Effects of Light Quality, Intensity and Duration from Different Artificial Light Sources on the Growth of Petunia (Petunia×hybrida Vilm.)

Abstract

The effect of light quality on the growth of petunia (Petunia×hybrida Vilm.) 'Baccarat Blue Picotee' was studied. Petunias were grown in growth chambers under a metal halide (MH), high pressure sodium (HPS) and blue (B) lamps, at different light intensities and duration, additionally, these were sprayed with GA₃ and Uniconazol, a growth retardant. 1. Plant shapes were more compact under HPS than under MH or B. The longest lateral shoot under HPS was about 30% shorter than that of plants grown under MH or B. The average internode length was also shorter under HPS than the others ; this result is attributed to the high-red : far-red light ratio (R/FR) of HPS, which was mediated by plant phytochromes. 2. Light intensities also influenced plant height, which increased with decreasing light intensity under MH and HPS. Furthermore, plant height and stem length under HPS were shorter than those under MH in all light intensities. 3. The rate of shoot elongation was reduced when the plants were transferred from MH to HPS. The final light quality determined the plant height. But, it had no residual effect. 4. The growth inhibition by HPS was reversible by the application of GA₃. Whereas, Uniconazol had no effect on stems exposed to HPS. These results suggest that the high R/FR ratio of HPS inhibits GA synthesis and, therefore, plant height was shorter than plant exposed to which has a lower R/FR ratio.