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Nihal C. Rajapakse and John W. Kelly

The response of chrysanthemum plants to varying R:FR ratios and phytochrome photoequilibrium values (Ø = Pfr/Ptot) was evaluated by growing plants under 6%, or 40% CuSO4 and water spectral filters. Using a narrow band-width (R = 655-665 and FR = 725-735 nm) and a broad bandwidth (R = 600-700 and FR = 700-800 nm) for R:FR calculation, 6% CUSO4 filter transmitted light with greater R:FR (3.9) and grater Ø (0.81) than 40% CuSO4 or water filters. Light transmitted through 40% CuSO4 and water filters had a similar narrow band R:FR ratio (1.2), but the broad band R:FR ratio (2.1) of 40% CuSO4 filter was higher than water filter. Estimated Ø value was similar for both water and 40% CuSO4 filters. Final height of plants grown in CuSO4 chambers was about 30% less than the plants in control chambers. The results suggest that broad band R:FR ratio correlated more closely to plant response than the narrow band R:FR ratio.

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Diego A. Mata and Javier F. Botto

correlates with the R/FR ratios in a wide range of light conditions ( Smith, 1981 ). Low R/FR ratios induce several responses in plants known as shade avoidance syndrome that include the promotion of elongation of internodes, petioles, and leaves; the

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Paul Kusuma and Bruce Bugbee

responses: phytochrome photoequilibrium (PPE) and the R:FR ratio. Issues with these metrics are exacerbated under light-emitting diodes (LEDs), which are important to photobiology because of their narrow bandwidth. Furthermore, the high efficiency output of

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Janni Bjerregaard Lund, Theo J. Blom, and Jesper Mazanti Aaslyng

-red ratio (R:FR ratio)] have been shown to limit elongation growth ( Khattak and Pearson, 2006 ; Mortensen and Strømme, 1987 ; Rajapakse and Kelly, 1992 ). However, the effect of changes in light quality is not always positive. A decrease in the R:FR ratio

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Steven P. Arthurs, Robert H. Stamps, and Frank F. Giglia

). Manipulation of the R/FR has been proposed as a way to modify horticultural crops. For example, high R/FR ratios induce beneficial physiological responses, most notably reduced stem extension and increased plant compactness ( Fletcher et al., 2005 ; Mata and

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Toshio Shibuya, Junki Komuro, Norio Hirai, Yoshiko Sakamoto, Ryosuke Endo, and Yoshiaki Kitaya

in these systems have shorter shoots than those grown under natural light ( Ohyama et al., 2003 ). The reduced shoot elongation is due to the high R:FR ratio of typical commercial FLs, which emit little FR irradiation. Thus, increasing the FR content

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Eva María Almansa, Antonio Espín, Rosa María Chica, and María Teresa Lao

of light treatment was found among treatments T 1 , T 2 , and T 3 except in cultivars S, A, D, C, and A N . These cultivars show the highest values in T 1 ; this can be related to the low level of R, the R:FR ratio, and ultraviolet and PAR

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Glenn L. Roberts and M. J. Tsujita

An experiment was conducted to determine whether the high R:FR ratio in high pressure sodium (HPS) lamps contributes to lateral bud breaking in roses. Rosa hybrida cv. `Samantha' plants were grown under HPS lamps, HPS lamps fitted with blue gel filters to reduce the R:FR ratio or metal halide lamps. Spectral graphs showed R:FR ratios of 1.05, 0.5 and 3.8 for HPS, filtered HPS and metal halide respectively. Although the R:FR ratio in metal halide was notably higher than in HPS the total energy in this range was much lower. At a 24hr supplemental PPF level of 70-75uEm-2s-1 more flowering shoots were produced under HPS and metal halide lighting than under filtered HPS. There were more dormant shoots under the filtered HPS. No differences in quality were found among flowers from any treatment.

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G.L. Roberts, M.J. Tsujita, and B. Dansereau

Rosa ×hybrida `Samantha' plants were grown under high-pressure sodium (HPS) lamps, HPS lamps fitted with blue gel filters to reduce the red to far-red (R:FR) ratio, or metal halide lamps. R: FR ratios were 1:0.95, 1:2, and 1:0.26 for HPS; filtered HPS, and metal halide, respectively. Although the R: FR ratio for metal halide was 3.5 times higher than for HPS, the total energy from 630 to 750 nm was 2.8 times lower. At a nighttime supplemental photosynthetic photon flux of 70 to 75 μmol·m-2.s-1, plants under HPS and metal halide lamps produced 49 % and 64% more flowering shoots, respectively, than those under filtered HPS (averaged over two crop cycles). The quality index for flowers under HPS, metal halide, and filtered HPS was 25.0, 23.3, and 18.5, respectively. Vase life was 10 to 11 days, regardless of treatment.

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Nihal C. Rajapakse, Robert K. Pollock, Margaret J. McMahon, John W. Kelly, and Roy E. Young

Experiments were conducted to correlate the response of chrysanthemum [Dendrathema ×grandiflorum (Ramat.) Kitamura] plants to light environment based on various quantitative light quality parameters by growing plants under 6% or 40% CuSO4 and water spectral filters. Using a narrow band width (R = 655-665 and FR = 725-735 nm) or a broad band width (R = 600-700 and FR = 700-800 nm) for R: FR ratio calculation, 6% CuSO4 filter transmitted light with a higher R: FR ratio than 40% CuSO4 or water filters. Light transmitted through 40% CuSO4 and water filters had similar narrow band R: FR ratios (≈1.2), but the broad band R: FR ratio (2.0) of 40% CuSO4 filter was higher than that of water filters. The estimated phytochrome photoequilibrium (ϕ) value varied considerably with the photochemical properties of phytochrome used for estimations. Final height and internode length of plants grown in 6% or 40% CuSO4 chambers was ≈30% less than of plants in corresponding control chambers. Leaf and stem dry weights were reduced by light transmitted through CuSO4 filters. The results suggest that broad band R: FR ratio correlated more closely to above plant responses than the narrow band R: FR ratio. Blue (B): R and B: FR ratios (not absolute amount of blue wavelengths) correlated well with plant response, suggesting that involvement of blue light should not be ignored in expressing plant response to light transmitted through CuSO4 filters. At present, the presentation of complete spectral data would be the most useful in explaining plant response to light environment.