Applications of Photomorphogenesis Research to Horticultural Systems

The photomorphogenesis research program at Clemson University consists of a group of scientists with diverse backgrounds and interests who share a common goal of learning how manipulation of the light environment can be used to regulate plant development. An important objective of their work that complements their overall goal is to incorporate new knowledge into systems that are more effective in growing horticultural crops. As this program continues to evolve and supply information to our horticultural discipline and supporting industries, it provides training to a new generation of research scientists.

Photomorphogenesis is defined as the ability of light to regulate plant growth and development, independent of photosynthesis. Phytochrome, derived from the Greek words for plant and color, is the pigment that controls photomorphogenesis. This photoreversible pigment system consists of two forms, Pr and Pfr, which have peak absorptions in red (660 nm) and far-red (730 nm) wavelengths of light, respectively. The conversion of the pigment from one form to another influences such aspects of growth and morphology as flowering and germination. Investigations continue, however, in order to more fully understand the mechanism behind this complex, light regulated system and its affects on plant development. These findings are essential for the further advancement of this sector of our horticultural industry.

While the photomorphogenesis research program at Clemson may be considered young in terms of length of existence, some of their findings have already had an impact on several horticulture industries. In 1985, Dennis Decoteau (Horticulture) collaborated with USDA-ARS scientists Mike Kasperbauer and Pat Hunt on the use of various-colored reflective polyethylene mulches for plant growth and production. Results suggested that the mulch surface color induced changes in the plant microclimate that could act through natural regulatory systems within the plant to influence plant growth and fruit production. In 1986, nematologist Bruce Fortnum began investigating the influence of colored mulches and light quality on nematode interactions with roots and plant productivity. This interaction of mulch color and nematode population has provided insight into non-chemical techniques for nematode control on susceptible crops such as tomato.

Decoteau and John W. Kelly (Horticulture) began collaborations in 1987 on the use of reflective colored surfaces for poinsettia production in the greenhouse. With the assistance of Peter Adler (Entomology), they demonstrated that colored reflective surfaces altered population densities of whiteflies, suggesting a possible use of colored reflective surfaces for non-chemical insect control.

In 1989 Kelly and Decoteau, along with Roy Young, Robert Pollock (Agricultural and Biological Engineering), and Margaret McMahon (Horticulture) began a research project to further develop the technology for using liquid spectral filters for greenhouses. A model greenhouse system was developed at Clemson University and subsequent research demonstrated that liquid spectral filters could be developed by placing various aqueous dyes in the double-layered acrylic or polycarbonate sheets that are used as greenhouse glazing. These liquid spectral filters served as selective filters for the photomorphogenetic wavelengths of radiation that affect plant morphology. The filters also reduced transmission of the heat component and solar background spectra and, thereby, affected greenhouse cooling.

Heather Hatt (Horticulture) and Decoteau began investigations in 1989 on the physiological mechanisms of the end-of-day red and far-red regulation of plant growth. This work led to a better understanding of phytochrome-regulated growth of watermelons and their additional investigations suggested the importance of light transmission in the development of future row cover materials for vegetable production. Jodi Benson (Horticulture) and Kelly found bedding plants to be highly responsive to spectral filters resulting in compact growth without chemical applications.

Light as a regulator of tissue-cultured plantlet development was investigated by Joan John (Horticulture). She observed that yam plantlet growth and protuber development could be affected by treating the plantlets with EOD R or FR light). In more recent work, Sandy Wilson (Horticulture) has been using transgenic tobacco to determine the role of cytokinins in photochrome regulated plant growth. The transgenic tobacco was transformed to over-produce cytokinins and facilitated measuring cytokinin concentrations in response to EOD R and FR light treatments. Trend analysis of plant responses to EOD light treatments suggests that R light increases cytokinin concentrations in plants.

Nihal Rajapakse (Horticulture) and Kelly have assumed a leading role in determining CuSO4 filter effects on greenhouse plant production and the biochemical constituents of the plant. Initial studies indicated that CuSO4 solutions reduced plant height and internode length of chrysanthemum plants similar to plants treated with chemical growth regulators. Reduction of plant height and internode length by CuSO4 filters could be reversed by weekly applications of gibberellic acid (GA) suggesting that GA metabolism may be altered under spectral filters. Sonja Maki (Horticulture) and Rajapakse are currently investigating the relationship between the responsiveness and sensitivity of gibberellins to specific wavelengths of the light spectrum. The role of carbohydrate metabolism and its relation to gibberellins in height control by spectral quality is also being explored.

