Quantitative Assay of Photoperiodic Floral Inhibition and Stimulation in Biloxi Soybean

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Abstract
Techniques are described by which quantitative measurements may be made of inhibition and stimulation imposed on the photoperiodic flowering response in Biloxi soybean (Glycine max). To assess highly inhibitory treatments which might otherwise prevent flowering, the inhibition is counterbalanced by specific applications of treatments causing floral stimulation. The degree of inhibition in such cases is measured by determining the amount of floral stimulation necessary to overcome the inhibiton. The results indicate that light applied during the 1st photophobe phase of a tridiurnal cycle is approximately twice as inhibitory as light applied during the 2nd photophobe phase, and that light given in the 2nd photophil phase may be twice as stimulatory as light given in the 1st photophil phase. The quantitative measure of specific inhibitory and stimulatory effects of light in photoperiodic treatments is used to interpret the nature of light action in photoperiodic responses and the involvement of endogenous rhythms in the biological timing mechanism.