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Full Research Article

Variability and Association Analysis in Groundnut Germplasm Lines for Yield and Yield Attributing Traits

K. Hariharan1, J. Vanitha1,*, R. Mahendran1, K. Satheeskumar2, Burusu Malini1, S.S. Kaviyarasan1
  • https://orcid.org/my-orcid?orcid=0009-0004-5175-2242
1Department of Genetics and Plant Breeding, SRM College of Agricultural Sciences, SRM Institute of Science and Technology, Chengalpattu-603 201, Tamil Nadu, India.
2Department of Basic Sciences, SRM College of Agricultural Sciences, SRM Institute of Science and Technology, Chengalpattu-603 201, Tamil Nadu, India.

ABSTRACT

Background: The present study was conducted using groundnut germplasm lines obtained from ICRISAT, Hyderabad to analyse the genetic variability and association among 93 groundnut germplasm lines along with 5 checks for yield and yield attributing traits.

Methods: An experiment was done to study 14 quantitative traits in 98 groundnut genotypes for yield and yield components. Data analyse for variability and correlation were done using R studio version 4.4.2 software.

Result: The traits of plant fresh weight, 100 pod weight, 100 seed weight, plant dry weight, kernel color, kernel shape, 100 shell weight and shelling percentage had high PCV and GCV. Shelling percentage had negative correlation with plant fresh weight, 100 pod weight, plant dry weight and 100 shell weight and it is positively correlates with the number of primary branches. These traits may be utilized as selection indices to improve yield in the groundnut breeding program.

INTRODUCTION

Groundnut (Arachis hypogaea L.) is a part of the Papilionaceae subfamily within the Fabaceae family (Kulheri et al., 2022 and Suchitra, 2022). Groundnut is the “king of oilseed crops” due to its high protein and oil content (Menge et al., 2018 and Meena, 2021). It is among the most significant oilseed crops that are cultivated worldwide in semi-arid and subtropical climates (Ibrahim et al., 2024). Groundnut ranks as the fifth most cultivated oilseed crop worldwide, occupying approximately 27.9 million hectares and producing 47 million tons annually with an average productivity of 1676 kg/ha. India ranks second after China in production. Groundnut global cultivation spans across 4.96 million hectares, yielding 10.03 million tons with a productivity of 1616 kg/ha (FAOSTAT, 2023).

Groundnut is a predominantly self-pollinated crop and is having less variation. Also it is an unpredictable legume due to the geotropic orientation of the pods. The available variability is being exhausted due to vicious breeding cycle of selection-hybridization-selection. Hence, it is necessary to access the extent of genetic variability available in the groundnut  germplasm to have a successful crop improvement program.

Groundnut is primarily cultivated as a rainfed crop in various countries around the world. Yield tends to be low and unstable under rain-dependent conditions due to erratic rainfall and frequent droughts during the growing season. This instability is intensified by the poor adaptation of improved varieties and the impact of drought stress varies based on its intensity, duration, growth stage and the specific genotype. Drought stress during critical reproductive phases, such as flowering and pod filling, significantly affects yield. However, tolerant groundnut varieties can achieve considerably better yields due to physiological and biochemical changes that occur in response to drought stress. This understanding is crucial for effective peanut breeding programs. Yield and quality in peanuts can be significantly influenced by environmental conditions.

Due to its allotetraploid nature, groundnuts had relatively low genetic variation. Therefore, to improve groundnut yield, breeding programmes should enrich genetic variability. Genetic variations are pivotal in crop improvement schemes. The presence and extent of the variations enable the selection of new genotypes with diverse traits. Heritability measures the specific traits which is inherited by offspring. Creating and utilizing diversity through appropriate breeding practices is the first step for genetic improvement.

The evaluation of genetic variation and the extent of transmission of desirable traits is deciding the successful breeding program. To separate the total variability into heritable and non-heritable factors, it is necessary to observe the different plant traits and its relationship with each other traits.

Additive gene activity and selection conditions are responsible for traits with high heritability and genetic gain. To improve groundnut production, breeding program must identify component traits that affect productivity. To make seed selection and increase pod yield, it is needed to know the degree of genetic variation, as well as how traits are inherited (Chauhan et al., 2022).

