Effects of foliar application of selenium on fruit quality and medicinal in- gredients of seabuckthorn

Abstract:【Objective】Selenium (Se) is one of the essential trace elements in the human body, and it is the composition ingredient of glutathione peroxidase (GPX). It is of great significance for preventing cardiovascular and cerebrovascular diseases, and improving the body’s immunity and delaying aging, and therefor it is called‘life elements’by the medical community. Seabuckthorn is a medicine and food homologous forest fruit. Its leaves and fruits contain a variety of vitamins, amino acids and a large amount of flavonoid compounds and fatty substances. It has a good clinical efficacy in anti-oxidation, anti-tumor and reducing high blood pressure, high blood sugar, and high blood lipids. The forest fruits have a good absorption conversion effect as a selenium carrier. However, there have been few reports on the effct of application of selenium on fruit quality and medicinal ingredients in Xinjiang seabuck- thorn. The aim of this paper was to study the effects of foliar application of selenium on the main nutri- tional indicators and medicinal components of seabuckthorn fruits and to clarify the tolerance of seabuckthorn trees to selenium and the optimal concentration for the spray of selenium.【Methods】The variety of Xinjiang seabuckthorn Wucifeng was used as the experimental material. The experiments were  performed in the town of Agedala, Qinghe county, Xinjiang, China. The soil of the field was sandy and yellow brown with pH 7.19, organic matter 23.83 g·kg-1, alkalihydrolyzable nitrogen 137 mg·kg-1, available phosphorus 10.34 mg · kg- 1, available potassium 188 mg · kg- 1, and total Se 0.091 9 mg · kg- 1. The planting density of seabuckthorn trees was 1800 plants·hm-2, the spacing is 2 m×4 m. The sodium sele- nite (Na2SeO3) solution was selected as selenium source for the experiment. There were seven Se con- centrations for spray treatment including 0, 5, 10, 20, 50, 100, 200 mg · L- 1. Randomized blok design was used, four trees for each treatment, each treatment was repeated three times. The amount of water for each tree was 1 L. Spray was conducted in the fruit expansion period (June 22, 2020), one spray ev- ery 15 days, and the spray of clear water was used as the control (CK). Totally six sprays were conduct- ed until September 18. The seabuckthorn fruits samples collection was performed on September 27, 2020, and three bags samples were randomly picked up from each sample tree. The samples were placed in the insulation foam boxes equipped with a ice bag and were taken back to the laboratory, stored in the -15 °C refrigerator. The pulp and seeds were separated for analyses of Se content, moisture contents, protein, Vitamin C, total acid, soluble sugar, polysaccharide, flavonoid and fat content in various parts of the fruit (peel, seed, pulp) of seabuckthorn fruit. The values of each item obtained from dif- ferent treatments were subjected to ANOVA and significant difference analysis by SPSS 20.0 software. Excel 2019 were used to accomplish the data finishing and generate graphs and tables【. Results】Spray- ing Na2SeO3 significantly increased Se content of the seabuckthorn fruits and the increment increased with the increase of Se concentration. When the treatment concentration was too high (100 mg · L- 1 to 200 mg·L-1), leaves of the seabuckthorn trees turned yellow and fell off. The various quality indexes decreased to various degrees. Except for moisture contents, with the continuous increase of spray concen- tration, the protein, vitamin C, total acid, soluble sugar, polysaccharide, flavonoid and fat content in var- ious parts of the fruit (peel, seed, pulp) of seabuckthorn fruit showed a trend of increase first and then decrease to various degrees. The optimal treatment for each index is compared with the control. The selenium content of the fruits for the treatment 7 was 0.448 6 mg·kg-1，which was 83 times as much as that of the control. The protein content of the fruits for the treatment 4 was 1.918 2% , which was 155.62% of that of the control. The vitamin C content of the fruits for the treatment 5 was 186.4 mg·100 g-1, which was 162.51% of that of the control. The total acid content of treatment 2 and treatment 6 were 6.67 mg·kg-1 and 9.11 mg·kg-1, respectively, which was 87.08% and 118.93% of the control. The poly- saccharide content and soluble sugar content of the fruits for the treatment 4 were 9.63% and 4.59%, re- spectively, which were 104.89% and 23.39% of those of the control. The flavonoid content of the fruits for the treatment 4 was 185 mg · 100 g- 1, which was 81.37% of those of the control. The fat content (peel, seed, pulp) of the fruits for the treatment 4 was 16.65 mg · 100 g- 1, 18.98 mg · 100 g- 1, and 13.06 mg·100 g-1, which were 48.26%, 38.44%, and 39.08% of those of the control. This paper used the weighting method to evaluate the comprehensive impact of various indicators. The treatment 4 had the highest comprehensive impact evaluation score (92.5). Finally, it was determined that the optimal spray-1 -2concentration was 20 mg · L .【Conclusion】For seabuckthorn, at a spraying volume of 1800 L · hm , the highest safe concentration of Se was 100 mg·L-1. The protein, vitamin C, total acid, soluble sugar, poly- saccharide, total flavonoid, and the fruit (peel, seed, pulp) fat content of the seabuckthorn treated with the optimal spray concentration were all increased compared with the control. In particular, the seleni- um content of the seabuckthorn fruits increased by about 10 times, and the selenium content reached the standard for selenium-rich forest fruits.