Disentangling the Effect of Light Quantity and Light Quality on Bud Break in a Rose Crop

Both light quantity (intensity) and light quality (spectrum) reaching the bud may affect bud break on a shoot remainder resulting from harvesting a flower shoot. In a rose canopy, both light quantity and light quality change with canopy depth. An experiment was set up to determine whether light quantity or light quality is more important in stimulating bud break. Four treatments were applied: two light intensities at plant base (different light quantities) in combination with two red-far red ratios (different light qualities). Light intensity was changed by applying grey crepe paper over the plant base and shoot remainder on which bud break was observed. This did not change light quality. Red-far red ratio was altered by application of far-red LEDs. Bud break was observed (buds longer than 3mm), and light intensity and red-far red ratio at the position of the buds were measured. The phytochrome photostationary state (PSS) was calculated from spectrum measurements. There was no interaction between effects of light intensity and red-far red ratio. High light intensity (no paper) resulted in PAR levels at the bud of 123 µmol m-2 s-1, compared to 17 µmol PAR m-2 s-1 when shaded with crepe paper. Red-far red ratio was 1.4 when no far-red LEDs were present and 0.31 when far-red LEDs were present; PSS was 0.79 and 0.67, respectively. Bud break was higher (2.6 broken buds) under high light intensity than under low light intensity (2.0 broken buds), compared to 2.4 and 2.3 broken buds under high and low red-far red ratio, respectively. Differences in bud break between the treatments corresponded to differences in light intensity. Similar trends were obtained in two other experiments were light quantity and light quality were varied. Hence, bud break in a rose crop was more affected by light quantity than by light quality.