Agriculture Reference
In-Depth Information
winter chilling. The failure of lateral buds to break under these conditions
leads to bare unbranched shoots with just a tuft of leaves and fruits at the tips.
This condition may be, in part, a consequence of the terminal buds breaking
long before lateral buds in warm-winter areas and therefore establishing
greater dominance (Saure,
).
There are large differences between cultivars of apple, and pear, in the de-
gree of apical dominance. This is shown by differences in the proportion of
the lateral buds which 'break' to give 'feathers', i.e. side branches, on nursery
trees. Volz
et al.
(
) showed that trees of 'Fuji', if not treated, produced
fewer lateral branches than trees of 'Braeburn' or 'Gala', although all cultivars
had similar numbers of side branches following bud-breaking hormonal treat-
ments. Similarly, Jaumien
et al.
(
) found that untreated trees of 'Cortland'
and 'Gloster' developed fewer lateral branches than those of 'Jonagold' and
'Melrose'. Mature trees of different cultivars show large differences in growth
habit attributable to differences in the degree of apical dominance and control
exerted by the leading shoot (Crabbe,
a; Lespinasse and Delort,
)as
shown in Figure
There is direct experimental evidence (Faust
et al.
,
.
) that cultivars with a
low requirement for winter chilling, e.g. 'Anna', have weaker apical dominance
than those with a high chilling requirement.
Spur-type cultivars are sometimes said to show strong apical dominance
because,especiallyinthecaseofthe'Wijcik'types,theyexhibitstronglyvertical
growth with few if any side branches. They do not, however, show inhibited
lateral budbreak: the buds break but give rise to spurs instead of long shoots.
They should therefore be considered as a special case.
Trace buds, buried under the bark in secondarily thickened branches in-
cluding the central trunk, are held dormant by correlative inhibition and are
released from dormancy when the branch above them is pruned off.
Other types of correlative inhibition
Champagnat and Come (
) concluded that, from spring to autumn, typi-
cal apical dominance is succeeded by a more diffuse inhibition from the large
leaves followed by an inhibition located in the stem and then, in November,
an inhibition located in the bud itself. Abbott (
) found that removal of
bud scales after incomplete winter chilling hastened and increased budburst.
Swartz
et al.
(
) showed that removal of bud scales can stimulate budbreak
in winter, especially from December onwards, in typical cultivars including
'Idared' and 'Millerspur Delicious'. Removal of apical bud scales also in-
creased percentage budbreak of the first lateral bud of 'Millerspur Delicious'
throughout the winter. Notodimedjo
et al.
(
) found that bud slicing, which
had the effect of removing bud scales, had a dramatic effect on lateral budburst
