Effects of osmotic stress by PEG-6000 on germination of Vicia unijuga seeds under different temperature conditions

Our aim was to identify the response of germination and growth of Vicia unijuga seeds to temperatures and water potentials. Germination experiments were conducted at three temperatures (15, 20 and 25 ℃) controlled by constant temperature incubators and six water potentials (ψ) (0, –0.2, –0.4, –0.6, –0.8, –1.0 MPa) created using different concentrations of polyethylene glycol (PEG-6000) in distilled water. The results showed that the germination parameters (germination percentage, rate and index, and vigor index) and growth parameters (sprout and radicle length) were significantly (P < 0.05) higher at 20 ℃ than at 15 ℃ and 25 ℃, respectively. Osmotic stress inhibited seed germination and seedling growth of V. unijuga, which could be alleviated by appropriately increased temperature. A significant (P < 0.05) improvement in germination rate, vigor index, and sprout and radicle length was at the lower water potential (–0.6 to –1.0 MPa) with 20 ℃ compared with 15 ℃, whereas a significant (P < 0.05) decreased in germination percentage, rate and index and vigor index was at the lower water potential with 25 ℃ compared with 15 ℃. Hydrotime model analysis showed that the basic water potential (Ψ_b) of V. unijuga seed increased with increasing temperature ranging from 15 °C to 20 °C and then decreased at 25 °C. The lowest Ψ_b value (–1.27 MPa) was attained at 20 °C, showed that this species could germinate constrained by the relative serious drought condition at this temperature regime.