Phenological development in bambara groundnut (Vigna subterranea) transferred from 14 to 11 h photoperiods.

The developmental phase in which photoperiod sensitivity for podding occurs was determined for two bambara groundnut genotypes grown in 1987 and 1990 in glasshouse experiments in the Netherlands, namely genotypes ‘Tiga Nicuru’ from Mali (day-neutral for flowering and photoperiod-sensitive for podding) and ‘Ankpa 4’ from Nigeria (photoperiod-sensitive for both flowering and podding). Eighteen photoperiod treatments were given to each genotype. Two treatments consisted of a constant 12 or 14 h photoperiod and started 21 days after sowing for ‘Tiga Nicuru’ and 18 days after sowing for ‘Ankpa 4’. Eight treatments were introduced by transferring plants with at least 20 flower buds (33-day-old plants of ‘Tiga Nicuru’ and 35-day-old plants of ‘Ankpa 4’) from a 12 to a 14 h photoperiod or vice versa. In ‘Tiga Nicuru’ transference was for 4, 8, 12 days or until harvest, and in ‘Ankpa 4’ it was for 8, 12, 16 days or until harvest. Another eight similar treatments were given to plants transferred after having had at least 20 open flowers (48-day-old plants of ‘Tiga Nicuru’ and 62-day-old plants of ‘Ankpa 4’). Transferring plants of ‘Tiga Nicuru’ to the 12 h photoperiod for at least 8 days induced podding. Plants were susceptible to podding induction for nearly 4 weeks: podding was induced in plants which had been in the natural photoperiod (≥ 15·5 h) for 21 days, followed by 12 days in the 12 h photoperiod and subsequently in the 14 h photoperiod until harvest, and it could still be induced in 48-day-old plants that had had > 20 open flowers. However, transference to the 12 h photoperiod for 16 days did not induce podding in ‘Ankpa 4’. Transferring plants from the 12 to the 14 h photoperiod or vice versa caused differences in the number of flowers and pods/plant, petiole length and leaf area. The influence of photoperiod was most obvious on the number of pods/plant. Leaf area and number of pods/plant seem suitable parameters for modelling crop growth under different photoperiods. Leaf area development correlated with the number of developing pods/plant, but was also more directly influenced by the prevailing photoperiod.