Exploring genetic variation In F2 population of groundnut using quantitative traits

Introduction

The cultivated peanut (Arachis hypogaea L.) is a significant crop in many tropical and subtropical regions and is the leading edible oilseed in India. Peanut seeds are particularly valuable due to their high oil content (43-54 per cent) and protein content (25-30 per cent). It belongs to the Fabaceae family and is classified into two subspecies, hypogaea and fastigiata, with various botanical varieties. Groundnut grows well in semi-arid areas situated between 40° N and 40° S latitudes, with its centre of origin located in the eastern foothills of the Andes (Southern Bolivia and Northern Argentina). In India, groundnut is primarily cultivated under rainfed conditions, making it crucial for crop diversification. The country has the largest groundnut area globally, covering 8.5 million hectares, but ranks second in production with 8.4 million tonnes, trailing behind China. Indian groundnut productivity is relatively low at an average of 988 kg/ha, compared to 2,995 kg/ha in the USA and 2,688 kg/ha in China. Cultivation occurs over three seasons-Kharif, Rabi and summer-mainly in Gujarat, Andhra Pradesh, Tamil Nadu, Karnataka and Maharashtra, which together account for 80 per cent of the total area and production. Karnataka ranks fourth in production, yielding 1.167 million tonnes annually from 1.22 million hectares (Anon. 2023) [2] . Genetic variability is the basic requirement for crop improvement as this provides a wider scope for selection. Thus, the effectiveness of selection is dependent upon the nature, extent and magnitude of genetic variability present in materials and the extent to which it is heritable. Despite being developed and released in 1940, TMV-2 continues to dominate the market, even though there are other varieties with higher pod yields. Oil mills prefer TMV-2 for oil extraction due to its uniformly sized pods and attractive kernels. However, since the government has officially withdrawn TMV-2, it is no longer available through the official seed distribution system. There is a pressing need to create a new variety that surpasses TMV-2 in yield but retains its desirable pod and kernel characteristics. This is essential to bridge the productivity gap between groundnut cultivation in Karnataka and the national average. For crop improvement, it is crucial to have access to genetic variability, as this offers a broader selection and heritability. Given that the existing variability has been maximized through selection, generating new variability in segregating populations by crossing top genotypes is necessary (Byadagi et al. 2018) [6] . In this study, we sought to assess the variation in key traits associated with pod yield and the factors influencing it. We also determined variability indices, including the genotypic co-efficient of variation (GCV), phenotypic co-efficient of variation (PCV), broad-sense heritability (h²bs) and genetic advance as a per cent of mean (GAM).

Materials and Methods

In the present investigation, F 2 population of cross TMV-2 × K-1812 consisting of 109 plants and seven checks namely R-8808, TMV-2, K-9, ICRC-1, Dh-256, Dh-257 and K-1812 belonging to both Virginia and Spanish habit groups were evaluated for genetic variability for pod yield and its attributing traits at All India Co-ordinated Research Project on groundnut research block, Main Agricultural Research Station (MARS), UAS, Raichur during Rabi/summer, 2023-24. The F 2 plants were planted in unreplicated block (Kempton and Gleeson 1997) [17] with 8 rows of F 2 population followed by two rows of each check planted with the a spacing of 30 cm between rows and 10 cm between plants respectively. The crop was raised by following all the agronomic practices as per the package of practices recommended for groundnuts in the North-eastern dry zone of Karnataka (Zone 2). Observations were recorded for ten quantitative characters viz. days to flowering, days to maturity, number of branches per plant, number of matured pods per plant, dry pod yield per plant (g), kernel weight per plant (g), shelling percentage (%), sound mature kernel (%), biological yield per plant (g) and harvest index (%). Observations on yield and yield-associated traits were recorded from individual plants since the F 2 population exhibits significant variability due to the segregation of genes at each locus where the parents differed. The mean and range were calculated as per Sunderaraj et al. (1972) [29] , while genotypic co-efficient of variance (GCV), and phenotypic co-efficient of variance (PCV) were computed for the F 2 population for each character as per the method suggested by Burton and Devane (1953) [5] . Heritability (%) in the broad sense was determined according to Lush's (1949) method, while genetic advance as a per cent of mean was estimated by using the formula of Johnson et al. (1955) [16] .

