Long-day effects on the terminal inflorescence development of a photoperiod-sensitive soybean [Glycine max (L.) Merr.] variety.

The type of terminal inflorescence is a key component for identifying soybean type. In this study, a late maturity and photoperiod-sensitive determinate soybean, cv. Zigongdongdou, was used to investigate effects of long-day (LD) on the formation and development of the terminal inflorescence. After emergence, soybean seedlings were subjected to 12 h short-day (SD) photoperiod for 13 days to induce the initiation of terminal inflorescence. The plants were then moved to 16 h LD treatment (LDT) for 0, 1, 2, 3, 4 and 5 wks, respectively. After LDT, plants were moved back to 12 h SD condition until the end of the experiment. The LDT greatly affected morphological and anatomical features of terminal inflorescence as well as the developmental rate of plants. Reversed flowers could be found in the reversed "inflorescences" in plants with 2-5 wks LDT. Such changes were confirmed through morphological observation and anatomical dissection. In the long-day treatments, the formation of flowers and the development of terminal inflorescence could be reversed and plant type of a soybean could be further changed. This long-day effect was a cumulative process, which increased with the increase in the duration of LDT.