Diversity Analysis for Seed Yield and its Component Traits among Faba Bean (Vicia faba L.) Germplasm Lines

Faba bean (Vicia faba L.) is one of the oldest cool season food legume crops in the world. It stands next to soybean (Glycine max L.) and pea (Pisum sativum L.) in respect to area and production (Mihailovic et al., 2005). It is popularly known as broad bean, horse bean, wonder bean, English bean, field bean, tick bean, winter bean, pigeon bean and Bakla in India. It is facultative cross-pollinated diploid (2n=2x=12) plant able to grow in diverse agro-climatic conditions (Kaur et al., 2014). Faba bean contains 22-24% protein constituting about 79% globulins, 7% albumins and 6% glutelins which is higher than the many other food legume crops (Burstin et al., 2011). It is used as human food in developing countries and also as animal feed in developed countries, as far as India is concerned, it is categorized as underutilized legume (Singh et al., 2010).
        
Assessment of genetic diversity is the fundamental rule of any crop breeding programme. A throughout knowledge of existing genetic variation among seed yield and its component traits is essential for developing high yielding varieties in faba bean. Study of genetic divergence plays a central role in selection of most diverse parents in hybridization programme for more heterotic response, more chances of better transgressive segregants in segregating generations and minimization of duplicates in germplasm conservation. For effective breeding strategy, variability, heritability and genetic advance is in prime importance for analysing the relative contributions of genetic and non-genetic factors to total phenotypic variances in a population. The degree of genetic variability can reflect the level of genetic progress in crop breeding. There is constant search for new diverse genetic resources for improvement and stabilization of faba bean yield as well as quality of produce. From above point of view, the present investigation was planned to assess the genetic diversity in faba bean germplasm.

The present investigation was carried out on 80 faba bean germplasm lines (Table 1) selected from MAP (Medicinal, Aromatic and Potential Crops) Section, Department of Genetics and Plant Breeding, CCS Haryana Agricultural University, Hisar, Haryana, India. The experiment was conducted in a randomized block design (RBD) with three replications at Research Farm of Department of Genetics and Plant Breeding, CCS Haryana Agricultural University, Hisar during Rabi, 2015-16.
 

        
The 10 quantitative traits were used to assess the genetic variability parameters and study of genetic divergence viz., days to 50% flowering, days to maturity, plant height, number of branches/ plant, number of clusters/ plant, number of pods/ plant, pod length, number of seeds/ pod, 100 seed weight and seed yield/ plant. Genotypic and phenotypic coefficients of variation (GCV and PCV) were estimated as per the method suggested by Burton and Devane (1953); heritability and genetic advance by Hanson et al., (1956) and Johnson et al., (1955), respectively; Hierarchical Euclidean cluster analysis by Mahalanobis D² statistic (Mahalanobis, 1936) based on minimum genetic distance using Tocher’s method as described by Rao (1952). Average intra- and inter-cluster distances were determined using INDOSTAT software as suggested by Singh and Chaudhary (1977). Similarly, regression analysis evaluated by Lush (1940) and principal component analysis (PCA) by Kaiser (1958) and Jeffers (1967) using SPSS software 2.0.

In the present investigation, PCV was not much higher than their corresponding GCV indicated the less influence of environmental factors on the expression of seed yield and its component traits. The GCV and PCV were observed high for 100 seed weight, seed yield/ plant and number of clusters/ plant indicated the presence of wide variations on these traits. High heritability coupled with high genetic advance were observed for traits viz., days to 50% flowering, plant height, number of branches/ plant, number of clusters/ plant, pod length, number of pods/ plant, 100 seed weight and seed yield/ plant that these traits are amenable for making efficient selection as well as combination breeding for improvement in seed yield. Similar findings were reported by findings of Ahmad (2016) and Tomas et al., (2016). The high GCV and PCV coupled with high heritability and genetic advance were found for traits such as 100 seed weight, number of clusters/ plant and seed yield/ plant, therefore, these traits could be used for selection of parents as well as genotypes of segregation generations in future breeding programme (Table 2).
 

 
Mahalanobis D² cluster analysis based on Tocher’s method grouped 80 faba bean germplasm lines into seven non-overlapping clusters indicated the significant amount of genetic diversity existed among germplasm lines (Fig 1). Dendrogram showing clustering pattern of faba bean germplasm lines using 10 quantitative traits in Fig 1. It revealed that the cluster IV (22) had highest number of genotypes followed by clusters I (15), III (14) and II (11), whereas, lowest number in clusters V, VI and VII (each with six genotypes). The results are broadly in agreement of report of Sharifi and Aminpane (2014) and Rebaa et al., (2017).
 

        
The intra- and inter-cluster distances among seven clusters were presented in Table 3 which exhibited maximum intra-cluster distances for cluster VI (3.964) followed by cluster VII (3.603) and minimum for cluster III (2.529) and VI (2.513), whereas, maximum inter-cluster distances between cluster VI and I (7.29) followed by cluster VI and III (6.80) and minimum in between cluster IV and VI (6.31). The result displayed that the inter-cluster distances were more than their intra-cluster distances which indicated the presence of ample amount of genetic variations between inter-clusters than the narrow variations within cluster. The genotypes found in the clusters I, III, IV and VI were genetically more diverse than the other clusters. The genotypes of these clusters could be used in hybridization programme which is expected to release better segregants for respective traits of clusters in segregation generations through recombination and transgressive breedings. Similar result was reported by Kumar et al., (2016) among 65 faba bean genotypes.
 

