The objective of this study was to investigate the involvement of phytochrome on the germination of achenes of Bidens gardneri Baker., known as black tick. The seeds were separated into short, medium and long sizes. Two experiments used only achenes medium due to differences in the response of germination in the dark, when they were artificially stored in Cerrado soil, in a previous study. The response of achenes short, medium and long to increase flow of white light was observed under a white light gradient from 0 to 46.44 µmol m-2 s-1 creep. The reversal of phytochrome far red (Pfr) in phytochrome red (Pr) in the dark, achenes medium newly collected and stored for 14 months at 4 °C, which were imbibed in water for 24 hours and incubated at 35 °C for 24, 48 and 72 hours in the dark and germination was 25 ° C in the dark and observed after 15 and 30 days. Finally, a gradient was constructed photoequilibrium for each size and age of achene in petri dishes moistened with distilled water, and the germination was observed every two days. In irradiances from 0 to 46.44 µmol m-2 s-1, germinability of achenes long and medium sizes increased with irradiance, but the seeds had low germination always short. Achenes medium stored imbibed for 24 h and incubated in the dark for 24 h, 48 h and 72 h at 35 °C remained response photoblastic when germination was observed every two days and after 15 and 30 days therefore showed no reversion Pfr for Pr in the dark. However, achenes medium newly collected and subjected to the same treatments were removed when the Pfr incubated for 48 and 72 hours. These achenes showed response very low fluence of light, when germination was observed every two days under green light. The results indicated that heteroblastism can check to the species different strategies of invasion and survival in the savanna: in places with low light availability may occur germination of achenes long, even in the rainy season (February). While short achenes can remain stored in the soil to germinate only come at the end of the dry season (in September). So, the short achene persists in the soil seed bank for seven months and is what allows the establishment of Bidens gardneri at the fields and savannah grasslands.
Far red light; phytochromes; heteroblastism; irradiance
