Physiological Response to Shade and Shade-tolerant Capability of Hevea brasiliensis Seedlings of Different Varieties

In order to compare the different adaptive ability of rubber seedlings to irradiance change among six varieties(‘GT1',‘RRIM600',‘PR107',‘Yunyan 77-4',‘Yunyan 77-2'and‘Reyan 523'),we grew the seedlings of each variety in four irradiance levels(100%,50%,25%,5%)for one year,then we compared some biochemical parameters of seedling leaves at dry and rainy season.The results indicated:(1)For each variety,there were significant differences for SOD,SS,Suc,Chl,Chl a/b,SP and RMP among four irradiances,and the varieties also have significant effect on these parameters.(2)For each variety,in dry season,SS and Chl decreased and SOD,SP,Suc,Chl a/b,Pro and MDA increased significantly when compared with rainy season.(3)For all six varieties,SP,SS,Suc,SOD and MDA decreased with the decreasing irradiance.(4)Seven parameters(SP,SS,Suc,SOD,Pro,Chla/b and MDA)were found that are strongly correlated with physiological adaptation to irradiance.(5)Comprehensive evaluation with subordinate functionmethod,we found‘RRIM600',‘Yunyan 77-4'and‘Yunyan 77-2'have stronger,while‘Reyan 523'has weaker adaptive ability to irradiance change,and‘GT1'and‘PR107'are intermediate.