White spruce (Piceaglauca) flowering in response to spray application of gibberellin A4/7

Abstract

Experiments were conducted on three populations of white spruce (Piceaglauca (Moench) Voss) to determine if calendar dates could be used as guidelines to spray gibberellin A_4/7 in an Aromox–ethanol solution to increase flowering and to determine if early flushing (EF) and late flushing (LF) clones, sprayed on the same dates, responded differently. Spraying from July 8 to September 9 was ineffective, but spraying from May 7 to July 1 gave a significant response. Elongating shoots sprayed from May 13 to June 3 produced significantly more ovulate and staminate strobili than did elongating shoots sprayed from June 10 to July 1, and both produced significantly more than the control. Gibberellin A_4/7 significantly increased production of ovulate and staminate strobili in the EF and LF clones that were sprayed only from June 2 to June 30. LF clones produced significantly more ovulate strobili than the EF clones, but there was no significant difference between them in staminate strobilus production. The studies demonstrated that the timing of gibberellin A_4/7 spray application affects the flowering response in white spruce.