Genetic Effects on Reproductive Phenology in Soybean Isolines Differing in Maturity Genes

Soybean (Glycine max (L.)) reproductive phenology is influenced by genotype, photo-period, and temperature. Backcross-derived isolines for three maturity genes, E 1 , E 2 , and E 3 were used. Three Harosoy and four Clark isolines were evaluated for flowering date (R1) in the Duke University Phytotron. Eight Clark isolines were tested in controlled-photoperiod and planting-date field experiments at Urbana, Illinois. The phytotron data showed a mean delay in flowering of 16, 7 and 2 d for E 1 , E 2 and E 3 vs. e 1 , e 2 and e 3 , respectively. The genes were mainly additive, as were temperature and photoperiod on rate of progress to flowering. Flowering was delayed 14.4, 5.4, and 2.7 d and 16.0, 6.6 and 5.5 d in the controlled-photoperiod and planting-date experiments by E 1 , E 2 and E 3 , respectively. Maturity was delayed 16.1, 7.1 and 4.3 d, and 10.8, 10.6 and 5.8 d in the controlled-photoperiod and planting-date field experiments by E 1 , E 2 and E 3 , respectively. Postflowering development (R1 to R8) was slowed by E 2 and E 3 , E 1 showed no effect in the controlled-photoperiod experiment, but hastened postflowering development in the planting-date experiment. Reproductive development periods prior to and after flowering can be affected by the same gene to different extents and in different directions.