Effect of different SH6 buried depths on hormone and ¹⁵N-urea utilization of dwarf apple trees

【Objectives】Intensive cultivation of dwarfed apple rootstocks is becoming a direction of efficient cultivation for apple at home and abroad. The application of dwarfed interstocks is the main routinein dwarfed apple cultivation, and because of the lack of standard cultivation technique and theoretical basis in 1/2 buried of interstocks, dwarfed apple trees are in low nitrogen utilization, weak tree vigor and fast senescence. Therefore, the effectof different buried depths of interstocks on nitrogen absorption and utilization of dwarfed interstocks and the endogenous hormonewas studied, aiming to provide a scientific basis on appropriate buried depth of the interstocks in apple production. 【Methods】Two-year-old Fuji/SH6/malus hupehensis Rehd trees were selected as materials for studying the nitrogen absorption and utilization by using the 15N isotope tracer technique. The buried depths were interstocks entirely buried(T1), interstocks 1/2 buried(T2)and interstocks entirely bared(T3)respectively. There were 5 replicates, and 0.5 g 15N-urea was applied respectively. At the vigorous growing stage and stop growing stage, the hormones in stem tips and fine roots were measured using the method of enzyme-linked immunoassay (ELISA). The whole plants were sampled when the shoot stop growing, and the fresh weight and dry weight of each part were weighed, and the plant total nitrogen and 15 N abundance were detemined.【Results】The results show that the plant growth of interstocks is significantly related with the buried depth, and the height and diameter of plant, total fresh weight and fine root biomass of the T1 treatment are the highest, while those of the T3 treatment are the lowest. The content of endogenous hormonevaries with the buried depth of interstocks, and the contents of gibberellin (GA) and auxin(IAA) of different buried depths are in order of T1T2T3 at the vigorous growing stage and the stop growing stage of the new shoot, while the abscisic acid (ABA) contents show an adverse tendency. The ratio of trans-zeatin-riboside(ZR)/gibberellin(GA) in shoot tips of T2 is 8.53% and 6.06% more than those of T1 and T3 at the new shoot stop growing period. The ratios of ABA/GA and ratios of ABA/IAA of stem tips and fine roots during the period are in order of T3 T2 T1. The values of (GA+ZR+IAA)/ABA of T1, T2 and T3 in shoot tips are 1.66, 0.83 and 0.71 at the new shoot growing stage. The plant total nitrogen, 15N uptake and fertilizer utilization rate of T1 treatment are the highest, those of the T2 treatment are in the second place and those of the T3 treatment are the lowest. The Ndff values also varied among treatments, and the value of the T3 treatment is significantly higher than those of the others.【Conclusions】The interstocks 1/2 buried of SH6 reduces the content of growth promoting hormone(IAA and GA)and(GA+ZR+IAA)/ABA ratio, and increases the ZR/GA ratio which relates to flower bud differentiation significantly. The interstocks buried 1/2 treatment can balance the hormone in plant, dwarf the tree, promote the bud differentiation and then increase the absorption and utilization of nitrogen, therefore, the interstocks buried 1/2 of SH6 apple trees present the best in production.