Efeitos da luz e temperatura na germina？？o de sementes de quatro espécies de plantas daninhas do gênero Digitaria

brazil has the largest number of native species of digitaria in the americas. this genus is considered as a weed causing problems in various economic crops and can be found throughout brazil in many different ecological situations. the object of this research was to evaluate the effects of light and temperature on the seed germination of four digitaria weed species. the experiment was conducted in germination chambers using a factorial 4 x 2 scheme of treatments under four temperatures (25 oc constant, alternating 20-30 oc, 20-35 oc and 15-35 oc) with alternate light cycles (8h light/16h darkness) or absolute darkness. the weed species studied were digitaria horizontalis willd., d. bicornis (lam.) roem. & schult., d.ciliaris (retz.) koel. and d. insularis (l.) fedde. the percentage and speed of germination were evaluated up to 21 days after the start of the germination test. the four species showed differing seed physiological responses. d. bicornis and d. horizontalis required light for germination while d. ciliaris and d. insularis did not. the best temperatures for germination are 20-35 oc for d. bicornis and d. ciliaris, and 20-35 oc or 15-35 oc for d. horizontalis and d. insularis.