2012 Annual Report 1a.Objectives (from AD-416): Identify genes responsible for Brown Stem Rot (BSR) resistance in resistant genotypes. 1b.Approach (from AD-416): Conduct experiments to silence candidate Brown Stem Rot (BSR) resistance genes in a resistant genotype. Silenced plants will be infected with BSR and assayed for resistance or susceptibility. 3.Progress Report: Plant mechanisms for controlling infection by Phiolophora gregata (the causal agent of Brown Stem Rot (BSR) in soybeans) are poorly understood. Unlike most soybean-pathogen systems, scoring resistance or susceptibility to BSR takes six to seven weeks. It is unclear if resistance is not induced until that time or if we are unable to detect early resistance by visual inspection. Using available mapping data, we have identified three clusters of resistance genes that are candidates for the Rbs3 P. gregata resistance gene. Using Virus Induced Gene Silencing (VIGS), we have targeted all three clusters of genes. We have run three separate VIGS trials and while the results appear promising, no clear candidate cluster has been identified. One of the difficulties is assessing when to treat with the VIGS vectors to optimize gene silencing and resistance phenotyping. To improve the VIGS protocol and disease assays, we have collected tissue from resistant and susceptible genotypes infected and mock infected with P. gregata over a broad time course. Microarray and bioinformatic analyses will be used to determine when resistance occurs. This information will be used to optimize the VIGS protocol.