Effect of temperature and humidity on seed germination of six different Thymus species

To investigate of tolerance levels and screening of different thyme species to the temperature stresses, a factorial experiment was conducted in a completely randomized design with three replications in the vitro condition. The experiment was conducted using six Thymus species (Th. fallax, Th. fedtschenkoi, Th. pubescens,Th. vulgaris, Th. daenensis and Th. kotschyanus), at two moisture levels (dry and wet) and at 15 temperature levels (from -8 ° C to 48 ° C with an increase of 4 ° C). Measured characteristics included germination percentage and mean germination time. According to the results, the highest germination percentage belonged to Th. pubescens (70.83%) and Th.daenensis (70.44%) and the lowest germination percentage belonged to Th. vulgaris (53.04%). The average percentage of germination of seeds in dry condition (74.66%) was significantly higher than wet condition (56.12%). The highest germination percentage was observed at -4 (79.44%), zero (78.33%) and 4 (79.72%) Celsius that had significant differences with others. Interactions of species with moisture conditions showed, the highest germination percentage related to Th. kotschyanus (79.40%), Th. pubescens (78.95%), Th. daenensis (78.08%) and Th. falax (77.53%) in dry conditions and the lowest germination percentage belonged to Th. vulgaris (45.46%) in wet conditions.Using the results, different species of Thymus can be screened for temperature tolerance in dry and humid conditions and recommended for cultivation in different regions. In this experiment, native species were more resistant to temperature stresses.