|Author: ||T. Winkelmann|
|Keywords: ||vegetative phase change, long cuttings, somatic embryogenesis, endophytic bacteria|
Estimation of the different ways of propagation in woody plant species including forestry in Germany reveals that seed propagation is still by far most often applied (860 million plants per year) followed by cutting propagation (110 million plants), graftings (15 million plants), other vegetative methods like layering (3 milČlion plants) and finally micropropagation (2 million plants). Different limitations are connected with the various propagation techniques.
This overview will focus on recent trends to overcome major problems.
However, many of the problems were encountered already more than 20 years ago and are still unsolved.
This is not only due to experimental or biological difficulties, but is also provoked by less research institutions worldwide working on woody plants and the time needed in perennial woody plants to fully evaluate a propagation system.
One problem still unsolved is the difficulty in propagating adult woody plants vegetatively.
In future, better understanding of molecular processes underlying aging and adventitious root formation should help to improve protocols.
On the other hand, during the last years propagation via long cuttings seemed to bear interesting possibilities for a number of woody plant species, including fruit trees and rootstocks.
While traditional cuttings are about 15-25 cm in length, long cuttings (60 to >100 cm) were shown to be an alternative for difficult to propagate species or cultivars or older mother plants.
Outbound registration of auxins in Germany requires searching for alternatives, which could be found in the group of growth promoting microorganisms.
In vitro culture techniques are still not applied to an extent that would correspond to the enormous opportunities offered by this technique.
Actual limitations for in vitro propagation of woody plants are strongly connected to endophytic microorganisms, exudation of phenolic compounds, quality and true-to-typeness of the propagated material.
Especially regarding endophytes, increasing efforts are made in research to identify and control them.
Somatic embryogenesis is a very efficient way to propagate plants and has been realized on commercial scale in conifers.
For this promising regeneration pathway, still major limitations are existing, but also first insights into the genetic and physiological events are given.
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