Quantifying photothermal influences on reproductive development in bambara groundnut ( Vigna subterranea): models and their validation

Abstract

The effects of photoperiod and temperature on reproductive development in two bambara groundnut ( Vigna subterranea) selections from contrasting origins were quantified by using linear models. The two selections were ‘DodR94’ from Tanzania (6°10′S) and ‘DipC94’ from Botswana (24°40′S). The models were based on a semicontrolled-environment study with four constant photoperiods (10.5, 11.8, 13.2, and 14.5 h per day, covering the range of photoperiods in the tropics) and four constant temperatures (20, 23, 26, and 29°C). Higher temperatures were also included, but plants died at constant temperatures of 33 and 36°C. The rate of progress from sowing to flowering of both selections could be described by a thermal response plane. For ‘DipC94’, the rate of progress from flowering to podding could be described well by a combination of a thermal response plane and a photothermal response plane. In the case of the podding response of ‘DodR94’, the intervals between the experimental photoperiods were too large to allow quantification of the photoperiod effect. Validation of the photothermal models with the results of glasshouse experiments in The Netherlands and field experiments in Tanzania and Botswana gave mixed results. Predicted and observed time to flowering for ‘DipC94’ corresponded well, and predicted and observed time from flowering to podding reasonably well. Flowering predictions for ‘DodR94’ were not accurate, possibly because flowering in this selection is influenced by long photoperiods at high temperatures.