ABSTRACT
Soybean (Glycine max L.) is a short-day plant species whose floral induction requires the daylength, or photoperiod, to be shorter than a critical value (Johnson et al., 1960; Bernard, 1972). The rate of soybean development, especially the time to first flowering, has long been recognized to be sensitive to temperature and photoperiod (Garner and Allard, 1930; Steinberg and Garner, 1936; Johnson et al., 1960; Hesketh et al., 1973; Major et al., 1975a; Summerfield and Wilcox, 1978; Cregan and Hartwig, 1984; Wilkerson et al., 1989; Summerfield et al., 1993, 1998; Cober et al., 2001; Salmerón and Purcell, 2016). In addition, the response of the soybean developmental rate to photoperiod during post-flowering stages has also been observed (Johnson et al., 1960; Major et al., 1975a; Summerfield et al., 1993; Asumadu et al., 1998). The impact of the photoperiod on soybean yield is also significant, with delayed planting often resulting in yield loss due to shortened vegetative growth and grain filling (Board et al., 1990; Board and Settimi, 1986). In general, higher temperature favours the development rate in both vegetative and reproductive stages, while a longer photoperiod has a negative effect on reproductive stages.
