Developmental Implications of Photoperiod Sensitivity in Soybean (Glycine max [L.] Merr.)

Abstract

Although the effects of photoperiod and temperature on flowering time are well established, their underlying physiology and implications for other aspects of growth and development require further investigation. The pattern of development in soybean (Glycine max L. Merr.) cultivars Biloxi (photoperiod sensitive) and Fiskeby V (photoperiod insensitive) are compared in an environment where photoperiod sensitivity was not expressed (11-h photoperiod) and in an environment where photoperiod sensitivity was maximally expressed (15.5-h photoperiod). A floral staging scale was developed to study the pattern of floral initiation and to compare rates of floral development. There were inherent differences between cultivars in earliness of flowering, vegetative development, and, therefore, in yield potential. When photoperiod sensitivity was not expressed, cv Biloxi had a short vegetative phase and floral primordia were apparent 14 d after sowing. Expression of photoperiod sensitivity, beginning 8-9 d after sowing, resulted in a much extended vegetative phase with increased rates of leaf initiation. Cultivar Fiskeby V had a minimal vegetative phase; floral primordia were apparent 9 d after sowing and initiation of primary nodes was complete 3 d later. There were inherent differences between cultivars in the duration of the transitional period between the initiation of the first lateral floral primordium and the initiation of the terminal inflorescence, a period that is important in determining yield potential. The pattern of floral initiation observed was primarily acropetal and reflected the competence of meristems to respond to the floral promoter. Meristems developing in the prophyll axes had consistently lower rates of leaf initiation and remained vegetative longer than other lateral meristems, indicating that there are subtle differences in the distribution of floral signals or that these meristems have different threshold requirements.