Line × Tester analysis for combining ability and yield it’s traits in maize (Zea mays L.)

Introduction

Maize (Zea mays L.; 2n = 2x = 20) is one of the most important cereal crops worldwide, known for its wide adaptability, high productivity, and diverse uses. As a C₄ plant, it exhibits high photosynthetic efficiency and biomass production, enabling successful cultivation across tropical and temperate regions. Due to its utilization as food, feed, fodder, and industrial rawmaterial, maize is often referred to as the "queen of cereals" and plays a vital role in global agriculture. Globally, maize is cultivated on around 200 million hectares and contributes significantly to food security, livestock production, and industrial sectors. The demand for maize continues to rise due to population growth, increasing consumption of animal products, and expanding industrial uses such as starch and biofuel production. Recent projections indicate steady growth in global production and consumption, emphasizing its economic and strategic importance. In India, maize ranks third after rice and wheat and is grown across diverse agroclimatic conditions. Its production has increased in recent years due to the adoption of improved hybrids and better agronomic practices. However, productivity remains relatively low during the Kharif season due to erratic rainfall, moisture stress, and biotic constraints. In contrast, Rabi and Zaid maize generally show higher productivity under more favourable growing conditions. In states like Uttar Pradesh, maize is cultivated across multiple seasons and contributes significantly to the cropping system, although its yield potential remains underexploited in many regions. Maize originated in Central America and was domesticated thousands of years ago before spreading worldwide. It is a highly cross-pollinated crop, resulting in considerable genetic variability and heterozygosity. While this enhances its adaptability, it also leads to inbreeding depression, making hybrid breeding essential for achieving higher productivity. The exploitation of heterosis has been a major breakthrough in maize improvement, leading to the development of high-yielding hybrids. Combining ability analysis, particularly general combining ability (GCA) and specific combining ability (SCA), is a valuable tool in maize breeding. GCA reflects additive gene effects, while SCA represents non-additive gene action, including dominance and epistasis. Understanding the relative importance of these genetic components helps breeders select superior parents and identify promising hybrid combinations. Traits governed by additive gene action can be improved through selection, whereas those controlled by non-additive effects are better exploited through hybrid breeding. With the increasing demand for maize in food, feed, and industrial sectors, including its growing role in biofuel production, there is a need to enhance yield potential and stability. Climate change, resource limitations, and biotic stresses pose additional challenges to maize production. Therefore, the development of high-yielding, earlymaturing, and stress-tolerant hybrids has become a major objective of maize breeding programmes. In this context, the present study was undertaken to evaluate the combining ability of maize inbred lines using a Line × Tester mating design. The objective was to identify superior parental lines and cross combinations for yield and its contributing traits, and to understand the nature of gene action governing these characters for effective crop improvement.

Materials and methods

Experimental site: The study was conducted at the Agricultural Research Farm of S. M. M. Town Post Graduate College, Ballia, Uttar Pradesh, India, during Kharif 2022, Zaid 2023, and Kharif 2023-2024. The experimental site lies in the middle Gangetic plains (25°33′-26°11′ N latitude and 83°38′-84°39′ E longitude) at an altitude of about 59 m above mean sea level. The region has a subtropical climate with hot summers and cool winters. The average annual temperature is around 25°C, with rainfall of approximately 648 mm, mostly received during the monsoon season. The soil is alluvial and suitable for maize cultivation.

Plant material and mating design

The experimental material comprised eight maize inbred lines (IC series) L1(IC 405284) L2(IC 569176) L3(IC 408327) L4(IC 405280) L5(IC 563954) L6(IC 584593) L7(IC 296599) L8(IC 405281) and three testers obtained from NBPGR, New Delhi. The lines represented diverse genetic backgrounds with variation in maturity, yield potential, and stress tolerance. The testers (PC-4, Jawahar, and Narmada Moti) were selected based on their agronomic performance. Crosses were made using a Line × Tester mating design (Kempthorne, 1957) [10] , where eight lines was crossed with three testers to produce 24 F₁ hybrids. Hybridization was carried out during Kharif 2022 using standard handpollination techniques, ensuring controlled crossing and genetic purity.

Development and evaluation of generations

During Zaid 2023, F₁ plants were selfed to produce F₂ seeds, and fresh crosses were also made to maintain F₁ seed. In Kharif 2023-2024, the F₁ hybrids, F₂ populations, parental lines, and three standard check varieties were evaluated in the field. The experiment was laid out in a Randomized Block Design (RBD) with three replications. Each entry was grown in three rows of 4 m length, maintaining a spacing of 60 cm between rows and 25 cm between plants. Standard agronomic practices were followed uniformly, and thinning was done to maintain one healthy plant per hill.

