Physiological Response To Drought Stress And Drought Resistance Evaluation Of Rhododendron Cultivars

Rhododendron is one of ten flowers in Chain,which has beautiful flowercolor and shape.And it has broad ecological applications and high omamental value.Rhododendron is an important garden greening plants in city.But Rhododendron has poor drought resistance,which limits its use in gardens of arid areas in North China.Therefore,study on the drought resistance of Rhododendron could provide a theoretical basis for its application in northern arid gardens.Four Rhododendron cultivars: R.’Lan Yin’,R.’Quo Qi Hong’,R.’Ai Ding Bao’,and R.’Fen Zhen Zhu’,were selected as test material.leaf anatomic structural characteristics and physiological responses to different degrees of drought stress were studied(2 factors 3 level complete randomized trial).A membership function was also used to rank drought resistance.In addition,two Rhododendron cultivars which has poor drought resistance: R.’Lan Yin’ and R.’Ning Bo Hong’ were selected as test material.Based on the observation of the external morphology and the determination of physiological indexes,the effect of the leaf on the stress resistance of Rhododendron was evaluated.Using the method of membership function to evaluate the effect of foreign aid hormone salicylic acid on Drought Resistance of Rhododendron.The results showed that:(1)Total water content of the leaf and the content of soluble sugar increased significantly as drought stress increased(P<0.05),but the content of chlorophyll,carotenoids,and the content of soluble proteins decreased significantly(P<0.05).In addition,cell membrane permeability significantly rose(P<0.05);whereas,peroxidase(POD)activities went up first then down.Furthermore,the H2O2 content of R.’Lan Yin’,and R.’Ai Ding Bao’ declined as drought stress increased,but H2O2 content of R.’Quo Qi Hong’ and R.’Fen Zhen Zhu’ decreased significantly(P<0.05)first and then increased significantly(P<0.05).Above all,the order of drought resistance was: R.’Lan Yin’ < R.’Quo Qi Hong’ < R.’Fen Zhen Zhu’ < R.’Ai Ding Bao’.(2)Key indicators and relativities in evaluating drought resistance of these Rhododendron cultivars were thickness of palisade tissue,0.850;thickness rate of palisade,0.733;sponge tissue,0.711;proline contents,0.893;leaf relative water content,0.703;and the content of H2O2,0.699.(3)The suitable concentration of salicylic acid can improve foreign hormone free water content,leaf bound water content and total water content of Rhododendron;can promote the synthesis of chlorophyll and carotenoid increased;soluble sugar,soluble protein and proline in cells such as cell infiltration through concentration regulating substances;superoxide dismutase and the activity of peroxidase and catalase,thereby reducing drought stress on Rhododendron damage,improve the drought resistance of Rhododendron.At the same time,too high concentration of foreign aid hormone salicylic acid is not conducive to improve the drought resistance of Rhododendron.And for R.’Ning Bo Hong’,the drought resistance was the best when theconcentration of salicylic acid under is 0.3mmol·L-1,followed by 0.5mmol·L-1 and 0.7mmol·L-1;and for the R.’Lan Yin’,the drought resistance was the best when the concentration of salicylic acid is 0.7mmol·L-1,followed by 0.3mmol·L-1 and 0.5mmol· L-1.