Ortet Age Effect, Anatomy and Physiology of Adventitious Rooting in Tilia mandshurica Softwood Cuttings

Tilia mandshurica is recognized as one of the most valuable timber, ornamental and nectariferous tree species, and its cutting propagation is very difficult. To evaluate the influence of ortet age on the rooting of T. mandshurica cuttings and the relationship between the variations of nutrients, enzyme activities, endogenous hormones and the formation of adventitious roots, a series of softwood cuttings of T. mandshurica were collected from 2-, 7-, 15- and 20-year-old healthy ortets, respectively. The rooting percentage, mean root number and total root length were investigated after 60 days of cultivation. Phenotypic and anatomical changes and the variations of organic nutrients, enzyme activities and endogenous hormones were measured during adventitious root formation. The results showed that ortet age effect existed in T. mandshurica softwood cuttings. The adventitious rooting of 2-year-old ortets was superior to that of 7-, 15- and 20-year-old ortets. No root primordium was visible in T. mandshurica softwood cuttings before cultivation, and the root primordia were induced after planting. The adventitious roots derived from vascular cambium and callus in cuttings. Soluble sugar increased during root primordium induction and decreased in adventitious root elongation. Soluble protein decreased during root primordium induction and increased in adventitious root elongation. Polyphenol oxidase (PPO) activity increasing and peroxidase (POD) and 3-indoleacetic acid oxidase (IAAO) activities decreasing were conducive to root primordium induction. High 3-indoleacetic acid (IAA) and gibberellin (GA3) level could promote root primordium induction and low IAA and GA3 level was beneficial to adventitious root elongation. Abscisic acid (ABA) and zeatin riboside (ZR) inhibited root primordium induction and adventitious root elongation. IAA, ABA and ZR coordinated with each other in the process of root primordium induction and adventitious root formation. IAA/ABA increasing could promote root primordium induction, and IAA/ZR increasing was beneficial to root primordium induction and adventitious root elongation. The soluble sugar content, PPO activity, IAA/ABA and IAA/ZR of softwood cuttings from 2-year-old ortets were relatively high, which may be the reason for the better adventitious rooting. The present study provides a reference to build a propagation by cuttings technology of linden trees.