International Journal of Mediterranean Ecology - Ecologia ...

ADEL DHIEF, MUSTAPHA GORAI, SAMIRA ASCHI-SMITI, MOHAMED NEFFATI
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mination des graines non traitées et le trempage
dans l’acide sulfurique (96 %) pendant
30 minutes était le plus efficace pour lever la
dormance des graines et augmenter par conséquent
le pourcentage de germination des trois
espèces de Calligonum.
Introduction
The Calligonum genus belongs to the Polygonaceae
family, represented by 60-80 species
(Singh 2004; Okasaka et al. 2004) distributed
throughout Western Asia, Southern Europe,
and North Africa. In Tunisia, the genus Calligonum
is represented by three species:
C. comosum L’Hérit., C. azel Maire and
C. arich Le Houérou (Le Houérou 1959;
Dhief et al. 2009). These species are dominant
perennials in active sand dunes and stabilized
sand field in Southern desert of
Tunisia and grow naturally in Eastern Great
Erg existing in different dune slope positions
(Dhief et al. 2009). They are considered the
most important woody species in the Saharan
zone of Tunisia (Aronson et al. 1993). They
are used for fuel and charcoal production by
local nomadic populations; the overuse in this
respect has contributed to their decrease (Le
Houérou 1959; Pottier-Alapetite 1979;
Auclair & Zaafouri 1996).
Dhief et al. (2009), showed that C. comosum
existing in the interdune sites ends all growth
activity in June, while C. azel and C. arich
existing in the dune slope crests extend the
period of their vegetative growth into the
months of low rainfall (July and August). The
flowering starts in March for C. azel and
C. comosum, while starting in April for
C. arich. The time period between the beginning
of flowering and mature fruit production
is approximately six weeks for all the three
species (Dhief et al. 2009). The seed germination
starts following the first rains of
Spring. The seed phase is arguably the most
important stage of the higher plant life cycle,
ensuring species survival. Most seeds are well
equipped to survive for long periods of
unfavourable conditions before germination
and to give plants in the most favourable conditions.
Seeds temporarily fail to germinate in
conditions that might be adequate for germination
(Baskin & Baskin 1998).
The forest seed plays a key role in breeding
and regenerating (Fan & Li 2004). Because
the great majority of seeds has a dormancy
phenomenon, the research about dormancy
and its determination is important. Physiological
seed dormancy (PD) is the most widespread
dormancy class of the new ecological
classification system proposed by Baskin &
Baskin (2004) which provides a comprehensive
ecological description of the ‘wholeseed’
dormancy response.
Physiological seed dormancy is present
throughout the plant kingdom and has a profound
impact on the structure and development
of plant communities across all major
climatic regions (Cohn 1996; Hilhorst 1997).
Baskin & Baskin (1998, 2004) have proposed
a comprehensive classification system including
five categories of seed dormancy: physiological
(PD), morphological (MD), morphophysiological
(MPD), physical (PY) and
combinational (PY + PD).
Seed coat hardness and impermeability to
water may be the most important causes of
Calligonum spp. dormancy (Yu & Wang
1998; Tao et al. 2000; Ren & Tao 2004). Several
pre-sowing treatments have been proposed
for reducing seed hardness and improving
the germination rate of the other species
of the same genus (Ren & Tao 2004). Baskin
& Baskin (1998) reported that physical and
physiological dormancies are equally important
among desert shrubs.
Although the three Calligonum species have
shown a great potential to provide different
products and services and a wide adaptability
to a large range of environmental conditions
(Dhief et al. 2009), little information is available
in literature on seed germination characteristics
and techniques for breaking its coatimposed
dormancy.
There has been little experimental research
done on the Tunisian Calligonum species and
we tried to investigate the factors controlling
seed germination. This study was conducted
to better understand seed germination of the
three Calligonum species occurring under the
arid-type climate in the Eastern Great Erg of
Tunisia by comparing different pre-sowing
seed treatments (mechanical, physical and
chemical scarifications) as practical methods
to break seed dormancy and enhance germination.
Information from this study provided
basic knowledge about germination that can
be used for re-establishing projects.
ecologia mediterranea – Vol. 38 (1) – 2012