Genetic analysis of sugar yield and physiological traits in sugar beet under salinity stress conditions

Salinity is one of the most important constraints in sugar beet production in Asia. An understanding the genetic basis of sugar beet (Beta vulgaris) performance under salinity stress is crucial to gaining insight into salinity tolerance trajectories as well as to designing appropriate breeding strategies in saline stress conditions. In this study, a mating design (North Carolina Design II) was used to generate 116 hybrid combinations (29 × 4) from four male sterile and ten pollinator parents in sugar beet. Genetic variance components, combining ability, and heritability of 24 physiological and root yield and quality related traits were estimated by growing the hybrids and their 14 parents under normal and salinity stress conditions in the field. The results showed high genetic variation among the tested populations for most of traits. Estimates of genetic components for root, sugar and white sugar yield showed higher contribution of the dominance variance (σD2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \upsigma_{\text{D}}^{2} $$\end{document}) than the additive variance (σA2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \upsigma_{\text{A}}^{2} $$\end{document}) in both growing conditions, but with much greater magnitude of the σD2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \upsigma_{\text{D}}^{2} $$\end{document} values observed for saline conditions. Narrow-sense heritability (Hn) was generally higher in stress environment for physiological traits compared to those of normal ones and the reverse held true for the yield traits. The results of general combining ability (GCA)for the yield traits showed a non-consistent trend across normal and stress environments. Both GCA and specific combining ability (SCA) were found to be important for the performance of individual hybrid combinations, and no clear relationship between GCA and SCA was found for these sugar beet genotypes. Given the higher impact of dominance variance and the lower narrow sense heritability of sugar yield in saline conditions compared to normal conditions, it can be concluded that hybrid breeding strategy should be more favored in saline environments than normal environments.