Evaluation Of Water Use Efficiency Of Different Apple Dwarfing Rootstocks Under Drought Conditions

China’s apple cultivation area and output rank first in the world,and it is the largest country of apple production and consumption.Among the major apple producing areas in China,the northwest Loess Plateau is the main apple producing area,which has excellent environmental conditions such as sufficient sunshine and large temperature difference.However,this area suffers from perennial water shortage and uneven distribution of precipitation in the annual cycle.Drought and water shortage have become the main environmental factors that restrict the development of apple industry in this area.Therefore,improving the water use efficiency(WUE)of apple plants under long-term drought is an important way to improve the production efficiency of apples in this area.Comparing the water use efficiency of different rootstocks and selecting the rootstocks with high water use efficiency has an important guiding role and potential application value for improving WUE in apple orchards.In this experiment,the ‘Qincui’ seedlings grafted on 10 kinds of rootstocks were treated with long-term moderate drought in pots.The influence of different rootstocks on water use efficiency of apples was comprehensively evaluated by phenotypic comparison and physiological index determination.The key results are below:Ten kinds of apple dwarfing self-rooted rootstocks were selected and grafted with ‘Qin cui’ as scion,then long-term drought treatment was carried out under potted conditions in g reenhouse,and the physiological indexes related to plant growth and drought stress damage were measured,and the effects of each rootstock on WUE of apple under drought were ana lyzed and compared.The results showed that during drought stress,the net growth of plant height and stem diameter,relative water content of leaves,photosynthetic rate,transpiration rate,maximum photochemical efficiency(Fv/Fm),relative increase of dry matter and stom atal opening of all plants were inhibited,and the contents of malondialdehyde(MDA)and proline(Pro)and the stomatal density increased in different degrees.With the addition of dr ought stress time,chlorophyll content decreased and relative electrical conductivity increas ed continuously,and activities of SOD,CAT and POD increased at first and then decreased.WUE of ‘Qincui’ plants grafted on some of these rootstocks increased under drought stres s,while others decreased.By calculating the drought coefficient of each index,a membersh ip function was establish.Then,the WUE of these apple plants grafted on 10 different roots tocks and growth under long-term drought condition was comprehensively evaluated,and t he order of evaluation results from strong to weak was ‘M26’,‘G41’,‘M9-Pajam2’,‘M9’,‘Gx’,‘G11’,‘M9-Pajam1’,‘G30’,‘G935’,‘M9-T337’.