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John W. Kelly

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John W. Kelly and Terri W. Starman

Physostegia purpurea Blake is a native, herbaceous perennial that has potential as a field-grown cut flower. Physostegia stems were harvested with one third of the florets open and were recut underwater in the laboratory. Fresh cut flowers treated with silver thiosulfate (STS) and held in a 2% preservative solution lasted 14 days, while control stems in deionized water (DI) lasted 6 days. Cut stems placed in darkness at 0C for 1 week had 8 days of vase life after removal from storage and treatment with STS and preservative, while stems held in DI after storage lasted only 4 days. Stems held dry at 22.5C and 43% RH for 8 hours before being placed in preservative had similar vase life as flowers placed in preservative immediately after harvest.

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Nihal C. Rajapakse and John W. Kelly

The interaction of light quality and growing season on growth and carbohydrate metabolism of chrysanthemum was evaluated using 6% CuSO4 and water as spectral filters. Light transmitted through the CuSO4 filter significantly reduced plant height and internode length compared to control plants regardless of the season. Light transmitted through CuSO4 filters delayed flowering. Total number of flowers was not affected but plants grown under CuSO4 filter had smaller flowers than those grown under the control filter. Light transmitted through CuSO4 filter reduced leaf and stem soluble sugar and starch concentrations regardless of the growing season. However, me magnitude of reduction was greater in spring than in fall-grown plants. Stems of fall-grown plants had mom starch deposition than spring-grown plants under both filters. The reduction of leaf and stem carbohydrate content (per organ basis) was greater than that of concentrations due to reduced stem elongation and total dry matter accumulation. Filters with specific spectral characteristics can be used as alternative means of controlling height and producing compact plants in the greenhouses regardless of the growing season. However, flowering should be evaluated with individual flower crops as flowering response may interact with the quality of light and growing season.

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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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David G. Clark and John W. Kelly

Potted miniature roses (Rosa × hybrida `Confection ' & `Meijikatar') were treated at the end of each 8 hour photoperiod with 30, min of red (R) or far-red (FR) light for 21 days. These light treatments convert phytochrome to the Pfr and Pr forms respectively. Plants were paper sleeved and stored in cardboard boxes at 16°C for 5 days to simulate postharvest shipping conditions. `Meijikatar' plants treated with FR light showed more postharvest leaf chlorosis than plants treated with R light or controls.

`Meijikatar' plants treated at the end of each 12 hour photoperiod with FR light exhibited more postharvest leaf chlorosis than plants treated with R light. There were no differences in postharvest leaf chlorosis between plants treated with FR light followed by R light or plants treated with R light followed by FR light. These results suggest that an avoidance of end-of-day FR light will result in less postharvest leaf chlorosis in potted roses.

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Margaret J McMahon and John W. Kelly

The growth of Rosa × hybrida and Exacum affine under different spectral filters was evaluated. Three filters that altered light quality were developed. One, a red textile dye, filtered out much of the blue/green portion of the light spectrum but did not change far-red to red (FR/R) light ratio. Another, a blue textile dye, raised FR/R by filtering out a portion of red light. The third, a salt (copper sulfate) lowered FR/R by filtering out a greater portion of far-red than red light. Two controls were used that did not alter light quality. The filters were installed in specally built growth chambers. Photosynthetic Photon Flux Density (PPFD) was adjusted to equal values in each chamber.

Plants of both species were significantly shorter and had higher leaf chlorophyll, when grown under the low FR/R filter.

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Nihal C. Rajapakse and John W. Kelly

Transpiration rates of chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] plants grown under spectral filters were evaluated as part of an investigation on using light quality to regulate plant growth. The 6% CuSO4·5H2O spectral filter reduced photosynthetic photon flux density in red (R) and far red (FR) wavelengths and increased the R: FR and blue (B): R ratios (B = 400 to 500 nm; R = 600 to 700 nm; FR = 700 to 800 nm) of transmitted light relative to the water (control) filter. After 28 days, cumulative water use of plants grown under CuSO4 filters was ≈37% less than that of control plants. Transpiration rates were similar among plants grown under CuSO4 and control filters when expressed as leaf area, a result suggesting that the reduced cumulative water loss was a result of smaller plant size. Plants grown under CuSO4 filters had slightly lower (10%) stomatal density than control plants. Light transmitted through CuSO4 filters did not alter the size of individual stomata; however, total number of stomata and total stomatal pore area per plant was ≈50% less in plants grown under CuSO4 filters than in those grown under control filters due to less leaf area. The results suggest that altering light quality may help reduce water use and fertilizer demands while controlling growth during greenhouse production.

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Nihal C. Rajapakse and John W. Kelly

The use of light quality as an alternate method for controlling ornamental plant growth was evaluated using copper sulfate solutions as optical filters, The light passed through CuSO4 solutions had high red/far-red (R/FR) ratio. Plant height and average internode length were significantly reduced by high R/FR light. Plants grown under high R/FR light had smaller leaves and a lower total leaf area but had thicker leaves, as indicated by specific leaf weight, than the control plants. Fresh and dry weights of leaves, stems and roots were reduced by high R/FR light. Dry matter accumulation in leaves was increased by high R/FR light while it was reduced in stems. Exogenous gibberellic acid (GA) application partially overcame the height reduction under high R/FR light indicating that GA biosynthesis maybe affected by light treatment. Results suggests alteration of light quality could be used in controlling ornamental plant growth as an alternate method to conventional chemical growth regulator applications.

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Margaret J. McMahon and John W. Kelly

`Spears' chrysanthemums were grown in chambers fitted with double-walled exolite filled with spectral filtering solutions: a blue textile dye that absorbed red light, CuSO4·5H2O that absorbed far-red light, and H2O that was spectrally non-selective (control).

Leaves of `Spears' grown under CuSO4-filters had increased chlorophyll a (23%), chlorophyll b (26%), xanthophyll (22%), and β-carotene (24%) compared to plants grown under H2O or blue-dye filters. Ratios of total carotenoid: chlorophyll and chlorophyll a: chlorophyll b were not affected by filter.

Individual leaf area was reduced 25% under CuSO4 filters compared to other filters. Stomates per unit area were not affected by filters, however stomates per leaf were reduced 25% under CuSO4 filters because of leaf size reduction. Stomate length and width were not affected by filter. Leaves from plants grown under CuSO4-filters had an internal structure resembling that of sun-type leaves. Other filters induced a shade-type leaf.