Introduction: Bell pepper (Capsicum annuum L.) is one of the most important greenhouse vegetables which need high light intensity. For indoor culture, light is a limiting factor in north of Iran, so low yield due to flower abortion and disordered fruit set is a serious concern of greenhouse owners in this district. Sucrose is considered as a main soluble and transferable form of carbohydrate which move in phloem vessels. Also, potassium and magnesium are frequently reported as underlying factors for phloem loading and transportation of carbohydrates. Because of this, a research was conducted to evaluate sucrose and minerals spraying to alleviate low light intensity stress leading to flower abscission control and more yield flourishing in Bell pepper growing in glasshouses without artificial light.
Material and Methods: This experiment was carried out in factorial format based on completely randomized design with two factors: sucrose (0 and 2 ⁒) and mineral fertilizers (boric acid 0.1, magnesium nitrate 0.5, and potassium nitrate 0.5 ⁒) in four replications and three samples. Seeds of Bell pepper, variety of California Wonder, were sown in a mixture culture medium comprising coco fiber and perlite (1:1) then transferred to bigger pots after four real leaves developed completely. For nutrition of plants, a nutrition solution based on Singh et al. (2018) was used by nutrition method. Each week, two times nutrition and one time distilled water were applied. The treatments were sprayed after the appearance of reproductive organs and replicated every week till end of the experiment. Evaluated parameters included flower abscission percentage, yield and yield components, vitamin C, and total antioxidant activity.
Results and discussion: The highest flower abscission of 31.2⁒ was recorded in control plants but its difference with boron and magnesium treatments was not statistically significant. Maximum number of fruit per plant (with 31.16 fruits) was produced in treatments of sucrose+ potassium and sucrose+ magnesium without significant difference between each other. The highest yield of 3653.85 g fruit per plant was observed in Sucrose+ Potassium which was significantly more than all tested treatments. In contrast, the lowest yield was produced in control plants and plants treated by solely boron. The treatments of solely sucrose and solely potassium caused moderate yield without significant difference between themselves. Total carbohydrates of generative organs including flowers and fruits was highest in sucrose+ potassium treatment with no significant difference with sucrose+ magnesium treatment indicating the importance of potassium and magnesium for sucrose translocation. All used treatments in this experiment caused more phenolic contents in comparison with control, therefor applying sucrose and minerals can elevate the nutritional value of Bell pepper fruits. Although the highest total antioxidant activity was achieved in plants treated by sucrose+ potassium, the difference among other treatments was not statistically significant. Treatment of sucrose+ potassium contributed to 180 mg vitamin C per 100 g extraction which was significantly more than all other treatments except sucrose+ magnesium. Results obviously showed that sucrose spraying in 2% concentration led to significant increment of total soluble solids in Bell pepper fruits.
Conclusions: Results showed that exogenous sucrose can partly supply Bell pepper carbohydrate need. Sucrose treatment alongside with potassium could decrease flower abscission and increase yield, antioxidant properties, and vitamin C, so it can be concluded that the mixture of sucrose and potassium can ameliorate the stress of low light intensity in Bell pepper especially in greenhouse cultivation. Moreover, evidences indicated that both potassium and magnesium have a crucial role in sucrose transportation from source to sink. Because of this, spray of sucrose plus potassium and magnesium can be absolutely recommended.