Photoperiodic Responses of Several Varieties of Soybeans

A study of floral differentiation has been made upon thirteen varieties of soybeans grown on nine different photoperiods, including continuous light. The varieties Agate, Mandell, Hudson Manchu, Minsoy, Mc Crostie's Mandarin, Wisconsin Early Black, Batorawka, and Mandarin initiated flower primordia on all photoperiodic treatments employed. These varieties normally mature seed in 105 days or less under field conditions. No plants of the varieties Biloxi, Avoyelles, Otootan, and Peking, and few of Tokyo, initiated flower primordia on photoperiods longer than 16 hours. These varieties require 125-175 days to mature seed in the field. 2. The initiation of flower primordia in many varieties under continuous light shows that darkness is not a necessary condition for floral initiation in them. 3. In Agate, one of the varieties that initiates flower buds most readily on continuous light, the reactions causing induction are accelerated if the plants are subjected to daily periods of darkness. Although these reactions take place in continuous light they proceed more rapidly if there is a daily alternation of light and dark. 4. Chemical analyses of the varieties Biloxi and Agate have been made at the ages of 2, 3, 4, 5, and 6 weeks. In general Agate contained less total and less soluble forms of nitrogen and more carbohydrates than Biloxi. The starch content of Agate reached a maximum at 3 weeks and declined progressively with age, while in Biloxi the trend of the data indicated that a maximum had not been reached during the experiment. The maximum carbohydrate content in Agate occurred at the time floral initiation was beginning.