MANIPULATION OF FLOWERING IN CINERARIA .1. EFFECTS OF PHOTOPERIOD

Effects of photoperiod on flowering, measured as days to macroscopic f lower visibility and as leaf number below the terminal inflorescence, were studied in three cultivars of cineraria, Cindy Blue, Cindy Pink a nd Cindy Dark Red. Short photoperiods accelerated, and long photoperio ds delayed, but did not prevent, flower initiation in plants grown und er commercial temperature regimes (8-14 degrees C) in glasshouse condi tions. The critical photoperiod for flower initiation was 12 h, at and below which plants produced the fewest leaves below the flowers. In c vs Cindy Blue and Cindy Pink, the ceiling photoperiod was 16 h, at and above which plants produced their maximum final leaf number. The rate s of progress to flower initiation and to flower visibility were shown to be faster in plants grown under 8-12 h photoperiods and both rates decreased approximately linearly as photoperiod increased from 12 to 16 h in cvs Cindy Blue and Cindy Pink. There was no ''minimum number'' of short-day cycles required for flower initiation. However, a minimu m of 15 short-day cycles was found to accelerate flower initiation in cv. Cindy Dark Red and 20 in cv. Cindy Blue. The axillary flowering no de was lower with short photoperiod treatments and the number of axill ary flowering branches was also increased.