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 in the US. 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.
• identify breeding lines and develop germplasm with resistance both to
Phytophthora and Pythium diseases.

We have already identified chromosomal locations of several genes/QTLs
controlling resistance to Phytophthora and Pythium. The next phase of the
project is to narrow down the resistance gene-containing chromosomal regions
for these diseases. Our available genome sequence data from 33 soybean
resistant lines obtained through USB funds will be used for this purpose. The
specific objectives of the project are as listed below.
• identify closely linked and new DNA markers for Phytophthora resistance
through comparative genome sequence analysis based on our current results
from association analysis and biparental mapping.
• develop breeder-friendly and easy to use DNA markers for genes conferring
resistance to Phytophthora root rot and Pythium diseases.
• continue developing breeding lines resistant both to Phytophthora and
Pythium diseases.

Expected Outcomes/Deliverables
• Additional year of agronomic trait data for Phytophthora-resistant breeding
lines.
• Making disease resistant germplasm available to public and industry breeders.
• Crosses and backcrosses of elite Virginia adapted lines with Phytophthoraand/or Pythium-resistant lines.
• Closely linked 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.
• Characterization of the resistance gene-containing chromosomal regions for
the eventual identification of candidate resistance genes.
• Publications in scientific journals on the chromosomal locations of genes/QTLs
controlling resistance to Phytophthora and Pythium species.
• Undergraduate student training.