Genetic Analysis of F₂ Populations for Quantitative Traits in Blackgram [Vigna mungo (L.) Hepper]

Pulses are the leguminous crops rich in dietary protein which is essential for the human growth and developmental process. Among the pulses, blackgram is the important crop that is majorly grown in India. It is cultivated in Indian subcontinent as intercrop with cereals, rice fallow and rainfed crop. It is consumed in a variety of forms in the Indian cuisine due to its nutritive qualities and is having high protein content (25%), carbohydrate (60%), fat (1.5%), minerals and vitamins (Mehra et al., 2016). The production of blackgram needs to be raised either through extensive cultivation or by enhancing productivity through developing high yielding cultivars to meet the growing demand. Every year, the area of arable land decreases as a result of urbanisation and industrialization. Thus, new high yielding cultivars are primarily responsible for making production enhancement. The creation of new variability through hybridization or mutation breeding will produce novel segregants for important yield attributing traits. The selection from the population will be effective if the traits have good genetic variability estimates (Reni et al., 2013). In this study, variability was created through hybridization and F₂ segregating populations were developed. In order to determine the proper selection criteria, the F₂ populations were investigated for the variability parameters and frequency distribution such as skewness and kurtosis to identify superior segregants (Rani et al., 2016).

The present study on blackgram was conducted in the Department of Pulses, Tamil Nadu Agricultural University, Coimbatore. The crosses CO 5 × VBN 9 and CO 6 × VBN 11 were made during summer, 2022 and the F₁ plants were raised along with parents during kharif, 2022. The true hybrid plants were identified based on the contrasting morphological traits of the respective parents and the individual plants were forwarded to F₂ generation. The F₂ populations of two crosses were raised during rabi, 2022 with the spacing of 30 × 10 cm. The good crop stand was established with recommended package of practices and plant protection measures on need basis. Nine quantitative traits viz., plant height (cm), number of branches per plant, number of clusters per plant, number of pods per cluster, number of pods per plant, pod length, number of seeds per pod, hundred seed weight (g) and seed yield per plant (g) were recorded from 62 and 71 plants in the F₂ populations of CO 5 × VBN 9 and CO 6 × VBN 11 crosses, respectively.
       
The F₂ data was subjected for estimation of second order statistics (genetic variability parameters). The phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV) for nine characters were calculated as per the formulae given by Burton (1952). These estimates were categorized by Sivasubramanian and Madhavamenon (1973) as low (<10%), moderate (10-20%) and high (>20%). To know the heritable portion of variability, broad sense heritability (h²) was estimated as the ratio of genotypic variance to the phenotypic variance (Lush et al., 1940) and categorized as low (<30%), moderate (30-60%) and high (>60%). The genetic advance was calculated (Johnson et al., 1955) and expressed as a per cent of mean (GAM). The GAM values were categorized into low (<10%), moderate (10-20%) and high (>20%). The third and fourth order statistics viz., skewness and kurtosis were estimated to analyse the nature of the frequency distribution (Snedecor and Cochran, 1989). The significance for these two estimates were examined by ‘t’ test. These analyses were performed using the statistical package SPSS 16.0 version.

Confirmation of F₁ hybridity
 
The two crosses were subjected for the hybrid confirmation through morphological traits contrasting between the parents. In the cross I (CO 5 × VBN 9), the parents were contrasting for leaf vein colour and immature pod colour (green in CO 5 and purple in VBN 9 for both the traits). The true F₁ plants were identified with the expression dominant trait purple leaf vein colour (Plate 1a) and purple pigmentation on immature pod (Plate 1b) which are the characteristics of male parent, VBN 9. In the cross II (CO 6 × VBN 11), for pod pubescence trait, the female parent is having glabrous pods and in case of male parent, it is hairy. Hence, the F₁ plants were identified with the presence of dominant trait, hairy pods (Plate 2).
 

 

 
Mean and range for seed yield per plant
 
The wide range of variations were observed in all the traits of F₂ populations which can be further analysed for genetic variability parameters for deciding the selection criteria. Among the traits, number of pods per plant and seed yield per plant were recorded with wider variations. The number of pods per plant ranged from 26.00 to 72.00 with the mean of 42.19 in cross I and it ranged between 29.00 and 86.00 with 45.89 mean value in cross II. A total of 25 plants in cross I and 30 plants in cross II excelled the F₂ mean value for number of pods per plant. In the cross I, the seed yield per plant ranged from 10.15 to 27.67 g with the mean value of 14.72 g (Table 1). Whereas, in cross II, it ranged between 10.32 g and 29.25 g with the average yield of 14.43 g. The number of plants outperformed for seed yield per plant over the F₂ mean were 24 and 23 in the cross I and II, respectively. This kind of wide variation and good segregants give scope for the yield improvement through selection process.
 

