Effect of polythene covers, a flower inducing treatment, on the content of endogenous gibberellin‐like substances in grafts of Norway spruce

In shoots of 12-year-old Norway spruce [Picea abies (L.) Karst.] grafts the content of endogenous gibberellin-like substances was analysed. Covering the crowns with polythene on the turn of June and July stimulated induction of male strobiles and significantly increased the levels of gibberellins. Polar gibberellin (at Rf 0.0–0.2) increased immediately and the less polar ones after one day. After 2 weeks the increased level was maintained only at Rf 0.4–0.6 and 9 days later the differences between covered and not covered grafts disappeared. Removal of the covers did not affect gibberellin levels. It is suggested that covering with polythene stimulates floral induction through an increase in endogenous gibberellin levels.