Physiological Response Characteristics Of Malus Baccata(L.)Borkh And Malus Hupehensis(Pamp.)Rehd To Salt Stress

Soil salinization in north of China is one of the main factors limiting apple cultivation.The discovery of salt-tolerant rootstock varieties from existing plant germplasm resources is a relatively straightforward and economical way to combat salt production in apples.In this paper,the one-year-old seedlings of Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd,which are commonly used root stock of apple were used as the tested materials.By pot experiment in greenhouse to study the growth patterns,resistance physiology,ionic metabolism,under different salt concentration treatments（0,1‰,3‰,5‰）and different salt stress times and the recovery ability of growth physiology and resistance physiology after salt leaching for 25d,to explore the difference of salt tolerance between Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Reh.,provide a reliable and theoretical basis for screening salt-tolerant rootstocks.The research results as follows:（1）With the increase of salt concentration and the salt stress days prolonged the salt injure index of Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd significant rise（p<0.05）,After salt leaching for 25 days,the original 1‰salt concentration of Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd could be completely restored to the control levelthe concentration.The concentration of 5‰could not restore the dryness of the leaves,while the new leaves of Hubei Haitang grew.The original 5‰concentration of Malus hupehensis（Pamp.）Rehd grew new leaves,and the Malus baccata（L.）Borkh can not restore.（2）After 35 days of stress,the survival rate of Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd decreased with the increase of salt concentration,and the survival rate of Malus hupehensis（Pamp.）Rehd was higher than that of Malus baccata（L.）Borkh under different density salt stress.Salt stress reduced root biomass,above ground biomass,total biomass,plant height relative growth rate,relative growth rate of ground diameter,and the higher the salt concentration,the more significant the decrease（p<0.05）.However,the reduction rate of Malus hupehensis（Pamp.）Rehd is lower than Malus baccata（L.）Borkh.（3）With the increase of salt concentration,Na⁺ion content in each organ of Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd increased significantly（p<0.05）,increased greatly in roots and leaves.The increase in the roots of Malus baccata（L.）Borkh is smaller than that of the seeds of Malus hupehensis（Pamp.）Rehd,opposite in the leaves.The increase in the root of Malus baccata（L.）Borkh is smaller than that in Malus hupehensis（Pamp.）Rehd,and the opposite is true in the leaves.With the increase of salt concentration,K⁺,Mg²⁺,K⁺/Na⁺of Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd decreased,it was significantly lower than that of the control.The decline of Malus hupehensis（Pamp.）Rehd was smaller than that of Malus baccata（L.）Borkh.With the increase of Nacl concentration,the S⁺_Na、_K⁺of Malus hupehensis（Pamp.）Rehd increased firstly and then decreased in the root-stem and root-leaf,and the stem-leaf decreased gradually.the S⁺_Na、_K⁺of Malus baccata（L.）Borkh rises first and then falls in the root-stem,and gradually decreases in the stem-leaf and root-leaf.（4）With the increase of salt concentration,soluble sugar,soluble protein and proline of Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd bream increased.With the increase of salt concentration in the early stage of stress,and increased first with the increase of salt concentration in the late stress stage.As the stress time prolonged,there was a tendency to increase first and then decrease.After salt leaching for 25d,in addition to the increase of soluble protein in Malus hupehensis（Pamp.）Rehd,the soluble sugar content and proline content of Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd decreased.（5）Within a certain salt concentration range,both Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd can improve SOD,POD,CAT,APX,GR etc antioxidant enzyme activities to eliminate ROS produced under stress.Under the same salt concentration,compared with the Malus baccata（L.）Borkh,Malus hupehensis（Pamp.）Rehd can increase the antioxidant enzyme activity to a greater extent,thereby more effectively clearing the active oxygen and exhibit strong salt tolerance.In addition,under the salt stress,the content of MDA in the leaves of Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd increased gradually,and the increase of Malus baccata（L.）Borkh was greater than that of Malus hupehensis（Pamp.）Rehd.After salt leaching for 25d,the MDA content was decreased,the original low concentration salt treatment MDA can be restored to the control level,while the medium and high concentration salt treatment group is still significantly higher than the control（p<0.05）.（6）During the whole stress process,the salt treatment resulted in different degrees of ABA in the leaves of Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd,and the increase of Malus baccata（L.）Borkh was higher than that of Malus hupehensis（Pamp.）Rehd（p<0.05）.The growth-promoting hormones such as IAA,GA,and ZR increased first and then decreased,and Malus hupehensis（Pamp.）Rehd were more stable than the Malus baccata（L.）Borkh,change range was small.After salt leaching for 25 days,the ABA content decreased,and the growth-promoting hormone content such as IAA,GA,and ZR increased.（7）Principal component analysis showed that the first three principal components covered88.1%of the original 26 indicators,so the first three principal components can summarize the effects of different concentrations of Na Cl on the Malus baccata（L.）Borkh and Malus hupehensis（Pamp.）Rehd..The Survival rate,the root-shoot ratio Na⁺,K⁺,K⁺/Na⁺,MDA and salt damage index is larger in the first principal component.The second principal component coefficient is higher in seedling height,ground diameter,Mg²⁺,soluble sugar,soluble protein,SOD,PODand IAA.The larger of the third principal components is CAT.The membership function method was used to comprehensively evaluate the salt tolerance of two species of bream seedlings based on the above 16 indicators selected by principal component analysis.It is concluded that the total salt tolerance of Malus baccata（L.）Borkh bream is0.406,and the total salt tolerance of montane sylvestris is 0.269,indicating that the salt tolerance of Malus hupehensis（Pamp.）Rehd is higher than that of Malus baccata（L.）Borkh.