A Third Allele at the Soybean dt1 Locus

Two loci ( Dt1 and Dt2 ) affect stem termination in soybean [ Glycine max (L.) Merr.]. Both of these alleles have been backcrossed into near‐isogenic lines (hereafter referred to as isolines) of the indeterminate cv. Clark ( Dt1Dt1 dt2dt2 ). The semi‐determinate isoline ( Dt1Dt1 Dt2Dt2 ) is ≈ 75% the height of Clark and the determinate isoline ( dt1dt1 dt2dt2 ) is ≈ 50% as tall as Clark. Recently, determinate Clark isolines have also been developed with the cv. Peking and Soysota as donor parents. These lines were similar in height to the semi‐determinate isoline. The objective of this research was to determine the genetic control of this new phenotype. The gene controlling the tall determinate phenotype was found to be identical in Peking and Soysota and allelic to dt1 The gene symbol dt1‐t has been approved by the Soybean Genetics Committee. Several leaf and stem characters were studied in the stem termination isolines. Although dt1‐tdt1‐t and Dt2Dt2 phenotypes are similar in plant height, dt1‐tdt1‐t is more similar to dt1dt1 when considering leaf and stem traits at the top of the plant.