Effects of drought stress on seed germination of ornamental sunflowers

The response to drought stress on germination was investigated on three hybrids of ornamental sunflower, ‘Hadar’, ‘Pazit’ and ‘Zohar’. Different levels of water potential (Ψ: 0.0 (control), -0.15, -0.30, -0.45, -0.60, -0.75 and -0.90 MPa were adopted using polyethyleneglycol-6000 (PEG6000) at four germination temperatures (15, 20, 25 and 30°C). Final germination percentage (FGP), mean germination time (MTG), germination index (GI), germination rate index (GRI) and germination stress tolerance index (GSI) were used to evaluate the genotype response to PEG-induced water stress. Shoot and root length and fresh and dry weight were measured on seeds germinated at 20 °C under the different levels of water potentials. During germination, the three ornamental sunflowers showed to be more sensitive to suboptimal temperature than to supraoptimal. Decreasing water potential of imbibition solution progressively inhibited and delayed seed germination. Among cultivars, ‘Hadar’ and ‘Pazit’ performed better at temperature lower than 30 °C. ‘Zohar’ showed a lower sensitivity to PEG-induced water stress at all temperature conditions. Water stress during seed germination depressed further seedling growth under favourable conditions, being shoot and root length and both fresh and dry weight significantly lower in seedlings from seed germinated at Ψ ≤ 0.45 MPa.