Characterization of the Photoperiodic Response of Post-flowering Development in Maturity Isolines of Soyabean [Glycine max(L.) Merrill] ‘Clark’

Plants of all eight isolines of three maturity genes (all combinations of two alleles at the three lociE1/e1,E2/e2,E3/e3) of soyabean [Glycine max(L.) Merrill] were grown in four different photoperiods (12, 13, 14 or 15 h d−1) at 30/24 °C from first flower opening to harvest maturity. Photoperiod, isoline, and their interaction, affected significantly (P<0.01) the duration between first and last flowering, and reproductive duration. The interactions between genotype and photoperiod were sufficiently strong that considerable differences in these durations were detected among isolines in the least-inductive environment (15 h d−1) whereas differences were negligible in the most-inductive regime (12 h d−1). There was a negative linear relation between photoperiod and both rate of progress from the appearance of the first to the last flower, and rate of progress from first flowering to harvest maturity; sensitivity to photoperiod varied (P<0.05) six- and five-fold, respectively, among the extreme isolines (e1e2e3andE1E2E3). The three dominant allelesE1,E2andE3, singly, had comparatively little effect on post-flowering traits, but considerable epistasis (particularly betweenE1andE2) was detected for sensitivity to photoperiod in respect of rates of progress from the appearance of the first to the last flower, and from first flower to harvest maturity. Thus the large variations detected for these traits are the consequence of gene×gene (×gene)×environment interactions.