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Nihal Rajapakse and William C. Newall

Morphological and physiological changes during maturation and ripening of eight Asian pear cultivars grown in the southeastern United States were evaluated. Fruit size increased throughout maturation. Flesh firmness decreased as fruit matured and averaged ≈30 to 35 N at harvest maturity. The average TSS in mature fruit ranged from 10% to 13%, with `Shinko' having the lowest and `Shinsui' having the highest. TSS increased during 4 weeks of storage at 1C, but the increase was greater in immature fruit than in mature fruit. Respiration rate declined as fruit matured. Ethylene production was low in `Hosui', `Kosui', `Nijisseiki', `Shinseiki', `Chojuro', and `Shinko' fruit. Mature `Ichiban' and `Shinsui' fruit produced high amounts of ethylene. `Kosui', `Shinsui', `Chojuro', and `Ichiban' fruit showed a climacteric rise in respiration and ethylene production at 20C, while `Hosui', `Nijisseiki', `Shinseiki', and `Shinko' behaved as nonclimacteric fruit. Ethylene production by 1C-stored `Kosui', `Shinsui', `Chojuro', and `Ichiban' fruit was increased on removal to 20C. Glucose and fructose were low during early maturation but sharply increased ≈80 to 85 days after full bloom (DAFB). Sucrose was low in immature fruit but accumulated rapidly late in maturation ≈100 to 107 DAFB. In mature `Hosui', `Kosui', `Nijisseiki', `Shinsui', `Shinko', and `Ichiban' fruit, fructose was the predominant sugar, while in `Shinseiki' and `Chojuro' fruit, sucrose was the predominant sugar.

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Nihal C. Rajapakse and William C. Newall

Changes in sugar composition during maturation and ripening of eight Asian pear cultivars were evaluated. Total soluble sugars (TSS) increased gradually throughout the maturation and averaged 10% to 13% in mature fruit. All cultivars, except `Shinko' and `Nijisseiki', had accumulated ≥10% TSS by 100 days after full bloom (DAFB). Starch accumulated during early stages of Asian pear fruit development but decreased as the maturity progressed coinciding with the rise in soluble sugars. Sorbitol, a sugar alcohol, was predominant in immature fruit and accounted for 35% to 60% of TSS fraction depending on the cultivar. Fructose rapidly increased during early maturation. Glucose increased during early maturation, but the increase was much smaller than that of fructose. Sucrose was low (<4%) in immature fruit but accumulated rapidly late in the maturation and continued to increase until harvest. In mature `Hosui', `Kosui', `Nijisseiki', `Shinsui', `Shinko', and `Ichiban' fruit, fructose was the predominant sugar which accounted for 47% to 60% of the TSS fraction. Glucose and sucrose accounted for 13% to 17% and 7% to 12%, respectively, in those cultivars. In mature `Shinseiki' fruit, sucrose was the predominant sugar (44% of TSS), while fructose and glucose accounted for 33% and 8%, respectively. Sucrose and fructose were present in equal amounts (29%) in mature `Chojuro' fruit. Late accumulation of sucrose in Asian pear cultivars suggest that sufficient time should be allowed before harvesting to obtain sweeter fruit.

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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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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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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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Venkat K. Reddy and Nihal C. Rajapakse

The influence of removal of specific wavelengths [red (R), blue (B), and farred (FR)] from sunlight on the height of chrysanthemum plants was investigated by overlaying Roscolux™ colored acetate films on 4% CuSO4 or water (control) spectral filters. CuSO4 filters removed FR wavelengths and significantly reduced plant height and internode length compared to control plants that received B, R, and FR wavelengths of light. Plants grown under Roscolux blue filters did not receive R light and were significantly taller compared to plants from any other treatments. Plants grown under Roscolux red filters did not receive B light and were significantly shorter compared to plants from other treatments. Leaf area, leaf dry weight, and stem dry weight were highest in plants grown under Roscolux red and control filter combination. The amount of leaf chlorophyll and the ratio of Chl A: Chl B was highest in plants grown under Roscolux blue filters. In general, plants that received FR light (control + film) were taller than the plants that did not receive FR light in the corresponding (CuSO4 + film) filter combination. The influence of removal of specific wavelengths on plant height control and developmental physiology will be discussed.

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Venkat K. Reddy and Nihal C. Rajapakse

The response of `Bright Golden Anne' chrysanthemum plants grown under CuSO4 spectral filters to exogenous GA3 application was evaluated to determine the relationship between gibberellins (GAs) and carbohydrate levels. The CuSO4 filters removed far red (FR) wavelengths of light and increased red: far red (R:FR), blue: far red (B:FR), blue: red (B:R) ratios, and phytochrome photoequilibrium (Ø) values of transmitted light compared to water (control) filter. Plant height, internode length, and leaf and stem dry weights were significantly reduced by light passing through CuSO4 filters in spring and summer seasons. Weekly applications of exogenous GA3 reversed the reduction in height and internode length induced by CuSO4 filters. Plants grown under CuSO4 filters responded more to exogenous GA3 application with respect to height and internode length, suggesting that the sensitivity to GA was not lowered. Light passing through CuSO4 filters reduced the carbohydrate levels, but the response varied with the season. Weekly GA3 application increased the carbohydrate levels, but did not totally reverse the reduction in carbohydrate levels under the CuSO4 filters. Although GA3 application increased the carbohydrate levels partially in CuSO4 filter-grown plants, the inhibition of GAs may not be solely responsible for reduction of carbohydrate levels under CuSO4 filters, showing that exogenous GAs and carbohydrate levels are not well correlated under CuSO4 spectral filters.

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Sonja L. Maki and Nihal C. Rajapakse

Endogenous gibberellins of chrysanthemum [Dendrathema×grandiflorum (Ramat) cv. Bright Golden Anne] were characterized in preparation for quantification of endogenous gibberellins in apices under control and CuSO4 spectral filters. Expanding shoots were separated into young expanding leaves and apices. Methanolic extracts of young expanding leaves were purified by solvent partitioning, PVPP column chromatography, and reversed-phase high performance liquid chromatography. Two bioactive regions corresponding to the HPLC retention times of GA and GA19 standards were detected in fractions using the recently developed non-dwarf rice bioassay. Dideuterated internal standards of GA12, GA53, GA19, GA20, and GA1 were added to similar extracts of shoot apices. The presence of endogenous GA53, GA19, GA20, and GA1 in chrysanthemum apices was confirmed by isotope dilution using gas chromatography–mass spectrometry-selected ion monitoring and Kovats retention indices. Ions for the deuterated internal standard of GA12 were detected, but not for endogenous GA12. The above results demonstrate that the early 13-hydroxylation pathway operates in chrysanthemum.

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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.