Revue internationale d'écologie méditerranéenne International ...

A. DJABEUR, M. KAID-HARCHE, D. CÔME, F. CORBINEAU
Figure 3 – Effects of
temperature on the
germination rate,
expressed as the
reciprocal of time to
obtain 50%
germination (T 50 ), of
after-ripened
dispersal units (A)
and isolated
caryopses (B)
collected in arid
highlands (diploid
cytotype) () and
semi-arid littoral
coast (polyploid
cytotype) ().
Regression
coefficients of the
lines were 0.97-0.98
and 0.96-0.98
(positive and
negative slopes,
respectively).
Figure 4 – Time
course of
germination in
continuous white
light, at 25 o C, of
freshly harvested (A)
and after-ripened (B)
dispersal units
collected in arid
highlands (diploid
cytotype) () and
semi-arid littoral
coast (polyploid
cytotype) ().
Means of results
obtained in
2 replicates of 25
seeds ± arithmetical
spread.
94
1/T 50(DAYS -1 )
GERMINATION (%)
GERMINATION (%)
40
30
20
10
50
25
100
0
75
50
25
0
0
A
0 5 10 15 20 25 30 35 40
A
TEMPERATURE (°C)
0 2 4 6 8 10 12 14 16
B
TIME (DAYS)
0 2 4 6 8 10 12 14 16
TIME (DAYS)
Table 2). At harvest (Figure 4A), only 34 and
30% dispersal units from arid area and semiarid
area, respectively, germinated within 14
days in the light as against 70% and 44% in
darkness (cf. Figure 1). This inhibitory effect
of light was also observed with isolated caryopses
(Table 4). It resulted then from both the
1/T 50(DAYS -1 )
40
30
20
10
0
B
5 10 15 20 25 30 35 40
TEMPERATURE (°C)
caryopsis itself and the lemma, since the
removal of the latter allowed the germination
of only 68% of freshly harvested caryopses
from arid highlands and 52% of those collected
in semi-arid littoral coast within 14
days, instead of 90 and 80%, respectively, in
darkness (Table 4).
After dry storage for 12 months, dispersal
units from both origins germinated faster
(Figure 4B) than at harvest time (Figure 4).
However, the germination of isolated caryopses
was similar in the dark and in the light
(Table 4). It seems therefore that the
inhibitory action of light involving the lemma
remained for a longer period during afterripening
than that resulting from the caryopsis
itself.
Effects of water potential
of the medium
At harvest time, dispersal units were very sensitive
to water potential of the germination
medium. The lower the water potential the
slower were the germination rate (data not
shown) and the final germination percentage
(Figure 5). Germination was nil or very weak
in a PEG solution at – 1.0 MPa, and dispersal
units collected in semi-arid littoral coast (Figure
5B) were more sensitive to low water
potentials than those originated from arid
highlands (Figure 5A). After-ripening resulted
in a reduced sensitivity of dispersal units to
water potential of the medium (Figure 5), but
those originated from semi-arid littoral coast
(Figure 5B) remained more sensitive to this
germination factor than those collected in arid
highlands (Figure 5A).
ecologia mediterranea – Vol. 36 (1) – 2010