Diseases are major constraints for soybean production. Phytophthora root and stem rot, caused by Phytophthora sojae, is the second most important disease problem after soybean cyst nematode. Pythium damping-off and root rot is another soybean disease which results in poor stands and reduces yield. Recent disease screenings have identified 55 Pythium species. Host resistance is the most cost-effective way to manage these soybean diseases. However, resistance genes become ineffective as the pathogen populations change over time. This project aims at identification of new and novel disease resistance genes and their associated DNA markers. Improved germplasm from this study should facilitate development of superior soybean cultivars for domestic and export markets and improve profitability of US soybean producers.
The long-term goal of the proposed study is to develop disease-resistant and high-yielding soybean cultivars adapted to the Virginia and the Mid-Atlantic growing conditions. Specific objectives of the project are to
• develop breeder-friendly and easy to use DNA markers for genes conferring resistance to Phytophthora root rot and Pythium diseases.
• conduct marker-assisted selection (MAS) studies towards pyramiding or stacking of the genes conferring resistance to Phytophthora root rot and Pythium diseases.
• identify breeding lines with resistance to multiple diseases.

• develop breeder-friendly and easy to use DNA markers for genes conferring resistance to Phytophthora root rot and Pythium diseases.
• conduct marker-assisted selection (MAS) studies towards pyramiding or stacking of genes conferring resistance to Phytophthora root rot and Pythium diseases. The latter soybean root disease is becoming more prevalent and 55 species have recently been identified.
• identify breeding lines with resistance to multiple diseases (Phytophthora and Pythium).

• Disease resistant breeding lines 150 Phytophthora-resistant breeding lines selected from five segregating populations provide a good germplasm source for use in breeding programs. Some of these lines will be used in breeding programs in Ohio, Michigan and Missouri (USB collaboration).
• Eight breeding populations Resistant breeding lines could directly be selected from these populations. The populations could also be used in our own breeding programs to study traits of economic importance other than diseases. Some of these populations maybe useful in Dr. Bo Zhang’s project for Soybean Cyst Nematode (SCN) resistance gene discovery.
• DNA markers for Phytophthora and Pythium resistance genes Such markers can be used for disease screening and marker-assisted selection to identify multiple disease-resistant lines in breeding programs.
• Whole genome DNA sequence data for 33 Phytophthora-resistant soybean lines.
• Genome-Wide Association mapping of resistance genes Analysis of disease data from 1000 lines from the USDA soybean collection together with 50,000 DNA marker data on the same lines to identify new resistance genes.
• Undergraduate and graduate student training Student training is an educational deliverable of this project.
• Publications in scientific journals and presentations in meetings and conferences Such activities provide an avenue to summarize results and make them available to the soybean scientific community, especially to the seed industry.

Improved germplasm from this study should facilitate development of superior soybean cultivars for domestic and export markets and improve profitability of US soybean producers.