The effects of salinity and temperature on germination responses of lemon balm (Melissa officinalis L.)

This study was conducted to evaluate the effect of salinity and temperature on seed germination characteristics of lemon balm (Mellissa officinalis L.) in various temperatures of 20, 23, 25, 27, 30 and 32ºC and water potentials of 0, -0.2, -0.4, -0.6 and -0.8 MPa were used as treatments in Seed Laboratory, College of Agriculture and Natural Resources, University of Tehran in 2015. Data were analyzed using combined statistical design. Percentage of germination decreased as salinity increased at each level of temperature. Estimate of threshold point for salinity was -0.132 MPa. Segmented function was evaluated to describe cardinal temperatures. The base, optimum and ceiling temperatures of lemon balm were 17.30, 30.9 and 35ºC under optimum conditions of water potential, respectively. Response curve of the base temperature increased linearly from 17°C (control) to about 23°C (-0.8 MPa) by decreasing water potential. The base and optimum temperature and the biological time for germination were increased by increasing salinity. The results showed that Melissa officinalis L. is sensitive to salinity in germination stage.