Comparison of Photoperiodic Sensitivity of Green-Leafed and Red-Leafed Perilla

The flowering responses of Perilla frutescens (L.) Britt. (green-leafed Perilla) and P. crispa (Thunb.) Tanaka (red-leafed Perilla) to different 24-hour photoperiodic regimes were compared quantitatively. Although both taxa are short-day plants, P. frutescens was less strict in its short-day requirement, forming macroscopically visible inflorescence primordia and open flowers even in continuous light after 77 to 85 and 132 days, respectively, compared to 12 and 22 days in 8-hour days. P. crispa took only 4 days longer to reach the same stages in 8-hour short days, but exhibited a sharply defined critical day-length between 14 and 16 hours. Two-hour light-breaks in the middle of a 16-hour night were more effective in inhibiting floral development in P. crispa than in P. frutescens, for which they had a small effect compared to true long-days, particularly on the formation of inflorescence primordia. The number of short days needed to obtain the flowering in P. frutescens plants raised in continuous light decreased in a linear manner with the age of the plants upon transfer to short days.