Phytophthroa sojae is a fungus-like oomycete microorganism. Each year, this pathogen causes severe soybean yield losses worldwide. It can infect soybean at every growth stage to cause soybean root and stem rot and other diseases. The effective way to control the diseases caused by this pathogen is through the deployment of resistance (R) genes and other strategies. However, new isolates are emerging, which are capable of overcoming the strong resistance mediated by previously-effective R genes, similar to the breakdown of R gene-mediated resistance in other pathosystems. Therefore, in the long run, partial resistance may be a good strategy, especially in combination with R gene-mediated resistance, to provide soybean plants with durable and broad-spectrum resistance to this pathogen. For this purpose, we have started searching for partial resistance quantitative trait loci (QTL) in different soybean varieties and have recently revealed a major QTL on chromosome 13 in the soybean line PI 408105A that is responsible for partial resistance to P. sojae. To reveal the mechanisms underlying this QTL, the candidate gene approach is employed to identify the gene(s) responsible for the observed partial resistance. Initially, forty candidate genes have been selected based on their annotation, expression pattern, and responsiveness to the inoculation of P. sojae. The genes showing differences in either sequence or expression between the two parental lines that were used to make the recombinant inbred lines for mapping the QTL, will be over-expressed and silenced in soybean hairy roots to infer their functions in defense against P. sojae.