Comparison of Determinate and Indeterminate Soybean Near‐Isolines and Their Response to Row Spacing and Planting Date

Abstract

Determinate (DET) and indeterminate (IND) soybeans [Glycine max (L.) Merr.] differ in growth habit and have responded differently to planting date and row spacing. The purpose of this study was to compare DET and IND near‐isolines for phenoiogical and agronomic traits and to determine similarity of response of the isolines to planting date and row width. Thirty‐eight F5‐derived DET and IND near‐isolines were randomly selected from six soybean populations. The lines were evaluated in three replications of a split (planting date), split (row spacing), split (isoline) plot design over a 2‐yr period. Data were recorded on the days to first flowering, days to maturity, length of the reproductive period, and on plant height, lodging, and seed yield. Lines within growth habits responded similarly to row spacing, but the interactions of planting dates with lines within growth habits were significant for all traits measured. The DET lines were very similar to their IND isoline counterparts for phenological traits measured at two planting dates (r = 0.84** and 0.90**), less similar for plant height (r = 0.71**), and even less similar for plant lodging (r = 0.53** and 0.64**). There was no association between DET and IND isolines for seed yield at the early planting date and a weak association at the late planting date. This suggests that the two plant types responded differently to environmental factors that affect seed yield. However, the highest yielding DET and IND isolines averaged over both years, planting dates, and row spacings were derived from the same F5 plant, providing evidence that loci affecting superior seed yield could be expressed in either plant type.