Any successful crop breeding programme, depends on the amount of variability in the source population. Generally genetic variability is estimated at variance level. But, the coefficient of variation is free from units and is comparable with any other trait. Hence, in the present inquiry the coefficient of variation at phenotypic and genotypic levels were estimated. Heritability was estimated to quantify the extent of genetic variation available in the reference population for the traits of interest. Genetic gains that are harvestable were also quantified the traits with high heritability coupled with high genetic gain were identified and to utilize in the current plant breeding programme.

MATERIALS AND METHODS

Five check varieties and ninety-three test genotypes obtained from ICRISAT, Hyderabad (Table 1), were used in the experiment. During Kharif 2024, these genotypes were sown in an augmented design in SRM College of Agricultural Sciences. Four blocks were used to repeat each check. The spacing adopted was 30 x 10 cm. The crop was raised in two rows plot of 3 m length. Recommended agronomic practices and need based plant protection measures were judiciously followed under irrigated conditions. Observations were recorded on 14 morphometric traits viz., days to 50% flowering (DFF), plant height at maturity (PH), number of primary branches (NPB), number of secondary branches (NSB), leaf size (LS), flowers on main axils (FMA), plant fresh weight (PFW), plant dry weight (PDW), 100 pod weight (HPW), 100 seed weight (HSW), kernel color (KC), kernel shape (KS), shelling percentage (SP) and 100 shell weight (HSW) were included for the analysis. Six plants were selected at random for each entry in each replication and their data were recorded. Biometric genetic analyses were performed by following the standard procedure, outlined by Burton (1952). The data were analysed using R software version 4.2.2.

Table 1: List of 98 groundnut genotypes assessed for yield and associated traits.

RESULTS AND DISCUSSION

The availability with sufficient diversity is an essential objective for any crop breeding program since it allows for selection based on predetermined goals. The estimates of the genetic variability parameters for the 98 genotypes in each of the 14 observable traits are presented in Table 2.

Table 2: Estimate of the mean, range and genetic variability for 14 quantitative traits in 98 groundnut genotypes.



The traits under this investigation are influenced by several genes. They are also significantly impacted by environmental factors. GCV is preferable since PCV considers environmental influences. It calculates the amount of total variability that is heritable (Allard, 1960). However, selection requires additional information than solely the genotypic coefficient of variation. GCV illustrates the possible genetic advantages of selection using heritability estimates (Burton, 1952). Genetic variability, heritability and selection intensity are therefore necessary for genetic advancement. GCV and PCV differed the least for the majority of characters studied (Thakur et al., 2013; Rao et al., 2014).

There was significant phenotypic and genotypic variation for every trait examined in the experiment, which included 98 germplasm lines. Low GCV and PCV indicated that the days to 50% flowering trait was not suitable for selection. Strong environmental influence on these traits is shown from the low GCV. A narrow genetic base for this trait is suggested by this study, which is consistent with earlier research on groundnut variability that similarly found low GCV and PCV for days to 50% flowering, according to Kadam (2016) and Vasanthi et al., (2015).

A high phenotypic coefficient of variation (PCV) and a modest genotypic coefficient of variation (GCV) for leaf size and the number of primary branches may suggest that these traits are influenced by the environment. The number of secondary branches, on the other hand, had low GCV and moderate PCV. Characteristics such as shelling %, kernel color, kernel shape, 100 shell weight, 100 pod weight, 100 seed weight, plant fresh weight and plant dry weight all showed significant PCV and GCV. Similar patterns of variations in shelling percentage were observed by Vinithashri et al., (2019), Mitra et al., (2021) and Zaman et al., (2011).
 
Heritability and genetic advance as per cent of mean
 
Estimates of heritability illustrate the inheritance patterns of traits. Developing selection strategies is aided by genetic advancement. There is little genetic advancement and heritability in the number of secondary branches. Non-additive gene action is indicated by this trait. According to Nath and Alam (2002), phenotypic selection for these traits will not be very successful.

