The effect of intermittent temperatures on germination indices of Centaurea balsamita Lam.
Centaurea balsamita is an annual plant that invades fallow and steep lands. In this regard, in order to evaluate the effect of intermittent temperatures on germination of Centaurea balsamita, a completely randomized design with six replications in vitro was conducted in the Faculty of Agriculture, Ferdowsi University of Mashhad. Temperature treatments were alternating day/night 15-5, 5-20, 20-10, 25-10, 25-15 and 30-15°C. The results showed that intermittent night and day temperatures showed the highest germination rate at 5-15°C. The highest percentage and rate of germination (83% and 8.9 seeds/day) were in the intermittent temperature of 5-15°C and the lowest in the intermittent temperature of 15-30°C. The highest values of root length (97 mm), shoot length (30 mm), root fresh weight (19 mg) and shoot fresh weight (52 mg) were obtained at 15-30, 5-15°C, respectively. Also, the highest value of the seedling vigor index (7.75) was related to the temperature treatment of 5-15°C, its lowest value (5.2) at an intermittent temperature of 10-25°C. Also, the results of this experiment were in agreement with the reality of the germination of this plant (germination in November with moisture condition). Based on the results of the present study considering that November is the peak time for the emergence of this weed in Mashhad, it is suggested that in order to perform better control and reduce the use of pesticides and consequently reduce financial and environmental costs, chemical control this weed is done at this time.