The Effect of Different Methods of Calculation of Germination Rate in Evaluation of Sprouting potential of Purple nutsedge (Cyperus rotundus L.) tuber and Estimation of Thermal Thresholds

Purple nutsedge, is one of the most burdensome weeds in the agroecosystems, due to the rapid growth and proliferation of underneath tubers. The tubers are the main means of propagation and distribution of Purple nutsedge. Information on environmental conditions that regulate the growth of the vegetative organs would help to predict the emergence time of perennial weeds. Several methods of germination were tested to compare the germination potential and determine the thresholds (the main temperatures) for germination of the tubers. The results showed that the () and ( methods are not an appropriate index for estimating the temperature thresholds and evaluating sprouting potential. Based on germination rate (tubers per day -1) and weighted germination rate (tubers per day-1) indices, temperatures of 25 and 30°C were the best temperatures. On the other hand, based on the thermal germination rate index, (tuber per°C -1 per day-1) the best temperature is 25°C. Among indices, the thermal germination rate index is a more justified assessment for precise description of sprouting potential versus temperature due to take into account the amount of used heat. In order to study the germination percentage, germination rate, weighted germination rate, Dent-like model showed better fit (R2 adjusted =0.83 to 0.99) but for study of the thermal germination rate index segmented model was superior model (R2 adjusted =0.76). In general, the minimum, optimal and maximum range of germination of Purple nutsedg was determined to be between 7.51 to 9.20, 28.5 to 32.62, and 0.43 to 42.49 ° C, respectively.