Creeping bentgrass (Agrostis stolonifera L.) is a turfgrass species highly suitable for use on golf course tees, greens, and fairways. As a result of its ability to provide exceptional quality playing surfaces when mowed short, it is used worldwide. Because of golf course construction features, bentgrass is often maintained under reduced light conditions. Although it tolerates partial shading, it grows best in full sunlight (Beard, 1973; Bell and Danneberger, 1999).
Turfgrasses can be subjected to both natural and artificial (neutral) shade from vegetation and building structures, respectively. While under neutral shade, turfgrasses respond to reduced light intensity; shade under vegetation canopy can reduce light intensity and alter spectral composition, which act in concert to determine turf performance. Reduction of PPF was shown to induce excessive vertical shoot growth in turfgrass plants at the expense of tiller formation and lateral spread, thereby resulting in a poor density of the turfgrass stand (Bell and Danneberger, 1999; Dudeck and Peacock, 1992; Koh et al., 2003; Wherley et al., 2005). Moreover, turfgrasses grown in low PPF environments were characterized by longer, thinner, and more succulent leaves (Allard et al., 1991; Wherley et al., 2005; Wilkinson and Beard, 1974). Alteration in spectral composition and specifically reduced R:FR further contribute to aforementioned morphological changes (Casal et al., 1990; Dudeck and Peacock, 1992; Frank and Hofman, 1994; Wherley et al., 2005). However, Wherley et al. (2005) reported that leaves of plants grown under low PPF but high R:FR were wider compared with those grown under low PPF and low R:FR environments.
Under golf course conditions, shaded creeping bentgrass is maintained by frequent mowing at reduced heights. As a result, the bentgrass suffers decreased photosynthetic capacity, which ultimately leads to poor stand quality. Wilson (1997) suggested that when selecting species for shaded environments, the focus should include: compact growth morphology, relatively insensitive to changes in PPF and R:FR, and lax, horizontally oriented leaves.
Plant responses to light stimuli, including light quality, quantity, and duration, are in part mediated by gibberellins (GAs) (Hedden and Kamiya, 1997; Sponsel and Hedden, 2004). GAs are phytohormones that are involved in many developmental processes including stem elongation (Davies, 2007). GAs act by inducing genes involved in cell elongation and division (Sun, 2004). GA levels can be reduced in plants through application of growth regulators or biotechnological manipulation of genes involved in the biosynthetic pathway (Busov et al., 2003; Coles et al., 1999; Tan and Qian, 2003).
Among GA-inhibiting growth regulators, trinexapac-ethyl (TE) suppresses vertical growth and improves overall turf quality under low light conditions (Goss et al., 2002; Steinke and Stier, 2003). TE competitively inhibits the conversion of GA20 to GA1 × 3-β-hydroxylase, reducing leaf cell elongation (Adams et al., 1992) but not cell division (Ervin and Koski, 2001). However, to ensure consistent and lasting effects, frequent applications of TE are required.
In plants, inactivation of bioactive gibberellins GA1 and GA4 is ensured by GA2-oxidases (GA2ox) that catalyze their 2β-hydroxylation yielding GA8 and GA34 (Hedden and Proebsting, 1999). Overexpression of OsGA2ox1 in rice caused a dwarf phenotype with leaves that were darker green, shorter, and wider than those of the wild-type plants and adversely affected development of reproductive organs (Sakamoto et al., 2001). A similar phenotype was obtained by expressing GA2ox in transgenic tobacco plants (Nicotiana tabacum) (Biemelt et al., 2004; Schomburg et al., 2003), poplar trees (Populus tremula × Populus alba) (Busov et al., 2003), and Arabidopsis (Arabidopsis thaliana) (Radi et al., 2006). Overexpression of AtGA2ox1 in bahiagrass (Paspalum notatum L.) produced a semidwarf phenotype with increased tillering, delayed flowering, and shorter inflorescence, thus enhancing its overall quality (Agharkar et al., 2007).
Creeping bentgrass plants containing the runner bean (Phaseolus coccineus) GA2-oxidase gene (PcGA2ox) have been developed, and through preliminary greenhouse and field studies (Yan, 2005), superior lines were chosen. These superior lines were characterized by more horizontal growth habit, inhibited vertical growth, internode extension, and leaf growth when grown under restricted light conditions. The objective of this study was to determine the effect of genetically induced dwarfism on creeping bentgrass performance under different shade treatments while being maintained at a low mowing height.
Adams, R., Kerber, E., Pfister, K. & Weiler, E.W. 1992 Studies on the action of the new growth retardant CGA 163’935 (cimectacarb), p. 818–827. In: Karssen, C.M., L.C. van Loon, and D. Vreugedenhil (eds.). Progress in plant growth regulation. Kluwer Academic, Dordrecht, The Netherlands.
Agharkar, M., Lomba, P., Altpeter, F., Zhang, H., Kenworthy, K. & Lange, T. 2007 Stable expression of AtGA2ox1 in a low-input turfgrass (Paspalum notatum Flugge) reduces bioactive gibberellin levels and improves turf quality under field conditions Plant Biotechnol. 5 791 801
Allard, G., Nelson, C.J. & Pallardy, S.G. 1991 Shade effect on growth of tall fescue. I. Leaf anatomy and dry matter partitioning Crop Sci. 31 163 167
Beard, J.B. 1973 Turfgrass: Science and culture. Prentice-Hall, Inc., Englewood Cliffs, NJ.
