Effect of foliar selenium supplementation on selenium content in red beauty
Li Xiaocheng et al
Red Beauty is a new citrus hybrid introduced from Japan, with a female parent of Nanka and a male parent of Amakusa, officially registered as Ehime Fruit Test No. 28, commonly known as Ehime 28. This variety is loved by consumers because of its orange-red skin, superior pulp residue to other varieties, excellent taste, rich in sugar, and sweet orange aroma. The ripening period is in late November and the ripening period is in early December each year, and the price is usually higher than that of ordinary varieties. Nowadays, people's living standards are constantly improving, and the demand for fruits is gradually shifting from simple appearance and flavor to high-quality fruits with excellent health care functions, and the demand for the quality of red beauties is also increasing. In China, products such as selenium-rich rice, Kaiyang selenium-rich loquat, Daozhen selenium-rich tea, and selenium-rich potatoes are also being introduced to the market and become geographical indication products. Xiangshan selenium-rich red beauty conforms to the development of the times and the needs of modern people, and has certain production and sales prospects.
Selenium is an indispensable trace element, it has the effect of antioxidant and enhancing the function of the immune system in the human body, can improve the activity of glutathione peroxidase, selenase and other enzymes, plays a very important role in the human body, protects the human body from immune-related diseases, and is known as the "king of anti-cancer". The lack of selenium in the human body puts the body in an unhealthy or sub-healthy state, resulting in the dysfunction of some key organs, which in turn leads to a variety of serious diseases. More than 40 countries worldwide face selenium deficiency. Among them, hundreds of millions of people in 22 provinces in China live in selenium-deficient or low-selenium areas, and the incidence of hemolytic anemia, Keshan disease, ischemic heart disease and other diseases in these areas is significantly higher than that in non-selenium-deficient areas. Studies have shown that moderate selenium supplementation has a positive effect on disease prevention, health promotion, and anti-aging.
Selenium can be divided into 2 forms, namely plant-active selenium and inorganic selenium. Inorganic selenium is commonly referred to as sodium selenite (Na2SeO3) and sodium selenite (Na2SeO4). Inorganic selenium compounds are highly toxic and not easily absorbed, so they are not suitable for use by humans and animals. In contrast, plant-active selenium is formed by biotransformation and binding of amino acids, usually in the form of selenomethionine, which is a safe and usable source of selenium for both humans and animals. In the production of functional fruits with high commercial value, the quality of the final product is as important as the selenium content. Therefore, it is necessary to analyze the effect of specific treatments on the quality of the final product in order to test the effect of foliar selenium spray on the fruit and to ensure the marketability.
In this study, two different selenium-containing solutions, namely sodium selenite solution and plant selenium nutrient solution, were used to study the selenium content and fruit quality of red beauty orange, and the effects of sodium selenite spraying solution and different frequencies of plant selenium nutrient solution on red beauty were explored, so as to provide a scientific basis for the rational selenium supplementation of red beauty in agricultural production in the future.
1 Materials and methods
1. 1 Experimental materials
The test was set up in Wenling Shuguang Modern Agriculture Co., Ltd., and the citrus for the test was a seven-year-old red beauty, and the rootstock was a goutou orange anvil. Basic soil fertility status of the test orchard: Soil pH 8. 4, Soil organic matter content is 22. 3g·kg-1; The contents of hydrolyzable nitrogen, available phosphorus and available potassium were 88 and 63, respectively. 8、 472mg·kg-1。
1. 2 Dealing with design
The trial consisted of 4 treatments. Water was used as the control (T0), and T1 was sprayed with sodium selenite 150mg·kg-1, sprayed once every 15 days, and sprayed 3 times continuously. T2 ~ T4 sprayed plant selenium nutrient solution, organic selenium (plant selenium nutrient solution) was prepared into a solution concentration of 13. 3ml· L-1。 1 spray of T2; T3 is sprayed 2 times continuously every 15 days; T4 was sprayed 3 times continuously every 15 days.
