Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/3/1996
Publication Date: N/A
Citation: Interpretive Summary: Stem termination is one of the major factors used in defining soybean varieties. Currently all soybean varieties are classified as either determinate, semi-determinate, or indeterminate. The type of stem termination has a major influence on plant height. Some experimental lines were developed that did not fit into the standard categories. These lines had many of the characteristics of determinate cultivars but were more than 50% taller. This research was initiated to determine if the genetic control of this type was different from the known stem termination types. We discovered that the gene that controls this taller plant type was different from any previously reported but that it occurs at the same place on the chromosome as the common determinate gene. The discovery of this new gene gives soybean breeders additional control over the architecture of the plant. Determinate cultivars grown in the northern U.S. are generally less than half the height of the indeterminate cultivars. This may be one reason for limited acceptance by the farmers despite the good performance of these cultivars. Developing taller determinate cultivars with this new gene may help to improve seed yield while still retaining the advantages of the shorter cultivars to stand upright in high populations.
Technical Abstract: Two loci (dt1 and Dt2) affect stem termination in soybean [Glycine max (L.) Merr.]. The dt1 allele produces a determinate stem termination whereas the phenotype of the Dt2 allele is called semi-determinate. Both of these alleles have been backcrossed into near-isogenic lines of the indeterminate cultivar Clark. The semi-determinate near-isogenic line is approximately 50% taller than the determinate near-isogenic line. More recently determinate Clark near-isogenic lines have been developed using the cultivars Peking and Soysota as donor parents. These lines were approximately 50% taller than other determinate (dt1) near-isogenic lines and similar in height to the semi-determinate (Dt2) near-isogenic line. The objective of this research was to determine the genetic control of this new phenotype. Crosses were made between the two tall determinate near-isogenic lines and between the tall determinate near-isogenic lines and other near-isogenic lines that differed at loci affecting stem termination and stem growth. The allele controlling the tall determinate phenotype is identical in Peking and Soysota and is allelic to dt1. The gene symbol dt1-t is proposed. Several leaf and stem characters were studied to identify traits that could separate the Dt2 from the dt1-t phenotype. There were average differences in final plant height and main-stem node number as well as in terminal raceme length and diameter of last internode, but the differences were not large enough to distinguish among individual plants. Terminal leaflet area on the last leaf measured at R6 was consistently larger for the tall determinate phenotype.