Failure of Supplementary Ultraviolet Radiation to Enhance Flower Color under Greenhouse Conditions

In order to determine whether the concentration of floral petal anthocyanin pigments could be increased, ultraviolet radiations in the UV-A and UV-B wavelength bands were presented to a variety of flowering plants to partly restore those wave- lengths filtered out by greenhouse glass. In no tested plant did the supplementary ultraviolet radiation enhance floral anthocyanin content. Supplementary UV radiation has no economic value in greenhouse production of flowering plants. A factor in the market acceptability of flowering annual plants sold for bedding or as gift plants is the brilliance of their flow- ers. Since, in New England, such plants are frequently grown under glass, the radiation environment must be considered in com- mercial production. Phytochrome and/or the high-energy blue-absorbing pigments play roles in the induction of enzyme systems leading to the synthesis of blue and red an- thocyanin pigments (Mohr and Drumm-Her- rel, 1983). The participation of ultraviolet wavelengths in anthocyanin synthesis has been known for more than a century (Bonner, 1880; Klein, 1976). For several test systems, either the near UV (UV-A = 320 to 385 nm) or the middle UV (UV-B = 290 to 320 nm) or both activate one or more of the enzymes involved in anthocyanin synthesis (Beggs and Wellmann, 1985). Although greenhouse glass is transparent to the visible and most UV-A wavelengths, UV-B is completely filtered out (Klein, 1979). Since both UV-A and UV-B may affect syn- thesis of flora1 anthocyanins, addition of these wavelengths might make it possible to grow flowering plants with more brilliant flowers. A study was conducted in which greenhouse solar radiation was supplemented with UV- A and UV-B radiation to determine if sup- plementary UV radiation might have some economic value in commercial production of flowering plants. Luminaires consisting of one each of com- mercially available UV-A lamps (BLB flu- orescent lamps with emission peaking at 365 nm) and UV-B lamps (Westinghouse FS Sunlight lamps filtered through two layers of