Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 25, 1996
Publication Date: N/A
Interpretive Summary: The number and size of branches on soybean plants are strongly influenced by the distance between plants, the date of planting and plant nutrition. Differences in branching have been noted among soybean varieties but because the environmental influences are so strong, the genetic control of branching has never been studied. The lack of information about the genetic control of branching in soybean limits the modifications that can be made to adapt the soybean plant to different management practices. This research was able to identify two genes in exotic soybean germplasm that have a dramatic effect on the branching pattern of soybean plants. The presence of these genes increases the number of branches and significantly alters the appearance of the plant. By identifying a branching type in soybean that is controlled by only two genes it will be possible to relatively easily transfer this trait into commercial cultivars or high yielding experimental lines. At this point the effect on seed yield is not known. However, these genes can be used to create new plant types which will be shorter and produce more pods on the branches. These types may be less prone to lodging and better adapted to certain crop management strategies. Future research will determine the effect of increased branching on seed yield and how best to manage these types of plants.
Technical Abstract: Many environmental factors, including plant spacing, photoperiod, and plant nutrition, can affect the number and distribution of branches on soybean 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. 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 F2:3 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 being proposed for these loci.