Far-red light absorbing photoselective plastic films affect growth and flowering of chrysanthemum cultivars

Growth and development responses of three chrysanthemum [Dendranthema xgrandiflora (Ramat.) Kitam. (syn. Chrysanthemum xmorifolium Ramat.)] cultivars ('Bright Golden Anne', 'Iridon', and 'Yellow Snowdon') to photoselective plastic films with varying concentrations (0 to 0.22 g(.)m(-2)) of a far-red (FR) light absorbing dye were investigated under greenhouse conditions. Photoselective films reduced stem elongation of all three cultivars. The greater the dye concentration in the film, the greater and earlier the reduction in stem elongation. After 4 weeks,'Yellow Snowden', 'Bright Golden Anne', and 'Iridon' plants grown under the film with the highest dye concentration (A(fr3) film) were 21%, 26%, and 26% shorter than control plants, respectively. Height reduction under photoselective films was caused by shorter internodes. Photoselective covers were most effective in reducing the stem elongation during the early vegetative period. Following transition to the reproductive stage, weekly stem elongation rates were reduced. At the time of flowering, 'Yellow Snowden', 'Bright Golden Anne', and 'Iridon' plants grown under the film with the highest dye concentration (A(fr3) film) were 12%, 7%, and 14% shorter than control plants, respectively. Photoselective covers did not affect the anthesis of chrysanthemum cultivars, but resulted in a 10% to 14% reduction in flower diameter depending on the cultivar. Although the films with higher dye concentration were more effective in reducing stem elongation of chrysanthemum, increased dye concentration reduced light transmission. Thus, photoselective covers that reduce light transmission over 25% would not be suitable for commercial production.