Combining Ability and Gene Action Analysis for Seed Yield and Component Traits in F₂ Generation of Vigna mungo L. Hepper by using Griffing Approach

Urdbean (2n=2x=22), also known as blackgram is an important short duration legume crop belonging to family Fabaceae, widely cultivated in Asia. Urdbean occupies an important position among pulses owing to its high seed protein (25-26%), carbohydrates (60%), fat (15%), minerals, amino acids and vitamins. Owing to its low water requirement, it is also suitable for rainfed conditions. It adapts well to various cropping systems owing to its ability to fix atmospheric nitrogen in symbiosis with soil bacteria, rapid growth and early maturity (Soren et al., 2012). It is a self pollinated short duration crop grown in many parts of India. Out of the various mating designs developed for determining the genetic architecture of a trait, diallel has been the most studied and used (Johnson 1963). Along with the combining ability, diallel also provides the measure of gene action. Combining ability analysis is one of the powerful tools available to estimate the combining ability effects and it aids in selecting the desirable parents and crosses for the exploitation of heterosis (Sarker et al., 2002). General combining ability (GCA) is attributed to additive gene effects and additive × additive epistasis and is theoretically fixable. On the other hand, specific combining ability (SCA) attributable to non-additive gene action, may be due to dominance or epistasis or both and is non-fixable. Therefore, the most suitable way is to identify the potential crosses with high heritable vigour and good combining ability by examining the F₂’s and thus exploiting residual heterosis by appropriate selection method at an early stage (Fasoulas, 1981). The diallel analysis is one which has been considered to throw light on the nature of inheritance of quantitative traits in crop plants and also provides the estimates of heterosis and gene action by giving the overall picture of the dominance relationship of the parents studied with or without reciprocals. Hence the half diallel analysis was adopted in present study to gather information on GCA (general combining abilities) and SCA (specific combining abilities) of 6 diverse parents and simultaneously estimating various types of gene effects involved in the expression of seed yield and related attributes in urdbean.

The F₁’s were developed during 2017 in 9 × 9 half diallel fashion by Sharma (2019) and these F₁’s were evaluated. Significant crosses on the basis of gene action and combining ability were selected for further advancement. The experimental material comprised of the six parents and 15 F₂’s of a 6 × 6 half diallel cross among six cultivars of urdbean (four are purelines viz., Palampur-93, HPBU-111, DU-1 and KU-553 and rest of the two are advanced and indigenous lines viz., Him Mash-1 and IC-281994). The F₂’s along with the parental genotypes were grown in a randomized block design (RBD) with three replications at Experimental Farm of the Department of Crop Improvement, COA, CSK HPKV, Palampur (H.P.) during Kharif, 2018. Each replication comprised two rows of 1.5 m length with spacing of 30 × 10 cm. The data were recorded on twenty randomly taken plants from each cross across replications for all the traits studied except days to 50 per cent flowering and days to 75 per cent maturity which were recorded on plot basis. The statistical analysis of variance for randomized block design was carried out by standard procedure given by Panse and Sukhatme (1984). Analysis of variance for combining ability was carried out according to method 2 Model-I (fixed effects) of Griffing (1956). The components of variance due to general combining ability (σ² GCA) and due to specific combining ability (σ² SCA) were estimated from the observed and expectations of mean squares under model-I to examine the relative roles of GCA and SCA and hence the nature of gene action.

The combining ability analysis partitions the genotypic variability into variances due to general combining ability (GCA) and specific combining ability (SCA) which represent additive and dominance effects, respectively. Through combining ability analysis, desirable parents can also identify which are used for a given trait in a breeding programme. Similarly, superior cross combinations can also be detected through this analysis. In the present study, the analysis of variance for six parents in half diallel fashion revealed significant differences among parents and F₂’s for all the characters studied. Hence, there is enough scope for selection among the cultivars.
       
Analysis of variance showed significant differences among the genotypes for all the traits viz., days to 50 per cent flowering, days to 75 per cent maturity, plant height, branches per plant, pods per plant, biological yield per plant, pod length, seeds per pod, seed yield per plant, harvest index, 100-seed weight and crude protein indicating sufficient genetic variability in the material under study. All the crosses were also significantly different from each other for all the traits except plant height and harvest index (Table 1) revealing enough variability that generated through hybridization programme. Mean squares due to Parents vs. crosses were significant for branches per plant, pod length, biological yield per plant, seed yield per plant, 100-seed weight and crude protein. Sufficient variability is must for any breeding programme as the selection efficiency for yield improvement depends upon the amount of genetic variability present. The results from the present study are in agreement with the reports of Gill et al., (2014), Panigrahi et al., (2015) and Abbas et al., (2016) in urdbean.
 

       
Analysis of variance for combing ability revealed that mean squares due to GCA were significant for all the traits studied except branches per plant and mean squares due to SCA were significant for all the characters except plant height, biological yield per plant and harvest index (Table 2). The highly significant variation due to gca and sca indicated the importance of additive as well as non-additive type of gene action for expression of these traits. Significant GCA indicates that at least one of the parental genotypes differ from others in relation to number of favourable genes with additive effects whereas, significant sca indicates that all the hybrids have higher or lower performance than expected, based on GCA (Oliboni et al., 2013). Similar results were recorded by Badhe et al., (2016), Dias et al., (2016) in cowpea and Dharmendra et al., (2002) in pea for GCA and SCA for all the traits. The ratio of GCA and SCA variances was less than unity for all the traits except harvest index suggesting the influence of non-additive gene action in inheritance of all the traits. Further, it revealed that both the additive and non-additive gene effects are important in inheritance of all characters. The comparison of magnitude of general combining ability and specific combining ability variance indicated that the non-additive genetic effects were predominant in the characters, days to 50 % flowering, days to 75% maturity, plant height, branches per plant, number of pods per plant, pod length, number of seeds per pod, biological yield per plant, seed yield per plant, 100-seed weight and protein content, which suggested prime role of non-additive gene action. These results are in line with Gill et al., (2014), Prasad and Murugan (2015) and Baradhan and Thangavel (2011) in blackgram, Chuwang et al., (2019), Dangariya et al., (2009). Badhe et al., (2016) also reported higher sca variances for days to 50 per cent flowering, plant height, number of branches per plant, pod length, number of seeds per pod, 100-seed weight, seed yield per plant and harvest index.
 

