Choosing the right kind of material

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
KINDS OF FOREST REPRODUCTIVE MATERIAL AND PROPAGATION
TYPE  OF
REPRODUCTION
INITIAL
PROCESSES
KIND OF MATERIAL
DEVELOPMENT
STAGES OR ACTIVITIES
END STAGE
NATURAL GROWTH AND DEVELOPMENT
Natural growth and development of tree
(i.e. "internal reproduction")
Meristematic growth >
Differentiation of tissues
Leaves,
stem,
shoots,
roots and
flowers
Growth >
Elongation >
Maturation >
Senescence >
Death
Whole tree (from which forest reproductive material is produced)
SEXUAL REPRODUCTION
Natural regeneration
Flowering >
Pollination >
Fertilisation >
Fruiting >
Pollen +
Ovule >
Embryo >
Seed >
(in fruit)
Dissemination >
Germination >
Natural establishment
(Vivipary = germination on tree)
Seedling
Artificial direct seeding
As above
As above
Collection
Seed coating
Sowing / broadcasting
Seedling
Breeding and artificial regeneration
(one parent known,
half-sib family;
both parents known,
full-sib family)
(Induced)
Flowering >
(Artificial) Pollination >
Fertilisation >
Fruiting
Pollen +
Ovule >
Embryo >
Seed >
(in fruit)
Seed harvesting >
Nursery
germination >
(Transplanting) >
(Stumping = removing roots and leaves) >
Planting
Seedling
(Stumped plant)
Sapling
ASEXUAL (VEGETATIVE) REPRODUCTION
Natural re-growth of existing plant
Differentiation >
Growth of vegetative organs
Root Sucker,
Tuber, etc.
Elongation >
Shoot growth
Shoots
Artificially induced re-growth of existing plant
Cutting (coppicing) of stem
Tree stump
Stump coppicing >
Shoot growth
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,
Shoots,
or Plantule
Dehiscence /
Abscission >
Rooting >
Dissemination >
Establishment
Rooted plantlets
Macro-propagation  
(Parent tree  = ortet offspring = ramet,
ramets from same ortet  form a clone)
Shoot cutting
Cutting
Planting >
Rooting >
(Transplanting)
Rooted cutting
(ramet)
Shoot / bud and root-stock cutting and preparation
Scion or
Bud +
Root stock
Grafting/budding>
Fusion of tissues >
Growth
Grafted tree
In-grafted branch
Branch layering
Layer
Severance >
Planting
Layered plant
Micro-propagation in laboratory (in-vitro)
Separation of fascicle
(conifer)
Fascicle
Rooting >
Planting
Rooted propagule
Excision of plant tissue (from meristematic tissue)
Explant
Callus formation >
Treatment >
Rooting/shooting >
Development
(= Organogenesis)
Plantule
(in-vitro)
Callus formation and/or cell suspension
Treatment >
Somatic embryos >
Embryo development
(= Somatic embryogenesis)
Plantule
(In-vitro)
As above +
Artificial coating >
Somatic (artificial) seed
Sowing >
Nursery germination (as seeds 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
    		•

    Source: Bornman & 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, seeRegulating and applying standards.
    last updated:  Wednesday, April 18, 2007