| In the study ,one and two-year seedings of some common used in manufacture citrus rootstock seedlings: Citrus gandis(L.)Osbeck, Citrus sinensis (L.) Osbeck, Poncirus trifoliate (L.)Raf, Citrus sinensis (L.) Osbeck×Poncicrus trifoliate (L.)Raf, Citrus vessucosa Hort, Citrus erythrosa Hort ex Tanaka were investigated . Using the method of simulated rainfalls to do the soil drought stress disposal, we studied 1) different growth increments of citrus rootstocks seedlings and their drought coefficients under soil drought stress, and evaluated the tested rootstocks ' strength of drought resistance; 2)morphological change ,related change in physiological and biochemical indexes and their relationships with drought resistance; 3)the relationship between leaf tissue structure and drought resistance ;4)using subordinate function method to synthesize various morphological,physiological and biochemical indexes to obtain the integrated appraisal to different strength drought resistance; 5)in the study ,we compared the diverse reliability of morphological, physiological and biochemical indexes to point out favorable indexes of appraisal and appropriate method to evaluate the strength of drought resistance.We did pot experiment on eight citrus rootstocks seedlings for drought resistance appraisal, did long-period and different intensity drought stress disposal to different rootstocks under different annual precipitations:1000mm,800mm,600mm(1200mm as a control) and measured the drought coefficients with related growth indexes. Through cluster analysis on damage of drought index and drought coefficient under different drought stress disposal, we concluded that: in the eight rootstocks,C.erythrosa Hort ex Tanaka and C.tangerina Hort.ex Tanaka have the best drought resistance; P.trifoliate (L.) Raf.and C.chuana Hort.ex Tseng are in the medium; C.grandis(L.)Osbeck,C.sinensis (L.) Osbeck,C.vessucosa Hort and C.sinensis (L.) Osbeck×P.trifoliate (L.) Raf are weaker in the drought resistance.The study stated that under drought stress,drought coefficient with different fresh weight and the drought resistance have extremely significantly positive correlation; that drought coefficient of different plant scapus is not remarkably correlated with strength of drought resistance; that drought coefficient of different plant height and drought resistance have extremely significantly negative correlation; and that coefficient of root-shoot ratio and drought resistance are prone to the positive correlation, but not very significant. And so, drought coefficient of different plant fresh weight and coefficient of plant height can be chosen as reliable indexes to identify drought resistance in different citrus rootstocks seedlings.From observation of tissue anatomy of different citrus rootstocks seedlings leaves, we knew that leaf stomata size and strength of drought resistance have significantly negative correlation; sponge rate has extremely significantly negative correlation with drought resistance; and leaf thickness and stomata density,leaf tissue tightness respectively have positive correlation significantly and extreme significantly with drought resistance.The research also showed that under different drought stress ,leaf tissue's changes in relative water content.chlorophyll content,free proline content,soluble sugar(Ssug) content,soluble protein(Spr) content,photosynthetic rate,water utilization efficiency,abscisic acid content,suoeroxide dismutase(SOD) activity and peroxidase(POD) activity are positively significant or extremely positively significant correlated with drought resistance ; changes of penetration of plasalemma of leaf and root system and ribosylzeation(ZR) content have extremely significantly negative correlation with drought resistance; under the drought stress of the annual precipitation 600mm ,gibberrllin(GA) content and malonidial dehyde(MDA) content,transpiration rate changes have significantly and extremely significantly negative correlation with drought resistance.In the study we did relevant analysis between all leaf tissue structure,physiological and biochemical indexes under different drought stress and damage of drought index , and figured out the contribution of them to the integrated evaluation of drought resistance through Subordinate Function to draw the conclusion that citrus rootstocks seedlings leaf relative water content(RWC),cut-leaf water loss rate(CLWR),nature water saturation deficit(NWSD),water requirement and CTR are appropriate indexes to evaluation drought resistance.Research on the relationship between drought resistance and leaf tissue relative water content,relative content (the percentage of them to that under annual precipitation 1200mm) of chlorophyll a(Chla),chlorophyll,relative penetration of plasalemma (RPP)of root system,SOD activity,water utilization efficiency(WUE),abscisic acid(ABA),Ssug,Spr,free praline showed that aside from relative penetration of plasalemma's extremely significantly negative correlation, the others all have extremely significantly positive correlation coefficient; under the drought stress of precipitation :600mm , each index has extremely significantly correlation coefficient, and therefore the above relative values of every physiological and biochemical index under drought stress of precipitation 600mm can reliably reflect citrus rootstocks seedlings drought resistance.
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