Deborah Samac

1991 Upper Buford Circle

495 Borlaug Hall

St. Paul, MN 55108

(612) 625-1243

Education

• B.A., Biology, The Colorado College
• Ph.D. Plant Pathology, University of Wisconsin-Madison

Research Interests

Research in my laboratory focuses on the diseases and pathogens of alfalfa with collaborations to develop a reference genome sequence for alfalfa and universal DNA markers for alfalfa breeding. The primary diseases of concern are Aphanomyces root rot, Pythium seed rot and damping off, and bacterial stem blight of alfalfa. We are also identifying and characterizing novel alfalfa pathogens involved in seedling diseases. My laboratory provides cultures of alfalfa pathogens for the research community and the highly regenerable alfalfa genotype RegenSY27x.

Aphanomyces root rot caused by Aphanomyces euteiches, is one of the most important diseases of alfalfa in the U.S. We showed that race-specific resistance involves a hypersensitive response of individual epidermal or cortical cells upon zoospore penetration. QTLS for resistance to race 2 strains map to different loci depending on the source of resistance. Markers are being developed to identify resistant plants to facilitate stacking resistance genes and to fine map loci for candidate gene identification. A panel of 3,000 SNP markers will be used to map resistance genes for Phytophthora root rot, Anthracnose, Fusarium wilt, and bacterial wilt. 

Bacterial stem blight was first described in 1904 but has recently emerged as a yield-limiting disease in numerous locations in the U.S. The disease is caused by Pseudomonas syringae pv. syringae and P. viridiflava. Although both bacteria are associated with foliar disease, it is not clear which is involved in causing the crown bud rot and root rot symptoms that are also associated with the disease. Complete genome sequences of both species were assembled and will form the basis of understanding pathogenicity on alfalfa through mutagenesis and gene expression. We are developing a standard test for identifying resistant plants for use in selection and breeding resistant alfalfa varieties.

Developing genomic resources for alfalfa improvement has been slow due to its large complex genome and the heterogeneity within cultivars. My lab coordinated the development of the reference genome for the alfalfa genotype RegenSY27x, which is used widely for genetic transformation. The assembly of an additional eight genomes of plants differing in fall dormancy is in progress.