Clemson's photomorphogenesis team has been joined by James Arnold and Teresa Cerny (Horticulture) for the latest area of focus; a three way partnership with Klerk's Plastic Products Manufacturing Inc. and Merck Pharmaceuticals. Recently, the two latter companies jointly patented a filtering material that can selectively reflect, block, or absorb certain wavelengths of light. This filtering material is being used to develop greenhouse coverings that reduce the amount of heat in the greenhouse while still maintaining maximum photosynthetic active radiation- PAR (the light range most needed for the plant's growth). Clemson's horticulture and agriculture engineering `light' group will conduct joint research with the two companies on a five year project to evaluate the effectiveness of these newly developed spectral containing greenhouse films on commercially valuable horticultural crops.

As the general public becomes more concerned about exogenous chemical applications to plants because of unwanted residue in food crops, toxic effects on nontargeted species, and contamination of the environment; interest in using alternative methodology such as light quality to regulate plant growth and to control disease and insect pests will increase. The photomorphogenesis program at Clemson will continue to generate new understandings in light and plant growth and use this new knowledge in developing environmentally sound horticultural systems for the successful production of vegetables, fruits, flowers and ornamental crops.

John W. Kelly - Horticulture, Department Chair

Dennis R. Decoteau - Horticulture

Nihal Rajapakse - Horticulture

Roy E. Young - Agricultural Engineering

Peter Adler - Entomology

Sonja Maki - Horticulture

Robert K. Pollock - Agricultural and Biological Engineering

Heather A. Hatt - Horticulture

Margaret J. McMahon - Horticulture

Sandy B. Wilson - Horticulture

Chris Ray - Horticulture

Teresa A. Cerny - Horticulture

Jodi Benson - Horticulture

David Clark - Horticulture

Joan John - Horticulture

Damayanthi Ranwala - Horticulture

James Arnold- Senior Horticulturist, South Carolina Botanical Garden

Kathy Brock - Research Technician

Rajapakse, N.C. and J.W. Kelly. 1995. Spectral filters and growing season influence growth and carbohydrate status of chrysanthemum. J. Amer. Soc. Hort. Sci. 120(1):78-83.

Hatt Graham, H.A. and D.R. Decoteau. 1995. Regulation of pepper transplant growth with light and subsequent effects on fruit production. HortScience 30:487-489.

Rajapakse, N.C., M.J. McMahon and J.W. Kelly. 1993. End-of-day far-red light reverses height reduction of chrysanthemum induced by CuSO4 spectral filters. Scientia Hort. 53(1993):249-259.

Rajapakse, N.C., and J.W. Kelly. 1993. Spectral filters influence transpirational water loss in chrysanthemum. HortScience 28(10):999-1001.

Rajapakse, N.C., and J.W. Kelly. 1992. Regulation of chrysanthemum growth by spectral filters. J. Amer. Soc. Hort. Sci. 117:481-485.

Decoteau, D.R. and H.H. Friend. 1991. Growth and subsequent yield of tomatoes following end-of-day light treatment of transplants. HortScience. 26:1528-1530.

Rajapakse, N.C., and J.W. Kelly. 1991. Influence of copper sulfate spectral filters, daminozide and exogenous gibberellic acid on growth of Dendranthema grandiflorum (Ramat.) Kitamura 'Bright Golden Anne'. J. Plant Growth Regul. 10:207-214.

McMahon, M.J., J.W. Kelly, D.R. Decoteau, R.E. Young, and R.K. Pollock. 1991. Growth of Dendranthema grandiflorum (Ramat.) Kitamura under various spectral filters. J. Amer. Soc. Hort. Sci. 116:950-954.

McMahon, M.J., J.W. Kelly, and D.R. Decoteau. 1990. Spectral transmittance of selected greenhouse construction and nursery shading materials. J. Env. Hort. 8:118-121.

Hatt Graham, H.A. and D.R. Decoteau. 1995. Development of a plastic mulch system that changes color in the field. HortScience 30:265-269.

