Flowering of Stylosanthes guianensis in relation to juvenility and the long-short day requirement

Seedlings of Stylosanthes guianensis var. guianensis were grown in long (14 h) days in five temperature regimes for varying periods before transfer to short (11 h) days at 30 °C/21 °C. The juvenile phase before seedlings responded to inductive conditions was c. 45–50 d, 50–60 d and 60–70 d for cv. Schofield, cv. Cook and C.P.I. 34906 respectively, which is positively related to their critical photoperiod for flowering. Temperatures favourable for growth (e.g. 30 °C/26 °C) reduced the juvenile phase in C.P.I. 34906 and in Cook, which did not flower in 11 h days unless previously exposed to more than 18 long days. In a second experiment cv. Cook was confirmed as a long-short day plant. Seedlings were grown for 50 d in a glasshouse with natural daylength extended to 13, 14, 16 or 24 h before transfer to 12 h photoperiods. Cook floral development was positively related to daylength provenance before transfer and plants in continuous 12 h did not flower. Shortening daylength after 48 cycles of 12 h to 11.75 h did not result in continued floral development in Cook plants but cv. Graham plants were initiated or transitional by 75 d.