| The experiment was conducted in the exprimental farm and pasture of Yangzhou University(32.39 degrees N,119.42 degrees E)during 2016-2017.A comparative experiment was conducted using two rice cultivars,Wuyunjing 30(Salt sensitive)and Zhendao 23309(Salt tolerant)which were screened according to the salt tolerance evaluation of rice varieties at seedling stage,to study the effects of different salt stresses(0%,0.07%,0.14%,0.21%,0.28%,0.35%)on rice yield,morphological structure,physiological characteristics and photosynthetic characteristics,which would provide basis for further research on salt tolerance physiological mechanism of rice,selection of salt tolerant varieties for Jiangsu coastal beach.The main results were showed as below:(1)Total of 51 varieties were evaluated for salt tolerance at three leaf stage using artificial sea water(salt content was 0.5%)in this study.Results indicated that growth of the rice seedlings was obviously suppressed under salt stress.The plant height,green leaf rate,root length and dry weight were measured respectively at 6,8,10 day after treatment,which showed a significant or extremely significant positive correlation between the relative values of them.Principal component analysis results showed that plant height at 8 day,green leaf rate and root length at 10 day after treatment were the most significant factors and were recommended as the main indexes to identify salinity tolerance at rice seedling stage.The 51 rice germplasms were classified into 3 main groups with cluster analysis.Zhendao 23309 and other 6 germplasms were salt tolerant;Yanfeng 47 and other 18 germplasms were moderate salt tolerant;Wunyunjing 30 and other 25 germplasms were salt sensitive.(2)Significant differences were determined in the effects of salt levels on grain yield between the two rice cultivars.The yield of both cultivars was reduced significantly(not significant for Zhendao 23309 at 0.07%salt)under salt stress and reduced gradually with the increase of salt content,while yield of Wuyunjing 30 was decreased more compared with that of Zhendao 23309.Under low salt concentration stress(0.07%),grain yield of Zhendao 23309 was insignificantly lower as compared with the control and the yield loss rate was low when the salt concentration was 0.14%.Zhendao 23309 showed stronger tolerance to saline stress than Wuyunjing 30,under 0.07%-0.14%concentration.The salt stress negatively affected grains per spike and seed setting rate,while Wuyunjing 30 was more susceptible to salt stress.(3)The effect of saline stress on activities of protective enzymes was not only related to salt concentration,but also related to cultivars.With salt concentration increasing,the activities of superoxide dismutase(SOD),peroxidase(POD),and catalase(CAT)of two cultivars in leaves were increased at low salt levels and decreased at high salt levels,while changes of MDA content showed an opposite trend.At the salt levels of 0 to 0.14%,the amplification of antioxidant enzymes and the decrements of MDA in Zhendao 23309 were more significant than those in Wuyunjing 30,whereas an opposite trend occurred at 0.21 to 0.35%salt levels.(4)At the jointing,heading and maturation stage of two cultivars,K+content in rice plants except that in leaves and K+/Na+ were significantly decreased while Na+ content was enhanced with the increase of salt concentration.For different cultivars,the change range of K+ and Na+concentration in all parts of Wuyunjing 30 were larger than those in Zhendao 23309,and K+/Na+ in Zhendao 23309 was always higher than that in Wuyunjing 30,causing Wuyunjing 30 exposed to greater salt damage.(5)The photosynthesis characteristics of flag leaf in two cultivars showed different tolerance at different salt concentrations at heading stage.The results showed that,under low salt concentration stress(0.07%),Pn,SPAD,WUE,AMC,Fv/Fo,Fv/Fm,?PS?,qp and qN were increased significantly compared with the control.When the salt concentration was 0.14%,all parameters of Zhendao 23309 were decreased except qN,which was more resistant to salt compared with Wuyunjing 30.Both cultivars showed significant decrease in photosynthesis when the salt concentration was higher than 0.14%,with the greater decrements in Wuyunjing 30.Zhendao 23309 was more tolerant to saline stress than Wuyunjing 30 under low salt concentration(0.07%).The decrease of net photosynthetic rate was considered as a result of no-stomatal restriction turning stomatal restriction along with salt concentration increase,and different cultivars had different transitional concentration.Within a certain salt concentration range,saline tolerant cultivar could protect the photosynthetic organs more effectively than saline sentitive cultivar through enhancing the heat dissipation in leaves. |
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