Effect of light on the germination of vegetable seeds

Abstract

Effect of light on the germination of vegetable seed was studied in this report. In addition, dorm-ancy of shungiku (Chrysanthemum coronarium L.) and temperature relation to the germination of onion seed were investigated. Three grades of temperature of 20°, 25°, and 30°C were used in most cases. Light was supplied from fluorescent lamp. Effect of wave-length of radiation was studied by the same method as is the case reported by NAKAMURA 15) 1. In Cruciferae, the germination of radish seed is inhibited by light, and seed of Brassica vegeta-bles is favored by light. The former is inhibited by light strongly at low temperature for a while after harvest. This strong light-inhibiting action at low temperature disappears with aging of seed, but radish seed is inhibited by light to some degree for over many years. Brassica seed is forced by light only in the period of dormancy. Both of radish and Brassica seeds lose their photo-sensitivity by such dormancy-breaking treatment as prechilling, thiourea treatment, etc. 2. Germination of dormant seed of shungiku is promoted by thiourea. 3. Seed of mitsuba (Chryptotaenia japonica HASSK.) is favored by light at any temperature. By alternating temperatures, these seeds are ger-minated almost completely in darkness. Photosensi-tivity of mitsuba seed is indifferent to seed age. Celery seed is also favored by light indifferently to seed age. 4. Germination speed of onion and Welsh onion seeds is retarded by light to some extent, and this light-inhibiting action is more remarkable in Welsh onion. Temperature of over about 28°C supresses germination of onion seed. Alternating temperatures of 33° to 25°C is effective, but 33° to 28°C is not. 5. Germination of egg-plant and tomato seeds is retarded by light at every temperature. Germination rate is also often lowered at 20°C in egg-plant, at 20° and 30°C in tomato. Germination of pepper seed is retarded by electric light at every temperature, but not retarded by fluorescent light. Seed of egg-plant does not lose itt photo-sensitivity by the removal of seed coat. 6. Seeds of watermelon, squash, calabash gourd, wax gourd, and balsum pear are hindered by light at any temperature, and the degree is greater at low temperature. Seeds of cucumber, melon, and shirouri (Cucumis melo var. conomon MAKINO) are inhibited by light only at low temperature. Vegetable sponge falls in between the two groups. Photo-sensitivity of Cucurbitaceous vegetable seeds is indifferent to their seed age, and light condition is not replaced by such factors as chemical treatment, alternating temperatures, prechilling, etc.. In the case of decoated seeds, too, the photosensitivity does, not disappear, and sometimes it will even augment. 7. Seed of perilla is favored by light at every temperature. Ramie seed is also promoted by light at any temperature. Photo-sensitivity of perilla and ramie seeds is indifferent to their seed age. 8. In the case of shungiku, carrot, spinach, beet, and Leguminosous seeds, no light effect was observed in our study. 9. Concerning the relation to the wave-length of radiation, that of mitsuba, celery, perilla, and ramie seeds is about the same as in edible burdock. In Cucurbitaceae, germination is inhibited at infr-ared and blue region, but not at green region. Egg-plant, tomato, and pepper seeds are strongly inhibited only at short infrared region, and also Brassica seed was inhibited to some degree only at this region. Onion and Welsh onion seeds did not show any reaction to the spectrum. 10. It is interesting that in the seeds retaining their photosensitivity in seed coat, their photo-sensitivity is related closely to their dormancy, accordingly it disappears or diminishes accomp-anying to the breaking of dormancy. On the contrary in the seeds which retain their photo-sensitivity in their embryo,