Abstract
Increased knowledge of Russian knapweed biology would facilitate development of an optimum control program. To examine germination characteristic of this weed, several experiments were conducted in Weed Research Department, Plant Pest and Diseases Research Institute of Tehran during 2003. First experiment was a factorial with 3 replications to break seed dormancy of this weed. First factor was water treatments with 2 levels (distilled water and 3% KNO3). Second factor was duration of storage in concentrated sulfuric acid with 6 periods of scarification (5, 10, 15, 20, 25 and 30 minutes). Second experiment was conducted as a completely randomized design with 26 treatments (constant temperature including 5, 10, 15, 20, 25, 30 and 35°c in both light or darkness condition and fluctuation temperatures including 2/10, 7/15, 12/20, 17/25, 22/30, 27/35 and fluctuation temperatures including 0/10, 5/15, 10/20, 15/25, 20/30 and 25/35. to determine optimum temperature of germination. In order to break of seed dormancy, 20 minutes treatment with concentrated sulfuric acid was required and two water treatments did not have significant effect on seed germination. The Optimum temperature for germination was 30/20˚C (16 hours light/8 hours dark) with 42% germination. Seed germination was strongly influenced by temperature. Light did not play a crucial role on seed germination of this weed. Therefore Russian knapweed seeds were not photoblastic and temperature fluctuations increased seed germination. The above characteristics are very important in making Russian knapweed an invasive weed. Having precise information of this traits enables us to a better management and control of this troublesome weed.

Keywords: Russian knapweed (Acroptilon repens L.), Seed germination, Seed dormancy, Constant temperature, Fluctuating temperature, Light