Subculture and Etiolation Treatment Promotes Rooting Ability of Upper Branches of Black Locust Crown

The black locust (Robinia pseudoacacia L.) is an economically and ecologically important tree worldwide. However, maturation and position effects affect its asexual reproduction. Despite etiolation treatment and successive subcultures promoting the plant cutting's rooting rate, whether the promoting effects of aging (upper) branches and young (lower) branches are consistent is unknown. Therefore, we evaluated the relevant rooting ability indicators of tree age effect and its location effect in 26-year-old R. pseudoacacia trees and the current-year branches of different parts. Branches of the upper and lower parts of these trees underwent accelerated germination to generate shoots as explants. We subjected the tissue culture-generated shoots to an etiolation treatment to investigate how the treatment and subculture time affected the rooting ability of the shoot explants induced by different parts of the black locust branch. Tissue culture shoots subjected to the etiolation treatment exhibited a 2-3 day shorter rooting time. Shoots from the upper crown organs achieved a rejuvenation effect, which manifested as enhanced rooting capacity. Our study results provide a theoretical basis for maintaining the juvenility and consistency of clones. Besides having theoretical and practical value, our study also guides the selection of suitable propagation materials for production. Study Implications: Asexual propagation has been widely used in forestry production and has broad prospects for further development. However, asexual propagation efficiency is easily affected by the age of the mother tree and the position of the branches taken from the original plant; that is, the aging phenomenon occurs under the influence of the maturity effect and position effect. When selecting excellent adult mother trees as materials for in vitro asexual propagation, problems like difficulty in rooting and low rooting rate are usually encountered. The rooting rate is vital in forestry production. Therefore, this study brings important economic value to forestry production.