Effects of salt and drought stress on seed germination and seedling growth in Portulaca

The effects of salt and water deficit on seed germination and early seedling growth were studied in six Portulaca accessions (P. oleracea L. ssp. oleracea, P. grandiflora Hook., P. grandiflora cvs. 'Sundial Mango', 'Double Pink' and 'Double White', and P. halimoides L.). The aims of the study were to evaluate their responses to abiotic stress and to establish the relative degree of tolerance of the selected taxa. Seeds were germinated in the presence of increasing concentrations of NaCl or polyethylene glycol 6000 (to mimic drought conditions), generating the same osmotic potentials: 0, -0.25, -0.5 and -0.1 MPa. Germination percentage, mean germination time, seedling fresh weight and vigour index, and radicle, hypocotyl and cotyledon lengths were determined. Seed germination and seedling development decreased in all taxa in the presence of PEG and NaCl, in a concentration-dependent manner, although the effect of salt was stronger than that of PEG, at the same osmotic potentials. Germination and seedling parameters varied for the different accessions but, in practical terms, considering only the final germination percentages under stress, P. halimoides L. appears to be the taxon most tolerant to water deficit, whereas P. grandiflora Hook. would be the most tolerant to salt stress..