Relationship between Plant Height and Flowering Date in Determinate Soybean

There is increasing interest in growing determinate soybean [ Glycine max (L.) Merr.] in the northern USA because of their yielding ability and lodging resistance. These cultivars are approximately half as tall as indeterminate cultivars. The objectives of this study were to estimate the heritabilities of days to R1 and R8, and plant heights at R1 and R8; and to evaluate the relationships among these traits to assess the possibility of selecting tall determinate plants with early flowering. Two determinate populations derived from PI 407711B ✕ PI 360835 and PI 417398 ✕ PI 423882A, were used. These two populations (containing 42 and 43 F 2 families) were studied in the F 3 and F 4 generation in 1984 and 1985, respectively, at Urbana, IL in a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll). A randomized complete‐block design with two replications was used for each population each year. Heritabilities estimated by parent‐offspring regression were high (0.67–1.21) for days to RI and R8, and for plant heights at these two stages except for days to R1 in one population (0.49). Positive genotypic and phenotypic correlations between days to R1 and R8, and plant height indicated obtaining tall, determinate plants with early flowering would be difficult. Main stem growth continued 1 week or more after R1. Plant height at R1 represented approximately 80% of the final plant height. Thus, selection for plant height can be effective at as early a stage as R1 for determinate soybean.