Absorption And Transformation Of Exogenous Selenium And Its Effects On The Preservation Of On-tree Fruit Of Longan

Selenium is an essential micronutrient for humans and animals,and selenium deficiency in human body can cause many diseases.Selenium resource is rich in Guangxi province,and longan is one of the most important economic fruit trees in Guangxi province.However,there are rarely reported about the characteristics of selenium absorption and transferring when applied with exogenous selenite or selenate.In addition,the mature stage of longan fruit was relatively short,the flavor and qualities were worsening rapidly with the harvest time delayed.So far,researches of the changes and regulation of fruit qualities on-tree storage were lack relatively.The longan seedlings as experimental materials was tested.Plot trials were conducted to identify the characterisitics of uptaking and transferring with exogenous selenium applied in longan seedlings.Various rates and methods(root-applied fertiliser,foliar application)of applying Se(selenite and selenate)were evaluated,and to determine whether applying other fertilisers(superphosphate,urea)would affects its uptake,and field trials were conducted to identify the effects of selenium on fruit qualities,minerals content and antioxides activities when longan on-tree storage.The aim of this study was to provide a theoretical basis for the production of Se-enriched longan and the regulation of maturity.The main results were as follows:(1)When foliar or root application of selenium,the biomass of shoots and roots decreased significantly if the selenate and selenite concentration reached 50 mg/L and 25mg/L respectively.Increasing selenium concentration caused a progressive reduction in dry weight,both roots and shoots.However,at low concentration exerted beneficial effects on the plant's growth.Selenate application was more stronger in bioavailability and toxicity for dry matter production of shoot and root than selenite.(2)When foliar application of selenium,content of selenium primarily accumulate in shoot,the rate of transferring in longan seedlings was faster with selenite than selenate.However,when root application of selenium,content of Se primarily accumulate in root with selenite,there no significant difference in content of Se weather selenite or selenate application.(3)The concentration of selenium in longan shoots and roots significantly increased as selenate and selenite rates increased;by contrast,the concentration of selenium decreased in longan root treated with selenate,nitrogen fertilizer had a significant effect on the absorption of sodium selenite,phosphate fertilizer has a significant promotion effect at low concentration,and has a significant inhibitory effect at high concentration,there was not significant interaction between nitrogen fertilizer and phosphate fertilizer.(4)Foliar application of selenium significantly increased the selenium content of longan leaves and fruits,and the selenium content in leaves and fruits increased with the increase of concentration.The highest selenium content in leaves and fruits appeared at sixth days and ninth days after the application of selenium,respectively.And the content of selenium in fruit has reached 5.86?g/Kg when spraying with 50 mg/L Na2SeO3.(5)When sprayed with 15?50 mg/L Na2SeO3,the abscission of fruit can be obviously reduced,the time of on-tree storage has been extented 2-3 d,and the content of soluble solids,titratable acid,soluble sugar,vitamin C can be alleviated,maintaining a higher qualities.(6)The content of K and Ca can be obviously improved by spraying Na2SeO3 with different concentrations,however,there was no obvious effect on Mg content in pulp.Correlation analysis showed that K was positively correlated with titratable acid,and Ca was positively correlated with soluble solids,soluble sugar,titratable acid and vitamin C,there was no significant correlation between Mg content and fruit qualities.(7)There was significantly decrease in the content of MDA in peel and pulp by spraying 15?50 mg/L Na2SeO3,membrane lipid peroxidation was alleviated,increased SOD,CAT and POD activity in pericarp and pulp,so as to improve the scavenging ability of reactive oxygen species.