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After dry storage for one year at ambient temperature,
dispersal units germinated better
than at harvest time (Figure 2). However, germination
remained impossible at 5 oC, at least
within 14 days, and dispersal units from semiarid
littoral coast (Figure 2B) germinated in a
larger range of temperatures than those from
arid highlands (Figure 2A).
After-ripening had also a beneficial effect on
the germination of isolated caryopses. After
14 days of germination, this effect was manifest
at 30 oC for caryopses collected in arid
highlands and at all temperatures for those
originated from semi-arid littoral coast
(Table 3).
There existed a positive linear relationship
between the rate of germination of after-ripened
dispersal units and isolated caryopses
(expressed as the reciprocal of T50 ) and temperature
up to the thermal optimum
(Figure 3). According to Covell et al. (1986),
extrapolation of the regression lines to the
temperature axis allowed the calculation of
the lower temperature for germination of each
GERMINATION (%)
100
75
50
25
0
A
ecologia mediterranea – Vol. 36 (1) – 2010
Environmental control of germination and dormancy of seeds of two cytotypes of Lygeum spartum L.,
a perennial grass of semi-arid and arid areas in Algeria
0 5 10 15 20 25 30 35
TEMPERATURE (°C)
type of organs. It was around 5 o C and 10 o C
for the after-ripened dispersal units collected
in semi-arid area and arid highlands, respectively
(Figure 3A), and about 10 o C for afterripened
isolated caryopses from both areas
(Figure 3B). The insufficient number of experimental
points at temperatures higher than
20 o C did not allow precise calculation of the
maximal temperature for germination, but it
was probably close to 30 o C for dispersal units
collected in arid highlands (Figure 3A), and
35 o C for those from semi-arid littoral cost
(Figure 3A) and for isolated caryopses from
both origins (Figure 3B). In all cases, the thermal
optimum, indicated by the intersection
of the regression lines, was about 25 o C
(Figure 3).
Effects of light
Continuous white light markedly inhibited the
germination at 25 o C of freshly harvested and
after-ripened dispersal units collected in arid
highlands and semi-arid littoral coast (Figure
4, to be compared with Figure 1 and
GERMINATION (%)
100
75
50
25
0
0 5 10 15 20 25 30 35
TEMPERATURE (°C)
Figure 2 – Effects of
temperature on the
germination
percentages
obtained after 14
days in darkness
with freshly
harvested () and
after-ripened ()
dispersal units of
the diploid cytotype
collected in arid
highlands (A) and of
the polyploid one
collected in semiarid
littoral coast (B).
Means of results
obtained in 2
replicates of 25 units
± arithmetical
spread.
Table 3 – Germination percentages obtained after 14 days in darkness at 5, 10, 15, 20, 25 and 30 o C with freshly harvested and afterripened
isolated caryopses collected in arid highlands and semi-arid littoral coast. Means of results obtained in 2 replicates
of 25 seeds ± arithmetical spread.
B
Germination (%) after 14 days at
Cytotype (Origin) Caryopses 5 o C 10 o C 15 o C 20 o C 25 o C 30 o C
Diploid freshly harvested 0 34 ± 4 68 ± 2 90 ± 2 90 ± 6 52 ± 8
(Arid highlands) after-ripened 0 30 ± 2 62 ± 9 94 ± 2 90 ± 4 82 ± 6
Polyploid freshly harvested 0 50 ± 2 60 ± 2 78 ± 2 80 ± 4 42 ± 2
(Semi-arid littoral coast) after-ripened 12 ± 2 52 ± 6 78 ± 2 94 ± 2 92 ± 2 62 ± 2
93