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Testing for Early Photoperiod Insensitivity in Soybean

USDA-ARS, Remote Sensing and Modeling Laboratory, BARC West, Beltsville, MD 20705-2350

^* Corresponding author (zwang{at}asrr.arsusda.gov)

To accurately model the flowering process in soybean, it is essential to identify photoperiod-sensitive and photoperiod-insensitive phases of development. Despite extensive studies, there remains some disagreement about when soybean plants first become sensitive to photoperiod. The length of the juvenile phase from emergence has been found to differ for the same cultivar. This experiment tested the hypothesis that the early phase in soybean development is truly photoperiod-independent. Soybean plants [Glycine max (L.) Merr. cv. Hutcheson; Maturity Group V] grown in controlled environments at a constant air temperature of 26°C were transferred from a noninductive 22-h photoperiod to an inductive 8-, 10-, 12-, or 14-h photoperiod at 2- to 5-d intervals after seedling emergence (defined as the day when the cotyledons appeared above the soil surface). The duration of the so-called juvenile phase was shown to be photoperiod-dependent, the photoperiod effect being nonlinear. Soybean plants became sensitive to an 8-, 10-, 12-, and 14-h photoperiod at -1, 0, 1, and 9 d after seedling emergence, respectively. Based on these and other results, we conclude that there is no juvenile phase in Hutcheson soybean, and that photoperiod sensitivity begins when seedlings are exposed to light, bat the rate of progress towards flowering depends on the photoperiod experience

Received for publication August 11, 1997.