Revue internationale d'écologie méditerranéenne International ...

Materials and methods
Plant material
The dispersal units of Lygeum spartum are
spikelets about 2 cm long and 4-5 mm large.
Each spikelet contains 1 to 4 developed caryopses
linked together and enveloped in the
lemma.
Mature dispersal units were collected in
June 1994 from plants growing in Algeria in
arid highlands near El Kheiter (diploid cytotype)
(34 o 09’ N, 00 o 04’ E; 1000 m, 200 mm
average rainfall per year) and in the semi-arid
littoral coast (polyploid cytotype) near Oran
(35 o 38’ N, 00 o 36’ E; 90 m, 350-400 mm average
rainfall per year). Table 1 gives the mean
climatic conditions of both collection sites
provided by the Office National of Meteorology
(Dar-El Beida, Alger) for the 1991-2000
period.
Immediately after harvest, part of the dispersal
units was stored at – 30 o C until the experiments
started for maintaining initial dormancy
(Lenoir et al. 1983; Gutterman &
Nevo 1994). These seeds will be referred as
to freshly harvested. The remaining dispersal
units were maintained dry for 12 months in
paper bags at ambient temperature (about 20-
25 o C) and in darkness, in order to break dormancy.
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
Germination assays
Each germination assay was carried out with
50 whole dispersal units or 50 isolated caryopses
placed in 10 cm Petri dishes (25 units
or caryopses per dish) on a layer of cotton
wool wetted with deionized water. Petri
dishes were maintained in darkness over a
range of constant temperatures between 5 and
30 o C (± 0.5 o C), or at 20 and 25 o C under continuous
white light (warm-white fluorescent
tubes, Mazdafluor 16 W, 100 µmol m -2 s -1 at
dish level).
Studies on the effects of water potential of the
medium on seed germination were performed
using aqueous solutions of polyethylene glycol
(PEG)-8000 (Sigma) at various water
potentials between 0 (water) and – 2 MPa.
The concentrations of the PEG solutions were
calculated according to Michel & Kaufmann
(1973).
An isolated caryopsis was scored as germinated
when the radicle protruded the seed
coat, and a dispersal unit was considered as
having germinated when the radicle of at least
one of its caryopses protruded the lemma
even if 2 caryopses generally germinated per
a dispersal unit as was found in the heteroblastic
dispersal unit of Aegilops ovata (Datta
et al. 1970). Germination counts were made
daily for 14 days. The results presented are
the means of the germination percentages
obtained in 2 replicates of 25 dispersal units
or isolated caryopses ± arithmetical spread.
Germination rate is expressed as the time to
reach 50% germination (T 50 ) or the reciprocal
of T 50 (1/T 50 ). T 50 was estimated graphically
from the cumulative germination curves.
Table 1 – Mean temperature and rainfall at the two collection sites (Oran & El Kheiter)
for the 1991-2000 period.
Data provided by the Office National de la Météorologie, Da-El Beida, Alger.
Month Mean temperature ( o C) at Mean rainfall (mm) at
Oran El Kheiter Oran El Kheiter
January 11.0 5.6 38.4 13.1
February 11.9 7.5 45.4 12.6
March 14.2 10.8 48.9 31.9
April 15.9 13.4 21.0 17.7
May 19.1 18.7 23.3 17.1
June 22.3 23.7 4.0 12.1
July 25.1 27.8 0.7 5.2
August 26.2 27.4 2.3 13.3
September 23.1 21.8 15.4 24.2
October 19.2 15.8 26.2 23.0
November 15.1 10.5 51.2 12.1
December 12.3 6.9 39.5 12.2
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