Resource Book on Horticulture Nursery Management

Cross Section of a Woody Plant Stem
In grafting, as well as budding, the vascular cambium of the scion or bud must be
aligned with the vascular cambium of rootstock. In woody plants the cambium is a very
thin ribbon of actively dividing cells located just below the bark. The cambium produces
conductive tissue for the actively growing plant. This vascular cambium initiates callus
tissue at the graft and bud unions in addition to stimulating tissue growth on the basal end
of many vegetative cuttings before they have rooted.
2.2.5 Micro-Propagation and Hardening of Plants
(A) Micro-Propagation
Micro-propagation means propagation of plants from very small plant parts called as
explants (piece of plant may be cell, tissue, or even organ), tissue grown aseptically in the
test tube or container under controlled nutritional and environmental conditions.
In vitro plantlets, which are free of pathogens, are used as initial material in such
propagation programs. The methods used in these micro propagation programs mainly
depend on their production volume and the available infrastructure. The basic micro
propagation methods are described as follows.
1. Micro-Propagation by Nodes: This method is based on the principle that the node of
an in vitro plantlet placed in an appropriate culture medium will induce the
development of the axillary bud, resulting in a new in vitro plantlet. This type of
propagation promotes the development of a pre-existing morphological structure. The
nutritional and hormonal condition of the medium breaks the dormancy of the axillary
bud and promotes its rapid development. Under controlled conditions micro
propagation is fast. Each node planted in propagation medium will produce a plantlet
which will occupy the full length of the test tube, after approximately four weeks for
potato, and six weeks for sweet potato. The resultant in vitro plantlets may be
transplanted to in vitro conditions in small pots in the greenhouse.
2. Micro-propagation by Node Cuttings in a Liquid Medium
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