Effects of Photoperiod on Growth and Development of Soybean Floral Bud in Different Maturity

Abstract

Growth and development of most soybean [Glycine max (L.) Merr.] plants is sensitive to photoperiod effects. Therefore, it is important to understand and quantify the processes involved. Studies were conducted to determine growing degree days required for growth of the floral bud from initiation to open flower of different maturity groups (MGs) in both field and controlled environments. Eighteen soybean strains, including ‘Clark’ back‐cross near‐isolines differing in maturity, were sown in the field at five different dates in 1992 and 1993. In growth chamber studies, plants of two strains differing in maturity were used and moved to 12−, 14−, and 16‐h daylengths after floral buds were initiated in 12 h. Results from both field and growth chamber studies indicated that planting dates had a significant effect on the thermal requirement for bud growth in the late‐maturing strains used. Shorter photoperiods during the bud growth period accelerated growth rates to open flower. Furthermore, in the growth chamber study, flowering was inhibited under 16‐h daylength in a late‐maturity (MG V) strain when plants were transferred immediately after floral bud initiation (FBI) under 12 h. Plants remaining 8 d after FBI before they were transferred to 16 h were not significantly delayed in flowering. This study indicated that photoperiod length and treatment duration affects soybean FBI and floral bud development in a quantitative way, which resulted in a profound photoperiod response in late maturity‐group soybean under field conditions.