Abstract
Introduction: Several species of the genus Portulaca are highly appreciated for their nutritional value and traditional culinary and medicinal uses (e.g., common purslane, P. oleracea L.), or as ornamental plants, because of its flower size and varied colours (e.g. P. glandiflora).
Aims: This work was carried out to evaluate the relative tolerance to osmotic and salt stress of three Portulaca species, at the seed germination stage, as a first step to select the most appropriate to be cultivated under non-optimal conditions.
Materials and Methods: Germination rates, radicle emergence, and radicle, hypocotyl and cotyledonary leaf growth (for 14 days) of Portulaca halimoides, P. grandiflora and P. oleracea seeds were determined at different osmotic potentials (0.25, 0.5, 1 MPa), generated by increasing concentrations of polyethylene glycol (PEG) or NaCl. Distilled water was use to germinate control, non-stressed seeds.
Results: Seed germination and seedling growth decreased in the presence of PEG and NaCl, in a concentration-dependent manner, for the three tested species. Yet, germination percentages were lower in salt-treated than in PEG-treated seeds, at the same osmotic potential, indicating that this process is relatively more sensitive to the toxicity of the salt than to its osmotic component. Moreover, significant differences were observed among the selected species, according to their relative degree of stress tolerance. Portulaca oleracea showed the lowest inhibition of seed germination and radicle and hypocotyl growth under salt stress conditions.
Conclusion: In the context of global climate change and reduced availability of fresh water for irrigation, development of novel stress-tolerant crops is becoming increasingly important for sustainable agriculture. The relatively salt-tolerant Portulaca oleracea appear to be a promising candidate for 'saline agriculture', to be cultivated using saline, 'recycled' water (sewage, waste water from industry and agriculture, brackish water) for irrigation
