Ecologia Mediterranea
Ecologia Mediterranea
Ecologia Mediterranea
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CHIRAZ CHAFFEI HAOUARI, AFEF HAJJAJI NASRAOUI, HOUDA GOUIA AND ALI HAOUARI<br />
18<br />
germinate and the embryonic tissues development<br />
towards a seedling.<br />
One of the most important abiotic factors limiting<br />
plant germination and early seedling<br />
stages is water stress brought about by<br />
drought and salinity (Mantovani & Iglesias<br />
2010). However, the presence of salt in the<br />
medium culture cause inhibitory effects on the<br />
seed’s water uptake and retard and/or suppress<br />
germination (Alatar 2011). Salinity and<br />
drought affect the plants in a similar way<br />
reducing water potential (Legocka & Kluk<br />
2005). Water stress acts by decreasing the percentage<br />
and rate of germination and seedling<br />
growth. The detrimental effects of NaCl on<br />
seeds germination are a consequence of both<br />
a water deficit resulting in osmotic stress and<br />
the effects of excess sodium ions on key biochemical<br />
processes. Seed germination and<br />
early seedling growth are critical stages for<br />
the establishment of plant populations under<br />
saline conditions (Srivastava et al. 2000).<br />
Plants differs in their upper limit of salinity<br />
tolerance as the increase in salinity concentration<br />
usually delays and reduces seed germination<br />
(Srivastava et al. 2000). The degree<br />
to which salinity affects germination by an<br />
osmotic effect or specific ion toxicity and<br />
whether salt tolerance varies in different<br />
species is still a subject of studies (Pilar et al.<br />
2011).<br />
The temperature variations have a major<br />
impact on a number of processes which regulate<br />
seed germination, including membrane<br />
permeability and the activity of membranebound<br />
as well as cytosolic enzymes (Ajmal<br />
Khan & Gulzar 2003) and its interaction with<br />
the variable soil water content in the surface<br />
layers of the soil. By consequence salinitytemperature<br />
interaction, determines seed<br />
germination pattern in many salt affected<br />
environments. Despite the importance of Pennisetum<br />
dichotomum, there is no available<br />
information on its autecology, and most<br />
drought resistant grasses of the Tunisia desert.<br />
The aim of this study is to investigate the<br />
effects of osmotic stress generated by NaCl<br />
and depth with temperature on germination<br />
characteristics (germination period and germination<br />
percentage) and seedling growth of<br />
Pennisetum dichotomum.<br />
Materials and methods<br />
Pennisetum dichotomum is a graminous<br />
(Mian 2003) grasses which inflorescence is a<br />
dense, spicate, terminal panicle. This is a useful<br />
grazing plant, much browsed by camels<br />
(Mandaville 1990).<br />
Seeds of P. dichotomum were collected during<br />
April, 2009, from naturally growing<br />
stands in the sandy soil of Mednine- South of<br />
Tunisia. Seeds were separated from inflorescences<br />
and stored dry at 4oC. During September<br />
2009, stored seeds were sterilized with<br />
0.5% sodium hypochlorite solution for 1 min<br />
and washed twice with distilled water.<br />
Effect of temperature on germination<br />
Seeds were germinated on double-layered<br />
with Whatman No. 1 filter papers placed in<br />
10cm diameter plastic dishes. Seeds were<br />
placed (30 seeds per Petri dishes) in a growth<br />
chamber (26 o C/70% relative humidity during<br />
the day, 20 o C/90% relative humidity during<br />
the night). The photoperiod was 16 h daily<br />
with a light irradiance of 150 µmol m -2 . s -1 at<br />
the canopy level. All of the Petri dishes were<br />
kept in dark incubators maintained at room<br />
temperature at four alternating night and day<br />
temperature regime (10, 25 and 35 o C) representing<br />
the seasonal common temperatures<br />
prevailing in some selected meteorological<br />
stations in south Tunisia (Mednine: 33 o 20’<br />
56.27” N, 10 o 29’ 41.26” E).<br />
Effect of depth<br />
In the nature, every sort is characterized by an<br />
optimal depth of sowing. This optimal depth<br />
depends on intrinsic characteristics of the<br />
semen. The basic rule is to sow a seed in<br />
a depth equal to 2-5 times the diameter<br />
(Seabloom 2007). In the present experiment<br />
six values of depth were tested: 1, 2, 3, 4, 5<br />
and 6 cm.<br />
Effect of water potential<br />
and NaCl doses<br />
Seeds were submitted to germination using<br />
osmotic potentials (0, – 0.2, – 0.4, – 0.6 and<br />
- 0.8 MPa) of sodium chloride solutions<br />
according to Murillo-Amador et al. (2002).<br />
Twenty-five seeds were germinated on double-layered<br />
with Whatman No. 1 filter papers<br />
ecologia mediterranea – Vol. 38 (2) – 2012