       
The estimates of general combining ability effects of parents for all the traits were given in the (Table 3). Two genotypes viz., DU-1 (-1.347) and Palampur-93 (-0.806) exhibited significant negative GCA effect indicating good general combiners for days to 50 per cent flowering, as negative significant GCA is desirable for this trait. Good general combiners for days to 75 per cent maturity were Him Mash-1 (-0.625) and IC-281994 (-0.625) as indicated by their significant negative GCA effect. Him Mash-1 (0.120) and KU-553(0.094) were identified as good general combiners as indicated by their significant positive GCA effects for seeds per pod. Overall, KU-553 was the best general combiner having significant positive GCA effects for seed yield per plant, pods per plant, seeds per pod and biological yield per plant. Present results are supported by the findings of Neog and Talukar (1999), Vaithiyalingan et al., (1999), Gopi et al., (2003) and Gill et al., (2014) in blackgram and Kapoor and Bhardwaj (2018) in ricebean. Significant negative SCA effect for days to 50 per cent flowering was observed in five crosses viz., DU-1 × IC-281994 (-6.119), Him mash-1 × HPBU-111(-3.786), Palampur-93 × DU-1 (-2.577), HPBU-111 x DU-1 (-1.702) and  Palampur-93 × KU-553 (-1.286) indicating their good specific combining ability for days to 50 per cent flowering (Table 4). Good specific combining ability as indicated by the significant negative SCA effect were observed in five crosses viz., Him Mash-1 × KU-553 (-1.833), DU-1 × KU-553 (-1.500), Palampur-93 × KU-553 (-1.286), KU-553 × IC-281994 (-1.167) and Him Mash-1 × HPBU-111 (-0.750) for days to 75 per cent maturity. Positive significant SCA effect was observed in three crosses viz., Him Mash-1 × KU-553(2.818), Him Mash-1 × HPBU-111(2.126) and Palampur-93 × IC-281994(1.049) indicating their good specific combining ability for plant height. Significant positive SCA effect was observed in five crosses viz., Palampur-93 × IC-281994 (2.065), Him Mash-1 × KU-553 (1.731), HPBU-111 × KU-553 (1.267), Him Mash-1 × HPBU-111 (0.817) and HPBU-111 × IC-281994 (0.694) indicating their good specific combining ability for pods per plant. Good specific combining ability as indicated by positive significant SCA effect was observed in five crosses viz., HPBU-111 × KU-553 (0.758), Palampur-93 × IC-281994 (0.628), Him Mash-1 × HPBU-111 (0.597), Palampur-93 × KU-553 (0.326), HPBU-111 × DU-1 (0.265)  for seed yield per plant. Overall, Him Mash-1 × HPBU-111 was good specific combiner for maximum number of traits (8) along with seed yield. Cross combination, Him Mash-1 × DU-1 and HPBU-111 × DU-1 revealed significant positive sca effect for 100 seed weight and crosses Him Mash-1 × HPBU-111, DU-1 × IC-281994 and KU-553 × IC-281994 recorded maximum significant positive SCA effect for the character protein content. Palampur-93 × IC-281994 and Palampur-93 × KU-553 were identified as good specific combiners for most of the traits viz., plant height, branches per plant, pods per plant, biological yield per plant, seed yield per plant, harvest index, 100-seed weight and crude protein content. The above results substantiated the findings of Naik et al., (2013), Gill et al., (2014), Panigrahi et al., (2015), Maida et al., (2017) in pigeonpea and Nath et al., (2018) in urdbean.
 

 

       
The relationship between GCA and SCA effects confirmed that significant and desirable SCA effects can occur in any group of GCA of parents indicating the presence of higher order interactions in the expression of these traits and in addition to this, SCA effects occurred because it all depends upon how well genes from two parents interact. The occurrence of high SCA effects in good × good group might be due to cumulative effect of high combining loci and no mutual cancelation of gene effects between high general combining loci. On the other hand high SCA effects in good × average or average × good, average × poor or poor × average group might be due to complementation of low, good and poor or average combining loci. Therefore, based on outstanding performance of selective parents and crosses in present study, can be concluded that desirable parents could be used as donors to get high yield and the selective crosses were identified as outstanding for seed yield and its components traits due to possessing high SCA effect for seed yield may further be utilized in future under breeding programme.

The ratio of additive variance (σ²A) and dominance variance (σ²D) was less than unity for all the traits except harvest index suggesting the influence of non-additive gene action in the inheritance of all traits. Number of seeds per pod, biological yield per plant and harvest index had partial dominance, whereas, all other traits had overdominance. Promising crosses with respect to seed yield and its component traits were Palampur-93 × IC-281994, HPBU-111 × KU-553, Palampur-93 × KU-553 and HPBU-111 × DU-1. Due to predominance of non-additive gene action, SSD or bulk pedigree method with selection in later generations will be the best breeding strategy to obtain maximum transgressive segregants.