Study On Salt And Alkali Tolerance Of Stevia Rebaudiana Bertoni

The growth and physiology parameters of five cultivars of Stevia rebaudiana,’Zhongshan No.2’,’Zhongshan No.3’,’Zhongshan No.4’,’Shoutian NO.2’ and ’Shoutian3’were studied under NaCl,Na2CO3,NaCl-Na2CO3mixed stress by medium culture method. In the same time, the tolerance mechanism of salinity of these cultivars were evaluated. The results showed were as follow:1. The Seedings growth and the tolerances of five cultivars of S. rebaudiana were carried out under stress of different NaCl concentrations.The results showed that the biomass of the Seedings of all cultivars were gradually inhibited as the NaCl concentration increased,However, the biomass of of’Zhongshan No.3’and’Shoutian No.2’ were not significantly with that of control under4.0g·L-1and3.5g·L-1NaCl stress, respectively, and both cultivars were relatively more tolerant than others. However, the biomass of ’Zhongshan No.2’ and ’Shoutian No.31was significantly decreased under3.0g·L-1NaCl stress and was intermediately salt-tolerant. Heights and root lengths of all cultivars were decreased significantly under different NaCl treatments, while, the values of root/shoot ratio dry weight increaseed. The decreasing trend with growth parameters of leaf numbers,leaf areas,node of stem and ramification were showed under salt stress.2. The physiological response of the five cultivars of S. rebaudiana were studied under NaCl stress. It showed that salt stress of3g·L-1increased the chlorophyll content of ’Shoutian No.2’ and ’Zhongshan No.3’ in leaf under NaCl treatment after7days. With the increase of salt concentrations and treatment time prolonged, SOD and POD activity of both ’Shoutian No.2’ and ’Zhongshan No.3’ increased at beginning and then decreased. MDA contents of ’Zhongshan No.3,’ and ’Shoutian No.2’ were lower than the control. MDA content of ’Zhongshan No.2’and ’Shoutian No.3’ increase more than others under4.5g·L-1NaCl treatment after28d. Different cultivars showed different changes of proline contents and proline contents of ’Zhongshan No.2’ and ’Shoutian No.3’ increase more significantly. 3. The Seedings growth and the tolerances of five cultivars of S. rebaudiana under the stress of different Na2CO3concentrations were evaluated. The results shows that’Shoutian No.2’and’ZhongshanNo.3’were alkali-tolerant cultivars,’Zhongshan No.2’ and ’Shoutian No.3’were alkali moderately tolerant and ’Shoutian No.4’ was alkali-sensitive; The root/shoot ratio increased first and then decreased except ’Shoutian No.3’. The shoot RWC was inhibited more than the root RWC under alkali stress, the root RWC of ’Shoutian No.2’ and ’Zhongshan No.3’were higher than control under0.6g·L-1. The growth parameters of plant height, root length, leaf number, leaf areas decreased under Na2CO3treatments. Correlation analysis showed that leaf number have the highest correlation coefficient with biomass.4. The effect of Na2CO3alkali on physiological metabolism of Stevia ’Zhongshan No.4’and’Shoutian NO.2’ were carried out, the results showed that:Chl content in alkali tolerance varieties of ’Shoutian No.2’ was higher than the control after7days, and ’Shoutian No.2’ have a stronger Ch1resilience than the ’Zhongshan No.4’; Both SOD and POD activity first increased and then decreased, POD activity of ’Zhongshan No.4’ decreased at all time, Combined with changes of SOD and POD enzymes that,’Shoutian No.2’showed a relatively strong ability to stress-induced resistance than ’Zhongshan No.4’; MDA content of twocultivars have different features.’Shoutian No.2’ increased no significantly. With the extension of the processing time all varieties increases Pro conten twith different levels, Pro content of ’Zhongshan No.4’ increased more significantly than ’Shoutian No.2’after alkaline stress for28day.5. Salt solution of different intensity were simulated by mixing NaCl and Na2CO3according to5:1molar ratio. The rusult shows that some cuttings of cultivars were died under4g·L-1mixed saline-alkali stress treatments except ’Zhongshan No.3’. Survival rate of all cultivars were declined sharply as concentration more than5g·L-1. The biomass of all cultivars were declined under mixed saline-alkali stress. The plants of ’Zhongshan No.4’were died under6g·L-1under mixed saline-alkali stress. Both the root and shoot RWC of ’Zhongshan No.3’increased first and then decreased unde rmixed salt stress. While the ’Zhongshan No.4’ decreased gradually and root of ’Shoutian No.2’ showed a relatively strong water-holding capacity. Root/shoot ratio of all cultivars increased at a relatively low mixed salinity-stress except’Zhongshan No.4’.saline-alkali stress of3g·L-1induced root length of ’Zhongshan No.3’and ’Shoutian No.2’.The plant height, leaf number, leaf area, and other growth indicator were decreased under saline-alkali stress.