Interaction of Photoperiod, Chilling and Exogenous Gibberellic Acid on Growth of Strawberry Petioles

Gibberellic acid (GA3) was applied to strawberry plants in varying doses. Lengths of successively emergent petioles increased in a manner indicating that they were responsive to exogenous GA3 during both pre- and especially postemergence phases of ontogeny. Exogenous GA3 interacted with photoperiod and chilling, but, because the responses were complicated by competition from aberrant stem elongation, GA3 could not be shown to replace the endogenous stimulus completely, although it may do so in part. On the other hand, a large component of the endogenous stimulus which promotes growth in long daylength and after chilling was not replaced by exogenous GA3. This is interpreted as evidence for non-gibberellin factors in the endogenous system. It appears that the stimuli generated by long daylength and by chilling are different, but the evidence is against the suggestion that one mediates the gibberellin system and the other the non-gibberellin one.