عنوان مقاله [English]
Introduction: Sugar beet (Beta vulgaris L.) is well-known as the second most important sugar-producing crop after sugarcane, contributing to more than 30% of world sugar production. Water stress is considered one of the main factors in reducing Sugar Beet yield, and therefore it is necessary to use strategies to reduce its adverse effects. the external application of growth regulators under stress conditions eliminates the lack of internal plant regulators and reduces the damage of stress on plant growth. Exogenous PA application can effectively upregulate the situation; among different types of PAs, putrescine, and spermidine were found to have the greatest significance in plants' water stress. polyamine can respond to different abiotic and biotic stresses by regulating physiological processes. The purpose of this research is to investigate the effect of irrigation regimes and polyamine foliar spraying on quantitative and qualitative traits and nutritional elements of Sugar Beet.
Materials and methods: This experiment was conducted as split plots based on a randomized complete block design with three replications in Rokh plains of Torbat Heydarieh city Torbat Heydarieh region of Razavi Khorasan province in 2020. The main plots were allocated to irrigation treatments including 100, 75 and 50% of water requirement and the subplots were allocated to polyamine treatment in the form of foliar spraying including putrescine (1 and 0.5 mM), spermidine (1 and 0.5 mM) and control (without foliar spraying) were placed in sub-plots. Drought stress was applied on the 8-leaf of the vegetative growth stage. The foliar application was made in two stages:8 leaves and the middle stage of the growing season (18 to 20 leaves). One week after foliar feeding, nutrients including nitrogen, phosphorus, potassium, calcium, magnesium, iron, zinc, copper, manganese, and boron were measured in leaf samples. At the end of the growing season, quantitative traits including the fresh and dry weight of the shoot, root weight, and root yield, and qualitative traits including the percentage of sugar, harmful nitrogen, potassium, and sodium were measured.
Results and discussion: The results showed the effect of polyamine foliar spraying and irrigation on all functional traits including biological yield, root yield, root dry weight, leaf fresh and dry weight and sugar content, qualitative yield traits including sugar yield, white sugar yield, extractable sugar and coefficient extraction of sugar and leaf nutrients was significant. In the foliar application of polyamines, 1 mM putrescine treatment had the highest quantitative, qualitative, and leaf nutrients, which has no significant difference with 1 mM spermidine. A significant difference was also observed between irrigation levels in all functional traits. Water stress caused the reduction of nutrients in the leaves and the highest amount of elements were obtained from the full irrigation treatment. The effects of polyamines * irrigation on some traits such as root yield, sugar yield, and white sugar yield were significant and there was no significant difference between putrescine and spermidine treatment at 100% and 75% of field capacity irrigation. In the mild stress treatment (75% irrigation), the amount of root yield was lower compared to the 100% irrigation level, at the same time, a small difference in root yield was observed between the application of two types of polyamine used at the level of 1 millimolar and the level of mild stress. Therefore, with foliar spraying of polyamines in the amount of one millimolar at a mild stress level, the root yield equivalent to the optimal irrigation level was reached.
Conclusion: In general, foliar spray with polyamines significantly improves the morphophysiological traits, Quantitative and qualitative yield of sugar beet and reduces the negative effect of drought stress, which is probably due to the important role of these elements in the process of osmotic regulation and other physiological, nutritional and biochemical reactions of plants. Therefore, polyamine foliar spraying (putrescine and spermidine) in 1 mM concentration with 75% of FC irrigation is recommended in sugar beet cultivation, especially in drought-stress conditions. These findings collectively provide a critical illustration of the use of polyamines in modulating drought tolerance in sugar beet plants.