Exploring Sugar Beet Traits and Molecular, Quantitative, and Qualitative Analysis with a Focus on Bolting Resistance

Extended Abstract Background: Sugar beet has various applications and nutritional benefits. It contains a high concentration of sucrose, making it a significant source of sugar. Autumn sugar beet is superior to spring cultivation due to its high production potential, optimal use of seasonal rains, low water requirement, and fewer pests and diseases. Considering the above-mentioned advantages, besides Khuzestan, the issue of autumn beet cultivation is discussed in other regions of the country, such as Fars, Kerman, Kermanshah, Ilam, Golestan, Khorasan, and Ardabil (Moghan) provinces. Resistant plants to bolting should be used due to planting in autumn and wintering of the plant. The bolting phenomenon, as one of the limiting factors in autumn sugar beet cultivation, severely affects the quantitative and qualitative performance of the product, especially in early planting fields. In years with cold and long winters, foreign and domestic sugar beet varieties depend on the existing weather conditions and face different bolt percentages. Therefore, foreign seed-producing companies send their bred varieties to the sugar beet seed institute every year to evaluate the bolting rate and quantitative and qualitative performance. This research was carried out at the request of the representative of Lion Seed Company in Iran to explore the hybrid varieties in the Golestan region as autumn cultivation. This research aims to firstly introduce a superior hybrid resistant to bolting and then investigate the relationship of the candidate molecular markers with the tolerance of genotypes to bolting. In the future, therefore, it can be used for the molecular screening of genotypes resistant to bolting in the institute. Methods: The present study was conducted by evaluating six different sugar beet cultivars at the Gonbad Agricultural Research Station during the 2022-2023 cropping season. The experiment was based on a randomized complete block design with four replications. The evaluated traits included root yield, white sugar yield, sugar content, sodium content, potassium, alpha amino nitrogen, white sugar content, extraction coefficient of sugar, and bolting percentage. The disease severity of the experimental cultivars to Cercospora was also recorded in this study. To genotype the studied cultivars, leaf samples were collected from bolting-sensitive and resistant plants in spring for a molecular assay using candidate markers. After obtaining the phenotypic data, the normality of the data was examined before any analysis. After confirming the normality of the experimental data, analysis of variance and mean comparison were performed using the least significant difference test for the studied traits. The simultaneous selection index of the multi-trait genotype-ideotype distance index (MGIDI) was calculated in R software to rank and select the superior cultivars based on all studied traits. Results: The results of the analysis of variance for the traits showed that the experimental cultivars were significantly different in all traits, including root yield, white sugar yield, sugar content, sodium content, potassium, alpha amino nitrogen, white sugar content, extraction coefficient of sugar, and bolting percentage, except for the Cercospora score. The mean comparison results of the experimental cultivars in terms of root yield confirmed the superiority of the Jerra cultivar with an average yield of 34.97 tons per hectare. The lowest root yield was obtained by the SHR01-P.12 cultivar with a yield of 47.25 tons per hectare. Among the six studied cultivars, five cultivars, including Jerra, Klara, Juncal, Shannon, and Granate, contained the highest values of white sugar yield with averages of 71.10, 22.10, 74.9, 69.9, and 36.9 tons per hectare, respectively. The SHR01-P.12 cultivar contained the lowest white sugar yield. According to the results, Klara, Granate, Juncal, and Shannon cultivars ranked first with 61.16, 39.15, 30.15, and 16.15% sugar content and 93.13, 26.12, 48.12, and 05.12% white sugar content, respectively. Klara, Juncal, Shannon, Granate, and Jerra cultivars had the lowest sodium content, while SHR01-P.12 had the highest level. In terms of potassium impurity, Klara, Juncal, Jerra, and Granate cultivars had the lowest values. The highest value of this trait belonged to the SHR01-P.12 cultivar. The SHR01-P.12 cultivar had the lowest alpha amino nitrogen content with an average of 12.1 milliequivalents per 100 g of root pulp. The highest alpha amino nitrogen content was recorded for the Granate cultivar. The highest extraction coefficients of sugar in the experimental cultivars were observed in Klara, Juncal, Granate, Shannon, and Jerra with averages of 82.83, 37.81, 64.79, 49.79, and 43.77%, respectively. The Jerra cultivar had no bolting and ranked first in terms of the lowest value of this trait. The Granate and Juncal cultivars ranked second with averages of 69.2 and 49.5%, respectively. The highest bolting percentage was recorded for the SHR01-P.12 cultivar with an average of 42.93%. Based on the MGIDI selection index, with a selection pressure of 30%, the Juncal cultivar ranked first with an MGIDI value of 21.0, followed by the Shannon cultivar with a value of 25.0. The SHR01-P.1 cultivar had the highest MGIDI value (56.2) and was considered an undesirable cultivar. Regarding the candidate molecular markers associated with bolting tolerance, two candidate markers showed relevant polymorphism, two candidate markers presented random polymorphism, and five other candidate markers were devoid of polymorphism. Conclusion: The results showed that the genetic diversity among the experimental cultivars caused different responses in the evaluated traits. However, the extent of the impact of genetic diversity on traits can vary depending on the conditions. The newly introduced cultivars are suitable for autumn sugar beet cultivation in Golestan Province, aiding in bolstering the nation's sugar production. Moreover, the polymorphic markers linked to bolting tolerance identified in this study can serve as valuable tools for upcoming research endeavors and the selection of bolting-resistant sugar beet breeding lines.