Flowering Control of Elsholtzia angustifolia (Loes.) Kitag., a Short-Day Plant

Abstract

This study was conducted to investigate the photoperiodic flowering response of Elsholtzia angustifolia. Plants were grown under 9/15 h (day/night) (short day, SD), 16/8 h (long day, LD), and night interruption (NI, 4 h around midnight) conditions. Supplemental lighting with a light intensity of 4 μmol·m -2 ·s -1 was applied for the LD and NI treatments. Plants under continuous SD conditions developed the first floral bud at 5 weeks after sowing during the seedling stage and showed 100% flowering at 9 weeks. Under continuous LD and NI conditions, there was no flowering, and plants continued vegetative growth only. Early flowering under continuous SD conditions showed a small number of flowers. It was not desirable for marketable potted plant production, indicating that there is a need for a certain period of vegetative growth before flowering. Among plants under LD and NI conditions, transfer to SD conditions was performed at 3 or 6 weeks after transplanting (WAT) to manipulate the flowering time. The percent flowering was 100% when plants were transferred to SDs. On average, there were approximately 36 days to flowering from transfer to SD conditions at 3 and 6 WAT, and there was no significant difference between the photoperiod and transfer treatments. The number of inflorescences significantly increased as the transfer date was delayed. The number of leaves and branches was also significantly increased by the delayed transfer date. These results indicate that E. angustifolia is an obligate SD plant and that non-forcing conditions, such as LD or NI, effectively inhibit early flowering. Additional key words: floral induction, inductive photoperiod, night break, photoperiodism, qualitative short-day plants