Articles
STUDIES ON THE PHASE DEVELOPMENT IN APPLE TREES
Some important results on the phase development of morphologic leaf characteristics are discussed.
The dynamic development of various characteristics can be correlated to a static initial state.
Grafts from the base (J = juvenile phase) and from the crown (A = adult phase) of ten about 10-year-old seedlings provided the material to obtain such standard values and were used also for other investigations.
Figure 1 shows the relative (based upon J = 100) mean phase differences with their deviations and P-values.
They were evaluated in the second and, after being cut back, in the sixth year after grafting.
They repeat principally the already well-known changes in the characteristics taking place during the ontogenetical development of higher plants as, e.g. the increase in the density of leaf venation (N) and in the pilous vesture (H) or the decrease in the surface area of epidermal cells (f) and their undulation (W). These changes are also often related to the illumination effect – to sun and shade leaves respectively.
In order to eliminate these environmental factors, plant parts of vegetatively propagated descendants must be investigated under equivalent environmental conditions.
Only then is it possible to determine true phase differences.
Changes in the leaf characteristics during the ontogenetical development of the grafts were studied in 1-year-old branches at first; Fig. 2 shows such an example (clone X ex 66). Leaf area (F) exhibited a maximum curve with one or two peaks.
The latter was caused by the second growth.
Various correlations are very clearly pronounced, e.g. a positive correlation of F with Z (number of epidermal cells), N, F.N or a negative correlation of F with f and W with H. Phase development from J to A, however, could neither be observed nor excluded.
In order to study the correlations to the leaf area (F) in more detail, individual leaves of a 1-year-old branch of a clone (X) were ranked according to the increasing values of F (Fig. 3) and 10 different clones were ranked according to their increasing mean values of leaf area (Fig. 4). The respective values of the characteristics Z, f, E, and N were related to the curves of the leaf areas.
The straight line of the regression of all listed characteristics which coordinate between J and A and which are marked in Fig. 3 have a parallel course within each characteristic of a clone (intraclonal). This suggests that phase differences of the characteristics of the 1-year-old branch are independent of the change in leaf size.
The same results were obtained with the mean values (interclonal), although only for the characteristics f, E, and N, whereas the phase differences of the characteristics F and Z increased with increasing