Data collection:

Observations were recorded on five randomly selected plants per plot, while phenological traits were recorded on a plot basis. The traits studied included days to 50% tasseling, days to 50% silking, plant height, ear height, number of leaves per plant, cob length, number of ears per plant, kernel rows per ear, days to maturity, biological yield per plant, grain yield per plant, thousand kernel weight, harvest index, and protein content. Harvest index was calculated as the ratio of grain yield to total biological yield and expressed in percentage. Protein content was estimated using the standard Kjeldahl method.

Statistical analysis:

Combining ability analysis was conducted using the Line × Tester mating design as proposed by Oscar Kempthorne (1957) [10] and further refined by V. Arunachalam (1974) [1] to assess the genetic control of quantitative traits in maize. This method partitioned the total genetic variance into general combining ability (GCA) and specific combining ability (SCA), representing additive and non-additive gene effects, respectively. The statistical model was applied, and analysis of variance was performed following R. A. Fisher (1935) [6] . Variance components were estimated using mean squares, where GCA and SCA variances were derived to determine the relative importance of gene action. The interpretation of results was based on the ratio of GCA to SCA variances, as suggested by H. F. Robinson et al. (1949) [16] , enabling identification of superior parents and cross combinations for maize improvement.

Results and discussion

Combining ability analysis (ANOVA)

The analysis of variance for combining ability revealed that mean squares due to crosses, lines, testers, and line × tester interactions were highly significant for all the characters in both F₁ and F₂ generations. This indicated the presence of substantial genetic variability among the parental lines and hybrids, and confirmed the effectiveness of the Line × Tester design in partitioning genetic components. Significant line and tester effects suggested the importance of general combining ability (GCA), reflecting additive gene action governing the inheritance of traits. Simultaneously, the significant line × tester interactions indicated the presence of specific combining ability (SCA), which is associated with non-additive gene action such as dominance and epistasis. The significance of both GCA and SCA in F₁ and F₂ generations demonstrated the involvement of both additive and non-additive genetic components, offering scope for both selection and hybrid breeding. These findings are in agreement with earlier reports of Sprague and Tatum (1942) and Moll et al. (1962) [13] .

General Combining Ability (GCA) Effects

The estimation of GCA effects revealed considerable variability among parental lines for all traits. Lines IC 296599 and IC 405281 emerged as superior general combiners for grain yield and most yield-contributing traits, exhibiting significant positive effects across both generations. Their consistent performance indicates the predominance of additive gene action and their suitability as reliable donors in breeding programmes.

Genetic implications

The simultaneous importance of GCA and SCA effects indicates that both additive and non-additive gene actions play a crucial role in controlling yield and its components in maize. Traits governed by additive effects can be improved through selection, whereas traits influenced by non-additive gene action are better exploited through heterosis breeding.

Overall, the study identified IC 296599 and IC 405281 as superior general combiners for yield, and IC 405284 and IC 569176 for earliness. Crosses such as IC 296599 × PC-4 and IC 405281 × Narmada Moti were found to be highly promising for hybrid development. These results emphasize the importance of integrating selection and hybrid breeding approaches for developing high-yielding and stable maize cultivars.

Conclusion

The study revealed significant genetic variability among maize genotypes, with both general combining ability (GCA) and specific combining ability (SCA) effects playing important roles in trait inheritance. Lines IC 296599 and IC 405281 were identified as superior general combiners for grain yield and related traits, while IC 405284 and IC 569176 were suitable for earliness. Among testers, Jawahar and PC-4 showed desirable contributions for yield and early maturity, respectively. The predominance of additive gene action for several traits suggests the effectiveness of selection, whereas significant SCA effects, particularly for grain yield, highlight the importance of heterosis breeding. Promising crosses such as IC 296599 × PC-4 and IC 405281 × Narmada Moti can be utilized for hybrid development.

Future scope and recommendations

The promising parental lines and cross combinations identified in the present study should be further evaluated across multiple locations and seasons to assess their stability and adaptability under diverse agro-climatic conditions. The superior hybrids, particularly IC 296599 × PC-4 and IC 405281 × Narmada Moti, may be advanced for large-scale testing and potential commercialization. Since both additive and non-additive gene actions were observed, a combined breeding approach involving hybrid development along with selection in segregating generations is recommended. Additionally, integration of molecular breeding tools and marker-assisted selection could enhance the efficiency of selecting superior genotypes for yield, earliness, and stress tolerance, thereby accelerating maize improvement programmes.

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