THE EFFECT OF RBS2 ON YIELD OF SOYBEAN

Brown stem rot (BSR), caused by Phialophora gregata (Allington & Chamb erlain) W. Gams, is a vascular-foliar soybean [Glycine max (L.) Merr.] disease of the north central USA. Although yield comparisons have bee n 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 r ot resistant and brown stem rot susceptible near-isogenic lines for yi eld and other agronomic traits. In this study, five pairs of near-isog enic lines for the Rbs2 resistance gene were grown at six locations in Illinois in 1994 and nine locations in Illinois in 1995, relying on n atural infection with P. gregata. Near-isogenic lines were evaluated f or disease incidence (percentage of plants exhibiting brown stem rot f oliar symptoms) and disease severity (degree of foliar chlorosis-necro sis) in late August and harvested in September and October, At seven l ocations with 13% or greater incidence of brown stem rot, a 10.6% yiel d advantage was associated with the resistance gene, Rbs2. At eight lo cations with less than 3% incidence of brown stem rot, there was no yi eld difference between resistant and susceptible near-isogenic lines. These results indicate that Rbs2 prevents yield loss in the presence o f brown stem rot.