The Effect of Rbs2 on Yield of Soybean

Brown stem rot (BSR), caused by Phialophora gregata (Ailington & Chamberlain) W. Gams, is a vascular‐foliar soybean [Glycine max (L.) Merr.] disease of the north central USA. Although yield comparisons have been made between susceptible and resistant lines, no study has evaluated yield differences between near‐isogenic lines differing in brown stem rot reaction. The objective of this study was to compare brown stem rot resistant and brown stem rot susceptible near‐isogenic lines for yield and other agronomic traits. In this study, five pairs of near‐isogenic lines for the Rbs2 resistance gene were grown at six locations in Illinois in 1994 and nine locations in Illinois in 1995, relying on natural infection with P. gregata. Near‐isogenic lines were evaluated for disease incidence (percentage of plants exhibiting brown stem rot foliar symptoms) and disease severity (degree of foliar chlorosis‐necrosis) in late August and harvested in September and October. At seven locations with 13% or greater incidence of brown stem rot, a 10.6% yield advantage was associated with the resistance gene, Rbs2. At eight locations with less than 3% incidence of brown stem rot, there was no yield difference between resistant and susceptible near‐isogenic lines. These results indicate that Rbs2 prevents yield loss in the presence of brown stem rot.