The Relationship between Exogenous Growth Inhibitors and Endogenous Levels of Ethylene, and Tuberization of Dahlias

Treatments with abscisic acid (ABA), succinic acid‐2,2‐dimethylhydrazide (SADH), or 2 chlorethyl phosphonic acid (ethephon) promoted the tuberization of dahlia plants in long‐days. This effect was smaller, however, than the effect short days have on tuberization. In contrast, gibberellic acid (GA) treatments inhibited tuberization. SADH and ethephon treatments of budless leaf‐cuttings inhibited tuberization whereas ABA treatments slightly enhanced it. Evolution of endogenous ethylene reached a peak between the second and third week after the start of short‐day treatments, and then decreased to the low level found in plants growing under long days. The peak in ethylene evolution occurred one week before the onset of tuberization.