Agriculture Reference
In-Depth Information
Lateral roots arise in the pericycle of the parent root some distance from
the apical meristem of this and grow out through the cortex. In apple and
pear root systems the first laterals produce secondary laterals and this process
continues to give up to eight 'orders' of laterals within a single season (Rom,
).
Factors influencing root initiation and emergence
These are of particular importance because the rootstock cultivars which have
the most desirable effects on the scions grafted on them are quite often difficult
to root.
In all woody plants there is a juvenile phase during which flowering does
not occur. When flowering occurs the tree is said to have attained maturity.
The phase change from juvenility to maturity is accompanied by changes in a
number of characteristics, one of which is a reduction in the ability to produce
adventitious roots from the shoots (Gardner,
).
In apple the juvenile phase, defined as time from seed to flowering, is short
compared with that of many trees. It ends when the tree reaches a charac-
teristic height or number of nodes and so is shortened by good management,
improvement in growing conditions and length of growing season. Visser
et al.
(
; Hackett,
years the juvenile period of com-
parable groups of seedlings was reduced from
) reported that through the course of
.
to
.
years in apple and
.
years in pear.
The period of high rooting ability is even shorter. Gardner (
to
) reported
that softwood cuttings from the tops of apple seedlings during the first year
of growth could be rooted easily whereas cuttings from
-year-old
seedlings rooted poorly. The technology of propagating apples through the
use of rooted cuttings from vegetatively propagated plants, some centuries
away from seedling progenitors, therefore requires a detailed understanding
of methods of maintaining and restoring the ready rooting normally associated
with juvenility in the face of apparently unpromising circumstances. Although
it is conventional to define juvenility in relation to flowering there is evidence
that juvenile behaviour as regards rooting may be separable from juvenile be-
haviour as regards flowering ability (Hackett,
-to
). In the following discussion
an effect on rooting will be considered as a juvenility effect if it is associated
with effects on other morphological, anatomical and physiological traits typ-
ical of a juvenile plant or part of a plant. Such traits include the presence of
many spines (short axillary laterals) on the stems, thin leaves, prolonged leaf
retention in autumn, reduced leaf and stem pubescence, and abundant antho-
cyanin production in leaves and stems (Stoutemyer,
; Howard,
).
Beakbane (
) also noted that in seedling apple trees the basal juvenile shoots
