Protocols for Micropropagation of Woody Trees and Fruits

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M. MHATRE AND V.A. BAPAT
2.3.2. Using in Vitro Produced Shoots
Tissue culture generated rootstock rooted plantlets, grown until several leaves are
produced (6–8 weeks) can be divided into 3–4 explants, each containing 1–2 nodes
with leaves. The apex of the rootstock nodal explant is cut longitudinally with a
sharp sterilized blade, producing a small (2–4 mm) longitudinal cleft leaving the
rootstock decapitated. An appropriate scion with a single node and a leaf can be
selected to match the size of the rootstock. The basal part of the stem of the scion
should be cut in such a way that the wedge formed, matches the cleft of the rootstock.
It is then fitted on to the cleft of the rootstock grown in the medium (Figure 2).
The graft tissue is allowed to develop around the union during subsequent subculture.
In this way, two grafts can be established per tissue culture vessel (Pathirana &
McKenzie, 2005). After insertion of the scion into the rootstock cleft, wrapping in
sterile aluminium foil to hold the graft can also be attempted to strengthen and
support the graft (Tanne et al., 1993). However, to accomplish this is laborious and
time consuming under aseptic conditions. In case the scion does not fit properly on
the rootstock, dipping the lower end of the scion in the medium before fitting it helps
to establish the graft. This is because of two reasons (i) the cut surfaces are kept moist
until relative humidity of the tub/vessel is established and (ii) dipping ensures that
the nutrients are directly supplied to the graft site (Pathirana & McKenzie, 2005).
Figure 2. Diagrammatic representation of in vitro micrografting.