Document Type : Research Article
In order to evaluate the response of Russian knapweed seeds to cardinal temperatures a factorial experiment was conducted base on completely randomized design with 3 replications. Russian knapweed seeds (collected from irrigated and rainfed wheat fields), and germination temperatures (constant temperatures of 10, 15, 20, 25, 30 and 35° C) were used as first and second levels of the experiment. Results showed that cardinal temperatures for germination of two Russian knapweed seeds had no significant differences and optimum temperature in both seeds was 25° C. We found significant differences in percentage and uniformity of seed germination between both seed types at different temperatures rates. In low temperature (15° C), the percentage of germination (PG) of seeds were collected irrigated of wheat field was 50% more than PG of seeds were collected from rainfed wheat field. While, in high temperature (30° C), PG of seeds were collected from rainfed wheat field was more than other. These results support the conclusion that drought stress in wheat field increases the seed tolerance to high temperature.