Agriculture Reference
In-Depth Information
length of the growing season (the shorter the season the greater the probability
that buds, especially buds on long shoots, will fail to produce flower primordia)
and the presence of fruits (heavily cropping trees have a lower proportion of
their buds producing flower primordia). These and other factors determining
the type of bud that forms are discussed in detail in the section on flowering,
but it is important at this stage to recognize that the balance between fruit
buds and vegetative buds is a variable and is controlled by cultivar, climate
and tree management.
Bud dormancy
Dormancy is used as a general term to indicate a period of temporary sus-
pension of visible growth of a plant structure containing a meristem (Lang,
). This is a practical definition which in the case of buds includes those
that are growing very slowly, such as fruit buds in winter (Abbott,
), and
axillary 'trace buds' which may persist for years under the bark while grow-
ing enough each year for the tip to keep pace with cambial growth (Esau,
).
Bud dormancy enables plants to survive adverse events and environments.
Entry into dormancy and emergence from it are therefore likely to involve
mechanisms relevant to the conditions under which the particular plant geno-
type evolved (Vegis,
).
The traditional view of apple and pear bud dormancy in temperate regions
is as follows.
In summer and early autumn the primary mechanism controlling bud dor-
mancy is correlative inhibition and the buds are classified as paradormant
(Lang,
). At this time they can be stimulated to grow out quickly if the
source of correlative inhibition is removed, either in the field when temper-
atures are suitable for growth or under so-called forcing conditions when
cut shoots are kept at adequate temperatures with their bases in water.
In late autumn and early winter (September, October, November and
December in western Europe) the buds on intact shoots require a much
longer period under forcing conditions to break dormancy. They are said
to be in a state of endodormancy, deep dormancy or rest.
Following exposure to a period of low temperatures (winter chilling) the
buds lose their endodormancy and can once more be induced into rapid
budbreakunderforcingconditions.Dormancyinthefieldismaintained by
low temperature. This period of ecodormancy lasts until the buds have
been exposed to enough high temperature to attain budbreak, which in
western Europe is usually in April or May.
