Abstract
As previously reported, the bulb formation of onion plant was induced by supplementary irradiation with far-red (FR) or blue (B) light but suppressed with red (R) light.
This work was undertaken to clarify the interaction between R and B or FR shown in the bulbing of onion plants under mixed light of R and B or FR.
1.The three- to four-leafed onion plants of“Kaizuka-wase”or“Tyogokuwase-shiro”were daily exposed to the sunlight for eight hours and followed by supplementary irradiation with mixed light of R and FR, of B and FR, and of R and B for sixteen hours.
Coloured fluorescent lamps (Mitsubishi FL-40 F-B and FL-40 F-R) and incandescent lamps were used for blue, red and far-red light, respectively. The sources of light were set 40cm above the plant, and the distance of the plant from source of light was varied from 0cm to 90cm. The radiant energy at plant level was determined by lux-meter and converted one lux into 0.43μw/cm2 and 1.12μw/cm2 for B and R light, respectively, and for incandescent light through cellophane filters and layer of water, viz., FR light converted one lux (for incandescent light) into 0.154μw/cm2.
2. When onion plants were irradiated by mixed light of R and FR light, in general, their bulbing-ratios (diameter of sheath or bulb/diameter of neck) increased with the intensity of FR light, decreased with the intensity of R light, But R light which has lower intensity than FR light in mixed light promoted the bulb formation.
In the case of higher R light, R light was antagonistic to FR light for the bulb formation. On the other hand, in the case of lower R light and higher FR light, R and FR light was synergistic to each other.
Colour of their leaves irradiated with mixed light of R and FR increased with intensity of R light, decreased with intensity of FR light.
These results suggest that no clear correlation is found between colour of leaf and bulb formation.
3. When onion plants were irradiated by mixed light of B and R, the bulbing-ratios increased with intensity of B light, decreased with intensity of R light. In the only case of higher B light and lower R light, bulbing was induced.
The effect of B and R light to the bulbing was antagonistic to each other.
4. When onion plants were irradiated by mixed light of B and FR, the bulbing-ratios increased with intensity of B, and of FR light.
The effect of B and FR light to the bulbing was synergistic to each other.
