​Genetic Diversity for Seed Yield and its Components in Clusterbean [Cymopsis tetragonaloba (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 and khutti etc. Vavilov (1951) suggested India as the geographic center of variability of guar, though no wild species was reported in this region. The word “guar” represents a derivation from the Sanskrit word “Gaaahar” which means cow food or fodder of livestock (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 legume crop. clusterbean is one of the most important and potential vegetable cum industrial crop grown for its tender pods for vegetable and for 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).
       
D² statistics developed by Mahalanobis (1928) provides a measure of magnitude for divergence between two genotypes under comparison. For broadening the genetic base of cultivars, the genetic diversity present in cultivated and wild relatives must be explored (Mishra et al., 2010). Generally, diverse germplasms are expected to give high hybrid vigor (Harington, 1940) and hence, it necessitates studying genetic divergence among the existing varieties and genotypes for the identification of parents for hybridization programme. The information on genetic divergence of various traits particularly of those that contribute to yield and quality would be of most useful in planning the breeding programme. The D² statistics is a useful multivariate statistical tool for effective discrimination among various genotypes on the basis of genetic diversity (Murthy and Arunachalam, 1966). Therefore, the present study was under taken to estimate the genetic divergence among 40 genotypes of cluster bean on the basis of 12 different yield and yield related traits in cluster bean.

The experimental material consisted of 40 clusterbean genotypes evaluated in randomized block design with four  replication was conducted at Agronomy Instructional Farm, Chimanbhai Patel College of Agriculture, Sardarkrushinagar Dantiwada Agricultural University, Sardarkrushinagar during kharif, 2019. The sowing was done on 5^th July, 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 crop production and protection practices were followed to raise the good crop. The observations on twelve metric traits viz., days to 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. Five competitive plants from each genotype were selected at random for recording observations except days to 50% flowering, days to maturity and test weight which are recorded on plot basis. Mahalanobis (1928) D² statistic was used for assessing the genetic divergence between different populations. Grouping of the genotypes in different clusters was done by using Tocher’s method (Rao, 1952). The inter-cluster distance was calculated by measuring the distance between clusters I and cluster II, between clusters I and cluster III, between clusters II and cluster III and so on. Likewise, one by one cluster was taken and their distances from other clusters were calculated.

The quantitative assessment of genetic divergence was made by adopting Mahalanobis’s D² statistics for yield and its contributing traits. Wilks test showed highly significant differences among the genotypes for the aggregate effect of 12 characters which suggested the existence of considerable divergence in the material. This observation confirms results of Goudar et al., (2017).
       
Distribution of genotypes into clusters grouping of the genotypes was carried out by following the Tocher’s method (Rao, 1952) with the assumption that the genotypes within the cluster have smaller D² values among themselves than those from groups belonging to different clusters. In all, nine clusters were formed from 40 genotypes. The distributions of genotypes into 9 clusters are presented in Table 1. The cluster I was the largest one contained twenty-one genotypes. Cluster II has eight genotypes, cluster III and VII contain two genotypes, cluster IV contains three genotypes and clusters V, VI, VIII and IX had a single genotype. Similar findings of Goudar et al., (2017), Mishra et al., (2019) and Remzeena et al., (2021) corroborated that the distribution of genotypes from different eco-geographical regions into clusters was at random, indicating geographical distribution does not necessarily exhibit genetic divergence. It was evident from the study that, there was considerable degree of variability for seed yield and its component characters. A few of the most promising genotypes for seed yield were GG 1, GG 2, IC-41057, IC-311444 and IC-113432. The intra and inter-cluster D² values among nine clusters are given in Table 2 and Fig 1. Intra cluster average D² values ranged from 0 to 154.37. Among the clusters, cluster II had the maximum intra-cluster distance (154.37), followed by cluster VII (D²=151), while the minimum intra-cluster distance was observed for cluster IV (D²=93.98). The zero intra-clusters distance was observed for clusters V, VI, VIII and IX (D²=0). This four clusters V, VI, VIII and IX was a solitary cluster. The present results are in conformity with the results of past worker Goudar et al., (2017). and Wankhade et al., (2017).






       
The maximum inter cluster distance was recorded between cluster VII and cluster I× (D²=1408.24) followed by that between I and IX (D²=962.95), while the minimum inter-cluster distance was observed between clusters III and VI (D²=157.16). Cluster I had the largest distance from cluster I× (D²=962.95) followed by cluster VIII (D²=576.22), cluster VII (D²=483.95) and cluster IV (D2=37.13). The D value between cluster I and III (D²=218.82) and cluster I and V (D²=225.06) were comparatively of two magnitude. The distance between clusters II and VII (D²=845.40) was highest followed by cluster I× (D²=758.28) and cluster VIII (D²=649.75). The closest cluster from cluster II was cluster V (D²=215.12). The cluster I× (D²=773.96) was far away from cluster III followed by cluster VIII (D²=405.54) and cluster VII (D²= 343.69). Cluster VI (D²= 157.16) was nearest to cluster III. Cluster IV deplicated maximum distance from cluster VII (D²= 576.71), which was followed by cluster I× (D²= 299.44). Whereas, it had minimum D² value with cluster V (D²= 187.41). Cluster VIII (D²= 677.62) and cluster I× (D²= 1408.24) were distantly placed away from cluster VII. Inter-cluster distances were higher than intra-cluster distances which indicated the existence of substantial diversity among the genotypes. The same results were also obtained by Goudar et al., (2017), Wankhade et al., (2017) and Remzeena et al. (2021). The selection of parents for crossing from divergent clusters may result in heterotic expression for yield and quality traits.
       
The mean performance of clusters for twelve characters is presented character wise in Table 3. Wider ranges of mean values among the clusters were recorded for different traits. The cluster I and II had the highest mean values and desirable rating for earliness on the basis of days to  maturity (74.49 days) and days to flowering (29.75). The cluster III had the highest mean values and desirable rating for protein content (25.48%). The cluster V had the highest mean values for plant height (85.18). The cluster VII had the highest mean values for the number of clusters per plant (6.77), number of branches per plant (5.57), number of pods per plant (16.53), seed yield per plant (4.30 g), test weight (3.30 g), gum content (28.72%) and number of seeds per pod (7.82). Cluster VIII had a desirable rating for pod length (5.64 cm). The cluster I× had a desirable rating for dwarfness (58.42 cm). Similar findings also observed by  Remzeena et al. (2021).


       
Relative Contribution of each character towards diversity are presented in Table 4 and Fig 2  Among all the characters, number of branches per plant (26.41%) contributed maximum to the diversity by taking the first rank 206 times out of 780 combinations, followed by gum content (20.38%) with 159 times, days to maturity (19.10%) with 149 times, days to flowering (13.33%) with 104 times. While, plant height (6.67%) with 52 times, pod length (5.38%) with 42 times, protein content (5.38%) with 42 times and seed yield per plant (2.18%) with17 times, number of clusters per plant (0.13%) with 1 time, number of seeds per pod (0.13%) with 1 time and test weight (0.89%) with 7 times contributed minimum towards total genetic divergence. While characters like the number of pods per plant contributed null towards the total genetic divergence as depicted in Table 4.

Ranking based on both mean performance and contribution of characters towards divergence resulted in the identification of GG 1, GG 2, IC-41057, IC-311444 and IC-113432 as genotypes and can be utilized as parents in the selection programme for the improvement of seed yield.