Evaluation of quantitative and qualitative yield, bolting rate and Cercospora leaf spot disease severity of different sugar beet genotypes in autumn cultivation

Extended Abstract
 Introduction
Autumn cultivation of sugar beet presents a viable solution to mitigate water scarcity issues in sugar beet production by leveraging its inherent advantages in plant growth and water use during the autumn and winter seasons. This cultivation method benefits from the seasonal precipitation patterns thereby reducing dependence on irrigation and contributing to water conservation. However, a significant challenge in autumn cultivation is the occurrence of bolting, where the plant transitions from vegetative to reproductive growth. Bolting negatively affects both the quantitative and qualitative yield of sugar beet, posing a serious threat to the economic feasibility of autumn cultivation. Consequently, the identification and development of bolting-resistant cultivars specifically adapted to autumn cultivation is of paramount importance. This study aims to evaluate the quantitative and qualitative yields, bolting rates, and resistance to Cercospora leaf spot disease of various sugar beet cultivars under autumn cultivation conditions. The findings are intended to support the selection of cultivars that can maximize yield while minimizing the adverse effects of bolting and Cercospora infection, ultimately enhancing the sustainability and productivity of sugar beet cultivation in water-limited regions.
 Material and methods
The study utilized a set of 19 experimental sugar beet hybrids, along with a control cultivar named Antek which has been specifically developed for bolting resistance. Field evaluations were conducted across two provinces: Fars (Fasa) and Khuzestan (Dezful), representing different environmental conditions. The experimental design was a randomized complete block design with four replications conducted over  the 2023-2024 growing season to minimize spatial variability. Data collection included counting the number of established plants before and after the frost period, determining the number of bolted plants in early June, and calculating the bolting percentage based on the total number of plants. Due to the absence of bolting at the Safiabad Agricultural Research Station in Dezful, this evaluation was limited to the Fasa Research Farm. The severity of leaf infection with Cercospora leaf spot disease was recorded on a scale of 1-9 in Dezful. All traits were examined for normality of distribution, and non-normal data were estimated using statistical methods. Variance analysis and mean comparison based on Duncan's multiple range method were performed on traits such as white sugar yield, root yield, sugar content, white sugar content, sodium content, potassium content, amino nitrogen content, extraction coefficient of sugar, and molasses sugar percentage. Cluster analysis of experimental genotypes in terms of disease severity was conducted using t he Ward method. All analyses were performed using Excel and R software to ensure accuracy and reliability of the results.
Results and discussion
The effect of genetic diversity on yield was clearly demonstrated in this study, as the genetic diversity among experimental genotypes significantly influenced most of the studied traits, including white sugar yield, root yield, sugar content, white sugar content, root sodium content, and sugar extraction efficiency. At the Fasa Research Farm, genotypes T-10075 and T-10042 exhibited the highest white sugar yields, averaging 18.44, and 18.07 t ha^-1, respectively, and were significantly superior to the control cultivar at the 1% probability level. At the Dezful Research Station, genotypes T-10038, T-10076, and T-10073 showed higher white sugar yields compared with other experimental genotypes, with average yields of 10.25, 9.52, and 8.41 t ha^-1, respectively, also significantly superior to the control cultivar. The evaluation of bolting rate at the Fasa Research Farm identified several genotypes with high resistance to bolting; 16 experimental genotypes did not show any bolting compared with the control variety Antek. Genotype T-10061 exhibited a low bolting rate of 1.58% and ranked second in terms of bolting resistance, while genotypes T-10043 and T-10053 had higher bolting rates of 8.74% and 10.92%, respectively, making them unsuitable for autumn cultivation. Based on the evaluation of white sugar yield and bolting rate, two genotypes—T-10075, and T-10042—are recommended for cultivation in regions with climatic conditions similar to Fasa, given their high average yields and absence of bolting. The evaluation of resistance to Cercospora leaf spot disease at the Safiabad Agricultural Research Station in Dezful revealed varying levels of resistance among the genotypes. Genotypes T-10075 and T-10076, along with the bolting-resistant control Antek, were classified in the resistant group, while genotypes T-10052, T-10053, T-10069, and T-10062 were classified as semi-resistant, and the remaining 13 genotypes were semi-susceptible. Notably, genotype T-10076 exhibited a high white sugar yield (9.52 t ha^-1), resistance to Cercospora leaf spot disease, and no bolting, making it highly recommended for cultivation in Dezful.
 
Conclusion:
In conclusion, this study highlights the significant impact of genetic diversity in influencing yield and resistance traits of sugar beet genotypes. The identification of high-performing genotypes such as T-10075, and T-10042 for white sugar yield and bolting resistance, and T-10076 for its integrated performance in yield, bolting resistance, and Cercospora leaf spot resistance, provides a strong foundation for future breeding efforts. These findings underscore the importance of comprehensive evaluations across multiple environments to identify genotypes with superior agronomic traits, ultimately contributing to the sustainability and productivity of sugar beet cultivation..