Soybean Cyst Nematode Resistance and Growth Defense Trade-off

Soybean cyst nematode (SCN, Heterodera glycines) is the most economically important pathogen of soybean (Glycine max). It is estimated that SCN causes roughly $1.2 billion in annual yield loss in the United States. The primary means of control for SCN is to plant resistant soybean cultivars. Roughly 95% of available elite cultivars have resistance to SCN derived from a single source, ‘PI 88788’. This source utilizes a high copy number of the rhg1 SCN resistance locus. The second most prominent source of SCN resistance (‘Peking’) uses low copy number of rhg1 with the addition of the Rhg4 SCN resistance locus. The research in this dissertation focuses on characterizing the effect of copy number variation (CNV) of rhg1 and Rhg4 on resistance to multiple Hg-types of SCN. Also evaluated is the potential trade-offs between plant growth and defense associated with CNV of both SCN resistance loci. Lastly, this research sought to identify novel sources of SCN resistance. The results from this dissertation display the important role elevated copy number of Rhg4 plays in providing broad-based resistance to multiple Hg-types of SCN. We observed few growth defense trade-offs associated with CNV for either rhg1 or Rhg4. This study also identified three novel SCN resistance genes that may be utilized in future breeding efforts.