In a series of experiments petiole lengths were increased, stem internode elongation induced, runner formation promoted, and flower initiation inhibited both in the perpetual-fruiting and the seasonal-fruiting varieties of strawberry by applications of gibberellic acid. Runners were induced to form in Fragaria vesca semperflorens var. Baron Solemacher, which does not normally runner. Thus the physiological processes which lead to the morphological differences between perpetual and seasonal fruiting types were overruled by treatment with gibberellic acid.
Gibberellins A1 A4 A7 and A9 like gibberellic acid (A3 induced elongation of petioles (a normal photoperiodic response), elongation of internodes on the main stem, and inhibition of flower formation in Baron Solemacher (responses not induced by photoperiod).
When applied to the cut stump of a debladed petiole, gibberellic acid inhibited flower formation at the growing apex of the stem, thus substituting for the leaf blade, which in long photoperiods inhibited flower formation.
A morphological study suggested that in Duchesnea indica, a related genus, flower initiation is not regulated by environmental circumstances, but is the inevitable consequence of growth. Although promoting increase in petiole length and in elongation of lateral growths as in strawberry, gibberellic acid did not inhibit flower initiation in this species, except in so far as it caused a retardation in the growth of certain axillary buds, so that a lower proportion of them reached the stage of flower initiation within the duration of the experiment.
These results are discussed in relation to the hypothesis that flower formation is regulated by an inhibitory hormone in seasonal-fruiting strawberries.