Peanut stem rot (white mold) is one of the most notorious peanut diseases, caused by the fungus Athelia rolfsii (syn. Sclerotium rolfsii). Thus far, cultivars only show moderate to low resistance to the disease. Hence, breeding cultivars with stronger resistance is essential. However, peanut has a narrow genetic background, so only some genetic sources can be utilized. Researchers seek extra sources in wild species to lessen this limitation. In this study, we aimed to evaluate stem rot resistance in plant materials derived from wild peanut and further utilize the resistance in breeding. Firstly, a greenhouse assay was devised to assess stem rot resistance using stem cutting inoculated with a mycelial plug. The disease evaluated by this assay reflects the field resistance. The next step was, using the devised assay and field evaluation, to identify the resistance in wild-derived materials (allotetraploids). One allotetraploid ValSten1 (A. stenosperma x A. valida, showed resistance. Hence, ValSten1-derived populations were used for the following objectives. A ValSten1-derived F2 population was used to identify genomic regions (quantitative trait locus, QTL) that confer resistance. Two sets of QTLs were identified, six associated with lower disease ratings (all derived from A. stenosperma), and seven associated with higher disease ratings (most derived from A. valida). Two lines from another ValSten1-derived population were found to be resistant and were used as resistance donors to cross with two moderately resistant peanut cultivars for stacking all resistances into a single genotype. In addition, the genome of one isolate of A. rolfsii was deep sequenced, and the sequences were assembled. The genome size was 71.75 MB. DNAs of another one hundred and seventeen isolates were extracted and sequenced. In summary, this study successfully devised a stem rot greenhouse assay, identified the resistance in wild-derived materials, identified genomic regions that conferred resistance, and initiated the resistance pyramiding program. Additionally, the genome of the causal pathogen was assembled. Information revealed in this study is a step toward breeding more robust and durable stem rot resistant cultivars.