Soybean yield in delayed plantings as affected by alleles increasing vegetative weight

The reduction in soybean [Glycine max (L.) Merr.] yield with delayed planting can be partially attributed to reduced vegetative growth. Alleles altering stem termination, internode length, and time of flowering can increase vegetative growth. The objective of this experiment was to determine if allele combinations which increase vegetative size at beginning pod fill (growth stage R5) would increase seed yield in delayed plantings. Nine isolines in the 'Clark' genetic background were planted at normal (18 May) and delayed (3 July) planting dates in wide (0.76-m) and narrow (0.38-m) row widths for 3 years at Lexington, KY. Isolines with indeterminate stem termination and elongated internodes (allele s-t) produced greater vegetative growth at growth stage R5 averaged over both planting dates than isolines with semi-determinate or determinate stem termination and normal internodes (allele S). Isolines with delayed flowering (alleles E₁e₂) did not produce greater vegetative growth at R5 than isolines with earlier flowering (alleles e₁E₂). The isolines with increased vegetative growth did not show a yield advantage averaged over both planting dates, and planting date X isoline interactions for yield were nonsignificant. Thus, increased vegetative growth conditioned by these alleles was not automatically advantageous to yield in delayed plantings.