There are few studies available on germination of tropical weed species, Tridax procumbens included, despite its importance as a crop weed. This study was carried out at the Laboratory of Plant Biophysics of Embrapa Cerrados, Planaltina, DF, to evaluate the effect of light and KNO3 on T. procumbens seed germination at constant and alternating temperatures. Four sub-samples of 75 seeds were submitted to a factorial combination of light (darkness; 12 daily hours of light photoperiod) and substrate moistened with KNO3 solution (0% of KNO3; 0.2% of KNO3) for the assays at 25 °C constant and 15 ºC/35 ºC alternating temperatures, arranged in a completely randomized experimental design. Seed germination was daily counted based on emission of primary roots, with accumulated germination percentage, germination speed and accumulated germination curve being evaluated. Light contributed to increase germination percentage and speed at constant temperature, while at alternating temperatures, increase of germination percentage and speed occurred with KNO3 application, regardless of the presence or absence of light. The accumulated germination curves at 25 ºC and 15 ºC/35 ºC were adjusted to the logistic model, showing seed germination asynchrony along time.
accumulated germination curve; dormancy; tridax daisy; germination speed
