Genetic gains in yield and quality traits of Iranian sugar beet cultivars over four decades

Sugar beet breeding has been a vital area of research in Iran for over eight decades, with the aim of improving the yield, and quality of this important crop. In this study, an analysis of the progress made in sugar beet breeding over the past 40 years has been presented. This study utilized 15 cultivars of sugar beet. Phenotypic evaluations of these experimental cultivars were carried out across two successive crop years (2022 and 2023). The experimental design adhered to a randomized complete blocks setup with four replications. In the assessment of sugar beet cultivars introduced between 1983 and 2023, the newer cultivars exhibited notably higher white sugar weight (WSW), marking a significant upward trend over the years. Analysis of root weight (RW) and white sugar content (WSC) trends indicated substantial enhancements in these key components impacting WSW. Peak values were evident in the most recent cultivars, contrasting with lower values recorded in earlier decades. Exploring the components of WSC further, sugar content (SC) showed a significant upward trajectory, while molasses sugar percentage (MS) showcased a distinct decrease. Noteworthy declines in sodium (Na⁺) were observed, in contrast to a non-significant rise in potassium (K⁺) and a highly significant increase in alpha-amino nitrogen (N). Pearson's correlation analysis identified positive correlations between WSW and factors like SC, RW, and N. A negative correlation was observed between WSW and Na⁺, emphasizing the importance of minimizing Na⁺ levels for optimal sugar production. A regression analysis identified SC and RW as the key contributors to WSW variations. Path analysis confirmed the positive direct effects of RW and SC on WSW. Additionally, an indirect positive effect of SC on WSW through RW was identified. Overall, this study highlights significant breeding progress in sugar beets, with substantial improvements in WSW, RW, and WSC. Therefore, breeding programs should focus on enhancing both RW and SC to achieve optimal sugar yield.