Study the effects of planting date on quantitative and qualitative performance of autumn sugar beet varieties in the Gonbad Kavus region, Iran

Extended Abstract
 Introduction
Sugar beet (Beta vulgaris L) is an important crop and the main source of sugar in temperate regions. The key advantage of autumn planting over spring planting is its enhanced water use efficiency. Water scarcity in the country is one of the most important limitations in the agricultural sector. Considering the limited water resources available, promoting autumn planting is the most effective strategy to conserve water for sugar production. Considering the importance of bolting in selecting suitable cultivars for autumn planting and the influence of planting dates on bolting occurrence, an appropriate planting date can be determined for each cultivar based on its bolting resistance. The present study evaluated the effect of different planting dates on bolting, and qualitative and quantitative yield of new sugar beet cultivars.
Materials and Methods
Thirteen foreign cultivars along with two foreign control cultivars resistant to bolting (Monatunno and Rosagold), which are sown in Golestan province, and one Iranian hybrid (061) were evaluated in split plot based on randomized complete block design at Gonbad-e Kavus Agricultural Research Station (55°12' E and 37°16' N, 45 m above sea level) during 2022-23 crop season. The planting date was assigned to the main plots at two levels including 12th October  and 16th November, in order to evaluate the response of cultivars to the early and late planting. Cultivars were arranged in subplots. Each cultivar was sown in three rows with 8 m length and 50 cm space between rows and 20 cm distance between plants. Bolting was recorded at four stages (17th April, 30th April, 20th May, and 10th June). Harvest performed on 17th June. Evaluated traits included root yield (t. ha^-1), white sugar yield (t. ha^-1), sugar content (%), root impurities including sodium, potassium, harmful nitrogen (meq/100 g root pulp), white sugar content (%), and extraction coefficient of sugar (%).
Results and Discussion
Planting date had a significant effect on root and white sugar yield. With a planting date of 12th October, the average root yield was 66.1 t ha-1. A 35-day delay in planting led to a 51.5% decrease in root yield. The interaction between planting date and cultivar on root yield was significant. On 12th October, cultivars Rosagold, Monatunno, Shannon, and Granate achieved the highest root yields of 95, 82.5, 79.1, and 78 t. ha^-1, respectively. On the second planting date, Shannon, Armesa, Tikal, and Rosagold had the highest root yields of 43, 40.9, 40.8, and 38.3 t. ha^-1, r
espectively. White sugar yield was significantly influenced by planting date. A 35-day delay in planting caused a 44% reduction in white sugar yield. The effect of cultivar on white sugar yield was also significant (P < 0.05). Rosagold and Shannon showed the highest white sugar yields of 9.2 and 7.8 t ha-1, respectively. The interaction between planting date and cultivar on sugar content was significant. On 20th October, Klara, Vanila, Nero, and Castellar obtained the highest sugar content of 20.1, 19.1, 18.8, and 18.7%, respectively. On 16th November, the highest sugar content was achieved by Klara, Castellar, Vanila, Rosagold, Nero, Tikal, Souani, Algar, Shannon, and Granate. The extraction coefficient of sugar was significantly influenced by the cultivar. Planting date and cultivar significantly affected bolting. Monatunno, Semper, Quiana, and Rosagold showed no bolting and were the most resistant cultivars. By the third count of bolting (up to November 16th), none of the cultivars showed bolting. Only in the fourth count (10th June) cultivar Armesa displayed 6% bolting.
Conclusion
In autumn cultivation, the selection of cultivars is initially based on resistance to bolting, and then the final selection is made based on white sugar yield among resistant cultivars. Cultivars Monatunno, Semper, Quiana, and Rosagold exhibited no bolting and demonstrated the highest resistance. Monatunno is recommended to be planted early in the optimal planting period in Golestan Province (second decade of October) due to its high resistance to bolting and white sugar yield of 9 t ha-1, while Rosagold, with the highest white sugar yield (12.5 t ha-1) and slightly less resistance to bolting than Monatunno, is recommended for planting with a bit delay. Cultivars Semper and Quiana which also showed no bolting and had white sugar yields of 8.5 and 7.8 t ha-1, respectively, can be recommended for planting in the optimal sowing period suggested by the Sugar Beet Seed Institute, which is from the second decade of October to the first decade of November. In the first decade of November in Golestan province, cultivars Tikal, Anoure, and Granate with 4.5%, 2.3%, and 2.7% bolting, respectively, and optimum white sugar yields can also be recommended. Due to the lack of bolting in cultivars sown on 16th November, selection can be made solely based on white sugar yield, and bolting is not a limiting factor. Therefore, for planting at the end of the optimal sowing period, cultivars Shannon and Castellar, with white sugar yields of 6.5 and 5.7 t ha-1, respectively may be recommended.