Effect of Sucrose Spray on some Phytochemical Characteristics of Stevia (Stevia rebaudiana Bertoni) under Field Conditions

Background: Sugars are one of the important components in the human diet, along with fats and proteins, which provide about 60-70% of their energy.Stevia is one of the most important medicinal plants with high antioxidant properties, obvious sugar characteristics, and without calories, which can replace sugars extracted from other sources.One of the features of this sweetener is that it is very useful for diabetics due to its lack of absorption in the digestive system.On the other hand, it is suitable for the diet of obese people due to its non-caloric nature.Sucrose is the transportable form of photosynthetic products, i.e. carbohydrates, in plants.Sucrose foliar spraying is important for the quick supply of compounds needed by plants.Methods: This factorial experiment was carried out based on a randomized complete block design (RCBD) with four replications at Sari Agricultural Sciences and Natural Resources University from 2014 to 2015.Evaluated treatments consisted of different concentrations of a sucrose solution (0, 2.5, 5, and 10%).Thus, the mentioned material was diluted in solvents such as methanol 15%, boric acid (3 ppm), and acetic acid (1 ppm).Treatments were sprayed on plants at 10-day intervals until plants started the flowering stage.Some parameters, such as total chlorophyll, carotenoids, total phenol, total flavonoid, antioxidant activity, steviozide, and ribodiozide contents were measured at the beginning of flowering.Results: The results of the analysis of variance showed that the simple effect of the solvent type and sucrose concentration on all studied traits at the probability level of 0.01 and the interaction effect of the treatments on all traits, except for the amount of ribodiozide, were significant at the probability level of 0.05 and on the amount of steviozide at the probability level of 0.01.The average data comparison results showed that the amount of total chlorophyll in 10% sucrose concentration was significantly higher than the other sucrose concentrations.There was a significant difference between different concentrations of sucrose in terms of carotenoid content so that the highest (10.72 mg/g fresh weight) and the lowest (9.56 mg/g fresh weight) levels were recorded at concentrations of 5% and 0% sucrose, respectively.The amount of carotenoid in the methanol solvent (11.99 mg/g fresh weight) was significantly higher than in the other solvents, namely boric acid, acetic acid, and distilled water (its lowest amount).The amount of flavonoid was significantly different between different concentrations of sucrose and also in different solvents.Five percent sucrose concentration (10.82 mg of quercetin per gram of dry weight) and zero percent sucrose concentration produced the lowest (9.31 mg of quercetin per gram of dry weight) flavonoids.Based on the results of the data, the highest and lowest flavonoid contents were obtained in methanol (11.51 mg quercetin per gram of dry weight), boric acid (10.74 mg quercetin per gram of dry weight), acetic acid (9.42 mg quercetin per gram of dry weight) ), and distilled water (8.32 mg of quercetin per gram of dry weight) solutions, respectively.The amount