Decoteau, D.R., M.J. Kasperbauer, and P.G. Hunt. 1990. Bell pepper development over mulches over diverse colors. HortScience 25:460-462.

Decoteau, D.R. and B.B. Rhodes. 1990. Characteristics and effectiveness of photodegradable mulch for use in watermelon production. Appl. Agr. Res. 5:9-12.

Decoteau, D.R., M.J. Kasperbauer and P.G. Hunt. 1989. Mulch color affects yield of fresh market tomatoes. J. Amer. Soc. Hort. Sci. 114:216-220.

Decoteau, D.R., M.J. Kasperbauer, D.D. Daniels and P.G. Hunt. 1988. Plastic mulch color effects on reflected light and tomato plant growth. Scientia Hort. 34:169-175.

Fortnum, B.A., D.R. Decoteau, M.J. Kasperbauer, and W. Bridges. 1995. Wavelength selective mulches affect Root-knot of tomato. Phytopath. 85:312-318._85:312-318._85:312-318.

Kelly, J.W., P. Adler, D.R. Decoteau, and S. Lawrence. 1989. Colored reflective surfaces to control whitefly on Poinsettia. HortScience 24:1045.

Rajapakse, N.C. and J.W. Kelly. 1994. Problems of reporting spectral quality and interpreting phytochrome-mediated responses. HortScience 29(12): 1404-1407.

Rajapakse, N.C., R. Pollock, M.J. McMahon, J.W. Kelly and R.E. Young. 1992. Interpretation of light quality measurements and plant response in spectral filter research. HortScience 27:1208-1211.

Keuhny, J.S. and D.R. Decoteau. 1994. Interrelationship of nitrogen and light on episodic growth of Ligustrm japonicum. J. Environ. Hort. 12:43-46.

Decoteau, D.R., H.A. Hatt, J.W. Kelly, M.J. McMahon, N.C. Rajapakse, R.E. Young and R.K. Pollock. 1993. Applications of photomorphogenesis research to horticultural systems. HortScience 28(10):974,1063. Cover article.

Clark, D.G., J.W. Kelly, and D.R. Decoteau. 1991. Influence of end-of-day red and far-red light on potted roses. J. Env. Hort. 9:123-127.

Decoteau, D.R. and H.H. Friend. 1991. Growth and subsequent yield of tomatoes following end-of-day light treatment of transplants. HortScience. 26:1528-1530.

Decoteau, D.R. and H.H. Friend. 1991. Phytochrome-regulated growth of young watermelon plants. J. Amer. Soc. Hort. Sci. 116:512-515.

Starman, T.W., J.W. Kelly, and H.B. Pemberton. 1990. The influence of ancymidol on morphology, anatomy, and chlorophyll levels in developing and mature Helianthus annuus leaves. Plant Growth Regulation 9:193-200.

McMahon, M.J. and J.W. Kelly. 1990. Influence of spectral filters on height, leaf chlorophyll and flowering of Rosa x hybrida 'Meirutral'. J. Environ. Hort. 8(4):209-211.

Starman, T.W., J.W. Kelly and H.B. Pemberton. 1990. Influence of gibberellin A3 and ancymidol on sunflower leaf anatomy. Can. J. Bot. 68(1):159-162.

Starman, T.W., J.W. Kelly and H.B. Pemberton. 1989. Characterization of ancymidol effects on growth and pigments of Helianthus annuus cultivars. J. Amer. Soc. Hort. Sci. 114:427-430.

Pertuit, A.J. and J.W. Kelly. 1987. Timing of a lighting period for Easter lily bulbs prior to forcing. HortScience 22:316.

Kelly, J.W. and J.J. Frett. 1986. Photoperiodic control of growth in waterlilies. HortScience 21:151.

Desamero, N.V., B.B. Rhodes, D.R. Decoteau, and W.C. Bridges. 1994. Picolinic acid-induced somatic embryogenesis in sweet potato. Plant, Cell, Tissue, and Organ Culture. 37:103-111.

John, J.L., W.H. Courtney, and D.R. Decoteau. 1993. The influence of plant growth regulators and light on microtuberization in Dioscorea alanta L. cultures. Plant, Cell, Tissue, and Organ Culture. 34:245-252.

John, J.L., W.H. Courtney, and D.R. Decoteau. 1993. Photocontrol of Dioscorea alanta plantlet growth. Scientia Hort. 54:255-265.

