A review of dipterocarps - Center for International Forestry Research

Seed Handling 82
Seedling storage under low light conditions
It is well established that dipterocarp seedlings usually
have high survival and slow growth rates over periods of
several months when grown under low intensity light.
Many studies, including those of Brown and Whitmore
(1992) and Press et al. (1996), report this phenomenon.
The idea of using this phenomenon for the storage of
recalcitrant-seeded species was first clearly proposed by
Hawkes (1980).
The two methods outlined below, have been tested at
FRIM: (i) storage of seedlings in a seedling chamber;
and (ii) storage of seedlings on the forest floor under
subdued-light conditions.
Seedling chamber storage
With this method, freshly collected seeds were surface
treated with a fungicide (0.1% benlate/thiram mixture)
and allowed to germinate under ambient conditions in
containers kept at high humidity with moistened tissue
paper. After radicle emergence, germinated seeds were
packed loosely in polythene bags, trays or boxes lined
with moist tissue paper and stored in a specially
constructed seedling chamber in which temperature,
humidity and light were controlled. The temperature was
16°C, the relative humidity was 80% and the photoperiod
was 4 hours. Light was supplied from a fluorescent source,
giving 80-1000 lux. Development of the germinated seeds
into seedlings occurred slowly in the chamber. Seventeen
dipterocarp species have been tested (Krishnapillay,
unpublished); these species, with the periods they have
been stored, are listed in Table 5.
Seedlings developed slowly in the chamber, barely
attaining the heights of 20-25 cm over the storage periods
tested. Seedlings which were transferred to the nursery
and grown in polythene bags needed to be weaned in at
least 70% shade for a period of 2-3 weeks before they
could be placed under direct sunlight. Survival percentage
was between 60 and 80%, dependent on the species.
Forest Floor
The second approach for storage of seedlings is on the
forest floor under subdued light. Areas were cleared of
undergrowth and freshly collected seeds were sown.
Seedlings developed very slowly and so can remain within
manageable heights for long periods of time.
Seedlings of Hopea odorata did not grow to a height
greater than 10 cm under these conditions over a period
of three years. Seedlings transferred to the nursery and
Table 5. Storage periods for Hopea, Dipterocarpus,
Shorea and Dryobalanops species in a subdued-light
chamber (Krishnapillay, unpublished).
Species Period of storage
(months)
Hopea odorata 9-12
Hopea helferi 9
Dipterocarpus cornutus 6
Shorea macrophylla 4
Shorea leprosula 6-9
Shorea acuminata 8
Shorea longisperma 6
Shorea parvifolia 8-9
Shorea ovalis 8-9
Shorea curtisii 8-9
Shorea platyclados 8-9
Shorea bracteolata 6
Shorea macroptera 6
Shorea maxwelliana 4
Shorea pauciflora 6
Dryobalanops aromatica 5
Dryobalanops oblongifolia 4
grown in polythene bags began to increase in size rapidly.
Weaning in 70% shade for 2 weeks before transfer to
direct sunlight was, however, necessary. Survival was
approximately 80-90%, depending on species. Eight
species have been tested.
The constraints with this method are as follows. In
the early stages after sowing, unprotected seeds are likely
to be predated by squirrels, birds and wild boars. Fencing
the area with barbed wire and covering the seed bed with
a plastic sheet is thus necessary. The plastic sheet can be
removed when the seedlings have emerged when damage
by birds and squirrels is unlikely.
Cryopreservation of dipterocarp seed material
Cryopreservation generally refers to the preservation of
material at -196°C, which is the temperature of liquid
nitrogen (LN). The method is being examined at FRIM
for the storage of dipterocarp seed material. At this
temperature, all metabolically related sources of
deterioration in the seed are greatly reduced or stopped,
thus supporting preservation for very long periods. Work
of this type has been carried out on some
recalcitrant-seeded tree species of temperate climates