Impact Of Juvenility On The Adventitious Rooting Of Leafy Cuttings In Apple Rootstocks

The application of apple dwarfing rootstocks is great guarantee to realize orchard garden’s intensive production and management. For perennial woody plants, cutting propagation is an efficient technique of rapidly propagating apple dwarfing rootstocks with a higher coefficient, shorter cycle and lower cost than layering, but inducing stem occur adventitious roots is the key to success for cutting. In order to establishing an efficient and rapid propagation system of apple dwarfing rootstocks cutting, in the paper, juvenility, IBA and H2O2were studied about the influence of rooting ability of apple dwarfing rootstocks.In the experiment, Malus xiaojinensis (MX), SH1, SH6, M9, M26etc. were used as material to study rooting ability of different apple rootstocks and influence factors of leafy cuttings rooting. Shoot apical meristem in adult reproductive phase MX, shoot tip meristems taken from apomictic seedlings of MX and adult phase M9, M26were used as explants. Research on serial subcultures induced rejuvenation of apple dwarfing rootstocks, and improve rooting ability of softwood leafy. The results are as follows:1. There are significant difference between varieties, the majority of apple rootstocks is not asy to root. The highest transplanting rates (94.00%) were observed in Malus xiaojinensis from apomictic seedlings (juvenile phase, J), followed by B9(62.17%), p22(52.17%), MM106(36.67%) and CG80(32.50%), and the worst is GM256, M7, M26and CG24.2. A lack of juvenility is the most important limiting factor governing adventitious rooting of leafy cuttings in apple rootstocks. Rooting rates of juvenile MX (J) from seedlings and juvenile like MX (S) from suckers were dramatically higher (94.00%,93.35%, respectively) than of adult materials MX (A)(15.01%), SH1(16.00%), SH6(34.67%) cuttings.3. Redox homeostasis was relate to rooting of apple dwarfing rootstock cuttings. The rooting ability cuttings were significantly higher in the treatment of3,000mg·L-1IBA+50mM H2O2than the other treatments. Treatments with H2O2alone, careless of concentrations, did not affect transplanting rates than water. Exogenous H2O2enhanced the effects of IBA on adventitious rooting and the enhanced portion of effect was abolished by H2O2inhibitor DPI (0.5mM). However, DPI didn’t diminish the effect of IBA on adventitious rooting.4. Serial subcultures in vitro caused successful rejuvenation of reproductively mature shoots. With the passages of subculture, the indole-3-acetic acid (IAA) contents, the expressions of rooting related genes CKI1, ARRO-1, ARF7, ARF19and the expressions of organ formation related genes KNAT1increased significantly in leaves of in vitro shoots derived from MX (J), MX (A), M9and M26. In contrary, the abscisic acid (ABA) contents, the expressions of DRM2gene and total DNA methylation levels decreased. After15passages of in vitro subculture, the micro-shoots of MX (A), M9and M26from adult phase explants were rejuvenated successfully, and the lobe on leaflets of MX (A) appeared. But the rooting ability of rejuvenated micro-shoots was recovered delayed at the18th or21st passage of subculture(42.48%,22.92%,74.28%respectively). The minimum IAA content threshold would be～130(ng·g-1fresh weight), at which level, the plantlets from MX (J), MX (A), M9and M26rooted well.5. Transplanting rates of leafy cuttings from tissue culture rejuvenated were significantly higher than from adult donor plants. Transplanting rates of leafy cuttings from MX (R) and M26(96.75%,81.82%, respectively) were significantly higher than from adult donor plants MX (A) and M26(A)(F=35.18, F0.05=3.48).6. The transplanting rates was also significantly affected by the cutting seasons. The transplanting rates of cuttings were much higher in May than in June or July (F=552.85, F0.05=5.14).7. Sand+peat (1:1, v/v) substrate is an suitable cutting substrate.Conclusively, a lack of juvenility is the most important limiting factor governing adventitious rooting of leafy cuttings in apple rootstocks. Serial subcultures in vitro caused successful rejuvenation of reproductively mature shoots and hence recover the ability of adventitious rooting ability of leafy cuttings.