In order to examine the effect of desiccation and freezing on Russian knapweed (Acroptilon repens) root regrowth, two experiments on basis of completely randomized design were conducted in Weed Research Department, Plant Pests and Diseases Research Institute of Tehran in 2003. To examine the effect of desiccation, the first experiment was a factorial arrangement with 4 replications. First factor (A) was desiccation length time (control, 24, 48, 96 and 192 hours), and second factor (B) was desiccation temperatures (5, 15 and 258C). To examine the effect of freezing, second experiment was also a factorial arrangement with 4 replications. First factor (A) was the freezing length time (control, 24, 48 and 96 hours) and second factor (B) was freezing temperatures (1,3 and58C). In the effect of desiccation experiment on root regrowth, factors A and B were significant on all of measured characters (water loss percent, shoot numbers, dry weight, leaf number and shoot length). Increasing in temperature and length time of desiccation leads to low regrowth. The interaction effect (AB) on water loss percent, shoot number and shoot length was significant. Regrowth stopped in 58C after 96 hours desiccation and in 158C and 258C after 24 hours. In freezing experiment, factors (A), (B) and their interaction were significant on all of measured characters (shoot number, leaf number and shoot length). Decreasing in temperature and increasing in freezing length time, leads to low regrowth. Regrowth reduced in18C with decreasing storage period from 96, to 48 and 24 hours. However, regrowth stopped in 38C and 58C after 48 and 24 hours freezing, respectively.

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