability that is due to genetic causes or the ratio of genotypic variance to the total variance. It is a good index of the transmission of characters from parents to their offspring (Falconer, 1960). High heritability was recorded for characters such as days to maturity, number of branches per plant, days to flowering, gum content, seed yield per plant, plant height, pod length, protein content, test weight and number of pods per plant (Table 2) suggesting little environmental influence on these characters. These characters also showed lesser difference between PCV and GCV and thus selection based on the phenotype of these traits would be rewarding. The present findings are in accordance with results of Patel et al., (2018), Rishitha et al., (2019) and Meghana et al., (2019) for days to flowering, while Meghana et al., (2019) for days to maturity and number of branches per plant, Santhosha et al., (2017) for seed yield per plant, pod length and protein content, Shobiya et al., (2019) for plant height, Rishitha et al., (2019) for the number of pods per plant and test weight, Moderate heritability was found for the characters number of seeds per pod and number of clusters per plant. Similar type of results were reported by Kumar and Ram (2015) and Revathi et al., (2017). It indicates that PCV is higher than GCV; there is a little influence of environment on the expression of these characters. Selection for improvement of such characters will be rewarding.
       
The high heritability coupled with high genetic advance as per centage of mean was observed for traits viz., days to maturity, number of branches per plant, days to flowering, seed yield per plant, plant height and test weight, which indicates the preponderance of additive gene action governing the inheritance of this character and offers the best possibility of improvement through simple selection procedure. Similar results were reported in earlier findings of Rai et al., (2012), Vir and Singh (2015) and Reddy et al., (2019). High heritability coupled with moderate genetic advance was observed for number of pods per plant. As these traits are largely controlled by additive gene action simple selection may be practiced for improving them.
       
High heritability coupled with low genetic advance was recorded for traits such as gum content, number of seeds per pod and protein content. This could be attributed to lesser magnitudes of genetic variability present in these characters and therefore, phenotypic selection based on this trait may not yield dividends. However, these traits could be improved by inter-mating superior genotypes followed by selection in the segregating generations.

In the present study higher GCV, PCV, heritability coupled with high genetic advance was recorded for the traits such as number of branches per plant, seed yield per plant and days to 50% flowering, indicated the role of additive gene action. Hence, simple phenotypic selection from the existing germplasm is suggested for further improvement.