1. 3 Sample collection and measurement
Sample collection. On October 19, 2022, normal growth fruits were picked around the middle of the canopy, 3 fruits were randomly picked from each tree, and a total of 15 fruits from 5 trees were used as a sample, and each treatment was repeated 3 times. After the samples were washed with deionized water, the water on the fruit surface was absorbed with filter paper and sealed and stored in a plastic bag for subsequent experiments. At the time of the assay, each sample will be measured 2 times in duplicate and then averaged.
Assay method. The weight of a single fruit is weighed on an electronic balance, and the sugar content is weighed using a saccharide meter. The first method for the determination of selenium content (SeC) in citrus fruits of Red Beauty was determined by AF-610A protofluorescence spectrometer according to the "Determination of Selenium in Food Safety National Standard Foods" (GB5009.93-2017).
1.4 Data analysis
The experimental data were statistically analyzed and graphed by SPSS ANOVA and Origin software, and the significance level was 0. 05。
2 Results and Analysis
2.1 Effect of foliar selenium spray on selenium content in red beauty fruit
According to the results of Table 1, compared with the control group (T0), the selenium content of C. rubrica increased significantly after 40 days of T1 treatment, and reached a level consistent with the content of selenium-rich fruits, indicating that foliar spray of sodium selenite solution could effectively increase the selenium content of C. chinensis fruits. According to the results of Wen Mingxia et al., when the selenium concentration of foliar spray solution was 200mg· kg-1, the selenium content in the fruit is 0. 021 ~0. 024mg · kg-1。 The highest selenium content in food should not exceed 0. 3mg·kg-1, the limit of selenium in fruits is less than or equal to 0. 05mg · kg-1, therefore, the upper limit of the selenium concentration of spraying is 200 mg·kg-1. In this experiment, the selenium concentration of sodium selenite solution was 150mg·kg-1. As can be seen from Table 1, the selenium content in fruits increased significantly after foliar spraying of plant selenium nutrient solution once, twice and three times, respectively, and reached the standard of selenium content in fruits.
Table 1 Effect of selenium nutrient solution on selenium content in fruits
Note: The absence of the same lowercase letter after the same column of data indicates significant differences between different treatments (P<0.05).
2.2 Effect of foliar selenium spray on fruit yield
According to Table 2, the foliar selenium supplementation method in the experiment did not adversely affect the current fruit yield. This means that growers can take advantage of this technology to increase the selenium content in their fruits without worrying about any adverse effects on existing fruit yields. Foliar selenium supplementation can improve the nutrient quality of the product while maintaining the original yield of fruits.
Table 2 Fruit yield in different experimental groups
2. 3 Effect of foliar selenium spray on agronomic traits of fruits
According to Table 3, the basic growth and quality characteristics of the fruit, such as skin thickness, fruit longitudinal diameter, fruit transverse diameter and number of fruit splits, were not affected by foliar selenium supplementation. Therefore, growers can confidently adopt foliar selenium supplementation to improve the nutrient content and health levels of their produce while maintaining crop yield and agronomic traits. This dual benefit highlights the effectiveness and practicability of foliar selenium spraying to increase selenium content in fruits.
Table 3 Agronomic traits of fruits in different experimental groups
2. 4 Effect of foliar selenium spray on fruit quality
One of the key factors influencing the mouthfeel and flavor of a fruit is its balance of acidity and sweetness, i.e. the sugar-acid ratio. According to the data in Table 4, the sugar-acid ratio of fruit was not significantly adversely affected by foliar selenium supplementation.
