Agriculture Reference
In-Depth Information
Temperature effect on flowering and flowers
The reported effects of temperature on flower initiation are contradictory.
From controlled environment studies, Abbott (
) concluded that warm
temperatures advance flower initiation and cool temperatures retard it but
otherwise do not have any direct effect. Indirectly, however, temperature in-
fluences the intensity of initiation by its effects on the rates of shoot and fruit
growth, high temperature stimulating shoot growth and so influencing flower-
ing negatively. (Abbott,
). The overall effect
of temperature seems to be a balance between positive (direct) and negative
(indirect) influences.
Apple fruit buds developed under warm conditions throughout the growing
season are, however, later to break in spring (Abbott,
;Tromp,
; Zhu
et al.
,
). The development
of buds of the
Pyrus
cvs. 'Comice', 'Concorde' and 'Conference' and their dates
of full bloom in spring are also delayed if the trees are subjected to October
and November temperatures typical of a warm autumn (Atkinson and Taylor,
). It seems that warm
(mild) conditions in autumn and early winter may delay entry into dormancy
and the processes of accumulation of chilling units and bud development.
Buddevelopmentcontinuesthroughthewinter(Abbott,
; Atkinson and Lucas,
; Atkinson
et al.
,
)buttherateat
which it does so is very dependent on cultivar. Cole
et al.
(
) found that buds
of
P. calleryana
have a much higher rate of development during autumn, when
temperatures are declining, than buds of
P. communis
. This is attributed to the
relatively higher rate of alternate pathway (cyanide-resistant) respiration under
low temperature conditions in
P. calleryana
, hence more energy for growth and
development. As a consequence
P. calleryana
enters winter with much larger,
better developed buds than
P. communis
and flowers much earlier in spring.
In many fruit-growing areas temperature effects on emergence from dor-
mancy, i.e. the meeting of winter-chilling and thermal time requirements to
achieve budbreak, are of dominant importance. These have been discussed in
Chapter
.
In cool-temperate climates temperatures in the early spring, prior to bud-
break and independent of frost damage effects, largely predetermine yield
( Jackson and Hamer,
).
This is at least in part the consequence of effects on ovule development and
longevity and, as a result, on fruit set (pp.
; Jackson
et al.
,
(Figure
.
); Lakso,
).
Frost damage to buds and blossoms is a major constraint on apple and pear
production in many areas. During late autumn dormant flower buds develop
a relatively high degree of resistance to cold. As they develop in spring they
become more vulnerable to damage by frost (Table
,
-
.
). In the earliest stages
−
◦
C is required to kill
of bud development, a temperature of about
%
−
◦
C
of the buds but during the stages around full bloom temperatures of
