Influence of photoselective films and growing season on stem growth and flowering of six plant species

Growth chambers constructed of photoselective plastic films were used to investigate light quality effects on fl owering and stem elongation of six fl owering plant species under strongly inductive and weakly inductive photoperiods. Three fi lms were used: a clear control fi lm, a far red (FR) light absorbing (AFR) fi lm and a red (R) light absorbing (AR) fi lm. The AFR and AR fi lms intercepted FR (700 to 800 nm) and R (600 to 700 nm) wavelengths with maximum interception at 730 and 690 nm, respectively. The phytochrome photoequilibrium estimates of transmitted light for the control, AFR, and AR fi lms were 0.71, 0.77, and 0.67. The broad band R:FR ratios were 1.05, 1.51, and 0.77, respectively. The photosynthetic photon fl ux was adjusted with neutral density fi lters to provide similar light transmission among chambers. Zinnia elegans Jacq. , Dendranthema ×grandifl orum Kitam. (chrysanthemum), Cosmos bipinnatus Cav. , and Petunia ×hybrida Vilm. -Andr. plants grown under the AFR fi lm were shorter than control plants. The AFR fi lm had no effect on height of Antirrhinum majus L. (snapdragon) or Rosa ×hybrida (miniature rose). Anthesis of zinnia, chrysanthemum, cosmos (short-day plants), and miniature rose (day-neutral plant) was not infl uenced by the AFR fi lms. Anthesis of petunia and snapdragon (long-day plants) was delayed up to 13 days by AFR fi lms under weakly inductive photoperiods. In petunia, initiation and development of fl oral structures were not affected by the AFR fi lms during strongly inductive photoperiods. However, during weakly inductive photoperiods, initiation of the fl oral primordia was signifi cantly delayed and overall development of the fl oral meristem was slower than control plants indicating that the AFR fi lms could increase the production time if long-day plants were produced off-season. Daylength extension with electric light sources could overcome this delay in anthesis yet achieve the benefi t of AFR fi lms for height reduction without the use of chemical growth regulators. the growing environment with FR light reduced time to fl ower of Arabidopsis mutants (Bagnall, 1993). In snapdragon, increasing incandescent light, which has more FR than R light, promoted fl owering (Cremer et al., 1998). Therefore, a concern with modifying a commercial greenhouse environment with photoselective fi lms is any additional effects it may have on fl ower production schedules and fl ower quality. For spectral fi lters to be used as a potential growth altering tool, a better understanding of their effects on time to fl ower on additional species must be established. The objective of this research was to investigate the infl uence of photoselective fi lms containing R and FR light absorbing dyes on fl oral induction and subsequent development of selected long-day (LD), short-day (SD), and day-neutral (DN) plants. Materials and Methods PHOTOSELECTIVE GROWTH CHAMBERS. Photoselective fi lms containing R and FR light absorbing dyes that transmitted 75% photosynthetic photon fl ux (PPF) were produced by Mitsui Chemicals, Inc., Japan and designated as FR light absorbing (AFR), and R light absorbing (AR) fi lms. Growth chamber frames (1.2 × 1.2 × 1.2 m) made from PVC pipe were covered with these fi lms and a clear (control) fi lm that transmitted 90% PPF. The PPF inside growth chambers was measured at three locations within each chamber between 1200 and 1400 HR with a quantum meter (LI-185; LI-COR, Lincoln, Nebr.) fi tted with a quantum sensor (LI-190SA). The PPF was adjusted for uniformity in all chambers with neutral density fi lters. Two fans, one located at the top of the chamber and the other located on the opposite lower side, provided ventilation for the chambers. Two replicate chambers were used for each fi lm treatment. The growth chambers were placed inside a clear double-layer polyethylene greenhouse. Greenhouse cooling/heating set points were 27/20 °C. Spectral quality inside the chambers was measured on clear The use of greenhouse covers that selectively absorb or refl ect far red (FR) light presents an alternative means for chemical plant growth regulation. Plants grown in FR light defi cient environments have shorter stems, similar to plants treated with chemical retardants (Mortensen and Stromme, 1987; Rajapakse and Kelly, 1992; vanHaeringen et al., 1998; Oyaert et al., 1999). The responses of a wide range of plants to modifi ed light environments created by photoselective fi lms with red (R) and FR light absorbing properties have been described. Most species studied are sensitive to light quality indicating that photoselective greenhouse covers can be an effective way to manipulate height in a wide range of plants (Cerny et al., 2000). Depending on the species, a 20% to 40% height reduction in chrysanthemum, tomato, bell pepper, and watermelon has been achieved with FR light absorbing photoselective fi lms, compared to clear polyethylene fi lms. The transition from the vegetative to reproductive stage of photoperiod sensitive crops can be altered by light quality. Far red light defi cient environments delayed fl ower initiation of chrysanthemum (Dendranthema ×grandifl orum Kitam.) (Rajapakse and Kelly, 1995), coreopsis (Coreopsis ×grandifl ora Hogg ex Sweet), Campanula carpatica Jacq. (Runkle and Heins, 2001) and snapdragon (Antirrhinum majus L.) (Cremer et al., 1998) but R light defi cient environments accelerated snapdragon fl ower development (vanHaeringen et al., 1998). With pansy (Viola ×wittrockiana Gams.), a FR light defi cient environment inhibited fl ower development (Runkle and Heins, 2001). Supplementing *Received for publication 10 June 2002. Accepted for publication 3 Apr. 2003. Technical contribution 4847 of the South Carolina Agricultural Experiment Station. The Fred C. Gloeckner Foundation and Mitsui Chemicals, Inc. Tokyo, Japan are gratefully acknowledged for the fi nancial support. We thank James Reick of the Department of Experimental Statistics at Clemson University for helping with the data analysis and Sonja Maki of Department of Horticulture for her valuable suggestions and help with electron microscopy. 1Current address: Department of Plants, Soils, and Biometeorology, Utah State University, Logan, UT 84322-4820. 2Corresponding author.