Variation in the Durations of the Photoperiod-sensitive and Photoperiod-insensitive Phases of Post-first Flowering Development in Maturity Isolines of Soyabean [Glycine max(L.) Merrill] 'Clark'

Plants of eight isolines of soyabean [ Glycine max (L.) Merrill], comprising all combinations of two alleles at the three loci E1 / e1 , E2 / e2 and E3 / e3 in the cultivar ‘Clark’ background, were transferred after different periods following first flowering from long days (LD, 14 h d −1 ) to short days (SD, 12 h d −1 ) and vice versa in a reciprocal-transfer experiment in a plastic house maintained at 30/24 °C (day/night). Photoperiod (0.10> P >0.05), transfer time ( P <0.001),>isoline ( P <0.001), and their interactions ( P <0.001) all affected flowering duration, i.e. the period from first flowering until the appearance of the last flower. The flowering duration comprised two distinct phases: a photoperiod-sensitive phase beginning at first flowering, and a subsequent photoperiod-insensitive phase. The duration of the photoperiod-sensitive phase varied much more among the isolines in LD than in SD. Only the dominant allele E1 increased the sensitivity of the photoperiod-sensitive phase of flowering duration to photoperiod singly, but positive epistatic effects were detected between E1 and E2 , E1 and E3 , and especially among all three dominant alleles. The increases in flowering duration resulting from the combined effects of gene and environment (i.e. photoperiod) were associated with considerable increases in biomass and seed yield at harvest maturity.