The ecology of Canada thistle (Cirsium arvense L.) seed germination

Canada thistle (Cirsium arvense) is a noxious weed and one of the most problematic weeds in field crops, orchards, vegetables, pastures and grasslands in Iran. Determining the ecological factors of this grass weed will contribute to development of its control programs. In order to study germination characteristics to water and salinity stress conditions at different temperatures, an experiment was conducted. Temperatures regimes included 5, 10, 15, 20, 25, 30 and 35°C. For each temperature the treatment, for salinity and water stress was 4 potentials (zero, -4, -8, and -12 bar) of NaCl and 4 potentials (zero, -4, -8, and -12 bar) of PEG. Results showed that increasing salinity stress decreased significantly germination rate and percentage. Tb germination was increased from 11°C to 22°C in -12 salinity potential and Tc decreased from 42°C to 33°C. Result showed that seed germination under drought was more sensitive, so that germination percentage at -8 bar was zero.  Obtained germination data for high salinity and drought clearly showed that the permissive temperature range for germination was limited.