Evolutionary Arms Race

Scot H. Hulbert  
Evolutionary Arms Race

Scot Hulbert in greenhouseThe easiest and most efficient way to control serious losses to plant diseases is by planting disease resistant crop varieties. The development of such varieties is the ongoing work of plant breeders and cooperating pathologists. The biggest difficulty lies in the fact that plant pathogenic microbes evolve very rapidly. Most disease resistance genes function by recognizing some component of the pathogen and initiating defense responses.  Pathogen isolates that are able to lose or change the recognized component then become virulent on the variety because they are no longer recognized.  The process is essentially an evolutionary arms race, where breeders direct the evolution of crop varieties with new sources of resistance, and pathogens evolve to overcome these resistances. Pathogens, like cereal rusts, are particularly troublesome because they produce huge numbers of spores, increasing the likelihood that some will mutate to new forms. This makes breeding particularly challenging for crops like wheat that are grown on large acreages and thereby maintaining large pathogen populations. The resistance of some cultivars is more durable than others, remaining effective for many years in the field. Cultivars with durable resistance are apparently more difficult for pathogen populations to overcome.

Dr. Scot Hulbert is researching why some sources of resistance are more durable than others and looking for methods to identify or engineer durable resistance. One aspect of this work considers resistance genes that may function by other methods than recognizing a pathogen component. Another major focus is on determining what resistance genes are recognizing in cereal rust pathogens.  Most are thought to be effector proteins or molecules that these fungi insert into the plant cells they infect to help them extract nutrients or inhibit plant defenses.  His group has been supported by the USDA’s AFRI program to characterize cereal rust effectors. They have developed methods to silence individual effector genes in the rust fungi as they are growing in the plant.  Silenced effectors that interfere with the pathogenicity of the fungus are considered to be essential.  Resistance genes that recognize essential effectors are likely to provide more durable resistance since the pathogen can not easily lose them.  Since resistance genes are simply not available for most effectors, Hulbert’s group is also engineering resistance in wheat by expressing double stranded RNAs with homology to essential effectors to silence their expression.  Such resistance is expected to more durable than that mediated by conventional resistance genes.

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Contact Information
Scott Hulbert, Ph.D.
R. James Cook Endowed Chair for Cropping Systems Pathology
Crop and Soil Sciences

Washington State University
PO Box 646430
Johnson 307
Pullman, WA 99164-6430

Telephone: 509-335-3722
Fax: 509-335-8674
E-mail: scot_hulbert@wsu.edu

Scot H. Hulbert, Ph.D., Childhood experiences on a family farm in western Washington led Dr. Hulbert to pursue a B.S. degree at Washington State University. After deciding to pursue a career in research, he went to the University of California at Davis for a M.S. degree and a Ph.D. in genetics. He became interested in the evolution of plant-fungal interactions working with Richard Michelmore at Davis. He began working on diseases of cereal crops with Jeff Bennetzen as a post doc at Purdue in 1987. He joined the faculty in the Department of Plant Pathology at Kansas State University in 1989. He remained there for 17 years, serving as interim head of the plant pathology department from 2004-2006. In 2006, Dr. Hulbert accepted the R. J. Cook Endowed Chair for cropping systems pathology. In addition to research and teaching, he has contributed in a variety of public service roles and has been elected as a Fellow to the American Phytopathological Society and the American Association for the Advancement of Science.