Ecological Genetics of the Cheatgrass - Head Smut Pathosystem
Dr. David L. Nelson (retired), Shrub Sciences Lab, Provo UT
Dr. Daniel Fairbanks, Brigham Young University, Provo UT
Dr. Craig Coleman, Brigham Young University, Provo UT
Dr. Mikel Stevens, Brigham Young University, Provo UT
Dana Quinney, Idaho Army National Guard, Boise ID
Suzette Clement, Shrub Sciences Laboratory, Provo UT
Alisa Ramakrishnan (M.S., Brigham Young University)
Toupta Boguena (Ph.D., Brigham Young University)
Jen Waters (Undergraduate, Brigham Young University)
Cheatgrass (Bromus tectorum) is an invasive exotic annual grass that has become the dominant plant on tens of millions of acres of former shrubland in the Intermountain West. This highly flammable grass has set the stage for an ever-widening cycle of fire and destruction. The only hope for restoring these vast acreages to diverse, productive native plant communities is through direct seeding. But in order to establish native seedlings in cheatgrass-infested areas, some form of weed control is necessary. Currently available methods for cheatgrass control, such as early season burning, tillage, and herbicides, are expensive, risky, and can be hard on remnant native vegetation. Our goal is to determine whether a naturally-occurring pathogen on cheatgrass, the fungus that causes head smut disease, can be used as a method for short-term biocontrol in conjunction with restoration seedings.
The head smut pathogen (Ustilago bullata) infects germinating seeds of cheatgrass, and the plants grow up appearing normal. But when the cheatgrass flowers, no seeds are produced, only the spores of the pathogen, thus effectively breaking the life cycle of this annual plant. Observational data suggest that head smut epidemics have temporarily wiped out cheatgrass over large areas in the past, but in the absence of restoration seeding, these areas revert to cheatgrass over time or are taken over by other weeds. Our goal is to understand the predisposing factors for the occurrence of these head smut epidemics, so that we can use them as a tool for restoration.
Our research on the cheatgrass-head smut pathosystem began in earnest in 1998, when we received funding from the CSREES NRI Plant-Microbe Interactions Program (then called the Plant Pathology Program). This funding was later renewed for a total of five years. We have received additional funding to work on more applied aspects of the research through the Idaho Army National Guard.
This multifaceted research program involves many collaborators and students. The principal plant pathology expertise on the project is provided by Dr. Nelson, while Dr. Meyer provides expertise in genetics and ecology, and Drs. Fairbanks, Coleman, and Stevens provide expertise in molecular biology.
Genetic variation in resistance to the pathogen has been a major focus of the research to date. This involved development of molecular genetic markers for identifying cheatgrass genotypes and studying their distribution within and among host populations. Alisa Ramakrishnan has carried out this research as a Master's project. It is also necessary to conduct very large cross-inoculation experiments to associate particular host genotypes with their resistance phenotypes; Dr. Nelson along with technician par excellence Suzette Clement have carried out this work.
We are also studying environmental factors, especially temperature, that mediate the infection of susceptible hosts, in both growth chamber and field settings. This includes consideration of genetic variation within and among pathogen populations in the conditions required for infection. These studies form the core of Toupta Boguena's doctoral research.
Other related studies include work on the possible threat from this pathogen to non-target host organisms, and development of methodology and trials for pathogen inoculum application in the field.
It is still too soon to tell how useful this approach will be in controlling cheatgrass, but the studies are producing a wealth of information about both host and pathogen, with many potential applications.