Photoperiodic Regulation of Flowering in Cowpeas (Vigna unguiculata (L.) Walp.)

To test the proposition that photoperiodic controls synchronize the flowering of cowpeas, Vigna unguiculata (L.) Walp. [V. sinensis (L.) Savi], the day-length requirements for floral initiation and for flowering were investigated in several short-day accessions. No evidence was found of different critical photoperiods at different stages of development, but exposure to only 2–4 short days was required for floral initiation compared with about 20 for development to open flowers. Pod setting was increased after exposure to even one short day more than the number required for flower opening. Floral buds at higher nodes appeared to require fewer short days for development to flowering than buds at the lower nodes, and displayed faster rates of development. Inflorescence buds did not resume development if they were exposed to 15 or more long days following inflorescence initiation. Thus, any tendency towards synchronous flowering in cowpeas is not due to the critical day-length for flower development being shorter than that for flower initiation, but could be the result of cumulative photoperiodic induction of plants and the more rapid development of later-formed flowers.