Decoteau, D.R. and H.A. Hatt Graham. 1994. Plant spatial arrangement affects growth, yield, and pod distribution of cayene peppers. HortScience 29:149-151.

Francis, R. and D.R. Decoteau. 1993. Developing an effective Southernpea and sweet corn intercrop system. HortTechnology 3:178-184.

Perry, K., D. Sanders, D. Granberry, T. Garrett, D. Decoteau, R. Nagata, R. Dufault, K. Batal, and W. McLaurin. 1993. Heat units, solar radiation and daylength as pepper harvest predictors Ag. Forest Methodology 65:197-205.

Decoteau, D.R. and H.H. Friend. 1991. Plant responses to wavelength selective mulches and row covers: A discussion of light quality effects on plants. Proc. Natl. Agr. Plastics. Congr. 23:46-51.

Friend, H.H. and D.R. Decoteau. 1990. Transmission properties of selected row cover materials and implications in early plant development. Proc. Natl. Agr. Plastics. Congr. 22:1-6.

Mao, Z., L.E. Craker, and D.R. Decoteau. 1989. Abscission in Coleus: Light and phytohormonal control. J. Expt. Bot. 40:1273-1277.

Decoteau, D.R. and L.E. Craker. 1987. Abscission: Ethylene and light control. Plant Physiol. 83:970-972.

Craker, L.E., S. Zhao and D.R. Decoteau. 1987. Abscission: Response to red and far-red light. J. Expt. Bot. 38:883-888.

Decoteau, D.R. and L.E. Craker. 1984. Abscission: Characterization of light control. Plant Physiol. 75:87-89.

Decoteau, D.R. and L.E. Craker. 1983. Abscission: Quantification of light control. Plant Physiol. 73:450-451.

Rajapakse, N.C. and J.W. Kelly. 1994. Postharvest differences with respect to storage potential and carbohydrate status of rooted chrysanthemum cuttings. Acta Horticulturae (In Press)

Rajapakse, N.C. and J.W. Kelly. 1994. Influence of spectral filters on growth and postharvest quality of potted miniature roses. Scientia Horticulturae 56(1994):245-255.

Rajapakse, N.C., D.G. Clark, J.W. Kelly and W.B. Miller. 1994. Carbohydrate status and postharvest leaf chlorosis of miniature roses as influenced by carbon dioxide enrichment. Postharvest Biol. and Tech. 4(1994):271-279.

Cushman, L.C., H.B. Pemberton and J.W. Kelly. 1994. Cultivar, flower stage, silver thiosulfate, and BA interactions affect performance of potted miniature roses. HortScience: 29(7): 805-808.

Clark, D.G., J.W. Kelly and N.C. Rajapakse. 1993. Production and postharvest characteristics of Rosa hybrida L. 'Meijikatar' grown in pots under carbon dioxide enrichment. J. Amer. Soc. Hort. Sci. 118(5):613-617.

Clark, D.G, J.W. Kelly and H.B. Pemberton. 1991. Postharvest quality characteristics of cultivars of potted rose in response to holding conditions and cytokinins. HortScience 26(9):1195-1197.

Rajapakse, N.C., D.Wm. Reed, and J.W. Kelly. 1991. Storage temperature and duration affect quality and post-storage recovery of vegetative Dendranthema x grandiflorum cv. Bright Golden Ann. J. Amer. Soc. Hort. Sci. 116:73-76.

Rajapakse, N.C., J.W. Kelly and D.Wm. Reed. 1990. Use of antitranspirants under low-light environments to control transpiration of Epipremnum aureum leaves. Scientia Horticulturae 43:307-312.

Rajapakse, N.C., D.Wm. Reed and J.W. Kelly. 1989. Effect of pre-treatments on transpiration of Chrysanthemum morifolium in the dark. HortScience 24(6):998-1000.

Thaxton, D.R., J.W. Kelly and J.J. Frett. 1988. Control of Hibiscus rosa-sinensis L. bud abscission during shipping. Scientia Horticulturae 34:131-137.

Rajapakse, N., J.W. Kelly and D.Wm. Reed. 1988. Transpiration and water use of potted floricultural plants under low-light conditions. J. Amer. Soc. Hort. Sci. 113(6):910-914.