The inheritance of a branching type in soybean

Many environmental factors including plant spacing, photoperiod, and plant nutrition can affect the number and distribution of branches on soybean [Glycine max (L.) Merr.] plants. Differences in branching have been noted among soybean lines, but because of the strong environmental influences on branching very little is known of the genetic control of this trait. The lack of information about the genetic control of branching in soybean limits the modifications that can be made in soybean plant architecture. Experimental lines developed from the cross of PI 391.583 (Jilin No. 10) by PI 189.916 were found to have very different branching patterns. The low-branching type had fewer branches and the branches were restricted to the lower portion of the main stem. The high-branching type had more branches and many branches originated at the upper nodes giving the plant a bushy appearance. Crosses were made among four lines of similar and different branching types in order to study inheritance. When similar branching types were crossed no segregation for branching type was observed among progeny. Crosses between high and low branching types produced progeny that segregated in a 9:7 ratio. It was necessary to observe the F(2:3) families in order to accurately determine the genotype of the F₂ plants. These data indicate that two dominant alleles at independent loci were necessary to produce the high branching phenotype. The gene symbols Br1 and Br2 are proposed for these loci.