Effects of salinity and temperature on germination and seedling growth of nine medicinal plants
Salinity stress is a major environmental constraint in arid and semi-arid regions such as Iran. Excessive amounts of salt in soil severely reduce seed germination and seedling growth of crops in agricultural systems. The purpose of this research was to study the effect of temperature, salinity and their interaction on the germination and seedling growth of nine medicinal plant species including Salvia nemorosa L., Marrubium vulgare L., Hyssopus officinalis L., Origanum majorana L., Ocimum basilicum L., Nepeta racemosa Lam., Oenothera biennis L., Silybum marianum L. and Cnicus benedictus L. Treatments included three temperatures (15, 25 and 35°C) and four NaCl concentrations (0, 5.3, 8.48 and 10.6g.l-1). A completely randomized design with three replications was used. Results showed that salinity treatments had significant effect on germination percentage, germination rate, seedling growth and seedling vigor in all nine medicinal plant species. Germination percentage and germination rate of all medicinal plant species gradually declined as the concentration of NaCl increased. Significant decrease in germination percentage and germination rate was observed at higher levels of salt concentration. Ocimum basilicum L. and Salvia nemorosa L. were the only two among nine medicinal plants in this study that germinated in salinity concentration higher than 5.3g.l–1. Germination rate and germination percentage of all species, except Ocimum basilicum were adversely affected by increasing temperature to 35°C. The highest seedling vigor in most species was observed in a temperature range of 15–25°C and increasing temperature up to 35°C, strongly decreased it. The interaction effect of temperature and NaCl concentration on final germination in all species was significant, indicating that germination response to salinity depended on temperature. The inhibitory effect of high salinity on final germination, germination rate, seedling growth and seedling vigor was greater at 35°C than at 15°C.
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