There is considerable genetic advancement and moderate heritability for characteristics such as plant dry weight and the flowers on main axis. The number of major branches and days to 50% flowering indicate a moderate level of genetic advance with high heredity. Shukla and Rai (2014), Yadav et al., (2023) and Poojitha et al., (2024) all reported similar results.

Several traits showed high genetic advance and high heritability. Plant height, leaf size, plant fresh weight, plant dry weight, 100 pod weight, 100 seed weight, kernel color, kernel shape, shelling percentage and 100 shell weight indicated these high genetic advance with high heritability. According to Mitra et al., (2021), a substantial additive variance in 100 pod weight is indicated by a stronger genetic advance with high heritability. Plant height at maturity, number of flowers on the main axis, plant fresh weight, plant dry weight, 100 pod weight, 100 shell weight, kernel color and kernel shape recorded high heritability estimates coupled with high genetic advance over mean. Hence, the aforementioned traits may be under the control of additive gene action. So, selection for these traits would be rewarding, immediately. This implied that additive gene activity primarily governs these traits, enabling improvement by direct selection.
 
Correlation among yield components
 
The data illustrated the relationships among yield components. This understanding will contribute towards improving yield traits and overall productivity in breeding programs (Table 3).

Table 3: Phenotypic correlation coefficients between 14 groundnut characteristics.



Days to 50% flowering exhibited positive correlation with multiple traits, including the number of secondary branches, plant dry weight and 100 shell weight. Plant height is significantly correlated with the number of secondary branches, leaf size, plant dry weight and 100 shell weight.

Number of primary branches had positive correlation with secondary branches but negative one with plant fresh weight, 100 pod weight, plant dry weight and 100 shell weight. Number of secondary branches showed a strong positive correlation with leaf size and plant dry weight, but a negative correlation with kernel colour. Leaf size positively correlated with plant dry weight. The leaf is vital for photosynthesis, respiration and transpiration in plants. Transpiration rates increases with larger leaf areas. This happens because wider leaves typically contain more stomata. Additionally, breeders use leaf dry weight as a key indicator of a plant’s resource use strategy.

The presence of flowers on the main axils exhibited negative correlation with plant fresh weight and 100 shell weight. Plant fresh weight exhibited positive correlation with 100 pod weight, 100 seed weight, plant dry weight, kernel shape and 100 shell weight. Significant correlation was observed between 100 pod weight and both 100 seed weight and plant dry weight. In addition, 100 seed weight was significantly associated with both plant dry weight and kernel color. Plant dry weight exhibited a significant positive correlation with 100 shell weight, while it negatively correlated with kernel colour. The shape of the kernel exhibited positive correlation with the 100 shell weight. Shoba et al., (2012), Rao (2016) and Rajarathinam et al., (2017) reported analogous findings concerning pod yield.

Shelling percentage positively correlates with the number of primary branches but negatively with plant fresh weight, 100 pod weight, plant dry weight and 100 shell weight. Shukla and Raj (2014), Vijayasekhar (2002), Pavan Kumar et al., (2014) and Yenikalayci (2021) found similar results for shelling percentage. Shelling percentage is crucial for seed yield in crops like peanuts, as it shows the ratio of edible seeds in harvested pods. Typically, as pod weight increases, shelling percentage decreases. In simpler terms, larger pods tend to have a lower seed weight compared to their total weight.

CONCLUSION

This study reveals significant genetic variability among the 98 groundnut genotypes for most of the 14 traits examined, offering promising ways for selection. Traits like plant height, pod weight and shelling percentage exhibit high heritability and genetic advance, suggesting effective improvement through direct selection due to additive gene action. Conversely, traits such as days to 50% flowering and the number of secondary branches show limitations for direct selection due to environmental influence or non-additive gene action. The identified correlations among yield components provide crucial insights for developing targeted breeding strategies to enhance overall productivity in groundnut.
 

ACKNOWLEDGEMENT

The authors are thankful to ICRISAT, Hyderabad for providing valuable groundnut germplasm resources.
 

CONFLICTS OF INTEREST

The authors declare no conflict of interest.

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