Revue internationale d'écologie méditerranéenne International ...

190
◆ A. ABBAD, M. CHERKAOUI & A. BENCHAABANE
Abridged version
Atriplex halimus L. (Chenopodiaceae) is a xero-halophyte, spontaneous,
perennial species of the arid and semi-arid Mediterranean
regions. Owing to its ecological (reducing erosion), energetic
(firewood) and fodder qualities, A. halimus is a choice shrub material
for the rehabilitation of the degraded lands in arid and semi-arid
areas. The species is characterized by an important polymorphism.
Few studies have been conducted until now on the evaluation of
this polymorphism, which is necessary for its good management and
valorisation. In that way, an analysis was carried out on the morphological
and allozyme variability of three natural populations of A.
halimus located in three different climatic contexts: semi arid bioclimate
(Sidi Bouzid in the Safi region), arid bioclimate (Marrakech
region) and Saharan bioclimate (Idelssen in the Ouarzazate region;
table 1). In each population, individuals were sampled randomly
with 28, 16, 16 individuals for the population of Sidi Bouzid,
Idelssen and Marrakech, respectively. The leaf area (SF), the leaf
length to maximum width ratio (RF), the average width of the leaf
(lm) and the leaves to branches ratio (F/R) were determined. The
same data were analysed on clones having three years old resulting
from semi woody cuttings taken from the three natural populations
and placed in a common garden in Marrakech. The genetic varia-
Lat.
N.
Long.
W
Altitude
(m)
P
(mm)
bility was evaluated by an isoenzymatic analysis with four systems
on 36 seedlings for each population.
The study showed a highly significant morphological variability
between individuals of the three studied populations (table 2).
This variability is more significant as the populations are distant
geographically and located in different climates. The Sidi Bouzidpopulation
individuals showed the highest leaf area and leaf length
to maximum width ratio (table 3). Their leaves were longer and
less broad giving a typically lanceolate form. The leaves to branches
ratio was also higher (table 4). For the population of Idelssen
station, the individuals have presented the smallest leaf area and
leaf length to maximum width ratio : the leaves are broader and
less long giving a generally ovate to obovate form and the leaves to
branches ratio is very low. The Marrakech population individuals
showed intermediate values for all the studied parameters. The
gradual character of this morphological variability along this climatic
gradient, have indicates a clinal differentiation than ecotypic.
The clones of each population placed in a common garden have
maintained the same leaf characteristics as the population sources,
suggesting a genetic fond of this variability. The study of the isoenzymatic
markers have confirmed this variability (P = 85.71 %;
He = 0.360; A = 2.14 and Gst’ = 0.11).
M
(°C)
m
(°C)
M-m (°C)
HR % Evaporation
moyenne
max min annuelle
Sidi Bouzid (Safi ) 32° 18’ 9° 15’ 15 353 29,7 8,4 21,3 80 70 1800
Marrakech 31° 37’ 8° 02’ 470 242 38,3 4,5 33,8 73 30 2700
Idelssen (Ouarzazate) 30° 56’ 6° 54’ 1135 115 39,4 1,0 38,4 ND ND ND
Lat. N. : Latitude Nord ; Long W : Longitude Ouest ; P : Précipitations moyennes annuelles ; M : Moyenne des maxima du mois le plus chaud ; m : Moyenne des minima du
mois le plus froid ; M – m : Amplitude thermique extrême moyen ; HR : Humidité maximale (max) et minimale (min) relative ; ND : Non déterminé.
Lat. N : North latitude ; Long. W : West longitude ; P: Mean annual rainfall ; M : Average temperature of the warmest month ; m : Average temperature of the coldest month ;
M – m: Thermic amplitude ; HR: maximal (max) and minimal (min) relative humidity ; ND: Not determined.
Tableau 1. Caractéristiques climatiques des stations des trois populations étudiées.
Table 1. Climatic characteristics of the stations of the three surveyed populations.
ecologia mediterranea, tome 29, fascicule 2, 2003