Estimates have been made of the quantitative contribution of each of the determinant factors, photoperiod, vernalization, and colysanthin (a presumed inhibitor of flower initiation formed in the cotyledon), in regulating flower initiation in the late-flowering pea cultivar Greenfeast.Photoperiod appears to be quantitatively related to the production of an inductive stimulus. This stimulus reaches its threshhold level at about node 12 under 18-hr photoperiods, but not until node 18 under an 8-hr photoperiod.Colysanthin delays events between photoperiodic induction and flower initiation (evocation), and causes a slightly greater delay to flower initiation in short than in long days (3 and 2 nodes respectively).Vernalization appears to have two separate effects, both of which promote flower initiation at an earlier node. The smaller effect is manifest on the cotyledonary inhibitor system, and probably results from a reduction of the effective level of colysanthin. The major effect does not appear to involve colysanthin, but is manifest on the young embryo and is effective before photoperiodic induction is completed. The embryo response to vernalization results in advanced flower initiation of some 4 nodes in long days and nearly 6 nodes in short days. This effect may be partially obscured by colysanthin, unless the cotyledons are excised soon after vernalization is completed.The evidence favours the view that the three determinant factors act in a complementary manner, rather than competitively, to regulate flower initiation in Greenfeast.
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