The final step in selecting the right material is to decide on the kind of reproductive material and method. That is, will propagation or improvement make use or sexual material, such as seeds or pollen, or will it be via asexual means, using cuttings or more advanced techniques of tissue culture etc.? In the majority of cases, forest reproductive material is synonymous with seed, but extensive use is also made of vegetative material, and a range of techniques are being developed based on biotechnological methods commonly used in agriculture. Many tropical species seed very infrequently, or are difficult to store and therefore vegetative means may be the preferred or only way to propagate the tree.
The table below provides an overview of the key kinds of material and methods used in natural and artificial propagation:
|
CLASSIFICATION AND TERMINOLOGY OF KEY | |||||
TYPE OF |
INITIAL |
KIND OF MATERIAL |
DEVELOPMENT |
END STAGE | |
NATURAL GROWTH AND DEVELOPMENT | |||||
Natural growth and development of tree |
Meristematic growth > |
Leaves, |
Growth > |
Whole tree (from which forest reproductive material is produced) | |
SEXUAL REPRODUCTION | |||||
Natural regeneration |
Flowering > |
Pollen + Ovule > |
Dissemination > |
Seedling | |
Artificial direct seeding |
As above |
As above |
Collection |
Seedling | |
Breeding and artificial regeneration |
(Induced) Flowering > |
Pollen + |
Seed harvesting > |
Seedling | |
ASEXUAL (VEGETATIVE) REPRODUCTION | |||||
Natural re-growth of existing plant |
Differentiation > |
Root Sucker, |
Elongation > |
Shoots | |
Artificially induced re-growth of existing plant |
Cutting (coppicing) of stem |
Tree stump |
Stump coppicing > |
New stems or branches | |
Lopping (pollarding) of crown |
Pollarded trunk |
Pollard shoots |
Re-sprouted crown | ||
Natural regeneration of separate plants |
Development of vegetative parts |
Leaves, |
Dehiscence / |
Rooted plantlets | |
Macro-propagation |
Shoot cutting |
Cutting |
Planting > |
Rooted cutting | |
Shoot / bud and root-stock cutting and preparation |
Scion or |
Grafting/budding> |
Grafted tree | ||
Branch layering |
Layer |
Severance > |
Layered plant | ||
Micro-propagation in laboratory (in-vitro) |
Separation of fascicle |
Fascicle |
Rooting > |
Rooted propagule | |
Excision of plant tissue (from meristematic tissue) |
Explant |
Callus formation > |
Plantule | ||
Callus formation and/or cell suspension |
Plantule | ||||
As above + |
Plantule | ||||
The next table summarizes some of the positive and negative aspects of each kind of reproductive material and propagation system
TYPE/SYSTEM |
Positive aspects |
Negative aspects |
|
TRUE SEEDS |
•Direct delivery in the field •High volume, large-scale multiplication •Very rapid multiplication rate •Low cost per plant |
•Genetic uniformity may not be maintained •Some seeds difficult to obtain and store |
|
ROOTED CUTTINGS |
•Genetic uniformity maintained |
•Rooting usually required before field planting •Low multiplication rate determined by size of explant •Low volume, small-scale propagation method •High cost per plant |
|
MICRO-PROPAGATION |
•Genetic uniformity maintained |
•Acclimatisation required before field planting •Relatively low multiplication rate •Relatively low-volume, small-scale propagation method •Very high cost per plant |
SYNTHETIC SEEDS |
•Genetic fidelity should be routinely checked for SV by molecular DNA markers •Direct delivery of propagules to field •Rapid multiplication rate of embryos potentially possible •Medium-volume, medium scale propagation method |
•Loss of embryogenecity •Cryopreservation dependence of cell lines •Field test with other species disappointing •Extremely high cost per plant |
from: Bornman and Botha 2000. Somatic seed: balancing expectations against achievements. In: Proceedings: Forest genetics for the next millennium. IUFRO Working Party 2.08.01 | ||
Note that the OECD Scheme for Certification of Forest Reproductive Material uses the terms type and category of material. These are distinct from kind of material used here. For an explanation, see REGULATING & APPLYING STANDARDS.