Results and Discussion

Genotypic and phenotypic co-efficient of variance

The studies on the co-efficient of variation use percentage of the mean to represent variance. The findings related to phenotypic co-efficient of variance (PCV), genotypic coefficient of variance (GCV), heritability, and genetic advance expressed as a percentage of the mean are detailed by trait in Table 1. The outcomes of PCV and GCV are depicted in fig. 1, further heritability and GAM in Fig. 2. These statistical values offer insights into the existing variability, gene action, and the potential for enhancing these traits through selective breeding or other genetic strategies. The phenotypic co-efficient of variation (PCV) ranged from 3.19 per cent (Sound matured kernels) to 40.25 per cent (biological yield per plant). The genotypic co-efficient of variation (GCV) ranged from 3.10 per cent (days to maturity) to 40.22 per cent (biological yield per plant). The slightly higher PCV compared to GCV indicates that environmental influences are minimal on these traits. An estimate of GCV and PCV for all characters studied revealed that the phenotypic co-efficient of variation (PCV) is slightly greater than the genotypic co-efficient of variation (GCV), it indicates minimal environmental influence on the traits studied. Higher magnitude of GCV and PCV were recorded for biological yield per plant (g) followed by number of matured pods per plant, dry pod yield per plant (g), kernel weight per plant (g), number of branches per plant and harvest index (%), suggesting sufficient amount of variability and thus offer better scope for genetic improvement through selection of these traits.

The results are in agreement with the findings of Ajith et al.

(2023) [1] for number of branches per plant; Makhan et al. (2003) for number of matured pods per plant; Hiremath et al. (2011) [12] for dry pod yield per plant (g); Shobha et al.

(2010) [27] for kernel weight per plant (g); Yadav et al.

(2023) [33] for biological yield per plant (g); Vasanthi and Reddy (2002) [31] for harvest index (%), who similarly reported that high PCV and GCV values are indicative of traits with a strong genetic basis and reduced environmental variability. Sound matured kernels (%), days to maturity, shelling percentage (%) and days to flowering recorded a low GCV as well as PCV values suggesting minimal genetic variability within these traits for selection. The results were in agreement with the findings of Zaman et al. (2011) [34] and Chavadhari et al. (2017) [27] for days to flowering, John et al. (2008) [11] and Meta and Monpara (2010) [20] for days to maturity, Vishnuvardhan et al. (2012) [32] and John et al.

(2011) [13] for sound matured kernels and Prasad et al.

(2002) [25] and Bhagat et al. (1986) [4] for shelling percentage.

Heritability and genetic advance

Broad-sense heritability varied from 70.23 per cent for days to flowering to 99.99 per cent for harvest index. The genetic advance as a per cent of mean ranged from 5.99 per cent for days to maturity to 82.80 per cent for biological yield per plant.

Higher estimates of broad sense heritability (bs) coupled with high genetic advance as per cent of mean were observed for number of branches per plant, number of matured pods per plant, dry pod yield per plant (g), kernel weight per plant (g), biological yield per plant (g) and harvest index (%) revealing that these traits are governed by additive gene action and direct selection for the higher phenotypic value of this trait will be effective. These results were on par with the findings of Sridevi et al.

(2022) [28] for number of branches per plant; Aparna et al.

(2018) [3] for number of matured pods per plant; Gowda (2021) [9] for dry pod yield per plant (g); Patidar and Nadaf (2017) [22] for kernel weight per plant (g); Gupta et al. (2015) for biological yield per plant (g); Patil et al. (2014) [23] for harvest index (%) who observed that traits with high heritability and genetic advance are primarily governed by additive genetic effects, making them highly amenable to selection. Days to flowering and shelling percentage recorded high heritability values but moderate GAM values, while sound matured kernels and days to maturity exhibited high heritability but low GAM values. These results reveals the prevalence of both additive and non-additive gene actions in these traits. Enhancing these traits can be accomplished through straightforward selection, progeny selection, or adjusted selection methods that emphasize stabilizing additive gene effects rather than depending exclusively on traditional selection. These results were on par with the findings of Mahalakshmi et al. (2005) [19] and Hampannavar et al. (2018) [11] for days to flowering, Gali et al. (2021) [8] and Savaliya et al. (2009) [26] for days to maturity, Narasimhulu et al. (2012) [21] and John et al. (2005) [15] for sound matured kernels and Prabhu et al. (2015) [24] and Suthar et al. (2023) [30] for shelling percentage.

Conclusion

The study revealed that most of the traits studied had sufficient genetic variability which shows its potential to be improved though selection. Phenotypic selection would be more effective for enhancing for number of branches per plant, number of matured pods per plant, dry pod yield per plant (g), kernel weight per plant (g), biological yield per plant (g) and harvest index (%) as these traits exhibited high genetic coefficient of variation (GCV), phenotypic coefficient of variation (PCV), heritability, and genetic advance over mean (GAM).

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