FAO Field Manual :
Plants have two ways of reproduction, sexual by means of seeds, and asexually or vegetatively by means of vegetative tissue. Both ways occur in living plants in nature. In nature, some plants reproduce mainly vegetatively while others rely almost totally on sexual reproduction. For the plant breeder it is desirable to be able to manipulate sexual and vegetative reproduction (propagation) to fit into the tree improvement programme.
Genetically the two ways of reproduction differ. Seeds contain genes from the female parent (where we collect the seeds) and the male parent (which contribute the pollen and which is often unknown). Vegetative material is genetically identical to the mother plant from where it was collected. The present guide entirely deals with vegetative propagation.
There are four main uses of vegetative propagation in a Tree Breeding Programme:
The establishment of clonal seed orchards.
The establishment of clonal banks.
The propagation of special breeding material, e.g. exceptional hybrids that are lost through sexual reproduction, sterile hybrids etc.
Mass propagation of selected materials.
There are several ways of vegetative propagation. The three main types in forest tree propagation are grafting, air-layering and the use of cuttings. The three types are referred to as macropropagation, as alternative to micropropagation or tissue culture. Propagation by cuttings is the most convenient and cheapest method and usually preferred when possible. Air-layering is a variation of propagation by stem cuttings in which root formation is initiated before the plant part is separated from the mother tree. In grafting, the shoot (scion) of the desired tree is joined with a root (stock or root stock) of different genetic origin.
Which methods of propagation to be used in a particular situation is a matter of experience with the individual tree species plus the purpose and conditions of the propagation. The methodologies of vegetative propagation should be adapted to the individual plant species. The same method may work differently at a different time of the year, etc.