Photoperiod Effect before and after Flowering on Branch Development in Determinate Soybean
1986
Board, J. E. | Settimi, J. R.
Previous research indicated that restricted branch development was a factor associated with soybean [Glycine max (L.) Merr.] seed yield reductions at late planting dates in the southeastern United States. The present studies were conducted to outline the progress of branch development at different planting dates and to determine the role of photoperiod in branch restriction at late planting dates. In field studies, eight cultivars were planted at early April (nonoptimal), mid-May (optimal), and mid-June (nonoptimal) planting dates in 1982 and 1983 at Baton Rouge, LA (30°N Lat), on an Olivier silt loam (fine-silty, mixed, thermic Aquic Fraguidalf) soil. Plants were sampled throughout the season for total branch length and number of branches. Photoperiod studies were conducted at the Phytotron, North Carolina State University, Raleigh, NC. Plants were subjected to combinations of preflowering and postflowering daylength simulations of optimal and late planting dates to determine photoperiod effects on branch development. Field results demonstrated that approximately two-thirds of total branch length and number of branches were produced between growth stages R1 and R5 and that the period from R1 to R5 declined with each delay in planting. Reduced total branch length and number of branches at late planting dates were associated with fewer days from R1 to R5, while reduction at early planting dates occurred because of short plants. Data from the photoperiod study showed that shorter R1 to R5 period and the associated reduction in branch number, total branch length, and branch node number were photoperiodically induced phenomena. Both preflowering and postflowering daylength regimes at a late planting date were involved in these events.
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