Photoperiod and Critical Duration for Flower Induction in Soybean1

A photoperiod sensitive (sensitive) soybean [Glycine max (L.) Merr.] line and photoperiod in sensitive (insensitive) line were used to determine the critical seedling stage before possible floral induction and the length of photoinduction required for anthesis. Seedlings of each entry were grown in pots and subjected to either a 10‐ hour or 16‐hour photoperiod. Beginning 3 days after emergence, two pots per entry in the 10‐hour room were exchanged daily with two pots from the 16‐hour photoperiod. No detectable differences between treatments were observed in the flowering time of the insensitive fine. However, the sensitive line exhibited the following: (i) The number of days to first flowering was not affected by the transfer from a 16‐hour to a 10‐hour photoperiod up to 9 days after emergence; (ii) Plants moved from a 10‐hour to a 16‐hour photoperiod before 36 days after emergence did not flower, indicating that induction was completed at 36 days after emergence; (iii) The earliest anthesis occurred 46 days after emergence. Therefore, we concluded that the induction period was 27 short days (10 hours) and that anthesis occurred 10 days after the completion of induction. The critical time to begin induction was 9 days after emergence for the sensitive line.