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], comprisin g all combinations of two alleles at the three loci E-1/e(1), E-2/e(2) and E-3/e(3) in the cultivar 'Clark' background, were transferred after differe nt periods following first flowering from long days (LD, 14 h d(-1)) to sho rt days (SD, 12 h d(-1)) and vice versa in a reciprocal-transfer experiment in a plastic house maintained at 30/24 degrees C (day/night). Photoperiod (0.10 > P < 0.05), transfer time (P < 0.001), isoline (P < 0.001), and thei r interactions (P < 0.001) all affected flowering duration, i.e. the period from first flowering until the appearance of the last flower. The flowerin g duration comprised two distinct phases: a photoperiod-sensitive phase beg inning at first flowering, and a subsequent photoperiod-insensitive phase. The duration of the photoperiod-sensitive phase varied much more among the isolines in LH) than in SD. Only the dominant allele E-1 increased the sens itivity of the photoperiod-sensitive phase of flowering duration to photope riod singly, but positive epistatic effects were detected between E-1 and E -2, E-1 and E-3, and especially among all three dominant alleles. The incre ases 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. (C) 1998 Annals of Botany Co mpany.