Identification of the Flower-inducing Factor Isolated from Aphid Honeydew as being Salicylic Acid

Honeydew produced by the aphid Dactynotus ambrosiae when feeding on flowering or vegetative plants of the short day plant Xanthium strumarium contains an active substance capable of inducing flowering in the long day plant Lemna gibba G3. In the present study, this active material has been identified as salicylic acid through the use of gas-liquid chromatography and mass, infrared, and ultraviolet spectrometry. Authentic salicylic acid induces flowering in L. gibba G3 under strict short day conditions with an optimal response at about 5.6 mum. The possible significance of salicylic acid for the control of flowering in Xanthium or L. gibba G3 is discussed.