 
Coefficient of variations
 
In any breeding programme, selection is the important process for the effective improvement of the traits. To make the selection, presence of variation is the prerequisite from which the plants can be selected and forwarded. Hence, to analyse the extent of variation, phenotypic and genotypic coefficient of variations were calculated. Phenotypic coefficient of variation in both F₂ populations was higher than the genotypic coefficient of variations (Table 1) with small range of difference between them. This suggests that genetic components contributed more towards population variability than environmental influences. The PCV values ranged from 6.38 to 41.60% in cross I and from 6.09 to 37.52% in cross II for the traits pod length and number of branches per plant, respectively. The GCV values ranged from 2.52 (hundred seed weight) to 28.07% (number of branches per plant) in cross I and from 1.69 (hundred seed weight) to 23.00% (seed yield per plant) in cross II. The high GCV values were observed for the traits viz., number of branches per plant (28.07%) and seed yield per plant (24.96%) in cross I. In cross II, plant height (22.10%), number of pods per plant (20.51%) and seed yield per plant (23.00%) were observed with high GCV. The straightforward selection process could enhance these traits in the respective populations. Similar findings of high GCV for number of branches per plant, number of pods per plant and seed yield per plant were also reported by Sowmini et al., (2013) and Vinoth et al., (2014) in RIL population of blackgram and Susmitha et al., (2018) in greengram. The values of GCV for the traits viz., plant height (16.55%), number of clusters per plant (13.28%) and number of pods per plant (17.47%) in cross I and number of branches per plant (15.96%), number of clusters per plant (16.14%) and number of pods per cluster (10.59%) in the cross II were found to be moderate which directs that the selection can be made in the later generations for these traits. Moderate GCV were also found in the reports of Vadivel et al., (2019), Sathya et al., (2021) and Ragul et al., (2021) for plant height and number of pods per cluster in blackgram.
 
Heritability and genetic advance
 
The selection for the improvement of particular trait will be effective when the variation present in population is more due to genetic cause. Hence, the heritability and genetic advance of the traits were analysed in both the populations and the values were given in the Table 1. In cross I, heritability ranged from 5.45 (number of pods per cluster) to 86.13% (plant height) and genetic advance ranged from 1.46 (hundred seed weight) to 44.76% (seed yield per plant). In cross II, heritability was observed between 1.84% (hundred seed weight) and 90.69% (number of seeds per pod). The genetic advance parameter ranged between 0.47% (hundred seed weight) and 43.31% (plant height) in cross II. The high heritability (>60.00%) accompanied with high genetic advance (>20%) were observed for the traits plant height and seed yield per plant in both the crosses. In addition to this, number of pods per plant also showed the high values of these parameters in the cross II. It suggests that selection of these traits may be advantageous and   the heritability is most likely caused by additive gene effects (Nadarajan et al., 2018). These higher estimates were also reported by Priya et al., (2019) for number of pods per plant and seed yield per plant in blackgram and Susmitha et al., (2018) for plant height in greengram. The moderate heritability (30-60%) together with substantial genetic advance (>20%) were found for the traits viz., number of branches per plant and number of pods per plant of cross I and number of clusters per plant of cross II. The moderate heritability is due to the environmental influences on these traits. This kind of variability for these three traits were also reported by Sathya et al., (2021) in F₂ population of blackgram. In certain circumstances, the selection might be successful for the improvement.
 
Skewness and kurtosis
 
The skewness was examined to analyse the surface nature of the distribution curve. These parameters were analysed to find out the presence of gene interaction and to decide the kind of selection intensity to be followed. Cross I was observed with significant positive skewness (Table 1; Fig 1) for the traits viz., number of branches per plant (0.63), number of pods per cluster (1.10), number of pods per plant (0.74), hundred seed weight (0.87) and seed yield per plant (1.10). Similarly, cross II also had significant positive skewness (Table 1; Fig 2) for the traits, number of clusters per plant (1.72), number of pods per cluster (0.65), number of pods per plant (1.45) and seed yield per plant (1.90). This kind of positive skewness in the population indicates the presence of dominant and complementary gene interaction. The genetic gain for these traits could be rapidly increased through intensive selection from the higher tail end of the distribution curve (Snape and Riggs, 1975; Bassuony et al., 2022). Similar findings of positive skewness were reported by Vadivel et al., (2019) for number of clusters per plant and seed yield per plant in blackgram, Devi et al., (2021) for hundred seed weight and seed yield per plant in RIL population of blackgram, Harshita et al., (2020) for number of branches per plant and number of pods per plant and Hema et al., (2022) for number of branches per plant and seed yield per plant in interspecific lines of greengram. Contrastingly, in cross II, number of seed per pod (-0.93) was negatively skewed which indicates the dominant and duplicate gene interaction controlling them and mild selection can be done from the higher end of the distribution curve for rapid improvement of these traits. The negative skewness for number of seeds per pod also reported by Vadivel et al., (2019) in blackgram. The normal distribution was noticed in the trait viz., plant height, number of clusters per plant, pod length and number seeds per pod of cross I and plant height, number of clusters per plant, pod length and hundred seed weight of cross II.
 



       
The kurtosis is peakness of the distribution curve. A distribution with positive kurtosis (excess) is called leptokurtic and negative kurtosis is called platykurtic which means the trait is controlled by large and fewer number of genes, respectively (Bassuony et al., 2022). The kurtosis value (Table 1; Fig 1) of hundred seed weight (2.70) in cross I and the traits viz., number of clusters per plant (5.01), number of pods per plant (2.71), pod length (1.35), number of seeds per pod (1.22) and seed yield per plant (3.59) in cross II were significant positive with leptokurtic nature (Table 1; Fig 2) which implies that fewer number of genes controlling them. Similar leptokurtic nature in RIL population for pod length and number of seeds per pod were found in the earlier reports (Devi et al., 2021; Vadivel et al., 2019).

Based on the above discussion, it was concluded that the improvement of the traits viz., plant height, number of branches per plant, number of clusters per plant, number of pods per cluster, number of pods per plant and seed yield per plant will be effective through simple selection process. The positive skewness and leptokurtic nature of the traits could be improved by stringent selection from higher end of the distribution for rapid improvement of the traits. Hence, the selection can be made from the segregating populations of the present study for the development of high yielding blackgram varieties.

The first author is grateful to the Council for Scientific and Industrial Research (CSIR), Ministry of Science and Technology, Government of India for offering a Senior Research Fellowship.

All authors declare that they have no conflict of interest.