Effects of Temperature and Photoperiod on Flowering in Soya bean [Glycine max (L.) Merrill]: a Quantitative Model

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Abstract
Factorial combinations of five photoperiods (8 h 20 min, 10 h, 11 h 40 min, 13 h 20 min and 15 h) and three night temperatures (14, 19 and 24 °C) combined with a single day temperature (30 °C) were imposed on nodulated plants of nine soya bean genotypes [Glycine max (L.) Merrill] grown in pots in growth cabinets. The times to first appearance of open flowers were recorded. For a photoperiod-insensitive cultivar, and for the remaining eight photoperiod-sensitive genotypes in photoperiods shorter than the critical daylength, the rates of progress towards flowering (the reciprocals of the times taken to flower) were linear functions of mean diurnal temperature. For all photoperiod-sensitive genotypes, times to flowering in photoperiods longer than the critical daylength increased as inverse functions of both increasing photoperiod and decreasing temperature. A consequence of these two relations is that the critical daylength becomes longer with higher mean temperatures. In the five photoperiod-sensitive genotypes which flowered in all environments before the experiment was terminated (after 150 d) the delays in flowering due to low temperatures or long photoperiods were limited by a maximum period to flowering specific for each genotype. These results are discussed in relation to the development of a simple technique for the large-scale screening of soya bean germplasm to determine photo-thermal response surfaces for flowering.