Biemelt, S., Tschiersch, H. & Sonnewald, U. 2004 Impact of altered gibberellin metabolism on biomass accumulation, lignin biosynthesis, and photosynthesis in transgenic tobacco plants Plant Physiol. 135 254 265
Brutnell, T. 2006 Phytochrome and light control of plant development, p. 417–443. In: Taiz, L. and E. Zeiger (eds.). Plant physiology. 4th Ed. Sinauer Associates, Inc. Publishers, Sunderland, MA.
Busov, V.B., Meilan, R., Pearce, D.W., Ma, C., Rood, S.B. & Strauss, S.H. 2003 Activation tagging of dominant gibberellin catabolism gene (GA 2-oxidase) from poplar regulates tree stature Plant Physiol. 132 1283 1291
Casal, J.J., Sanchez, R.A. & Gibson, D. 1990 The significances of changes in the red/far-red ratio associated either with neighbor plants or twilight for tillering in Lolium multiflorum Lam New Phytol. 116 565 572
Coles, J.P., Phillips, A.L., Croker, S.J., Garcia-Lepe, R., Lewis, M.J. & Hedden, P. 1999 Modification of gibberellin production and plant development in Arabidopsis by sense and antisense expression of gibberellin 20-oxidase Plant J. 17 547 556
Davies, P.J. 2007 The plant hormones: Their nature, occurrence, and functions, p. 1–15. In: Davis, P.J. (ed.). Plant hormones: Physiology, biochemistry and molecular biology. Kluwer Academic Publishers, Dordrecht, The Netherlands.
Dudeck, A.E. & Peacock, C.H. 1992 Shade and turfgrass culture, p. 269–284. In: Waddington, D.V., R.N. Carrow, and R.C. Shearman (eds.). Turfgrass Agron. Monogr. 32. ASA-CSSA-SSSA, Madison, WI.
Ervin, E.H. & Koski, A.J. 2001 Trinexapac-ethyl increases kentucky bluegrass leaf cell density and chlorophyll concentration HortScience 36 787 789
Ervin, E.H., Zhang, X., Askew, S.D. & Goatley, J.M. Jr 2004 Trinexapac-ethyl, propiconazole, iron, and biostimulant effects on shades creeping bentgrass HortTechnology 14 500 506
Goss, R.M., Baird, J.H., Kelm, S.L. & Calhoun, R.N. 2002 Trinexapac-ethyl and nitrogen effects on creeping bentgrass grown under reduced light conditions Crop Sci. 42 472 479
Koh, K.J., Bell, G.E., Martin, D.L. & Walker, N.R. 2003 Shade and airflow restriction effects on creeping bentgrass golf greens Crop Sci. 43 2182 2188
Nangle, E. 2008 The effect of trinexapac ethyl and three nitrogen sources on creeping bentgrass (Agrostis stolonifera) grown under three light environments. MS thesis, The Ohio State Univ., Columbus, OH.
Radi, A., Lange, T., Niki, T., Koshioka, M. & Pimenta Lange, M.J. 2006 Ectopic expression of pumpkin gibberellin oxidases alters gibberellin biosynthesis and development of transgenic Arabidopsis plants Plant Physiol. 140 528 536
Sakamoto, T., Kobayashi, M., Itoh, H., Tagiri, A., Kayano, T., Tanaka, H., Iwahori, S. & Matsuoka, M. 2001 Expression of a gibberellin 2-oxidase gene around the shoot apex is related to phase transition in rice Plant Physiol. 125 1508 1516
Schomburg, F.M., Bizzell, C.M., Lee, D.J., Zeevaart, J.A.D. & Amasino, R.M. 2003 Overexpression of novel class of gibberelin 2-oxidases decreases gibberellin levels and creates dwarf plants Plant Cell 15 152 163
Sponsel, V.M. & Hedden, P. 2004 Gibberellin biosynthesis and inactivation, p. 63–94. In: Davis, P.J. (ed.). Plant hormones. Biosynthesis, signal transduction, action! Springer, Dordrecht, Heidelberg, London, New York.
Steinke, K. & Stier, J.C. 2003 Nitrogen selection and growth regulator application for improving shaded turf performance Crop Sci. 43 1399 1406
Studzinska, A.K., Gardner, D., Yan, J., Nangle, E. & Dannebereger, K. 2009 Development and characterization of transgenic creeping bentgrass transformed with Arabidopsis BAS1 gene Intl. Turfgrass Soc. Res. J. 11 859 869
Sun, T. 2004 Gibberellin signal transduction in stem elongation and leaf growth, p. 304–320. In: Davis, P.J. (ed.). Plant hormones—Biosynthesis, signal transduction, action. Springer, Dordrecht, Heidelberg, London, New York.
Wherley, B.G., Gardner, D.S. & Metzger, J.D. 2005 Tall fescue photomorphogenesis as influenced by changes in the spectral composition and light intensity Crop Sci. 45 562 568
Wilkinson, J.F. & Beard, J.B. (1974) Morphological responses of Poa pratensis and Festuca rubra to reduced light intensity, p. 231–240. In: Roberts, E.C. (ed.). Proc. Second International Turfgrass Research Conference. International Turfgrass Society and ASA and CSSA, Madison, WI.
Wilson, J.R. 1997 Adoptive responses of grasses to shade: Relevance to turfgrass for low light environments Intl. Turfgrass Soc. Res. J. 8 575 591
Yan, J. 2005 Effects of gibberellin 2-oxidase, phytochrome B1, and BAS1 gene transformation on creeping bentgrass photomorphogenesis under various light conditions. PhD diss., The Ohio State Univ., Columbus, OH. 29 Jan. 2012. <http://etd.ohiolink.edu/view.cgi?acc_num=osu1168027982>.