Growth responses of chrysanthemum and bell pepper transplants to photoselective plastic films

Plant response to photoselective plastic films with three concentrations of a far-red (FR) light absorbing dye (named as YCE-1 #80, YCE-1 #75 and YCE-1 #65) was tested using chrysanthemum (Dendranthema x grandiflorum (Ramat.) Kitamura) and bell pepper (Capsicum annuum L.) as model plants. The dye in films intercepted FR wavelengths of sunlight with maximum interception at 760 nm. FR light interception increased and transmission of photosynthetic photon flux (PPF) decreased as the dye concentration increased. The R:FR ratio and estimated phytochrome photoequilibrium (phi(c)) of transmitted light increased from 1.1 to 3.7 and from 0.72 to 0.81, respectively, with increase in dye concentration. Light transmitted through photoselective films reduced plant height and internode length by 10-35% depending on the crop and dye concentration in the film. Photoselective films reduced the leaf area and shoot dry weight of plants. Specific leaf dry weight (dry weight per unit leaf area) and specific stem dry weight (dry weight per unit length of stem) were also slightly reduced in plants grown inside photoselective film chambers suggesting that both small plants and reduced dry matter assimilation may have contributed to the reduction in shoot dry weight. Reduction in plant height was apparent within 2 weeks after initiation of the treatment. Plant height progressively decreased as the dye concentration increased. Although films with higher dye concentrations are more effective in height reduction, the reduction in PPF with increasing dye concentration can adversely affect plant growth and development, and this fact should be considered in commercial production of photoselective films. Our results indicate that a photoselective film with a R:FR ratio of 2.2 (or phi(c) of 0.78, which corresponds to 75% light transmission) caused about 20% height reduction in chrysanthemum and 30% height reduction in bell pepper after 4 weeks of treatment. This initial work demonstrates that the use of greenhouse films with FR light absorbing dyes to control plant height is as effective as chemical growth regulators or CuSO4 filters. With the commercial development of photoselective greenhouse covers or shade material, nursery and greenhouse industry could reduce costs for growth regulating chemicals, reduce health risks to their workers and consumers, and reduce potential environmental pollution. (C) 2000 Elsevier Science B.V. All rights reserved.