Ph.D. (Plant Pathology), Michigan State University, 1985
B.S. (Botany), Michigan State University, 1979
Areas of Interest
Plant Bacterial Pathogen Interactions
My current research is directed to determining the genome sequence of the bacterial ring rot pathogen, Clavibacter michiganensis subsp. sepedonicus (Cms) and applying that information in the seed industry. Cms can survive in plants for several generations without producing noticeable disease symptoms, posing a major challenge to potato seed certification and ring rot eradication. Though high-GC (Guanine-Cytosine) gram-positive bacteria such as Cms cause significant losses in several important U.S. crops, very little is known about their molecular determinants of pathogenicity. Therefore, my long-term research goal is to identify the basis for pathogenicity in Cms. Identifying the genes affecting pathogenicity could lead to a better understanding of how this pathogen persists in apparently healthy plants. It could also provide a rationale for practical methods of reducing or eliminating latent infections.
My other research objective is to reveal any concordances in pathogenicity among high-GC gram-positive plant and animal pathogens. Very little is known about the functions or genetic regulation of a large number of predicted proteins in the genomes of actinomycetes. Almost nothing is known about how phytopathogenic coryneform bacteria respond to a host’s environment or which particular bacterial proteins are required for disease development. It is also not known if any genes required for pathogenicity in plants share homology to similar functional genes in animals, as has been shown for several gram-negative animal and plant pathogens.
Science is not only knowledge, but is an ongoing activity where the application of this knowledge can help explain nature in a reproducible way.
This sentiment uttered by professor Linda Kinkel at the beginning of the Plant Pathology freshman seminar course “Antibiotics: Promise, Profits, and Pitfalls” set a precedent for a day of hands-on laboratory exercises where undergraduate students spent the day applying the teachings of Kinkel and fellow professor Carol Ishimaru on the scientific method by evaluating various antibiotics and learning about pharmaceutical drug discovery. The seminar focuses on providing a holistic perspective of antibiotics for freshman undergraduates across the University with topics ranging from antibiotics in the natural world, drug development and patent law, and media perceptions of antibiotics, in order to help the next generation of students develop scientific literacy and critical thinking skills.
One re-emerging and two new and emerging diseases that affect important crops in the state and the region are the current research focus of the Ishimaru Lab. These diseases include Goss’s wilt of corn, bacterial leaf streak on small grains, and bacterial soft rot of potato. In collaboration with Dr. Dean Malvick, Research and Extension Professor, our lab group continues to explore explanations for the re-emergence and spread of Goss’s leaf blight and wilt of maize in the U.S. and Canada. We have made significant advances in this research, but there is more progress that needs to be made. Ryan McNally, Post-Doctoral Research Associate, has succeeded in developing a highly sensitive and specific PCR assay for detecting the causal agent of Goss’s wilt, Clavibacter michiganensis subsp. nebraskensis (Cmn). The new assay was published in 2016 and has received rave reviews from diagnosticians. Ryan is also leading several investigative angles on the re-emergence story for Goss’s wilt. One hypothesis is that the pathogen has evolved to become more adapted to or virulent on current maize inbreds and hybrids. Ryan, Rebecca Curland (Research Fellow) and Blake Webster (Research Assistant) are working together to evaluate a large collection of historical and regional field isolates of Cmn. Blake detected the first reported association between geographic origin and genetic diversity within the Cmn population. In addition, Rebecca and Blake identified several avirulent isolates of Cmn within the collection. Ryan has obtained complete genome sequences of some of the avirulent isolates. He is currently comparing the genomes of virulent and avirulent strains to identify genomic elements associated with virulence in the pathogen.
Bacterial leaf streak (BLS) on small grains, caused by Xanthomonas translucens, has become a significant problem in the Upper Midwest in recent years. Rebecca and I continue to evaluate the genetic diversity of pathovars causing BLS on barley and wheat. Some of our current work builds on previous findings from collaborative projects with Dr. Ruth Dill-Macky (Professor, Small Grains Pathology) and other small grains breeders and pathologists. Through MLSA studies on X. translucens, Rebecca has found two major pathovars are present in the region, pv. translucens and pv. undulosa, with the former possessing the greater genetic diversity of the two. Rebecca has also shown that virulence of isolates varies significantly within each pathovar. She will soon know how much of the genetic variability documented at the regional scale is present in individual fields within the region. Our goal is to assist plant-breeding programs in developing improved resistance of small grains to BLS. We are grateful for funding from the Minnesota Small Grain Initiative that has supported our BLS studies.
A bacterial soft rot of potatoes is the other emerging disease that has captured our attention in the past two years. We’ve had the fun task of isolating pectolytic bacteria from rotten, smelly potatoes! The pathogen, Dickeya dianthicola, was first observed to cause devastating economic losses for potato growers in Maine in 2015. This newly introduced pathogen is a very aggressive type of soft rotting bacteria. Because potatoes are clonally propagated, the pathogen has spread quickly to other states through infected seed potato. We obtained funding from state, federal and commodity sources to conduct a survey of soft rot bacteria present in the Northern Plains. We have identified three new types that have not been previously reported in Minnesota or North Dakota. Although Dickeya was one of the types found, D. dianthicola has not become widely established yet in these states based on our results. Ryan, Rebecca, Blake and I have become the MLSA-arm of a USDA/ARS Public Partnership Potato Project. As such, we are evaluating the genetic diversity of soft rot isolates from Main, New York, Pennsylvania, Michigan, Wisconsin, Minnesota and North Dakota. The four of us, however, are working diligently to wrap up all of our lab and writing projects in anticipation of my full retirement in March 2019. As part of phased-out retirement, I am currently working on a 75% appointment which will transition to 25% in January 2019. This semester, I am enjoying teaching PlPa 8105 Plant Bacteriology and plan to teach it again during spring 2018.