Alkali-tolerance Of Apple Rootstock Seedlings And The Differences In Nutrient Elements Accumulation

Apple(Malus) is one of the most important temperate fruits, but its productivity is adversely affected by many environment factors. Due to the advantageous environmental conditions such as wide temperature fluctuations between day and night, deep soils and adequate light support cultivation, the arid and semi-arid regions in China are the optimal ecological zones for this crop. However, reduced rainfall together with greater soil evaporation led to severer soil alkalization, which further affects the drought-limited fruit yield and quality, hence the apple fruit industry. This can have serious consequences for the apple fruit industry. The susceptibility to damage from alkali stress is determined by the degree of tolerance by an apple rootstocks. Abundant germplasm resources of apple rootstocks with strong tolerance to various environmental challenges are already available in China, but the alkali tolerance of some apple rootstocks has not yet been fully evaluated.Therefore, it is critical to evaluate the tolerance of apple rootstocks to alkali stress, for rationally selecting and utilizing the most suitable apple rootstock resources and directionally cultivating the excellent apple rootstocks with strong alkali-tolerance. In present study, we used hydroponics culturing to comprehensively evaluate the tolerance of 17 genotypes of apple rootstocks under alkali stress, with Na2CO3: Na HCO3 = 1:1 for making p H up to 8.5,then selected Hubeihaitang(M. hupehensis Rehd., with high alkali-tolerance) and Xiaojinhaitang(M. tiaojinensis Cheng et Jiang., with low alkali- tolerance) were used as materials to study their differences in nutrient elements accumulation in roots, shoots and leaves. The results were as follows:1. Compared with the normally grown controls, alkali-stressed plants showed fewer new leaves, and shorter roots and shoots and lower fresh and dry weights after 15 days of exposure to alkaline conditions. All those indicated that alkali stress restraint apple plants’ growth and the severity varies from different genotypes. For all the alkali-stressed rootstocks, electrolyte leakage and the concentration of malondialdehyde increased while levels of chlorophyll decreased. Changes in root activity(up or down), the activities of peroxidase, superoxidedismutase, as well as catalase were rootstock-dependent, possibly reflecting their differences in alkali tolerance. Reduced root/shoot ratios indicates that the roots had been more severely damaged.2. Based on the alkali injury index, coefficients of adversity resistance, cluster analysis,and evaluation of their physiological responses, we classified these 17 genotypes into three groups:(1) high tolerance: Hubeihaitang, Wushanbianyehaitang, Laoshanhaitang Ls2,Xiaojinbianyehaitang, and Fupingqiuzi;(2) moderate tolerance: Pingyitiancha,Laoshanhaitang Ls3, Hubeihaitang A1, Deqinhaitang, Balenghaitang, Maoshandingzi,Shandingzi, and Xinjiangyepingguo; or(3) low tolerance: Pingdinghaitang,Hongsanyehaitang, Xiaojinhaitang, and Sanyehaitang.3. Alkali stress had influences on P, Na accumulations and Na/K ratio. Under alkali stress, for both apple rootstocks, Hubeihaitang(with high alkali-tolerance) and Xiaojinhaitang(with low alkali-tolerance), P content in roots, shoots and leaves were significantly reduced while Na accumulations and Na/K ratios were increased.4. The accumulations of nutrient elements differed among plant tissues of apple rootstocks and nutrient elements varied in different alkali-tolerance of apple rootstocks under alkali stress. For Hubeihaitang(with high alkali-tolerance), Mn content and Cu content were decreased in root and leaf while increased in shoot. But for Xiaojinhaitang(with low alkali-tolerance), N accumulation was elevated in shoot while reduced in root and leaf and Ca,Fe, Zn and Cu accumulations were different in different plant tissues. Under alkali stress, the decrement of P and the increment of Na in Xiaojinhaitang(with low alkali-tolerance) were severer than in Hubeihaitang(with high alkali-tolerance). For Hubeihaitang(with high alkali-tolerance), N content in shoot and the contents of Ca, Fe and Zn in leaves were decreased compared with control while increased in Xiaojinhaitang(with low alkali-tolerance). For both rootstocks, the contents of P, K and Mg were all decreased.