Determination of cardinal germination temperatures of two ecotypes of Thymus daenensis subsp daenensis

Thymus daenensis is an important endemic medicinal plant of Iran. In the present study, the germination behaviour of two ecotypes of T. daenensis subsp. daenensis, Elam and Isfahan, was studied at various temperatures (3 to 40 degrees C) to (1) calculate cardinal temperatures and (2) determine whether germination behaviour varied between ecotypes. To determine the cardinal temperatures, the relationship between germination rate and temperature was considered. Temperature had a significant effect on both final germination percentage and germination rate in both ecotypes. The optimum germination rate occurred within the temperature range 11.2 to 24.3 degrees C for the Elam ecotype and 23 to 34.6 degrees C for the Isfahan ecotype. The calculated base temperatures (T-b) for the Elam and Isfahan ecotypes were between 0.3 and 1.3 degrees C and 1.3 and 4.4 degrees C, respectively. The ceiling temperature (T-c) for the Elam and Isfahan ecotypes was 40.9 and 42.3 degrees C, respectively. The Elam ecotype appears to be adapted for germination at lower temperatures to avoid summer drought and maximise the benefit of water availability in winter. Conversely, the Isfahan ecotype was adapted to germinate at higher temperatures.