Growth of chrysanthemum under coloured plastic films with different light qualities and quantities

Several spectral filters were tested on Dendranthema x grandiflorum 'White Reagan' (Chrysanthemum morifolium), as an alternative for chemical growth r egulators. Three blue polyethylene (PE) films and one vaporised interferenc e film were compared to four neutral filters with corresponding PPFD transm ittances (differing from 25% to 73%). The blue PE films had blue:red ratios (B:R) from 6.2 to 85.5 with increasing pigment concentration, and red:far red ratios (R:FRn,) between 0.43 and 1.45. The vaporised film had a relativ e low B :R (1.41) and a high R:FRn, (2.06). B :R and R:FRn of the control f ilters were approximate to 1. All coloured filters altered plant habit dras tically. The inhibition of stem elongation increased with increasing pigmen t concentration under the blue PE films, with a maximum of 22% growth reduc tion compared to the control. Although fewer leaves were developed, intemod e length was significantly shorter under all coloured filters compared to t he corresponding controls. The blue filters resulted in a lower number of a xillary shoots, a smaller leaf area and a lower total dry weight than the c ontrol filters. Furthermore, dry weight was translocated from stem to leave s. The vaporised film, which was characterised by the highest light transmi ssion percentage, resulted in a relative small growth reduction compared to the corresponding control. Since this film had no significant effect on br anching rate, leaf area and dry weight, plant quality remained intact. If t he vaporising technique could be improved, more extreme B : R and R : FR ra tios could be obtained, which would result in larger growth reductions. Suc h a spectral filter would provide growers with an environment-friendly tool for growth regulation of ornamental crops. (C) 1999 Elsevier Science B.V. All rights reserved.