This work was carried out with the objective of evaluating light and temperature influence on germination of five weed species. The experiment was accomplished during the year of 2005, in a germination chamber, and was constituted by a factorial combination of four germination conditions and five weed species of the Amaranthus genus. The four germination conditions were: photoperiod (8 hours of light/16 hours of dark) with alternating temperature (8 hours at 30 C/16 hours at 20 °C), photoperiod at constant temperature (25 ºC); dark at alternating temperature and dark at constant temperature. The weed species studied were: Amaranthus deflexus, A. hybridus, A. retroflexus, A. spinosus and A. viridis. The experimental design was randomized blocks with four replicates. Percentage of germination was evaluated at 2, 4, 6, 8, 10, 12 and 14 days after seeding. Also, the speed of germination rate was calculated for the species. Data were analyzed using the F test of the analyses of variance, followed by non-linear regressions or Tukey's test (5%). It was observed that light and temperature interfere with the germination of all Amaranthus species, and the highest germination and speed rates were reached in the condition of photoperiod and alternating temperature (8 hours of light at 30 ºC/16 hours of dark at 20 ºC). Using less favorable conditions, A. viridis and A. hybridus reached higher germination rates than the other species. In general, A. deflexus and A. spinosus were the species that exhibited the smallest speed of germination.
pigweed; speed of germination; biology; seeds
