A review of dipterocarps - Center for International Forestry Research

Seed Handling 83
(Pence 1992). In addition, material from the recalcitrant
seed of the tropical forest tree Araucaria hunsteinii can
be cryopreserved; storage of species for four years at
-20°C has been achieved, viability being measured in
terms of callus production (Pritchard et al. 1995).
Growth occurred from the radicle end of the embryo axis.
Some results achieved by Krishnapillay and
colleagues (unpublished) are described. Studies were
conducted on the recalcitrant-seeded dipterocarp species
Hopea odorata and Dryobalanops aromatica. Embryos
were first subjected to cryoprotection treatment using
sucrose and dimethyl sulphoxide; following this, the
embryos were partially dried to a moisture content near
14-15%. The temperature of the material was then taken
to -30°C at the rate of 1°C per minute, finally being
reduced to -196°C by plunging into LN. After one week
the embryo axes were removed, thawed at 40°C and
evaluated for survival. About 5% showed signs of
swelling and/or the emergence of growth initials. These
post-thawing changes were observed in the epicotylar
region; no development was observed in the radicle region
and none of the embryonic axes were able to grow into
whole plants. Improvements to the protocol are being
sought. A total of 50 excised embryo axes were used in 5
replicates for each study and for each species.
Cryopreservation has also been used for whole seeds
of Dipterocarpus alatus and D. intricatus (Krishnapillay
and Marzalina, unpublished). However, these species are
basically orthodox in storage physiology (Tompsett
1987). Cryopreservation is not recommended for species
of this storage physiology type because of the comparative
practical benefits of using conventional seedbank storage
at -20°C (Pritchard 1995).
The greatest proven uses of this approach have been
with small pieces of tissue. Complete success in the
production of entire seedlings after freezing of tissues
may require the development of in vitro culture methods
(see Chapter 3). In addition, nursery techniques for
weaning the developed plantlets are required.
Considerable investment of research time and resources
may thus be needed to assess if the method can be useful
in practice for recalcitrant-seeded material.
Summary of Seed Handling Methods
For South and Southeast Asian Dipterocarpaceae, the
following current seed handling recommendations have
been made (Tompsett and Kemp 1996a, b).
Collection Recommendations
Check a small sample of seeds before collecting, since
insect infestation may be excessive. Collect seeds from
the tree when the wings are turning from green to brown.
Collection is best accomplished by shaking or plucking
branches; a climber may be needed where branches are
inaccessible from the ground. Plan the collection to
minimise the period of time (preferably a maximum of
three days) between harvest and either nursery sowing or
short-term storage at the seed centre.
Transport Recommendations
Recalcitrant and OLDA seeds are considered separately.
Recalcitrant seeds should be transported moist and in
ventilated containers; they should be kept as cool as
possible but not below 18°C. If the wings are left intact,
a reservoir of air is created which provides oxygen for
respiration. This method reduces both the imbibition of
moisture in the container and the accumulation of heat
produced by respiration, thereby limiting the chance of
germination during transport. Possible containers include
open, folded-over polythene bags, closed polythene bags
with small ventilation holes, and open-weave sacks.
Where greater rigidity is required, the bags or sacks should
be enclosed in cardboard or wooden boxes with
ventilation holes. Care should be taken to avoid overheating
by exposure of the containers to direct sunlight.
Additionally, seed should be retained above its lowest-safe
moisture content
For species with OLDA storage physiology seeds,
collections may sometimes need to be made from the
ground with moisture contents at or below 12%. Dry seed
of this type should be transported as follows. For use in
the short-term, transport the seed at a cool temperature
above 2°C; for use in the long term, transport material at
as low a temperature as possible, but not below -20°C.
Retain the dry seed in sealed containers during transport.
For moist OLDA seed, follow the methods described for
transport of recalcitrant seed.
Processing Recommendations
Remove wings for ease of handling and to reduce storage
bulk for all species.
Other processing applies to OLDA species. Seeds of
this type will dry well in 20°C or higher with a low relative
humidity. Material should be transferred to the appropriate
storage conditions as soon as the desired moisture content
is reached. Retaining seeds in a monolayer in a flow of