is associated with Genetic variation of morphological and yield-related traits in backcrossed and selfed population of maize

The number of genes controlling the morphological and yield-related traits and their mode of action plays a vital role in selecting traits and favourable progenies in a segregating population. In this study, we analysed the skewness and kurtosis in the backcrossed and selfed populations of SC11-2×UMI1230 β 1 + . Negative skewness refers to redundant gene activity, positive skewness is connected to complementary gene action. Positive kurtosis suggests the existence of gene activity controlled by a smaller number of genes. Negative kurtosis shows a lack of gene activity and is controlled by a large number of genes. The BC 2 F 2 population of plant height and single plant yield showed positive skewness and platykurtic distribution, suggesting that the genes were governed by complementary gene action and controlled by the large number of genes. This implied need for rigorous selection to achieve a genetic gain in later generations. Cob length and kernel weight showed a duplicate gene action which implied that mild selection can fix these traits and accelerate genetic gain.


INTRODUCTION
Zea mays L. saccharata, known as sweet corn, is one of the most consumed vegetables in nations like the United States and Canada. It has also gained popularity in the urban market of India and other Asian nations. Sweet corn is consumed as a fresh and processed vegetable due to its sweet taste, tender nature, easy digestibility, and nutritional values (Mehta et al., 2017). Fresh sweet corn was first produced in the USA and has since been exported to several nations, where it has gained appeal as a preferred vegetable (Revilla et al., 2021). Corn is processed to lengthen its shelf life, but as a result, leaching or heat degradation might result in a large loss of nutrients . Corn gained the worldwide lead among the most significant grains produced, with a production output of 1.2 billion metric tonnes. The production volume of corn produced in India during 2021 was 30 million metric tonnes. This decreased compared to the previous year when the production volume of corn was about 32 million metric tonnes.
The critical analysis of distribution properties by third-order statistics such as skewness and kurtosis, which are more important than first and second-order statistics that reveal only the interaction effects, is usually used to determine the nature of gene action and the number of genes controlling the trait (Rani et al., 2016). The frequency distribution is a graphical depiction of the number of individuals in each category on a measurement scale (Gravetter et al., 2020). The skewness is used to indicate the nature of gene action and to quantify the symmetry of the population, or more precisely, the lack of symmetry (Fisher et al., 1932). Kurtosis identifies the number of genes that control the feature and whether the data is left-or right-tailed in comparison to its normal distribution (Robson, 1956). The non-additive gene activity will be dominant, and the genotype affects the skewness of the distribution. Positive skewness is associated with Saha et al. complementary gene activity, while negative skewness is related to duplicate gene action. Kapur (1980) classified kurtosis into three types: (i) leptokurtic (positive kurtosis), (ii) platykurtic (negative kurtosis), and (iii) mesokurtic (Zero kurtosis). Several studies have investigated the diversity and frequency distribution of maize lines that have improved nutritional content (Lal & Singh, 2014;Chandana, 2018;Nagalakshmi et al., 2018;Pukalenthy et al., 2018;Sarankumar et al., 2019).
The present study focuses on estimations of the descriptive statistics of the improved sweet corn inbred lines of SC11-2. The current research sought to investigate backcross populations (BC 1 F 1 , BC 2 F 1 , and BC 2 F 2 ) of SC11-2 × UMI 1230β1 + for descriptive statistics, frequency distribution patterns based on skewness and kurtosis and to obtain beneficial individuals with high yield coupled with adequate agronomical features.

Plant Genetic Materials
A sweet corn inbred SC11-2, developed at the Department of Millets, Tamil Nadu Agricultural University, Coimbatore, India, was selected as their current parent. UMI1230β1 + , a provitamin A biofortified maize, developed at the Centre for Plant Molecular Biology and Biotechnology, Tamil Nadu Agricultural University, Coimbatore, India was chosen as the donor parent. All the studies were carried out at the Eastern block farm, Tamil Nadu Agricultural University, Coimbatore, India, during 2019-2020.

