Agriculture Reference
In-Depth Information
Figure 9.3
Apple flower split longitudinally and diagrammed to
show its parts (MacDaniels and Heinicke,1929).
factors. Variations in the number and 'quality' of flowers at blossom time are
the main cause of year-to-year variations in yield in many apple and pear
growing regions so much effort is devoted to understanding and controlling
the causal factors.
Effects of fruits on flowering
Heavy cropping in one year can inhibit flower bud initiation and so reduce
flowering in the following year. Some cultivars consequently tend to become
biennial in cropping, with a heavily cropping 'on' year followed by an 'off'
year in which crop is light or even absent.
Intheorchardbiennialbearingmaydevelopovertimebutformanycultivars
it tends to be triggered by frost damage with a consequent low crop and
excessive flower bud initiation. In its most severe form it therefore is a whole-
tree, indeed a whole-orchard, phenomenon. Heavy fruiting on one branch
may reduce flower bud formation on adjacent ones, but the inhibitory effect
is usually more localized and Parry (
) showed that halves of an apple tree
can be maintained so that one half is 'on' and one 'off' each year. Moreover,
within a single branch fruits may inhibit fruit bud formation only on the
part of the branch on which the fruits are borne or parts nearer to the trunk
but not those nearer to the end of the branch (Fulford,
). Huet (
,
) concluded that flower initiation in spurs is controlled mainly by factors,
including presence of fruits, operating within each individual spur system
