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CROP PHYSIOLOGY & METABOLISM

Both Promoters and Inhibitors Affected Flowering Time in Grafted Soybean Flowering-Time Isolines

^a Eastern Cereal and Oilseed Research Centre (ECORC), Agric. & Agri-Food Canada, Bldg. 110, Central Exp. Farm, Ottawa, ON, Canada, K1A 0C6
^b Biofloral Inc., 38723 Fingal Line, RR#1, St. Thomas, ON, Canada, N5P 3S5

^* Corresponding author (coberer{at}agr.gc.ca)

Understanding the control of flowering time in photoperiod-sensitive plants has been furthered by grafting experiments. In soybean [Glycine max (L.) Merr.], genes which control flowering time have been identified and their responses to photoperiod characterized. Grafting experiments allow the study of interactions between genotypes. The objective of our study was to characterize the flowering response of scions from a grafted series of early- to late-flowering soybean near-isogenic lines. Seedling scions were grafted to 1-wk-older rootstocks and grown under noninductive 16-h days. Rootstocks were allowed to develop a single axillary shoot to allow interaction between rootstock and scion shoots. Late-flowering rootstocks did not delay flowering of the earliest-flowering isolines but delayed flowering of intermediate-flowering isolines. Some floral inhibition was also seen within scions since defoliated late-flowering scions grafted to early-flowering rootstocks flowered earlier compared with nondefoliated scions of the same graft combination. Early-flowering rootstocks promoted flowering of late-flowering scions both within and across genetic backgrounds. Early-flowering scions flowered early (27 to 30 d) regardless of rootstock genotype. This early flowering was observed even when the scions were defoliated, indicating that floral promoters might be produced or sensed in unexpanded leaves or buds. The activity of floral promoters and inhibitors was demonstrated in soybean and these factors appeared to mediate flowering time antagonistically.

Abbreviations: MG, maturity group • PHY, phytochrome