Combining ability and heterosis estimates for fiber yield and quality traits in NCII crosses of G. hirsutum

Background: Heterosis, i.e. hybrid vigor, is a commonly observed biological phenomenon used in crop production. The use of heterosis has greatly improved the productivity of cotton worldwide. Knowing the degree of heterosis, either relative to the parent (mean parent or better) or to the commercial control parent, is important in assessing whether hybrids outperform existing varieties. This information can influence the decision to invest in hybrid development. This research was conducted to estimate the effects of genes, heritability, and heterosis to determine the appropriate breeding methods to improve fiber quality and performance parameters and to determine the most efficient method of heterotic grouping for line classification.
 Materials and methods: In this study, seven maternal genotypes and three paternal genotypes of cotton from different heterotypic groups were crossed in the 2020 crop year in a North Carolina design (II). Three sets of hybrids produced along with their parents were grown in a baseline design of randomized complete blocks with four replicates at the National Cotton Research Institute's Hashemabad Research Station experimental field.
 Results: Analysis of the variance of the qualitative and quantitative parameters of the fibers showed that the effect of females, the effect of males, and the interaction between males and females were significant for all parameters except uniformity. The study of genetic parameters showed that the qualitative traits were affected by the additive and non-additive effects of genes. The proportion of non-additive effects in the genetic control of uniformity was higher than the additive effects, while for micronaire strength and 25% fiber length, the proportion of additive effects was higher. The high values of the narrow heritability estimates indicate that the occurrence of qualitative parameters is more influenced by genetic effects. Given the presence of additive effects and low estimates of narrow heritability for the trait kail proportion, it is promising to use breeding programs based on crosses to improve this trait. For other qualitative parameters, estimates of narrow heritability were high. Therefore, the use of breeding programs based on selection to improve these traits is promising. Examination of relative heterosis based on average parents showed that the range of heterosis was from -2.73 to 7.87%1, from 4.52 to 22.23%, from -0.05 to 4.32%, and from 1.25 to 55. For each of the micronaire, strength, elongation, and fiber quality index attributes, the heterosis was 6%.
 Conclusions: These results show that since both additive and non-additive effects are involved in controlling fiber quality, it is possible to increase the possibility of collecting suitable additive genes and exploiting variance by choosing an appropriate breeding method such as periodic selection. It provided dominance. These results provide a basis for accelerating the development of hybrids with high fiber quality in cotton.