        
The cluster mean values in Table 4 shown considerable difference among seven clusters for various seed yield and its component traits viz., lowest mean values for days to 50% flowering (48.489), days to maturity (149.133) and plant height (87.266) were observed in cluster I, whereas, highest for branches/ plant (5.142), clusters/ plant and pods/ plant (56.344) in cluster II; similarly for seed yield/ plant (110.923), pod length (8.332) and number of seeds/ pod (3.871) in cluster VI. Comparative study of cluster mean values suggested that clusters II and VI had highest cluster means for seed yield and its contributing traits, therefore, these clusters may be considered superior for selecting promising parents in hybridization programme. These findings are broadly in agreement from the finding of Chaieb et al., (2011). The promising faba bean genotypes identified from both the divergence and cluster mean analysis were EC-591828, EC-628922, ET-3104, ET-3128, ET-3131 and ET-4105 from cluster VI; EC-628957, ET-3160 and ET-4107 from cluster V; EC-628929 and EC-628955 form cluster VII; HB-82 and HB-85 from cluster II, and EC-628940 from cluster IV based on various seed yield and its component traits. The genotypes from most diverse clusters I, IV and VI  together with higher cluster mean analysis could be used for hybridization programme for more heterotic response and better segregants in segregating generations.
 
 

The diverse and superior genotypes identified from different clusters on the basis of various quantitative traits (Table 5). These genotypes could be used in future faba bean breeding programme for selection, hybridization and recover of transgressive segregants with highest yield potential.
 

 
Principal component analysis (PCA)
 
PCA provides information related to extent of genetic diversity in germplasm and also helps in identification and ranking of genotypes and important economic traits contributing in genetic diversity. In present investigation, PCA was performed for yield and its component traits in faba bean in which principal components (PCs) greater than one Eigen value were selected for interpretation. Out of 10, only two PCs exhibited greater than 1.0 Eigen value viz., 4.305 and 2.275, respectively and explained 65.788% variability of the total variation among 80 faba bean germplasm lines (Table 6). Therefore, these two PCs were given important for further explanation and shared 43.053% and 22.735% of total variability, respectively (Table 6). The PC 1 accounted for maximum proportion of total variability (43.053%) in yield contributing traits which could be used for selection of faba bean genotypes in future breeding programme for developing superior hybrid.
 

        
Further, principal factor analysis was carried out with Varimax roation method (Kaiser, 1958) to derive interaction among yield component traits with respective principal factors (correlation values > ±0.5). Principal factor-1 (PF-1) mostly correlated to yield contributing traits viz., 100 seed weight, pod length, seed yield/ plant, days to 50% flowering, days to maturity, number of seeds/ pod and plant height, whereas, principal factor-2 (PF-2) dominated by number of pods/ plant and number of clusters/ plant  (Table 7). Thus, PF-1 had shown maximum genetic variation to seed yield and its component traits which could be used for selection of promising faba bean genotypes to bring out rapid improvement in yield. Screen plot explained the percentage of variation associated with each PC obtained by drawing a graph between Eigen value and PCs (Fig 2). These results are in support from the findings of Tiwari and Singh (2019).
 

 

 
Stepwise multiple regression analysis
 
The results of stepwise multiple regression analysis was presented in Table 8. The seed yield/ plant considered a dependent variable, while other traits as independent variables. Firstly, 100 seed weight entered in the model and explained 56.70% of total observed variations followed by number of pods/ plant, number of seeds/ pod and days to 50% flowering. The cumulative variations explained by combination of traits such as number of pods/ plant with 100 seed weight by 84.50%; number of seeds/ pod together with number of pods/ plant and 100 seed weight by 89.80% and only little amount of variation added in cumulative variation by days to 50% flowering (90.50%). Thus, stepwise multiple regression analysis identified the most important economic traits viz., 100 seed weight, number of pods/ plant and number of seeds/pod contributing to faba bean seed yield which could be used for effective selection of promising faba bean genotypes in segregating generations. These findings are in accordance with the reports of Tiwari and Singh (2019). The PCA together with stepwise multiple regression analysis identified most variants and yield contributing traits viz., 100 seed weight, number of pods/ plant and number of seeds/pod which could be used in yield enhancement of faba bean.
 

The results obtained from present investigation would provide valuable guidelines in selection diverse genotypes, prediction of possible merits for genetic recombination and also be valuables in formulating ideal plant type. Available knowledge of genetic diversity in faba bean germplasm helps in selection of parents for hybridization programme and effective in germplasm conservation as well. Mahalanobis D2 cluster analysis and PCA have been used successfully for assessment of genetic diversity in 80 faba bean germplasm lines. On the basis of cluster mean values and genetic divergence study 14 promising genotypes viz., EC-591828, EC-628922, EC-628929, EC-628940, EC-628955, EC-628957, ET-3104, ET-3128, ET-3131, ET-3160, ET-4105, ET-4107, HB-82 and HB-85 identified for seed yield and its component traits which could be used in hybridization programme for higher heterotic response and expected to release better segregants in faba bean breeding programmes for yield enhancement. The PCA together with stepwise multiple regression analysis identified most variants and yield contributing traits viz., 100 seed weight, number of pods/ plant and number of seeds/ pod which could be used for effective selection of parents and promising faba bean germplasm lines in future faba bean breeding programme.