Generation of Backcross and Selfed Progenies
The backcross population of SC11-2 x UMI1230β1 + was developed to introgress the crtRB1 favourable allele into the sweet corn inbred from the donor parent to enhance the provitamin A concentration. A single cross between SC11-2 and UMI1230β1 + was made in Rabi 2019 and the F 1 's were evaluated in Kharif 2020. The F 1 progenies were backcrossed with the recurrent parent in Kharif 2020 to generate BC 1 F 1 . The BC 1 F 1 progenies were considered in Rabi 2020. The selected plants in BC 1 F 1 were backcrossed in Rabi 2020 to generate the BC 2 F 1 generation. The BC 1 F 1 generation was grown in the Summer 2021, and the selected plants were selfed to produce BC 2 F 2 cobs. The BC 2 F 2 was raised in field and evaluated in Kharif 2021.

RESULT
The frequency distribution of the 14 morphological and yieldrelated traits was studied for SC11-2 × UMI 1230β + in BC 1 F 1 , BC 2 F 1 , and BC 2 F 2 generations. Among the traits, plant height, ear height,100 kernel weight, and single plant yield showed a wide range of variation. The frequency distribution graphs were represented in Figure 1. The cob length variation was represented in Figure 2. The statistical data of range, standard deviation, and variance were presented in Table 1. Skewness and kurtosis were presented in Table 2.

BC 2 F 1 Generation
In BC 2 F 1, plant height ranged from 162 cm to 178 cm, with a mean of 170.37 cm. The skewness calculated was -1.16, while

DISCUSSION
Skewness and kurtosis are the descriptive statistics used to study the nature of gene action and the number of genes responsible for controlling the traits. Skewness defines the cluster of deviations across the central tendency. Skewness also describes the positive or negative extend of individuals in the population. Positive skewness is associated with complementary gene action, while negative skewness describes duplicate gene action. Kurtosis is the measure of peakedness over the population. Positive kurtosis indicates the presence of gene action, which is controlled by the lesser number of genes. Negative kurtosis indicates the absence of gene action and is controlled by many genes (Pooni et al., 1977).
The backcrossed and selfed population showed a wide variation among the morphological and yield-related traits. The variations can be attributed to segregations of background alleles of the genes in consecutive generations. Positive skewness and platykurtic distribution were observed in the case of plant height and ear height, indicating that the genes were governed by dominant × dominant based complementary gene action and controlled by a large number of genes (Neelima et al., 2020). The weight of kernels exhibited negatively skewed platykurtic distribution, which suggests that the genes show duplicate gene action controlled by a large number of genes. Single plant yield showed negative skewness and platykurtic distribution in the BC 1 F 1 generation. This suggests duplicate gene action controlled by many genes (Sarankumar et al., 2019, Neelima et al., 2020. Cob length is also governed by a large number of genes showing complimentary effects, which contradicts the results reported by Pukalenthy et al. (2018). This difference can be attributed to the diverse background of the parents, sweet corn, and normal maize used in the crossing programme. This study indicates that the traits controlled by complementary gene action have to be selected in the later generations. For traits controlled by duplicate gene action, selection should be practiced in the early generations of the breeding programme.

CONCLUSION
Precise selection of morphological and yield traits is important for the success of plant breeding programmes. Statistical parameters like skewness and kurtosis explain the gene interaction and their number responsible for governing the traits. This study examined the frequency distribution and statistical analysis of morphological and yield-related traits in the backcrossed and selfed populations of SC11-2× UMI1230β1 + . The study suggested that the plant height and single plant yield were governed by complimentary gene action of several genes. Cob length and kernel weight were determined by duplicate gene action of few genes-this facilitated understanding the selection criteria for these traits in breeding programmes.

ACKNOWLEDGMENT
Financial support from the Department of Biotechnology (DBT), Government of India (GOI), through the project entitled "Incorporation of crtRB1 Allele into sweet corn inbreds and north eastern landraces for development of biofortified sweet corn" (BT/PR42333/NER/95/1866/2021 dt. 18.2.2022) is acknowledged. The funders had no role in the work design, data collection, and analysis, or decision and preparation of the manuscript.