PHOTOPERIOD SENSITIVITY DURING SOYBEAN FLOWER DEVELOPMENT

[Glycine max (L.) Merr.] is difficult to pre-dict because the influences of photoperiod(P) and temperature are not well understood. The purpose of this research was to improve our understanding of how the photoperiod-sensitive and-insensitive phases of flower devel-opment are controlled by P. Controlled-environment studies were conducted in which ']ohnston ' (maturity group vm) soybean plants were switched from Ps between 12 hand 14.75 h to a P of 22 h. All chambers were maintained at 25±1°C. The P experienced by plants before they were switched to 22 h did not influence the length of the photoperiod-sensitive phase of flower development for P:S::13.5 h. For P>13.5 h, there was a linear increase in the number of days needed for P to cause flower induction (L e. irreversible flower devel-opment) as P increased. The length of the photoperiod-insensitive phase also showed an increase when P during the photoperiod-sensitive phase was>13.5 h. One of the reasons why it has been so difficult to predict flowering times in soybean is because the P experienced during the photoperiod-sensitive phase of flower development also affects the length of the photoperiod-insensitive phase. Key words: Glycine max (L.) Merr; photoperiodic induction