International Journal of Mediterranean Ecology - Ecologia ...

Many treatments have been proposed to overcome
the hard testa imposed dormancy and to
improve the germination rate in other species
of the same genus. Yu & Wang (1998) showed
that the seed dormancy rates of the three Calligonum
species are more than 95%, and the
dormant degrees are rather deep. Ren & Tao
(2004) studied the effects of abrasion, sulphuric
acid, boiling water, cold stratification
and seed exudates (water-soluble inhibitors
from the testa) treatments on the germination
of 10 Calligonum species. They concluded
that the rate and the percentage of the germination
of these species are greatly increased
by mechanical or chemical scarification; however,
the lowest values are obtained with the
exudate treatment. According to Zhang
(1992), the most appropriate pretreatments for
Calligonum species are sulfuric acid and cold
stratification. In the present study, the seed
germination percentage of the three species
was enhanced by an immersion time in sulphuric
acid and increased with time until
30 min. Zou & Chen (2008) showed that germination
potential and rate of Sophora
flavescens were modified by different treatments:
H2SO4 (98%), grinding with sand and
scalding with boiling water. H2SO4 (98%)
shows the best result and improves the germination
potential to 82.0% and the germination
rate to 86.7%.
The seed dormancy is an innate seed property
that defines the environmental conditions in
which the seed is able to germinate (Finch-
Savage & Leubner-Metzger 2006). Analyzing
the seed phylogenetic tree based on the
internal morphology of the embryo and
endosperm in mature angiosperm seeds, these
authors noticed that seeds of the Polygonaceae
family present a non dormancy (ND)
and a physiological dormancy (PD). In the
present study, scarifying seeds of the three
Calligonum species with sulphuric acid for 30
min could break the dormancy of viable seeds
and increase their germination compared to
the control and other treatments. The seed viability
rates of the three Calligonum species
were low (22-57%). Therefore, it was recommended
to use a large number of seeds in
order to increase the germination rate. Our
results were in accordance with those from
the study by Yu & Wang (1998) showing that
seed viability is variable for 10 Calligonum
species originated in China, but is generally
between 30 and 50%. At the end of the experiments,
the ungerminated seeds of the studied
species showed a large fraction of mortality.
ecologia mediterranea – Vol. 38 (1) – 2012
Effects of some seed-coat dormancy breaking treatments on germination
of three Calligonum species occurring in Southern desert of Tunisia
Yu & Wang (1998) showed that the major
causes of seed dormancy are the inhibitors
existing in peels and seeds. The mortality of
seeds may be caused by water-soluble exudate
inhibitors in the seed coat that significantly
reduce germination and increase dormancy
(Ren & Tao 2003). The dormancy should not
just be associated with the absence of germination,
It is a characteristic of the seed that
determines the conditions required for germination
(Vleeshouwers et al. 1995; Thompson
2000; Fenner & Thompson 2005). Gardarin
(2010) showed that the seed mortality of
13 herbaceous species decreases according to
the increasing seed coat thickness. The same
authors showed that the thickness of the seed
coat, which is varying between 17 and 231μm
over the studied range, can protect the seed
from external attacks and slow down the seed
decay. Yan et al. (2003) showed, that the
process of the seed water absorbing consists
of a rapid water absorbing phase, slows the
water absorbing phase and the saturation
phase of 13 species of Calligonum L. The balance
time of water absorbing was in 28 hours,
and the phase of rapid water absorbing was
between four to eight hours. The seed characteristics
of water absorbing had a great similarity
within Calligonum genus but varied
among species. The capacity of water absorbing
and it speed had a close relationship with
temperature. Being a negatively photoblastic
species, it is shown that light inhibits the germination
of C. comosum seeds and they need
to be covered by sand in order to germinate
(Koller 1956). This author demonstrated that
light, high temperature (>30 o C) and close
contact with water are factors that inhibit germination
of this shrub. Studying the germination
of 10 Calligonum species. Ren et al.
(2002) found that seeds germinate at soil
depths ranging from 2 to 14 cm, but as burial
depth increases both seed germination and
seedling emergence decrease. The same
author showed that the seed dormancy does
not exist because all the seeds (or fruits) can
absorb water and expand after having been
soaked in water for 24 hours under room temperature,
and their morphology and structure
are favorable to water absorbing and gas (O 2 )
exchanging. Bond et al. (1999) showed that
the seed germination is directly related to the
seed size and the seed depth. Müller et al.
(2006) showed, that the endosperm is a barrier
for radicle protrusion of many angiosperm
seeds. Rupture of the testa (seed coat) and
rupture of the endosperm are two sequential
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