‘A low profile feature in Stem Cutting propagation but significant especially in Conifers’

 

This term describes the influence of the apical meristem of a stem cutting on the growth habit of the newly created plant. The orientational and organisational state of the meristem which determines the growth habit of a shoot is fixed by the position of the lateral bud from where the cutting emanates and from which it originates. Consequently the habit of growth which this shoot has adopted, on the donor plant, will become that of the new plant – it is the inherent characteristic of a propagule to grow in the same orientation as the branch from which it was isolated. This condition remains stable through vegetative propagation. It should be emphasized however that these influences are, in the majority of plant species, very short lived and do not significantly affect the production of a normally oriented plant.

 

It is particularly this effect which has given rise to the various prostrate varieties of Sequoia sempervirens – where the cutting material has been taken from the tips of the mature downward sweeping branches and the habit of the resulting new plant continues in a prostrate fashion. This cannot even be mitigated by attempting to train the stem vertically up a cane – as soon as the constraint is lifted at the top of the cane the stem will revert to becoming prostrate. Eventually the habit from an apical bud may revert to the orthotropic upright habit.

 

Cutting material taken from shoots of Alnus glutinosa Pyramidalis will only produce true to type erect plants when the material is selected from orthotropic upright shoots, the plagiotropic lateral shots do not grow erect.

 

The same response was found in Gingko biloba where only vertical shoots produce the patterns of typical growth.

 

The normal pattern of growth is described as orthotropic and the habit of growth from a particular lateral bud is described as plagiotropic. Eventually the exhibited plagiotropic growth in the new plant will revert to the normal orthotropic growth and in most species this occurs almost immediately but in others this may take some long time – ie there is a species related duration to this influence. The influence of plagiotropism appears to be hormonally controlled as the effect increases from the apical meristem – affecting the lateral buds and increasing in influence in a basipetal direction.

 

The effect of topophysis is particularly apparent in the selection of cutting material from Conifers and has been demonstrated especially so in Araucaria, the Redwoods, Abies, Picea, Pinus, Pseudotsuga, Tsuga, Taxus and Podocarpus.

 

However there has been some investigation into the effects of topophysis on less obvious characteristics which may influence the quality and uniformity, albeit only marginally, of an otherwise normal broadleaf crop. These influences are often short lived but can affect the uniformity of a relatively fast growing crop. These investigations have chiefly been conducted on Roses grown for cut flower production – where the uniformity of crop responses and exacting production schedules are an essential feature. It has been shown that a stem which has been divided into successive single leaf bud cuttings will demonstrate differing characteristics according to the acropetal position of the bud on the original stem - affecting the thickness of the shoot, internode length and size and precocity of flowering on the resultant plant.

 

 

In woody plant propagation practice this consideration is only significant when regenerating those species in which this characteristic is sufficiently dominant to affect the outcome.