Seed germination in Amaranthus retroflexus L. as affected by the photoperiod and age during flower induction of the parent plants

Seed germination in Amaranthtis retroflexus, a facultative short day plant, was affected by the parental photoperiodic conditions. Seeds from parents grown continuously in short days (SD, 8 h) had a higher dark germination and a greater response (at 30 °C) to a short irradiation or low temperature pretreatment than seeds from plants grown continuously in long days (LD, 16 h). Daily night breaks of 1 h in the middle of the long-night inhibited the SD induction of flowering as well as the SD promotion of germinability. Germinability of seeds produced by plants induced to flower in LD by 1, 2, or 3 SD was lower than that of seeds produced by plants grown continuously in SD, and decreased with the age of the parent plants at the time of flower induction.