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