A review of dipterocarps - Center for International Forestry Research

Seed Physiology
P.B. Tompsett
Seed is the natural vehicle for gene movement and
storage. It is the usual form in which germplasm is
collected. When procedures can be devised to transport
and retain material in this form, many of the technical
problems associated with other methods can be avoided.
This advantage renders seed especially appropriate for
users in tropical and subtropical countries. In general,
seed is the most common form of propagation for
afforestation and is the form in which breeding stock is
usually retained. There are, however, considerable
problems remaining in the use of seed. Some of these
are discussed below for dipterocarp species in relation
to the underlying seed physiology processes.
Much pioneering work on agricultural crop seed
physiology was conducted over the last 20 years (see
below for some references) and the principles
discovered often apply to seed of woody species. These
earlier results have been translated into technological
principles. Thus, manuals have been published on the
design of seed storage facilities (Cromarty et al. 1982),
seed management techniques (Ellis et al. 1984) and a
handbook on seed technology for genebanks (Ellis et al.
1985). Knowledge of seed physiology has thus improved
practical handling and management of crop seeds.
Compared to crop species, relatively little research
has been published on tropical and subtropical tree seed
technology and physiology. Publications have been
produced following IUFRO Seed Problems Group
meetings, the most recent of which was held in Tanzania
(Olsen 1996). Another source of information is a
summary of some relevant seed physiology projects
which has recently been published in database form
(Tompsett and Kemp 1996a, b). Also, a seed compendium
has been published which supplies succinct entries on
many tropical trees (Hong et al. 1996).
A considerable amount of empirical work on the
storage of forest tree seed has been carried out; a
sampling is given in Chapter 4. A more physiological
research approach is relatively new. Many tree species
have seed that is desiccation-sensitive (‘recalcitrant’),
Chapter 3
so that moisture physiology is especially important for
this group. However, in a recent review article on water
in relation to seed storage, the section on desiccationsensitive
seeds comprised only 4% of the article
(Roberts and Ellis 1989). More attention is, however,
now being given to recalcitrant seeds (see, for example,
Berjak and Pammenter 1996).
Framework of the Review
Germination is basic to all aspects of seed studies; work
on germination physiology, especially in relation to
temperature, is thus considered first. Another important
experimental consideration is the physiological
condition of the seed at the time of harvest, moisture
content being the single most important factor; this is
considered next in the review. Thirdly, the effect of
desiccation is discussed; knowledge of this factor enables
seed to be classed as orthodox (tolerant) or recalcitrant
(intolerant). Finally, the effects of seed storage are
considered.
The Review
Germination
In general, dipterocarp seeds germinate quickly under
moist, warm conditions.
Early germination studies took the form of nursery
assessments leading to ecological conclusions. A major
study of this type, in which 56 dipterocarp species were
assessed for germination rate and final germination, is
that of Ng (1980); no conclusions can be made
concerning temperature effects. Conditions were more
closely controlled in experiments on Shorea roxburghii,
S. robusta and S. almon by Tompsett (1985); results
showed optimum germination in the range 26-31°C for
these three species. Corbineau and Come (1986) found
that final germination reached nearly 100% for both
Hopea odorata and S. roxburghii over a broad range of
temperatures, but 30-35°C was deemed optimal because
germination rates were faster. More recently, a standard