Abstract
The objectives of this survey were to determine the effect of temperature on germination and seedling growth of Hyssop (Hyssopus officinalis L.), Sweet basil (Ocimum basilicum L.) and Oregano (Origanum vulgare L.) (Lamiaceae family) as well as comparing species regarding germination behavior and growth characteristics. Seeds were germinated on a temperature-gradient bar varying between 5 and 40 °C (with 5 °C intervals). Results indicated that the highest germination percentage of hyssop (92-98%), sweet basil (86-90%) and oregano (74-77%) occurred at 20-30 °C, 25-30 °C and 20-30 °C, respectively; therefore, moderate and warm temperatures are proper for germination of all species. In all species the maximum germination rate obtained at 30 °C. Among all species, Day 10 % of Sweet basil Germination had the lowest value, which indicates faster germination. The cardinal temperatures (base, optimum and ceiling or maximum) were estimated by the segmented model. Base temperature (Tb) was calculated for hyssop, sweet basil and oregano as 3.42, 5.70 and 5.46 °C, respectively. Optimal temperature (To) calculated for all species was approximately 30°C, So warmer temperatures are much more proper for them. The species showed different maximum temperatures (Tm) from 42.91 (Oregano) to 48.05 °C (Hyssop). In Hyssop and Sweet basil optimum growth of seedlings were observed at 30°C while Oregano reached its best growth at 25°C. The difference between maximum and minimum temperatures of germination knowing as temperature range (TR) index could show adaptation capability to broad sites for planting and domestication. Regarding this index Hyssop stood in the first place.
Highlights
Germination necessities are species-specific and the expansion and rate at which the process takes place in non-dormant seeds, is affected by several environmental factors, such as light, oxygen, water and temperature (De Villiers et al, 2002)
Since cardinal temperature is very important for seed germination and there is not any comprehensive information about cardinal temperatures and the response of seed germination to varying temperatures for Hyssop (Hyssopus officinalis L.), Basil (Ocimum basilicum L.) and Oregano (Origanum vulgare L.) from Lamiaceae family, the goal of this study was to probe the effects of temperature on seed germination and seedling growth in these medicinal plants and to calculate the base (Tb), optimum (To) and ceiling temperature (Tc) for them
Germination absence of two other species at 5°C, notes to the short period of 14 days because seed germination reduction at low temperatures is extremely related to germination rate decrease (Finch-Savage and Phelps, 1993)
Summary
Germination necessities are species-specific and the expansion and rate at which the process takes place in non-dormant seeds, is affected by several environmental factors, such as light, oxygen, water and temperature (De Villiers et al, 2002). Temperature range as one of the most significant factors affecting the seed germination process is characterized by cardinal temperatures, i.e., base temperature (Tb) below which it doesn’t germinate, ceiling temperature (Tc) above which the germination is zero and optimum temperature (or range of temperatures) (To) at which the germination rate is the highest (Phartyal et al, 2003). Temperature affects the onset, potential and rate of germination (Flores and Briones, 2001; Roberts, 1988), and is thereby always the most critical factor determining success or failure of plant establishment (Kader and Jutzi, 2004). Knowing germination procedure will be very useful in growing medicinal crops as this information will help in domestication and successful establishment of the seedlings when there are wild species. Since cardinal temperature is very important for seed germination and there is not any comprehensive information about cardinal temperatures and the response of seed germination to varying temperatures for Hyssop (Hyssopus officinalis L.), Basil (Ocimum basilicum L.) and Oregano (Origanum vulgare L.) from Lamiaceae family, the goal of this study was to probe the effects of temperature on seed germination and seedling growth in these medicinal plants and to calculate the base (Tb), optimum (To) and ceiling temperature (Tc) for them
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