Effects Of Different Exogenous Selenium On Tomatoes And Its Application In Fortification Of Selenium

Selenium（Se）is an essential trace element for human body,and the Se needed by human body mainly comes from daily diet.Se-rich crops obtained by Se biofortification are the best choice for residents in many Se-deficient areas to supplement Se.In addition,the range between Se deficiency and poisoning level is very narrow,so it is of great significance to develop safe and effective Se supplement technology.Tomatoes are one of the most widely planted,produced,processed and consumed fruits and vegetables in the world,with high nutritional value.At present,there is no systematic study on Se biofortification of tomatoes.In this study,pot experiment and field experiment were conducted to systematically explore the effects of exogenous Se application（Se fertilizer type,Se application mode,dosage,period）on Se accumulation,transport and fruits quality of tomatoes,and the feasibility of Se and zinc biofortification of tomatoes was discussed.the Se application technology for the production of Se-rich tomatoes was established.The main results are as follows:1.The effects of different Se fertilizers,Se application methods,periods and doses on Se accumulation and fruits quality of tomatoes were systematically compared.All the experimental treatments increased the fruit biomass of tomatoes.Under the same Se application rate,the Se enrichment efficiency of different Se application treatments was soil sodium selenite>leaf spraying sodium selenite>soil application of sodium selenite,and the Se enrichment efficiency of spraying Se fertilizer in flowering and fruiting stage was higher than that in seedling stage.Exogenous Se application significantly improved the soluble sugar content,sugar-acid ratio and vitamin C content of tomatoes（Jin-mei-li-na）（except sodium selenite treatment by spraying 6 mg/plant）.Considering the Se enrichment effect,quality and production cost of tomatoes fruits,spraying sodium selenite solution（1.5 mg Se/plant）on tomatoes leaves during flowering and fruits setting stage was the best Se application scheme,but the Se content of tomatoes fruits was close to the upper limit of Se enrichment standard,so the amount of Se application in field verification experiment could be reduced appropriately.2.The effects of zinc on Se accumulation and fruits quality of tomatoes were studied.Spraying zinc and selenium or single application of selenium/zinc increased fruit biomass at flowering stage,but had no significant effect at green ripening stage.Leaf spraying zinc sulfate solution significantly inhibited fruits Se accumulation on the whole.It was worth noting that spraying 1.5 mg Se+20 mg Zn/plants at the fruits setting stage promoted the accumulation of Se in tomatoes fruits,which indicated the feasibility of dual biological strengthening of Se and zinc.At the same time,the content of manganese in tomatoes increased,but the content of iron did not change significantly under this treatment.In addition,regardless of the application period,foliar spraying Se alone inhibited the soluble sugar content and sugar-acid ratio in tomatoes fruits（Fei-te-er）,but foliar Se-zinc combined application alleviated the decrease of soluble sugar and sugar-acid ratio caused by Se application alone.According to the effects of combined application of Se and zinc on Se accumulation,quality,fruits yield and other trace elements（iron and manganese）content in fruits,it was suggested that the technology of enriching Se and zinc should be established on the basis of spraying 1.5 mg Se/plant+20 mg Zn/plant in fruits setting stage.3.The effects of spraying sodium selenite on Se accumulation and quality of tomatoes at three-ear fruits stage and topping stage were verified in the field.The Se enrichment effect of four tomatoes varieties at the third ear stage was significantly higher than that at the topping stage（p<0.05）,and the Se enrichment ability of jadeite tomatoes was the strongest.The effect of variety and Se application period on Se accumulation of tomatoes fruits was interactive,among which jadeite tomatoes had the best Se enrichment effect by spraying 42 g Na₂Se O₃/hm² sodium selenite（changed to pure Se about 19 g Se/hm²）in the third ear fruits stage,and the Se content in fresh fruits was 0.056 mg/kg,which reached the Se-rich standard（DB5115/T 17-2020）.At the same time,the application of Se in the third ear of jadeite tomatoes significantly（p<0.05）inhibited the soluble sugar content of the fruits,increased the total organic acid content of the fruits,and then reduced the sugar-acid ratio of the fruits by53.38%,but improved the taste of tomatoes.In addition,Se application did not significantly affect the soluble protein content of jadeite tomatoes fruits,but significantly increased the zinc content and iron and manganese content of jadeite tomatoes.To sum up,exogenous Se application significantly increased the Se content of tomatoes fruits,and the foliar spraying of sodium selenite at flowering and fruits setting stage had the best effect on Se enrichment.When planting in the field,it is suggested that the selenium solution of 42 g Na₂Se O₃/hm²（1.4 mg Na₂Se O₃/plant）should be sprayed on the leaves of tomatoes at the third ear stage for Se-enriched cultivation.