Dynamic Analysis Of Photosynthetic Characteristics And Glycoside Content Of Stevia Rebaudiana And Screening Of Fine Lines

Stevia rebaudiana Bertoni,belongs to perennial short day plants of compositae,which is native to Paraguay,Brazil,Argentina and other subtropical high altitude areas,is a new type of natural sweetener,with low heat energe,high sweetness,do not participate in metabolism,non-toxic and so on.In this paper,6 strains were selected as materials,new variety "Huinong No.4" as control?hereinafter referred to as "Hui 4"?,using randomized block experiment design.The photosynthetic physiological characteristics,dynamic changes test of Glycoside content in different growth period and agronomic traits for different genotypes of stevia were investigated,and the high yield and high quality lines of stevia were screened.This study lay the foundation for new species declaration and provide a theoretical reference for guiding the appropriate harvest period of stevia.The main findings are as follows:1.Investigation of agronomic traitsThe agronomic traits in field were related to the leaf yield of stevia.There was a significant positive correlation between leaf length and dry leaf yield,stem yield,fresh plant yield,and positively correlated with fresh leaf yield.Plant height and dry leaf yield,fresh plant yield,stem yield and fresh leaf yield all have a significant positive correlation.There was a negative correlation between growth period and yield traits,such as dry leaf yield,fresh plant yield,stem yield and fresh leaf yield,but not significant.In yield traits,there were significant positive correlations among dry leaf yield,fresh plant yield,stem yield and fresh leaf yield.Among the seven tested lines,the dry leaf yield of two materials higher than control species 'Huinong No.4',the order of dry leaf yield from high to low was 4×2B1-16>H7>Hui4>Y13>-5-1>B13-5>4 +.2.Changes in photosynthetic physiological characteristicsIn this study,the order of average photosynthetic rate from high to low was as follows:H7>4×2B1-16>Hui 4>Y13>4+>B13-5>-5-1;the average transpiration rate of different strains was Hui4>H7>Y13>B13-5>4+>4×2B1-16>-5-1;During the whole study period,the order of average stomatal conductance was H7>4×2B1-16>Hui 4>4 + B13-5>Y13>-5-1;the intercellular CO₂ concentration was 4×2B1-16>Y13>-5-1>B13-5>4+>Hui 4>H7.3.Dynamic change of glycoside?1?The content of GT in different stevia lines was 9.43%?17.75%.During the whole study period,the content of GT in the five materials Hui4?4+?Y13?4×2B1-16?B13-5 showed a bimodal curve change,and the peak appeared in different periods.Among them,the highest GT content of 'hui 4' appeared in post-anthesis,while 4+,B13-5,Y13 three materials appeared in the middle period of growth,4×2B1-16 appeared in florescence.The peak of-5-1 appeared in the middle stage of growth,and the H7 appeared at bud stage.The highest GT content of different lines was B13-5>4+>Y13>-5-1>H7>4×2B1-16>Hui4.?2?In our survey,RA content of Hui 4 and B13-5 showed a decreasing trend,and the maximum RA content was 7.44%and 11.76%at the initial stage of growth,respectively.The highest RA content of Y13,4 +,-5-1,H7,4×2B1-16 appeared in the middle stage of growth,and the value was 9.75%,10.17%,10.14%,8.31%and 8.78%,respectively.The order of highest RA content of all tested materials was B13-5>4 ?>-5-1>Y13>4 ×2B1-16>H7>Hui 4.?3?STV content varied between 0.26%?8.45%from the initial stage of growth to later stage of blooming and went straight up in Hui 4?4+?Y13?4×2B1-16?-5-1?H7 with different time in peak,but they all happened in later stage of blooming with exception of B13-5,which showed a high-low-high profile.The lowest value of B13-5 appeared in the budding period,consistent with time of the lowest glycoside level.4.Correlation analysis of Photosynthesis.glycoside and dry leaf yield in different periodsObvious differences were not observed during initial period between the photosyn-thetic physiological characteristics and the yield of glycosides and dry leaves while during middle groth the correlation coefficient was high There was a significant correlation between the photosynthetic rate and the transpiration rate of the stevia.In squaring stage,a significant negative correlation exists between the concentration of CO₂ and total glycoside,STV/?RA + STV?,STV glycosideit which showed extremely significant negative correlation.A significant positive correlation exists between the concentration of CO₂ and RA/GT and RA/?RA + STV?;There was a significant negative correlation between the transpiration rate and RA during the Flowering stage.At the later stage of flowering,there was a significant negative correlation between STV glycoside and RA/GT and RA/?RA + STV?,and STV/?RA + STV?showed a significant positive correlation with dry leaf yield.5.Excellent Stevia species determinedConprehensive analysis shows that high quality and high yield is the primary condition and the goal of breeding.The results showed that the peak content of B13-5 RA was in the early stage of growth,the content of RA was up to 11.76%and the harvest time should be from the initial stage of growth to the middle of the harvest.The content of STV glycosides was 8.45%and 7.63%,and dry leaf yield of the two materials were is relatively high,which is 169.41kg/hm² and 430.90 kg/hm² higher than Hui 4.