2018 Faculty Update: Deborah Samac
The Samac lab is part of the USDA-ARS-Plant Science Research Unit (PSRU) and has a broad portfolio of alfalfa research projects. Retirement of PSRU scientists in 2015 resulted in transfer of technical staff to the lab, giving us the opportunity to pursue several exciting new projects and work as a team on lab, greenhouse, and field experiments.
One large project is focused on Aphanomyces root rot (ARR) of alfalfa, a serious problem of alfalfa across the US. Our surveys in Minnesota and other states found that race 2 of Aphanomyces euteiches is the most common race, but there were some soils that were atypical, suggesting the presence of additional races. Mindy Dornbusch isolated over 80 strains from these soils and tested them for race type. We then embarked on a complex project to characterize and map resistance in alfalfa to ARR. We now have evidence that there are many races of the pathogen. Fortunately, there appear to be multiple resistance genes in alfalfa varieties. These are most likely genes that trigger a hypersensitive response, which occurs soon after pathogen invasion of root cells, beautifully demonstrated by Dr. Bruna Bucciarelli. Although we have locations for several resistance genes, identifying DNA markers will take additional research due to the complicated tetraploid genetics of alfalfa. The surveys also found fields that had frequently been in alfalfa had high levels of damping-off pathogens particularly Pythium and Fusarium species causing seed rot and damping-off, many of which are not controlled by traditional fungicide seed treatments. We are currently testing fungicides for greater effectiveness against these pathogens and are also selecting for resistance to damping-off using methods developed in the 1990s by alumnus Dr. Nora Altier.
Across the United States, the most difficult disease problem has been crown rot, caused by a complex of pathogens. Ph.D. student Andrew Sathoff has investigated antimicrobial peptides to solve this disease problem. Working with Mindy, transgenic alfalfa expressing peptides with the widest range of activity were generated. Results of preliminary experiments are very exciting and indicate that plants have increased disease resistance. Moreover, Andrew’s research indicates that these peptides are an untapped resource for combating animal and human pathogens.
As a result of attending a forage meeting in California, the lab became involved in investigating a bacterial disease of alfalfa that has been recognized for many years, but is having an increasing impact on alfalfa grown at high elevations. Bacterial stem blight of alfalfa, caused by Pseudomonas syringae, is associated with frost damage due to the ability of the pathogen to form ice nuclei. With funding from USDA-NIFA, Savana Lipps (a summer intern from University of Wisconsin) and Peter Lenz are continuing to characterize the pathogen, while a Ph.D. student starting in July will focus on host resistance and epidemiology.
A long-term focus of the PSRU is to develop new uses for alfalfa. With funding from the Minnesota Department of Agriculture, M.S. student Jessica Corburn, working with Ted Jeo, has shown that non-lodging alfalfa can provide multiple products, including leaf protein for aquaculture feeds. The lab continues to focus on alfalfa biotechnology, now using genome-editing methods. Susan Miller constructed vectors for editing genes involved in phosphate uptake for use in bioremediation. Mutations occurred in the targeted areas and we are currently evaluating the resulting phenotypes and inheritance of edited genes. Dr. Claudia Castell-Miller continues to collaborate with the lab in diseases of wild rice and provides highly valued disease management information to the state’s wild rice growers.