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

The effects of photoperiod and temperature on reproductive development in t wo bambara groundnut (Vigna subterranea) selections from contrasting origin s were quantified by using linear models. The two selections were 'DodR94' from Tanzania (6 degrees 10'S) and 'DipC94' from Botswana (24 degrees 40'S) . The models were based on a semicontrolled-environment study with four con stant photoperiods (10.5, 11.8, 13.2, and 14.5 h per day, covering the rang e of photoperiods in the tropics) and four constant temperatures (20, 23, 2 6, and 29 degrees C). Higher temperatures were also included, but plants di ed at constant temperatures of 33 and 36 degrees C. The rate of progress fr om sowing to flowering of both selections could be described by a thermal r esponse 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 'DodR9 4', the intervals between the experimental photoperiods were too large to a llow quantification of the photoperiod effect. Validation of the phototherm al models with the results of glasshouse experiments in The Netherlands and field experiments in Tanzania and Botswana gave mixed results. Predicted a nd observed time to flowering for 'DipC94' corresponded well, and predicted and observed time from flowering to podding reasonably well. Flowering pre dictions for 'DodR94' were not accurate, possibly because flowering in this selection is influenced by long photoperiods at high temperatures. (C) 200 0 Elsevier Science B.V. All rights reserved.