Table 4 Fruit quality in different treatment groups
2. 5 Safety evaluation of selenium content in red beauty fruit
In this experiment, when sodium selenite solution at a concentration of 150mg·kg-1 was sprayed three times, the selenium content in the red beauty citrus fruit was 0. 015~0. 020mg·kg-1, based on the consumption of 2 red beauty fruits (total weight 400g) per person per day, the amount of selenium ingested by the human body is 20μg. According to the recommendations of the Chinese Nutrition Society, the recommended intake of selenium in a day varies among different age groups: the recommended intake of selenium for children under 7 years old within 1 day is 15 ~ 35μg; The recommended intake for adolescents over the age of seven to under eighteen is 35 ~ 50μg; The recommended amount for adults is 400μg. According to the results of Table 1, the selenium content of selenium-rich red beauty fruit obtained by foliar spray of 1, 2 or 3 times of selenium nutrient solution was within the safe amount of selenium supplementation for children and adults, so there was no potential threat of selenium poisoning when consuming selenium-rich red beauty. In selenium-rich areas, due to the high selenium content in the soil, local agricultural products and farmed animals are often rich in selenium, which can more easily consume enough selenium, thereby strengthening the immune system, reducing the risk of selenium-related diseases, and promoting overall health. However, naturally produced animal and plant products in selenium-deficient areas cannot meet the body's demand for selenium. Therefore, the production of selenium-rich fruits plays an extremely important role in improving the daily dietary selenium intake of residents in selenium-deficient areas.
3 Discussion
Sodium selenite belongs to inorganic selenium, and foliar spraying of sodium selenite solution can be converted from inorganic selenium to organic selenium in citrus during plant production during the plant production stage, and the intake of selenium in selenium-deficient people can be increased by eating selenium-rich red beauty citrus. The experimental results showed that the method of foliar selenium spraying to produce selenium-rich citrus had obvious effect, and the selenium content was within the safety standard. Therefore, the production of safe fruits can be achieved by foliar selenium supplementation at the young fruit stage of red beauty citrus. This method helps to ensure that the fruit receives an adequate supply of selenium at the beginning of growth, thereby increasing the selenium content and improving the nutritional value of the fruit. The plant selenium nutrient solution is an organic selenium nutrient solution, which can be directly absorbed into organic selenium in citrus without transformation after foliar spraying, and the selenium content of red beauty fruit increases with each increase in the number of spraying, but no absorption inhibition phenomenon is found, indicating that the absorption of selenium in citrus is cumulative, or because the selenium concentration sprayed in this experiment does not reach the concentration that inhibits absorption.
At present, in practice, the method of external selenium addition is mostly used to produce selenium-rich fruits. There are mainly soil selenium application, leaf selenium application, soaking seed dressing, and soil and foliar combined selenium application, which can improve the selenium content in plants. Reasonable selenium application is an effective cultivation measure to increase the selenium content and improve the fruit quality of tree fruits, but there are certain drawbacks of soil selenium fertilizer, that is, the utilization efficiency is low. The study of Qin Yuyan et al. showed that in terms of increasing the selenium content of fruits, foliar selenium spraying increased selenium content much more than soil selenium fertilizer. Therefore, it is more cost-effective to produce selenium-rich fruits by foliar spray. However, foliar selenium sprays also have some drawbacks, such as high selenium fertilizer concentrations may cause damage to the skin of the fruit, increasing the potential risk of excessive selenium content in the fruit. Controlling the concentration and frequency of spraying is key to ensuring the appearance and safety of the fruit.
4 Conclusion
The results of the experiment showed that spraying sodium selenite at the young fruit stage of Red Beauty could be converted into citrus organic selenium after the fruit was ripe, and it was necessary to spray it at the young fruit stage, not too late, and avoid the high temperature period when spraying foliar spray, which was prone to pesticide damage. Foliar spraying of plant selenium nutrient solution, no need to convert after spraying, directly absorb organic selenium, with the increase of the number of spraying, the selenium content in the red beauty fruit gradually increased, the ingredients are more safe and reliable, and it is not easy to appear pesticide damage.
The selenium content of the fruit increased significantly after spraying sodium selenite, but sodium selenite is an inorganic selenium, which needs to be converted into organic selenium by plants, which may lead to low selenium absorption efficiency. Moreover, inorganic selenium compounds are toxic and may have an impact on the health of operators during the spraying process. Therefore, in the second half of the experiment, the spraying effect of organic selenium solution instead of inorganic selenium solution was studied, that is, selenium nutrient solution replaced sodium selenite solution, which increased plant utilization efficiency and protected the operator. The effect of spraying frequency on selenium content was also studied. The results showed that foliar spraying of selenium nutrient solution could also increase the selenium content in fruits, and the selenium content increased with the increase of spraying times. Fruit quality and yield are not affected by foliar selenium spray.