A review of dipterocarps - Center for International Forestry Research

Seed Physiology 67
Table 6. Viability constants and standard errors for two OLDA species of dipterocarps (Tompsett and Kemp
1996a, b).
Species KE (se) CW (se) CH (se) CQ (se)
Dipterocarpus
alatus
Dipterocarpus
intricatus
6.44 (0.72) 3.09 (0.61) 0.0329 (0.0017) 0.000478 (0.000000)
6.34 (0.81) 2.70 (0.68) 0.0329 (0.0017) 0.000478 (0.000000)
common to all seedlots of a species. The equation has
been shown to apply to tropical and temperate tree
species (Tompsett 1986).
Equation 1 was derived using the following equation:
log10 s = K - C log m - C t - C t2
E W 10 H Q ............. (Eqn 2).
In this equation, s represents the rate of loss of viability
in days per probit.
The viability constants K E , C W , C H and C Q of Eqn 2
are reported for two dipterocarp species in Table 6.
Ageing was observed under at least 4 temperature
conditions and with several moisture content treatments
at each temperature in order to obtain the parameters
presented for these species. Further details of method
are in Tompsett and Kemp (1996a, b).
The constants for the two Dipterocarpus species were
similar and can be used to predict viability at the end of
any storage period when moisture content and
temperature are known. Thus, for D. alatus, a 64-year
period is predicted before seed ages to 85% germination,
provided the initial viability of the seed is 99.4% and
storage is at -13°C with 7% moisture content.
Calculations should be based on sound seed only. This
approach enables decisions to be made about the
cheapest conditions commensurate with attaining the
objectives of storage for different purposes. The 7%
moisture content value for D. alatus was chosen, in part,
because it has proved difficult to dry the seed further.
Oil content of the seed
Details of embryo oil contents for dipterocarps are given
in Table 2 and show much lower values for Hopea and
Dipterocarpus than for Shorea.
In the predictive viability equation given above, the
water status of seed was assessed using moisture content.
However, a more accurate measure of seed water status
in relation to physiological activity is seed water
potential. Water potential is in turn related to the relative
humidity which produces, at equilibrium, the moisture
content under consideration. These relationships have
been considered in connection with storage life by
Roberts and Ellis (1989). The reason why relative
humidity is of importance may be illustrated by
considering the influence on longevity of the reserves
in an oily seed. For a species with an oil content of 50%,
ageing-associated physiological responses would be
predicted at a moisture content which is about half the
moisture content for the same responses in a non-oily
seed, provided all other factors are identical. This is
because of the hydrophobic nature of the oily reserve.
The relative humidity value at equilibrium for the same
physiological responses, however, would be expected to
be similar for both species. Since seeds of
Dipterocarpus alatus are not oily, it is not surprising
that optimum longevity is at a relatively high moisture
content near 7%. By contrast, the oily seed of Swietenia
humilis (Meliaceae) is best stored at near 3% moisture
content.
Tissue Culture
Tissue culture has been suggested as a means of storage
of gene resources under slow growth conditions.
Additionally, this technique can be employed for
micropropagation. It is also likely that tissue culture
would be needed to grow the resulting tissue after
cryopreservation if the latter method proves practical.
However, tissue culture of dipterocarps is not easy, high
rates of cell necrosis having been observed for some
species. High resin content within the tissues may be at
least partly responsible for this effect for some species.
However, some success has been achieved by Smits and
Struycken (1983), Scott et al. (1988) and Linington
(1991) in culturing the tissues of some Shorea and
Dipterocarpus species.
Association of storage physiology with seed
characters and tree habitat
Various associations have been noted for dipterocarp
seeds. The LSMC, defined as the moisture content below