Effects of red- and far-red-rich spectral treatments and diurnal temperature alternation on the growth and development of Petunia

The effects of Red- and Far-red-rich spectral (R- and FR-rich) treatments o n the growth, development, and morphological changes of Petunia were invest igated under diurnal temperature alternations (DIF). The light spectrum tre atments were created by using plastic films containing photo-selective dye compounds. The R-rich treatment inhibited elongation of the main stem compa red to the control and the FR-rich treatments. Positive DIF (high day / low night temperatures, P-DIF) promoted the main stern elongation, whereas neg ative DIF (low day / high night temperatures, N-DIF) inhibited it and flowe ring compared to the control. Inhibition of the main stem elongation by the R-rich treatment under P-DIF and zero DIF (0-DIF) was comparable to N-DIF; however, flowering was not delayed by the R-rich treatment. The R-rich tre atment under P-DIF further improved plant morphology by increasing the size and number of lateral shoots, growth of lateral shoots, and the number of flowers on these lateral shoots. Therefore, by creating a R-rich environmen t with a photo- selective plastic film, one can produce compact Petunia pla nts, i.e., a short, main stem but more lateral shoots without interrupting the flowering process.