Abstract
Three concentrations each of gibberellin A4/7 (GA4/7) and naphthaleneacetic acid (NAA) were tested in factorial combination on shoots in the upper and lower crown of young, potted Piceaengelmannii grafts. There was no interaction between the two growth regulators, both of which promoted flowering but affected sex expression differently. GA4/7 at 125 and 625 μg/shoot increased similarly the production of seed-cone buds without affecting male flowering. NAA promoted male flowering at the expense of seed-cone buds when applied at 5 μg/shoot, but was phytotoxic at 25 μg/shoot. GA4/7 was more effective in promoting seed-cone buds on shoots in the upper than the lower crown, whereas the male flowering response to NAA was independent of crown position. Present results indicate that sex expression in P. engelmannii can be manipulated practically by application of appropriate growth regulators to facilitate pollen and seed-crop management in indoor-potted orchards.
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