Agriculture Reference
In-Depth Information
Detailed studies have shown that these three types of dormancy interact, over-
lap in time, and may involve mechanisms in common. In particular, lateral
buds can be induced to break under forcing conditions at any time of year and
chilling influences the effect of post-chilling temperatures on the rate of bud
development.
In relation to the practical management of bud dormancy it is most relevant
to consider it under two headings. The first is correlative inhibition, under-
standing of which is fundamental to tree management by pruning and branch
training. The second is seasonal bud dormancy. This is of critical importance
with respect to adaptation to different environments and the overcoming of
some major environmental constraints. It involves correlative inhibition as
well as endodormancy and ecodormancy effects of temperature and, in some
circumstances, water stress.
Dormancy through correlative
inhibition
Apical dominance
Dormant lateral buds represent a very small commitment of resources both
in terms of tree constituents and of maintenance respiration. They are main-
tained in a state of dormancy by the shoot distal to them. This apical domi-
nance is shown throughout the tree structure. If the apical portions of a shoot
are eaten by browsing animals, or if a branch is broken or pruned back, the
lateral buds are released from dormancy and grow as new replacement shoots.
The uppermost bud nearest to the previous source of dominance breaks out
first,followedbythefewjustbelowit,and,asitgrows,re-imposesthedormancy
influence on the buds lower down. This process is relatively conservative in
the use of resources and tends to ensure effective utilization of available light
by provision of replacement shoots where they can best exploit this.
Axillary buds on shoots sprout to give lateral branches when the growing
shoot tips or young growing leaves are removed (Barlow and Hancock,
,
) confirmed this and also found that removal of fully ex-
panded leaves does not release the axillary buds from dormancy although
there is some evidence of inconsistency in this respect. Removal of a segment
of stem tissue including bark and cambium above a lateral bud (notching)
will also release the bud from dormancy (Greene and Autio,
). Mika (
). Bending
branches towards the horizontal has a similar effect, the lateral buds on the
upper side of the branch being released from dormancy to give either long or
short shoots (spurs) while those on the lower side stay dormant (Faust,
).
The apical dominance exerted by a shoot tip over lateral buds is charac-
teristically much more pronounced in warm-winter areas with low levels of
