Research Topics
Department of Crop Sciences
Ph.D. (1996) Michigan State University
Research Topics
Research Interests
A common theme among most of the research projects in my laboratory is variability within weed species. Many species owe their success as weeds to their underlying genetic diversity and, consequently, to their ability to adapt to a variety of cropping practices. Probably the best example of weed adaptation to a particular cropping practice is the development of herbicide resistance. For this reason, several past and current projects in my lab focus on mechanisms and evolution of herbicide resistance.
We have investigated several weed biotypes that are resistant to herbicides that act by inhibiting acetolactate synthase (ALS). In most cases of resistance to ALS inhibitors, resistance is due to one of several point mutations in the ALS gene. Our work on resistance to these herbicides has focused on identifying the specific ALS mutations in the resistant biotypes.
Waterhemp is considered by many to be the worst weed in Illinois, and much of our research focuses on this species. We recently identified a novel type of triazine resistance in waterhemp. Typically, triazine resistance is mediated by an altered triazine-binding site (the D1 protein), but in this case resistance is mediated by a different mechanism, which we are trying to elucidate. We are also trying to elucidate the mechanism of resistance to protoporphyrinogen oxidase-inhibiting herbicides in a waterhemp biotype. Resistance to this class of herbicides has not yet been observed in any weed species other than waterhemp.
Waterhemp is by no means the only weedy Amaranthus (pigweed) species that is commonly found in Illinois. In fact, eight pigweed species (or nine if you distinguish the two waterhemp species) are commonly encountered in our state. Because these species are closely related, they may occasionally hybridize. We therefore initiated a project to determine the contribution of gene exchange among the pigweed species to their weediness. We have documented introgression of a herbicide-resistance gene from smooth pigweed into waterhemp, and are now using field studies in an effort to quantify the frequency at which hybridization and subsequent gene introgression might occur. We are also using various cytogenetic approaches to address questions related to chromosome pairing, gene exchange, and ploidy in interspecific hybrids and backcross progeny.
Herbicide resistance is not the only consequence of genetic variability within weed species. We have been investigating variability of other traits in common cocklebur. This species is a very widespread and competitive weed, and has a complex taxonomic history. We used molecular fingerprinting to better understand genetic relationships among U.S. cocklebur accessions. These accessions were separated by our molecular markers into two main groups, which followed a north-south distribution. The significance of intraspecific variability in common cocklebur was documented in a field experiment, in which accessions were shown to differ in their potentials to reduce soybean yield.
Key words
Molecular Evolution, Molecular Systematics, Herbicide Mechanisms, Cytogenetics
Current Research Funding USDA-NRI, C-FAR, ISPOB