Rate, timing, and mode of gibberellin application for female strobilus production by grafted loblolly pine

Abstract

Gibberellin A₄, gibberellin A₇, and their mixture (60:40, GA₄:GA₇) were approximately equally effective in promoting female strobilus production on 3-year-old grafted mature scions of loblolly pine (Pinustaeda L.). Gibberellin A₃ was ineffective. The female flowering response to GA_4/7 was proportional to the log of its concentration, but no significant effect on male flowering was observed. Topical application from June through September was the most effective mode of application. Application for shorter intervals during this period resulted in proportionately less flowering. GA was equally effective prior to and following female bud initiation, but most effective during both.