Effect of photoperiod on flowering in ornamental annuals
Mukesh Singh Mer, Brij Lal Attri
.Photoperiodism is a response to the seasonal variation of day length and changes in day length above or below the critical level affects the blooming of flower (Irwin, 1982) . Flowering is the end result of physiological processes, biochemical sequences, and gene action, with the whole system responding by the influence of photoperiod. Many flowering plants have a photoreceptor protein, such as phytochrome or cryptochrome, to sense seasonal changes in day length, which act as signals to flower. Photoperiodic response to flower induction, initiation and development of many plant species are synchronized temporarily during the year with night length. The emergence of flower being extends by using artificial light, black cloth, black polythene sheets. Photoperiod manipulation through the use of black cloth or night interruption lighting may be for controlling flowering. reported by Biondo and Noland (2006) . Short day induction, it took 4 days to reach the growing point hypertrophy stage, 8 days to finish involucres primordial differentiation, 12 days to finish floret primordial differentiation, crown formation in the chrysanthemum cultivars ‘Jingyun’ (Jiang et al., 2010) . Primula malacoides Franch. ‘Primula Lilac’ was grown at 160C or 200C in combination with short day (SD, 8 hours) or long day (LD, 16 hours). Time to flower (first horizontal petals) at 160C increased from 56 to 64 days as so increased from 1 week to continuous conditions in SD, while LD decreased time to flower from 64 to56 days. Time to flower at 200C varied from 73 to 87 days with additional SD exposure resulting in flower and LD in faster flowering (Karlsson and Werner, 2002) . The flowering was hastened up to 16, 15, 10, 11, 14, and 29 days for Zinnia, Sunflower, French Marigold, African Marigold, Cockscomb, Cosmos under SD environment respectively reported by (Baloch et al., 2010) . Delayed or no flowering of obligate long day plant/facultative long day plant can be alleviated by delivery of long day conditions when ambient short day conditions are prevalent (Mattson and Ervin (2005) . Photoperiod increased from 9 h to 13 h, the total flower numbers decreased from 45 flowers to 13 flowers Kalanchoe uniflora (a short day plant). All species of Kalanchoe flowered when grown under photoperiods under ranging from 9-12 h and percentage of flowering plants decreased for all species as the photoperiod increased from 12 h to 14 h. No flowering occurred on plants grown under a 15 h photoperiod (Curry and Ervin, 2010) . Flowers can also be grown under non-inductive environment during juvenile phase to improve their quality for marketing viewpoint. Off-season flower will produce by use of photoperiod and light intensity that provide a year-round production of flowers, which will eventually increase the income of ornamental growers.