Agriculture Reference
In-Depth Information
Releasing buds from correlative inhibition
The economic success of a modern orchard depends on the ability of the fruit
grower to bring his trees into cropping at an early age ( Jackson
et al.
,
).
The potential of a young tree to produce adequate crops in its early years is
related to the number and length of the lateral branches present when the tree,
whether apple or pear, is transplanted from the nursery (van Oosten,
;
Lawes
et al.
,
).
Removal of the shoot tips of trees in the nursery releases some lateral buds
from dormancy, but, in the initial absence of auxin flow from above, these
lateral shoots tend to form very narrow angles with the main stem. Such
'narrow crotch angles' are mechanically weak and the branches readily break
off at the junction with the trunk when bearing heavy crops. Removal of
the young, not fully expanded, leaves while leaving the growing point intact
can lead to lateral budbreak giving wide-angled side shoots (Wertheim,
),
presumably because the interruption of auxin supply is less prolonged.
Treatment with an auxin transport inhibitor (M & B
,whichis
n
-propyl-
-
t
-butylphenoxyacetate) can increase lateral budbreak to give wide-
angled branches of apple and pear (Wertheim,
; Quinlan,
; Cody
et al.
,
).
Application of BA to lateral buds of nursery trees leads to an increase in
budbreak (Figure
.
) and to branches with wide crotch angles (Williams and
Billingsley,
).ThisiscommonlyappliedincombinationwithGA
+
which,
although it does not increase budbreak, induces greater extension growth. The
combination of BA and GA
+
(Promalin) therefore increases both the number
and the length of lateral branches.
Lateral budbreak and the development of a large number of 'feathers' can
be greatly increased by growing nursery plants at a wide rather than close
within-row spacing (Wilson and Jarassamrit,
). This was considered to be
a response to reducing interplant competition for light. Jaumien
et al.
(
)
reportedadverseeffectsofdroughtonbranchingofnurserytreesintheabsence
of irrigation and that, in general, the better quality (size) of the rootstock
the more lateral branches were produced by scions grafted on them. Chip
budding, which gives a more rapid graft union than shield budding, hence a
longer effective growing season and, presumably, less risk of water stress in the
scion, induces more laterals per scion tree (Howard
et al.
,
).
Failure of lateral budbreak in orchard trees results in problems of bare wood,
i.e. failure to occupy the canopy volume with an adequate number of fruit-
bearing long shoots and spurs.
