Genetics of yield and yield contributing traits in quality protein maize (Zea mays L.)

Introduction

Maize (Zea mays L.) is one of the world's most important cereal crops and serves as a staple food, feed, and industrial raw material. It ranks after rice and wheat in global importance and contributes significantly to calorie and protein intake in developing countries. However, conventional maize protein is deficient in essential amino acids such as lysine and tryptophan, which limits its nutritional value. Quality Protein Maize (QPM) was developed to overcome this limitation through incorporation of the opaque-2 gene and modifier genes that improve protein quality. Improvement of grain yield in QPM is a major breeding objective because yield is a complex quantitative trait influenced by several genetic and environmental factors. Knowledge of gene action, combining ability, and heterosis is essential for designing efficient breeding strategies. Diallel analysis provides valuable information regarding additive and non-additive gene effects through estimates of general combining ability (GCA) and specific combining ability (SCA). The present investigation was therefore undertaken with the objective to study the genetic control of yield and yield contributing traits in QPM under different environmental conditions.

Materials and Methods

The experimental material comprised eight QPM inbred lines: HUZQPM 10, HUZQPM 9, CML 163, CML 169, CML 451(P2), HKI 193-1, VQL 1, and VQL 16. These parents were crossed in all possible combinations including reciprocals following an 8 × 8 diallel mating design. The experimental material consisting of parents and hybrids was evaluated during rabi-2023, rabi-2024, and kharif-2024 seasons. Observations were recorded for days to 50% tasseling, days to 50% silking, plant height, ear height, ear length, ear diameter, kernel rows per ear, kernels per row, 100-kernel weight, and grain yield per plant. Analysis of variance (ANOVA) was performed to determine the significance of genotypic differences. Graphical analysis following Hayman's approach was carried out using Vr-Wr regression to estimate the nature of gene action. Genetic components including additive variance (D), dominance variance (H1 and H2), net dominance effect (F), and environmental component (E) were estimated.

Results and Discussion

Analysis of variance over seasons revealed highly significant differences among genotypes, seasons, and genotype × season interactions for all traits studied, indicating considerable variability among experimental materials. Significant variation among parents and hybrids suggested the presence of diverse genetic constitution among parental lines. The ANOVA for the diallel set indicated significant mean squares for treatments, parents, hybrids, and parent versus hybrids for all yield traits. The significant parent versus hybrid contrast indicated the importance of heterosis in QPM improvement. Graphical analysis revealed different degrees of dominance for various traits. Days to 50% tasseling and silking exhibited partial dominance during rabi seasons and over-dominance during kharif season. Plant height and ear height consistently showed over-dominance across seasons. Ear length, kernel rows per ear, kernels per row, 100-kernel weight, and grain yield per plant also exhibited over-dominance in most environments. The regression analysis indicated limited genotype × environment interaction for several traits, whereas some traits exhibited epistatic interactions due to significant deviation of regression coefficient from unity. Estimates of genetic components showed that dominance variance components (H1 and H2) were generally greater than additive variance (D) for most yield traits. This confirmed the predominance of non-additive gene action. Significant positive dominance effects for grain yield per plant and related traits indicated the potential utility of hybrid breeding. The results are in agreement with earlier findings reported in maize by Haq et al. (2010) [6] , Wattoo et al. (2009) [26] , Zare et al.

(2011) [27] , and Kumar et al. (2012) [12] , who also reported overdominance for grain yield and yield attributes.

Conclusion

The present study demonstrated substantial genetic variability among QPM inbred lines and hybrids. Over-dominance and nonadditive gene action predominated for most yield traits, especially grain yield per plant. Therefore, heterosis breeding and hybrid development appear to be the most effective approaches for improving yield in QPM. The identified superior parental lines and hybrids can be further exploited in breeding programmes for development of high-yielding QPM hybrids.

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