Evaluation Of Stress Resistance Of ‘Qinguan’ Apple(Malus Domestica) And M. Prunifolia

Apple is one of the most important cultivated fruit trees in the world,while China is the largest apple producer and consumer.As the main apple producing area in China,the northwest loess plateau is often threatened by drought,saline and alkaline land,soil nutrient deficiency and other stress conditions.Therefore,it is of great significance to evaluate the stress resistance of different apple cultivars and rootstocks in this region.In this study,the apple cultivar‘Qinguan’（Malus domestica）and rootstock M.prunifolia were used as test materials,four apple cultivars‘Guoguang’（M.domestica Borkh.）、‘Gala’（M.domestica Borkh.）、‘Fuji’（M.pumila Mill.）、‘Hanfu’（M.pumila Mill.）,and two rootstocks of M.sieversii Roem.,and Malus hupehensis（Pamp）Rehd.were used as control.There,eight materials were treated with long-term drought,short-term drought,salt stress and low nutrient stress,respectively.In addition,the self-rooted seedings‘Qinguan’and Fupingqiuzi were also used as test materials,with the cultivar‘Honeycrisp’and two rootstocks G935 and G41（Ottawa 3×Robusta 5）as control.These five kinds of self-root seedlings were treated with short-term drought and salt stress treatment,respectively.By measuring the physiological and biochemical indexes under different treatments,the stress resistance of different apple cultivars and rootstocks was evaluated by the method of membership function.The main findings are as follows:1.Under the long-term drought stress,the average drought injury index showed that:‘Gala’>‘Fuji’>‘Guoguang’>‘Hanfu’>‘Qinguan’,M.hupehensis（Pamp）Rehd.>M.prunifolia>M.sieversii Roem..Phenotypic analysis showed that the drought resistance of‘Qinguan’was greater than that of other cultivars,while the resistance of the rootstock M.prunifolia was greater than that of M.hupehensis（Pamp）Rehd.,which showed moderate drought resistance.The net photosynthetic rate（Pn）,chlorophyll content and decrease of WUEI‘Qinguan’seedlings were smaller than other cultivars.On the other hand,the increase of the activity of antioxidant enzymes and WUEL in‘Qinguan’were greater than that of other cultivars.For different rootstocks,Pn,chlorophyll content,decrease of WUEI and increase of MDA and H₂O₂ content in M.prunifolia is smaller than that in M.hupehensis（Pamp）Rehd.and M.sieversii Roem..Gene expression levels of PIP2:1 and TIP1:1 in M.sieversii Roem.were higher than those of M.hupehensis（Pamp）Rehd.and M.sieversii Roem..Using the above indexs to calculate the membership function,the results showed that the drought resistance of‘Qinguan’was the strongest among different cultivars,and the drought resistance of M.prunifolia was the strongest among rootstocks.2.Under the stress of short-term drought,the decrease of net photosynthetic rate,total chlorophyll content and the increase of MDA and H₂O₂ content of self-root‘Qinguan’seedlings were lower than that of‘Honeycrisp’,On the other hand,the content of proline,POD and SOD and the expression level of drought-related genes of‘Qinguan’is higher than that of‘Honeycrisp’.Besides,the content of MDA and H₂O₂ in leaves of M.prunifolia was less than that of G935 and G41,and the increase of proline,POD and SOD was higher than that of G935 and G41.The results of membership function calculation showed that the drought resistance of‘Qinguan’was higher than that of‘Honeycrisp’,and the drought resistance of M.prunifolia was greater than that of G935 and G41.3.Under salt stress,the average salt injury index showed that‘Gala’>‘Hanfu’>‘Guoguang’>‘Qinguan’>‘Fuji’,and M.prunifolia>M.sieversii Roem.>M.hupehensis（Pamp）Rehd..Phenotypic analysis showed that‘Fuji’exhibit the strongest salt resistance among different cultivars,and M.prunifolia exhibit the strongest salt resistance among rootstocks.The decrease of biomass and Pn in‘Qinguan’was greater than that of other cultivars,and the increase of root-crown ratio and relative conductivity in‘Qinguan’was smaller than that of other cultivars.The content of MDA and H₂O₂ in leaves of M.prunifolia was less than that of G935 and G41,and the increase of proline,POD and SOD was greater than of G935 and G41.The calculation results of the membership function showed that the salt tolerance of‘Qinguan’was relatively weak;the M.sieversii Roem.showed the strongest salt tolerance,and the M.prunifolia exhibited moderate salt tolerance.4.Under low nutritional stress,the decrease of dry fresh weight,total root length,chlorophyll content,net photosynthetic rate and other indexes of‘Qinguan’was smaller than that of‘Guoguang’,and these indexs of M.prunifolia decreased less than that of M.hupehensis（Pamp）Rehd..The result of membership function showed that,under nutrition deficit conditions,‘Qinguan’exhibit the strongest resistance among cultivars,and M.prunifolia exhibit the strongest resistance among rootstocks.