The Control of Flowering in the Strawberry Fragaria ananassa Duch: II. The Role of Gibberellins

Activity of gibberellin-like substances was lacking in leavesof strawberry plants at time of flower initiation, but peduncleelongation was accompanied by significant activity of two substancesprobably related to GA₃ and GA₇. Exogenous gibberellin (GAS),applied to strawberry plants at the flower-differentiation stage,strongly promoted peduncle elongation, while similar applicationof the growth-retardant (2 chloro-ethyl) trimethylammonium chloride(CCC), an inhibitor of gibberellin biosynthesis, inhibited peduncleelongation. These treatments also affected subsequent runnering,GA increasing the number of runners, as well as their mean individuallength, while CCC caused the opposite effect. Application of gibberellin immediately after flower-bud initiation,but before peduncle emergence, affected the distribution offruit yield. GA-treated plants produced more than untreatedones in the first half of the fruiting season, but the situationwas reversed in the second half of the season—so thattotal yields were unaffected. It was suggested that the exogenousgibberellin hastened yield by anticipating the endogenous gibberellinwhich is normally formed at a somewhat later stage in the plant'sdevelopment. The parallel responses with regard to elongationof vegetative runners and flower peduncles together with thedata of the other experiments seem to indicate that peduncleelongation is a typical vegetative growth response enhancedby gibberellin and checked by substances which inhibit biosynthesisof endogenous gibberellin.