Articles
PREPARATION OF MOTHER PLANTS FOR BOTH CUTTING AND GRAFTING PROPAGATION
The new plant produced will be only as good as the material source used to produce it.
The considerations which the propagator must have in mind, during this preparation phase, fall into three broad categories: physiological, nutritional and pathological.
These will, to some extent, be inter-dependent, but it is convenient to consider them separately at this stage.
The physiological considerations start with the selection of an individual plant to act as the parent.
Within what is generally regarded as a clone, sub-clones may be identified as having greater potential to develop roots, or to develop graft unions.
For example, our experience in New Zealand has indicated that certain selections of Daphne odora rubra have greater potential to form roots in cuttings than other selections, although the plants cannot be distinguished from each other by any visual means.
Obviously the detection and use of these superior propagating clones will be of considerable importance to our industry in the future.
The reason for this superior performance is not yet clear, in the case of cutting propagation it may well be related to the production of certain growth regulator compounds, but we must not ignore the possibility that systemic pathogens may also be involved in less satisfactory clones.
This is very likely to be the case in relation to reduced capacity to form graft unions.
Having sought out the "best" sub-clone, the next step is to maintain it in a juvenile stage.
This may involve causing a mature plant to revert to the juvenile stage, usually by very heavy pruning, a process which may take several years.
In doing this the aim should be to induce new growth as close to the roots as is practicable since it has been shown that such shoots have a high potential for propagation.
The importance of the juvenile phase in mother plants has been discussed elsewhere during this conference, and I do not need to dwell on it at this time.
In addition, it may be an advantage to modify the environment in which the mother plant is grown.
Shading may create a semi-etiolated type of growth, which can be important in some plants, while temperature and/or day length may also influence the capacity to develop roots on cuttings.
These latter factors may be very closely related to the delay of flowering or leaf abcission, and are therefore closely related to juvenility.
Generally we have not considered this type of environment manipulation to be practical for most plants, yet I would predict that it will become much more important over the next few years.
The second group of factors lie in the area of nutrition of the mother plant.
It has been common, in the past, to subdivide these into two areas, carbohydrates and minerals.
We should not regard them as separate, both are merely the raw materials which the plant will use in the creation of new cells and tissues.
Once we separate the propagule from its parent