A 3RD ALLELE AT THE SOYBEAN DT1 LOCUS

Two loci (Dt1 and Dt2) affect stem termination in soybean [Glycine mar (L.) Merr.]. Both of these alleles have been backcrossed into near-is ogenic lines (hereafter referred to as isolines) of the indeterminate cv. Clark (Dt1Dt1 dt2dt2). The semi-determinate isoline (Dt1Dt1 Dt2Dt2 ) is approximate to 75% the height of Clark and the determinate isolin e (dt1dt1 dt2dt2) is approximate to 50% as tall as Clark. Recently, de terminate Clark isolines have also been developed with the cv. Peking and Soysota as donor parents. These lines were similar in height to th e semideterminate isoline. The objective of this research was to deter mine the genetic control of this new phenotype. The gene controlling t he 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 Dt2 Dt2 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 pla nt.