Germination response of Galium spurium L. to light

The effects of intensity, duration and spectral quality of light were investigated on the germination of Galium spurium L. Light inhibited germination and the degree of this inhibition was related to the intensity and duration of exposure to light beyond the initial 36-h imbibition period. Subsequent dry storage for up to 7 weeks and reincubation in the dark did not remove this inhibitory effect, indicating that a secondary dormancy was induced by continuous exposure to light. Germination was completely inhibited with intermittent 1-h exposures of light every 3, 7 or 11 h for 8 days. Red, far-red and blue light inhibited germination and the degree of inhibition was related to the duration of exposure. Far-red light was more inhibitory than red or blue light. Green light promoted germination slightly. Nitrate salts in the medium during light exposure did not prevent the onset of light-induced dormancy. In subsequent dark incubation, light-induced dormancy was overcome by the addition of nitrates and, to a lesser extent, by kinetin and GA₃.