Assessment of genetic variability, heritability and genetic advance among determinate F4 progenies in Dolichos bean (Lablab purpureus L. var. typicus)

Introduction

Dolichos bean (Lablab purpureus L. var. typicus) is one of the important legume vegetable crop grown throughout India for its tender green pods especially in Madhya Pradesh, Uttar Pradesh, Tamil Nadu, Andhra Pradesh, Maharashtra, Gujarat and Karnataka. Botanically, it belongs to family Fabaceae with chromosome number 2n=2x=22. Evidently, it is originated in India. Dolichos bean is synonymously known as Indian bean, Egyptian bean, Hyacinth bean, Field bean, Sem, Bonavist bean etc. "Dolichos" is a Greek word meaning "long" and "lablab" is derived from Egyptian or Arabic language to mean "dull rattle of the seed inside the dry pod" (Chaudhury, 1972) [6] . Botanists identify two types of Dolichos bean based on the angle of attachment of seeds to the suture of the pods (Magoon et al. 1974) [12] . The Lablab purpureus L. var. typicus is commonly used for green vegetable and Lablab purpureus L. var. lignosus is used as a pulse. Longer, flat, and more tapering pods with long axis of seeds parallel to the suture of the pod are the attribute of Lablab purpureus var. typicus. It finds predominant usage as fleshy and soft whole pods and is often trained due to its twinning habit. Lablab purpureus var. lignosus is bushy type annual plant. Pods are comparatively shorter and more abruptly truncated and long axis of the seeds is perpendicular to the suture of the pod. It is cultivated for fresh immature seeds used as a vegetable and to a rarely as pulse. The foliage of the crop provides green manure, silage and hay.

Crop improvement is a dynamic process focussing on the changing needs and the emerging problems in crop productivity. Availability of naturally existing or generated genetic variability is a prerequisite for any crop improvement as it provides a wide scope for breeder to select. The fruitfulness of selection depends on the variability and its nature, extent, and magnitude. The degree of heritability is another facet of effectiveness of selection. Existing variability has been exploited to the maximum possible extent by selection; thus, there is a need to generate variability afresh by crossing superior diverse genotypes. Yield is a complex trait controlled by polygenes and to the significant extent by environment. There are ample proofs to show that selection directly for yield in plants is not so effective. The knowledge on existing variability and degree of relationship between economical traits viz., fresh pod yield and its component traits and their relative contribution to fresh pod yield is essential for effective selection.

Estimates like heritability and genetic advance are reliable genetic parameters for breeders to impose selection. Heritability is an important aspect of the genetic constitution of the breeding material, which has a close relevance on the response to selection. "Heritability is the transmissibility of characters from parents to off-springs". It is of great significance in selection as it reflects the reliability of phenotypic value as guide to breeding value. Heritability is a useful indicator of the advance that can be expected by practising selection on the resilient population. However, a measure of heritability alone does not give the information about the expected gain in the next generation, while consideration of genetic advance in conjunction with heritability is more precise. Thus, high yield can be achieved by selection for those characters that have high heritability and genetic advance.

Material and Methods

Experimental site

The experiment was carried out during Kharif-2018-19 in the experimental plot of Zonal Agricultural Research Station (ZARS), University of Agricultural Sciences (UAS), Gandhi Krishi Vignana Kendra (GKVK), Bengaluru. The experimental plots are located at an altitude of 930 m above mean sea level (MSL) 12° 58' North and 77° 35' East latitude and longitude, respectively.

Experimental Material

The material for the study consisted of progenies of 281 selected F 3 determinate selections of Lablab purpureus L. var typicus and two checks (Arka Jay and Avami). These F 4 progenies were derived from ten determinate × indeterminate crosses out of 21 crosses made (Table 1).

Evaluation of experimental material

Progenies of F 3 determinate selections along with two checks (Arka Jay and Avami) were sown at GKVK, Bengaluru during kharif-2018-19 following Augmented design (Federer, 1956) [8] in six compact blocks. Each block consisted of 47 determinate F 3 progenies, two checks (replicated thrice) and four border entries. Each entry in each block was sown in a single row of 4 m length, with a spacing of 0.45 m between rows and 0.3 m between plants within a row. A basal dose of 25:50:25 Kg NPK ha -1 was applied to the experimental plot. Recommended agronomic and plant protection practices were followed to raise a healthy crop.

Data collection

Observations were recorded on 10 randomly selected plants in each entry on eight quantitative characters namely, Plant height (cm), Days to 50% flowering, Racemes plant -1 , Raceme length (cm), Primary branches plant -1 , Fresh pods plant -1 , Fresh pod length (cm) and Fresh pod yield plant -1 (g).

Statistical analysis

The statistical analysis was carried out using the adjusted trait means of 281 F 4 progenies. Mean values of the 10 randomly selected plants in F 4 progenies and checks were used for statistical analysis. ANOVA was performed following Augmented design (Federer, 1956) [8] using SAS version 9.3 software to examine statistical significance or otherwise of the differences among F 4 progenies. Adjusted quantitative trait means of 281 F 4 progenies were used for estimating eight quantitative traits mean, absolute range (highest -lowest trait mean), standardized range, Phenotypic coefficient of variation (PCV), Genotypic coefficient of variation (GCV), heritability (broad sense) and expected genetic advance as per cent of mean (GAM).

