Quality and quantity estimation of solor ultraviolet radiation on development of horticultural plants under the unfavorable environmental conditions.

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For breeding of vegetables tolerant to unfavorable environmental conditions, and its practical application under undesired cultural conditions, we tried to estimate the effect of ultraviolet on the development of vegetables (turnip and lettuce) under the solar radiation and artificial irradiation.1. Seasonal variation of solar ultraviolet-B : The variation of ultraviolet-B per day paralleled strongly that of photosynthetic active solar radiation (photosynthetic photo flux density : PPFD) , especially under fine weather. The ultraviolet-B radiation under the cloudy weather amounted to 30-35% of that under fine weather. The ultraviolet-B radiation between june and july amounted to 2-3 times of that between november and december.2. Effect of elimination of ultraviolet below 400 nm were investigated on the development of turnip (Brrasica campestris L.). Pants under the vinyl film eliminating ultraviolet below 400 nm were superior in plant length and leaf stalk to those under the vinyl film … More transmitting ultraviolet in the experiment between late spring and early summer.3. The supplemented UV-B to turnip plants induced bronzed leaves and dwarfed plants, and suppressed strongly the development of plants. Photosynthetic rate per unit leaf area under the supplemented UV-B was not significantly different from that under the control (UVT).4. Using lettuce (cv.Okayama sarada) , we investigated the effect of UV-B on development and photosynthetic activity. Nineteen day old seedlings were irradiated with UV-B which changed in irradiance and the time of irradiation under the artificial light (10000 Lux 16hr-daylength) for I week. Effect of UV-B was strongly observed on the expanded leaves, and increased with the age of leaves. Irradiated young leaves with UV-B became thcik, slender and dark green, curled inside, and stood up. The UV-B irradiated during dark period surpressed the development much stronger than that during light period. Maximum photosynthetic rate, chlorophyll, and anthocyanine per unit leaf area were increased by UV-B when compared. Less