Abstract
Problem statement: Water stress due to drought and salinity is probably the most significant abiotic factor limiting plant and also crop growth and development. Salinity and drought stresses are physiologically related, because both induce osmotic stress and most of the metabolic responses of the affected plants are similar to some extent. Water deficit affects the germination of seed and the growth of seedlings negatively. Temperature is an exceedingly important factor in seed germination. It directly affects whether a plant can sprout and, if so, how long it will take to emerge from the ground. Approach: The objective of this investigation was to determine the effect of four alternating temperature regime, drought and salt stress on germination characteristics of Pennisetum divisum. Seeds were germinated at four alternating temperatures (10/20, 15/25, 20/35 and 25/40°C at 12 h light). Seeds were also germinated with the iso-osmotic concentrations of sodium chloride (NaCl) or in polyethylene glycol PEG8000 (0, -0.2, -0.4, -0.6 and -0.8 MPa) for 14 days. Concentrations were applied to determine their effects on seed germination and seedling growth under laboratory conditions. The effects of different osmotic concentrations of NaCl and PEG were compared to distilled water (control). Results: Optimum germination was attained at 15/25°C which corresponds to temperatures prevailing during spring time. The highest values of germination parameters were obtained with no osmotic potential (0 MPa) under 15/25°C. The final germination percentage and rate of germination in the Pennisetum divisum treated seeds were decreased with the increase of the osmotic potential. At treatment by PEG, the germination was severely decreased at -0.6 MPa. While, no germination occurred at- 0.8 MPa by NaCl. The results of the effects of the different osmotic potential of NaCl and PEG on the Radicle Length (RL) and the Hypocotyl Length (HL) mm of the tested P. divisum seeds were retarded when compared to the control. Conclusion: Results indicated germination sensitive to both the stresses. However, seedling growth was more sensitive to NaCl than was germination. However, seedling growth was more sensitive to NaCl than was germination responses to water stress induced by PEG and NaCl. Results also indicated that seed germination of P. divisum is less sensitive to osmotic potential indicating that the seeds of the species are efficient in osmotically adjusting to soluble salts. This suggests the possibility of revegtating moderately salt affected soils.
Highlights
Grasses play an important role in land stabilization and animal nutrition due to their protein, carbohydrates, fats, fibers and mineral contents, soil protection and sand dune fixation
The aim of this study is to investigate the effects of osmotic stress generated by NaCl or Polyethylene Glycol (PEG) and combined effects of these stress factors with temperature on germination characteristics and seedling growth of Pennisetum divisum
These results indicate that seeds of this specie in germinable in Saudi Arabia desert regions at any time between mid-spring to mid-autumn
Summary
Grasses play an important role in land stabilization and animal nutrition due to their protein, carbohydrates, fats, fibers and mineral contents, soil protection and sand dune fixation. Gramineae grasses with inflorescence a dense, spicate, panicle terminal, widely distributed and most drought resistant grasses of the Saudi desert in coastal sands and sands around rocky ground places. This is a useful grazing plant, much browsed by camels (Mandaville, 1990). Despite the importance of P. divisum, there is no available information on its autecology. Plants are constantly confronted with various biotic and abiotic stress factors such as low or high temperature, salt, drought, flooding, heat, oxidative stress and heavy metal toxicity (Mahajan and Tuteja, 2005; Achuo et al, 2006; Jaleel et al, 2007). Water availability and temperature are important factors that determine whether or not dispersed seeds germinate. Salts and other solutes in the medium cause osmotic
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