What is Cheatgrass?
Cheatgrass, or downy brome (Latin name: Bromus tectorum), is an exotic weed that has invaded western North American rangelands and is responsible for extensive ecological and economical damage. Most of that damage is generated by the increased frequency of rangeland fires occurring on cheatgrass dominated landscapes. It is widely believed that cheatgrass was introduced into North America from Europe as a grain contaminant nearly 150 years ago, although its center of origin is likely Central Asia. Remarkably, it has become the dominant species on millions of hectares of western North American rangelands. The core habitat for cheatgrass in North America is mid-elevation temperate zones usually referred to as sagebrush-steppe. The cold, wet winters of the sagebrush-steppe zone provide ideal conditions to meet the plant's vernalization requirement for flowering. It is an annual grass and an obligate inbreeder. The botanical term we use to describe the plant is cleistogamous, meaning it sheds its pollen before the flower opens and is receptive to external pollen. You can learn more about this very successful invader at the National Invasive Species Information Center.
Cheatgrass Genetics at BYU
Our lab has been collaborating with scientists at the USDA Forest Service Shrub Labin Provo for nearly 20 years to study the genetics of cheatgrass and associated fungal pathogens in order to help inform management strategies. Our goal is to reduce the spread of the weed in established habitats and prevent its introduction into new habitats. Although we started the genetics work using microsatellite markers as a means to assess genetic diversity and to establish a genetic basis for ecologically adaptive traits, we now use a panel of 96 single-nucleotide polymorphism (SNP) markers. The SNP markers were developed from a partially sequenced transcriptome deposited in GenBank and described in a paper published in Applications in Plant Science. Our current hypothesis is that preadapted genetic variation which arose in the native range (Central Eurasia) has been transferred to North America via multiple invasions, allowing the plant to successfully establish in a wide range of ecological habitats over a very short period of time. We believe that divergence between populations is sufficient to prevent gene flow and are planning experiments to demonstrate the existence of reproductive barriers between different types of cheatgrass. Through our work we have demonstrated wide genetic divergence between populations residing in different habitats. For instance, we have published work showing cheatgrass populations in warm desert regions are genetically distinct from those found in sagebrush-steppe habitats. We have also published work (in press) showing populations at high elevations (> 2000 m.a.s.l.) include cheatgrass haplotypes distinct, although related, to those prevalent at lower elevations.
Currently, we are focused on a project to characterize cheatgrass stand failures, or die-offs, in the Great Basin region. A die-off occurs when cheatgrass is infected with a fungal pathogen causing it to bleach and lodge before seeds mature on the plant. During the following year, seed germination is inhibited and cheatgrass density in the die-off area is extremely low. We believe the fungus which causes cheatgrass plants to bleach is a Rutstroemia species related to Sclerotinia homeocarpa, the pathogen responsible for dollar spot disease in turf grass. Another pathogen which may play a role in this process is Epicoccum nigrum. Germination inhibition in die-off areas may be caused by fungal seed pathogens, including a Fusarium species in the trinctum group and Pyrenophora semeniperda. Our lab is interested in genetically characterizing these pathogens and learning how they interact with cheatgrass to generate die-offs. You can find out about this work by clicking on the Cheatgrass Pathogen link on the tool bar above. Our research is funded by a grant from the Joint Fire Science Program.