Evaluation Of Salt Resistance And Nitrogen Use Efficiency Of Seven Apple Rootstocks

Apple(Malus domesica Borkh.)is one of the main fruit trees in the world.The Loess Plateau is the largest area of apple production in China.However,drought,salinity,low temperature and soil infertile have seriously affected the yield and quality of fruits in this area.Therefore,it is of great significance for the sustainable development of the industry to evaluate and identify apple rootstocks with strong stress resistance and wide suitable cultivation areas.In this study,three apple vigorous rootstocks of M.prumiolia Borkh.,M.robusta Rehd.,M.sieversii Ldb.and four apple dwarfing rootstocks of G935,M26,M9-T337 and G41 were used as materials.The tissue culture system of different materials was established,and then the clonal rootstock seedlings were obtained by subculture and rooting culture.Then,the different rootstock seedlings were independently treated with Na Cl for 10 days and low nitrogen for 40 days in hydroponic environment.The tolerance of different apple rootstocks to salt stress was evaluated by analyzing the morphological characteristics of leaves and roots of different plants under salt stress,measuring the biomass,photosynthetic parameters,chlorophyll content,chlorophyll fluorescence,relative conductivity,malondialdehyde,active oxygen ccumulation,sodium potassiumion and amino acid content and related enzymes activity of different root.By analyzing the leaf and root characteristics of different apple rootstock plants under low nitrogen stress,the biomass,photosynthetic parameters,chlorophyll content,chlorophyll fluorescence,nitrogen content and related enzyme activities of the plants were measured,and the resistance to low nitrogen and nitrogen use efficiency of different rootstocks were evaluated.The main results are as follows:1.Under salt stress,the apple vigorous rootstocks and apple dwarfing rootstocks were damaged to varying degrees.The leaves of different rootstocks showed different degrees of necrosis,and the photosynthetic parameters,chlorophyll content,chlorophyll fluorescence parameters and biomass of the plants decreased significantly.Under salt stress,the relative conductivity,malondialdehyde and hydrogen peroxide content of rootstocks increased significantly,and the amino acid content also changed to varying degrees,among which the proline content increased significantly.The antioxidant enzymes activities of different rootstocks were enhanced under salt stress.In addition,the Na~+content of rootstocks increased significantly,while the K~+content and K~+/Na~+decreased significantly.The injury degree,net photosynthetic rate,chlorophyll content,relative conductivity and malondialdehyde content of leaves of different rootstocks under salt stress were comprehensively analyzed.The results showed that the salt stress injury of M.prumiolia.was the smallest,followed by M.sieversii,and the injury of M.robusta was the largest.Among the apple dwarfing rootstocks,M9-T337 suffered the least,followed by G935,and M26suffered the most.According to the statistical analysis and cluster analysis of salt damage index,the following conclusions are drawn,Fupingqiuzi,M9-T337 and G935 were high salt-tolerant rootstocks,and Malus robusta,Malus sieversii and M26 were low salt-tolerant rootstocks.2.Under low nitrogen stress,the biomass,photosynthetic parameters,chlorophyll content and chlorophyll fluorescence of seven apple rootstocks decreased to varying degrees,the nitrogen content of each part of the plant decreased significantly,and the activities of nitrogen assimilation related enzymes such as nitrate reductase(NR),nitrite reductase(Ni R),glutamine synthetase(Gs)and glutamate synthetase(GOGAT)decreased.The low nitrogen tolerance of seven rootstocks was evaluated according to the decrease degree of different indexes.It was found that among the apple vigorous rootstocks,M.prumiolia was the least affected by low nitrogen stress,followed by M.sieversii,and M.robusta which was the most affected.Among the apple dwarfing rootstocks,M26 was the least affected by low nitrogen stress,followed by G935 and G41,and M9-T337 was the most affected.Cluster analysis was carried out by using main parameters such as biomass,Pn,chlorophyll content,nitrogen content,NUE and RGR.It was concluded that M.prumiolia,M26 and G935 were high NUE rootstocks,G41 was medium NUE rootstock,Malus robusta,Malus sieversii and M9-T337were low NUE rootstocks.