EXPERIMENTS ON THE PRECOCIOUS FLOWERING OF WESTERN RED CEDAR AND FOUR SPECIES OF CUPRESSUS WITH GIBBERELLINS A3 AND A4/A7 MIXTURE

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Abstract
Induction of staminate and ovulate strobili was obtained on western red cedar (Thuja plicata Donn) by foliar application of gibberellin A3. Staminate strobili could be induced as early as age 4 months after 3.5 months of treatment under long-day conditions, but further development of the strobilus required a photoperiodic sequence of long-day — short-day — long-day. Induction of the ovulate strobilus may also have occurred under long-day conditions at an early age, but development did not become apparent until the above photoperiodic sequence had been given. Age at this time was 12 months. It is concluded that induction and development of the strobilus is under photoperiodic as well as hormonal control.Foliar application of gibberellin A3 and a gibberellin A4/A7 mixture to pygmy cypress (Cupressus pygmaea Sarg.), Portuguese cypress (Cupressus lusitanica Mill.), and Arizona cypress (Cupressus arizonica Greene) at age 7–9 months resulted in induction of staminate strobili on all plants. Length of time to flowering varied both with species of plant and gibberellin. Application of gibberellin A3 to Arizona and Portuguese cypress seedlings resulted in production of ovulate as well as staminate strobili at ages 21 and 10 months respectively. Mourning cypress (Cupressus funebris Endl.) still in a juvenile needle stage at age 9 months has proved unresponsive to foliar application of gibberellin A3 for at least 100 days.