Agriculture Reference
In-Depth Information
in the callus mass proceeds inwards from the original stock and scion
cambium and through the callus bridge until there is a continuous cambial
connection between stock and scion.
The newly formed cambial layer in the callus bridge lays down new xylem
towards the inside and new phloem towards the outside. The new xylem
tissue originates from the activities of the scion tissues rather than those of
the stock (Yeager,
). Induction of vascular tissue in the callus appears
to be under the control of material originating in shoot apices and can
be artificially induced by the supply of auxins, cytokinins, gibberellins and
sugars (Torrey
et al.
,
; Wetmore and Rier,
).
Union formation in T-budding and
chip budding
In T-budding of apple, when the bark of the rootstock is lifted for bud in-
sertion, the separation occurs in the young, undifferentiated, xylem and the
cambial zone remains attached to the inside of the barkflaps. A necrotic plate
develops from the cut cells shortly after the bud shield is inserted. After about
two days callus parenchyma cells start to develop from the rootstock xylem
Figure 4.1
(
cont.
)
scion is much smaller in diameter than the stock the slice taken from
the stock should be shallow (E) so that the cambia of stock and scion
are well matched at the sides and top (F and G).
(
b
) Bench grafting on roots is usually done using whip-and-tongue
grafts and can be used for stocks and scions of either similar (A) or
dissimilar (B) size.
(
c
) The cleft graft is used in top-working trees with new scion
cultivars. Scion bud sticks of 3 or 4 buds are inserted in splits made
in the cut ends of tree trunks or large limbs. The scions are prepared
with two slanting cuts at their base giving a long tapering wedge (A),
preferably with a bud (B) between the cut surfaces as shown. The
cleft (C) in the limb is opened by insertion of a wedge or grafting tool,
the scions are inserted so that their cambial regions are in contact
with those of the trunk or limb. The wedge or tool is removed and the
scions are held fast by the pressure of the cleft moving to close.
In oblique cleft grafting (
d
) the clefts do not extend right across the
branch. All exposed cut surfaces are sealed with grafting wax after
first rubbing some clay into the clefts to prevent the wax running
down inside.
(
e
) Rind or crown grafting involves inserting a scion,prepared as for
whip-and-tongue grafting but without the tongue,between the rind
(A) and the wood (B) of the tree to be top-worked. This can only be
done when the bark will separate readily from the wood and the graft
must be tied firmly in place before waxing. After Garner (1988).
Reproduced with permission of Mrs I.L. Garner.
