Revue internationale d'écologie méditerranéenne International ...

200
◆ Y. ZAOUALI, C. MESSOUAD & M. BOUSSAID
Abstract
Rosmarinus officinalis L. is widespread in Central and North-
Western Tunisia on sites belonging to sub-humid, semi arid superior
and arid superior bioclimatic levels. This plant species reproduces
exclusively by vegetative propagation. In all populations, regeneration
from seeds is extremely rare because of abortion during nutlets
maturation and the low rate of seedling establishment.
The habitat destruction linked to human activities (vegetation
clearing, overgrazing, over-collecting and oils exploitation) and the
rarity of new plants establishment via seeds had led to a decrease
in population number and size.
Using starch gel electrophoresis, we analyzed the polymorphism of
19 Tunisian natural populations belonging to three bioclimatical
stages (sub humid, semi arid superior and arid superior) to determine
their genetic diversity and structuring.
At ten polymorphic loci, the species maintained high levels of genetic
variation within populations, despite its predominant vegetative
reproduction and the low rate of seedling establishment. The high
genotypical diversity of genets, in the starting population, and the
outcrossing breeding system should act in favor of this high genetic
variability.
An average of 11.3% of the variation resides among populations,
indicating a substantial level of interpopulational differentiation.
A significant population differentiation was observed within each
of the three ecological groups. The level of structuring varied in
relationship with the population separation and the quality of sites.
Differentiation between continuous groups was lower than that
Abridged english version
Rosmarinus officinalis L., a diploid (2n=2x= 24)
and outcrossing species, is well represented in the
Mediterranean basin. The species is exploited for the quality
of its essential oils used mainly in traditional medicine
and in pharmaceutical and cosmetic industries.
In Tunisia, wild Rosmary populations grow in Central
and North Western Tunisia in sub-humid, semi-arid superior
and arid superior bioclimatic stages, under a rainfall
ranging between 150 and 700 mm/year. Populations
developed in different sites (forests and garrigues) are
often disturbed by human activities (overgrazing, clearing,
over collecting…).
The species exhibits either vegetative or sexual reproduction.
The first reproductive mode is predominant.
Regeneration of genets from seeds is extremely rare
because of the low survival rate of embryos in mature
seeds and of the difficulty of seedling survival, mainly
observed for discontiguous ones.
Nei’s (1972) genetic distance values between pairs of populations
were low (0.005