Short-Day Cycle Requirements for Floral Initiation of Stylosanthes guianensis (Aublet) Sw. var. guianensis

Abstract

Mature plants of the tropical legume Stylosanthes guianensis var. guianensis cv. Schofield required 20 short-day (SD) cycles (of 10-h days) for irrevocable commitment to floral initiation when returned to natural long days (LD), although the morphological changes associated with floral initiation were evident after 12-18 SD cycles. Commitment to flowering and spike production were favoured by 20 or more SD cycles. Floret number per spike and percentage seed set were not affected by return to LD. Within individual plants, sections of terminal and branch apices revealed a range of development stages. Terminal apices of well developed lateral branches were able to initiate as soon as, or sooner than, terminal apices of the main branch in this usually determinate plant; this points to individual branches having some autonomy for floral initiation, but suggests dissections made from well developed lateral branches would be a feasible method for determining floral initiation where plant replication is limited.