Results and Discussion

Analysis of variance

Exploitation of natural genetic variability is a short-term strategy to meet immediate requirement of the farmers, consumers and end-users. In the past, selection by farmers and/or plant breeders in the available natural genetic variability has resulted in significant genetic improvement in crop productivity. However, continued crop genetic improvement to meet medium-and/long-term requirements requires generation of variability induced through deliberately planned crosses among the genotypes harbouring desired combination of traits. Analysis of variance (ANOVA) is a diagnostic tool and a pre-requisite step for preliminary detection of genetic variability in the working genetic material (Govindaraju et al., 2015; Hawkes, 1991) [9,10] . ANOVA (Table 2) revealed significant variability among F 4 progenies for all the traits. Significant mean squares due to checks for most of the traits suggested considerable variability between the checks for most of the traits. Significant mean squares attributable to 'F 4 progenies vs checks' suggested that F 4 progenies as a unit differed substantially from checks for all traits except raceme length (Table 2). The photograph (Plate 1) is a testimony to considerable variability for pod traits among the 281 F 4 progenies.

Plate 1: Variability for pod traits among the 281 F4 progenies of the ten crosses

Genetic variability among F4 progenies Phenotypic coefficient of variation (PCV) and Genotypic coefficient of variation (GCV)

As expected, the magnitude of phenotypic coefficient of variation was higher than the corresponding genotypic coefficient of variation for all the traits. The estimates of PCV ranged from 1.78 to 11.72 per cent (Table 3; Figure 1). The estimates of PCV were moderate for racemes plant -1 (11.72), compared to those of fresh pods plant -1 and primary branches plant -1 (Table 3; Figure 1). These results were in line with the findings of Chaitanya et al. (2014) [4] , Sharma et al. (2014) [14] and Verma et al. (2014) [16] . The estimates of GCV values ranged from 0.99 to 9.42 per cent (Table 3; Figure 1). The estimates of GCV were lower for fresh pods plant -1 (9.42) compared to those of fresh pod yield plant -1 , racemes plant -1 , raceme length, primary branches plant -1 , plant height, fresh pod length, and days to 50% flowering (0.99) (Table 3; Figure 1). Similar results were obtained by Chaitanya et al. (2014) [4] , Sharma et al.

(2014) [14] and Asaduzzaman et al. (2015) [1] . The magnitudes of PCV were higher than those of GCV for all the traits (Table 3; Figure 1). Narrow difference between the estimates of PCV and GCV suggested limited influence of weather variables and edaphic factors on the expression of all the traits except racemes plant -1 , raceme length, and primary branches plant -1 (Table 3; Figure 1). These results were in harmony with those of Basu et al. (1999) [3] and Chattopadhyay and Dutta (2010) [5] . The narrow differences between PCV and GCV estimates suggests effectiveness of selection of desired genotypes for all the traits under study.

Wider difference between the estimates of PCV and GCV for racemes plant -1 , raceme length, and primary branches plant -1 indicating larger influence of environment on the expression of these traits. Similar findings were reported by Bahadur et al (2013) [2] , Chaitanya et al. (2014) [4] and Asaduzzaman et al. (2015) [1] .

Heritability (broad sense)

Heritability provides information regarding the amount of transmissible genetic variation. It also determines response to selection. High heritability estimates are helpful in making selection of superior genotypes apparently from phenotypic performance. In the present study, heritability values ranged from 15.89 to 89.79 per cent. The estimates of heritability were high for fresh pod yield plant -1 followed by plant height and fresh pods plant -1 (Table 3; Figure 2). High heritability indicates the effectiveness of selection for these traits. These results were in conformity with those of Magalingam et al. (2013) [11] , Chaitany et al. (2014) [4] , Verma et al. (2014) [16] and Singh et al. (2015) [15] . The estimates of heritability were moderate for fresh pod length, raceme length, racemes plant -1 and days to 50% flowering (Table 3; Figure 2). These findings were in agreement with the findings of Savitha (2008) [13] .

Genetic Advance

The estimates of expected GAM ranged from 4.43 to 29.26 per cent. The expected GAM was least for days to 50% flowering and highest for racemes plant -1 followed by primary branches plant -1 and fresh pods plant -1 (Table 3; Figure 2). These results are in accordance with the findings of Magalingam et al. (2013) [11] , Sharma et al. (2014) [14] and Singh et al. (2015) [15] . The estimates of expected GAM were moderate for fresh pod yield plant -1 followed by raceme length and fresh pod length (Table 3; Figure 2). These results were in conformity with the findings of Magalingam et al. (2013) [11] . The estimates of expected GAM were low for plant height followed by days to 50% flowering. These findings were in agreement with the results of Das et al. (2015) [7] and Singh et al. (2015) [15] . High heritability coupled with high expected GAM indicated effectiveness of selection for the improvement of fresh pods plant -1 and fresh pod yield plant -1 . These results are in line with the findings of Magalingam et al. (2013) [11] Sharma et al. (2014) [14] and Singh et al. (2015) [15] .

Conclusion

Highly significant mean sum of squares indicated substantial variability not only among the F 4 progenies but also their significant differences with check varieties for most of the quantitative traits as indicated by ANOVA which is a diagnostic tool for detection of variability. Absolute range and standardized range showed that F 4 progenies have got high variation for fresh pods plant -1 followed by fresh pod yield plant -1 , racemes plant -1 , raceme length, fresh pod length, primary branches plant -1 and plant height and least variation for days to 50% flowering. Wider difference between the PCV and GCV was reported for racemes plant -1 , raceme length, and primary branches plant -1 indicating larger influence of environment on the expression of these traits. While narrow difference between PCV and GCV was recorded for days to 50% flowering, plant height, fresh pod length, fresh pods plant -1 and fresh pod yield plant - 1 representing marginal influence of environment on the expression of these traits. Hence, there is an ample scope for improvement of these traits. The high heritability estimates were reported for fresh pod yield plant -1 followed by plant height, and fresh pods plant -1 indicating the effectiveness of selection. High heritability coupled with high GAM were reported for fresh pods plant -1 and fresh pod yield plant -1 indicated the presence of larger number of fixable additive factors which help in improvement of these traits through simple selection procedures.

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