Floral Induction in a Short-Day Plant, Plumbago indica L., by 2-Chloroethanephosphonic Acid

Whereas long-day species can be brought to flower under non-inductive conditions by the application of chemicals such as gibberellic acid (see review by Lang, 1965), short-day species have been refractory so far to chemical induction. The outstanding exception is the pineapple (Ananassa sativa L.) which can be forced to flower by applications of ethylene and compounds releasing ethylene such as 2-chloroethanephosphonic acid (4), of acetylene, and of synthetic auxins (3). Certain varieties of pineapple, however, may 'be only quantitative short-day plants (5). The present report shows that applications of 2-chloroethanephosphonic acid can induce flowering in a qualitative short-day plant, the clone "Angkor" of Plumbago indica L. (13). Experiments done in vitro with this clone had shown that exposure of internode segments to 0.1 % ethylene in air for 1 week caused the formation of floral meristems (10, 11). L-Methionine, a metabolic precursor of ethylene (2,9) had a similar effect. Finally, experiments were done in vitro by incorporating 2-chloroethanephosphonic acid in the culture medium. At the concentration of 10-5 M, this compound caused 25 % of the cultures to produce floral buds instead of vegetative ones (12). The results obtained by the in vitro technique led us to try 2-chloroethanephosphonic acid on whole plants in the greenhouse. The cuttings were grown at 280 to 30° (day) and 20° (night) under long days of 16 hr of light. When they were about 30 cm in height, they were sprayed with aqueous solutions containing various concentrations of 2-chloroethanephosphonic acid'. "Tween-80" was used as a wetting agent, at the concentration of 0.1 % in the final solution. Two different series of experiments were performed. The results are presented in table I. In the first experiment, 78 % of the plants sprayed once with 240 mg/l of AMCHEM produced inflorescences which were visible 6 weeks after.