Agriculture Reference
In-Depth Information
Figure 6.2
Bud structure showing,in ascending order,nine bud
scales,three transition leaves,six true leaves and three bracts. The
axis is terminated by a flower primordium (the king flower) and lateral
primordia are formed in the axils of the three bracts and three distal
leaves. After Abbott (1970). Reproduced with permission.
part of the growing season both extension shoots and spurs are terminated by
a naked bud but as the season progresses bud scales instead of leaves develop
and enclose the terminal bud. At this stage it is commonly referred to as a
resting bud. The time when terminal and axillary buds form on extension
shoots varies with the length of the shoot.
Each bud can be considered as a very compressed incipient or unelongated
shoot. It has a very short axis on which are borne, in spiral sequence,
leaf
formations made up of nine bud scales, three transition leaves, sixtrue leaves
and three bracts (Figure
). All of the buds are potentially mixed buds, com-
monly referred to as fruit buds in which the axis is terminated by a flower
primordium (the 'king flower' primordium), and lateral flower primordia are
formed in the axils of the bracts and three upper true leaves. Vegetative primor-
dia form in the axils of the lower leaves. Flower induction does not, however,
begin until a critical node (leaf formation) number has been reached. In apple
the critical node number is about
.
for 'Cox's Orange Pippin' and
for
'Golden Delicious' (Luckwill,
). If this critical node number is not reached
the bud remains smaller and more pointed, and is capable of only vegetative
growth. Such 'leaf buds' or 'wood buds' are the ones used in budding and
grafting, and pruning to just above them is a standard technique for inducing
new shoots.
Whether a bud becomes a fruit bud or remains at the solely vegetative stage
depends on the type of bud (development of buds on pre-existent spurs starts
earlier than that of terminal buds on long shoots or lateral buds on these), the
