Extremely early flowering (production of staminate strobili 88 days from germination) of Arizona cypress (Cupressus arizonica Greene) was obtained with foliar application of gibberellin A3 commencing at age 55 days. Trials with differing concentrations of gibberellin at various ages indicated that flower bud differentiation depends on both age and gibberellin concentration, younger seedlings requiring more exogenous gibberellin. Simultaneous application of two growth retardants (AMO-1618 and B-995) had no effect upon the number of flowers, but flower size was increased where B-995 and gibberellin were given together. The period of time between initial spraying and first visible appearance of staminate strobili is 23 to 25 days. On most plants 60 to 80% of the growing vegetative meristems are changed into flower buds within 60 days of the initial treatment, often resulting in over 500 flower buds on one plant. The pollen is viable.
Induction of male strobili in Arizona cypress (Cupressus arizonica Greene) by exogenous gibberellin A3 (GA3) appears to have an absolute requirement for light, a quantitative requirement for long day (LD), and as shown by interruption of the dark periods, is in part under photoperiodic control. Under LD conditions the total number of new meristems produced is 10-fold greater than under short day (SD) even though this species exhibits indeterminate growth and does not set dormant buds under SD. Hence the total number of strobili resulting from GA3 application is higher under LD than under SD. However, strobili produced by GA3, when expressed as a percentage of the total number of meristems, is the same under both LD and SD, provided the GA3 concentration under SD is increased, and a longer period of time is allowed under SD. The factor(s) responsible for the enhanced meristem production under LD decrease(s) to an apparent steady state within the first 10 days after transfer of the plant to SD.
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