This work aimed to examine dormancy breaking and optimum temperature for germination of Russian knapweed seed (Acroptilon repens L.). To examine germination characteristic of this weed, several experiments were conducted. First experiment was a factorial with 3 replications to break seed dormancy of this weed. First factor was KNO3 and Second factor was duration of storage in concentrated sulfuric acid with 6 periods of scarification. 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 situations and fluctuate temperatures including 2/10, 7/15, 12/20, 17/25, 22/30, 27/35°C and fluctuate temperatures including 0/10, 5/15, 10/20, 15/25, 20/30 and 25/35°C to determine optimum temperature of germination. In order to break of seed dormancy, 20 minutes treatment with concentrated sulfuric acid was required and KNO3 (1 and 3% v/v) treatments did not have significant effect on seed germination. The Optimum temperature for germination was 20/30˚C (8 hours dark/16 hours light) 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 fluctuating temperature increased seed germination. The above characteristics are very important in making Russian knapweed an invasive weed.

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