Photoperiod regulation of development and growth in bambara groundnut (Vigna subterranea)

The influence of constant photoperiods of 10, 12, 14 and 16 h on development and growth in two bambara groundnut genotypes (Vigna subterranea (L.) Verdc., syn. Voandzeia subterranea (L.) Thouars) was studied in a greenhouse experiment in the Netherlands. Data on dry matter accumulation were collected by sequential harvesting. Photoperiod influenced the onset of flowering in one genotype (‘Ankpa 4’) and the onset of podding in both (‘Tiga Nicuru’ and ‘Ankpa 4’). Under 14- and 16-h photoperiods plants of ‘Ankpa 4’ produced no pods. Photoperiod did not influence total aboveground dry matter production per plant in ‘Ankpa 4’ and had only a slight effect on ‘Tiga Nicuru’. Photoperiod indirectly affected dry matter partitioning via its influence on development: in both genotypes assimilate distribution changed after the photoperiod-induced onset of podding. In addition, a direct influence of photoperiod on partitioning was observed. Firstly, just after the onset of flowering (40 DAS), ‘Tiga Nicuru’ plants under 10- and 12-h photoperiods had accumulated more dry matter as leaf blades and less as stem material than plants under 14- and 16-h photoperiods. Secondly, for ‘Ankpa 4’ the increase in pod dry weight per plant under the 10-h photoperiod was nearly double the increase under the 12-h photoperiod. This difference was associated with a smaller number of developing pods under the 12-h photoperiod. Photoperiod apparently strongly affects the number of developing sinks and, as a consequence, the total sink-strength of the plant, irrespective of the numerous ovaries present on plants of all treatments (including plants of ‘Ankpa 4’ under 14- and 16-h photoperiods).