Kenneth B. Johnson was born on June 17, 1957, in Minnesota. He obtained his B.S. degree in plant health technology in 1979 from the University of Minnesota and his M.S. degree in plant pathology from Oregon State University in 1982. He completed his Ph.D. degree in plant pathology in 1986 at the University of Minnesota, continued as a post-doctoral associate and lecturer until 1988, and then joined the faculty of the Department of Botany and Plant Pathology at Oregon State University, where he is now a professor.
The hallmark of Johnson’s career is his ability to address fundamental questions of importance in plant disease epidemiology while simultaneously using that information to develop improved management practices for growers of vegetable and tree crops. Johnson’s contributions to epidemiology and disease management began with his graduate studies, demonstrating the mechanistic basis for disease loss caused by multiple pests of potato. He developed both the methodology and empirical data to demonstrate that effects of both pathogens and insects could be explained via impacts on interception of solar radiation and radiation use efficiency. When Johnson began his faculty position in Oregon, eastern filbert blight threatened to eliminate the hazelnut crop in that state, which produces 99% of the U.S. crop. Johnson was part of an integrated team that developed an impressive set of studies on the basic biology of the pathogen, which is complicated by a 2-year disease cycle, and on the elucidation of the specific weather conditions that drive this cycle. This team developed a set of cultural, chemical, and breeding approaches that have allowed the hazelnut industry to thrive despite the threat from this devastating disease. A similar situation arose when blackberry rust was introduced into Oregon in 2005. Johnson, with colleagues, quickly developed an integrated management program founded on the underlying biology and epidemiology of the disease.
One of Johnson’s most significant scientific contributions was to develop the concept of “pathogen refuge” relative to the biological control of plant pathogens, which is one of the most important conceptual advances in theoretical epidemiology in recent decades. He demonstrated mathematically that even a small proportion of pathogen refuge can reduce the efficacy of biological control (by much larger amounts than other epidemiologists had previously recognized) and provided a mechanistic basis for understanding biocontrol failures. He used empirical data from the literature and field data he collected on crown gall of cherry to test these concepts. This conceptual approach sets the stage for understanding mechanisms behind successful biological control and envisioning approaches to minimize the pathogen refuge.
Many of Johnson’s contributions to plant pathology have arisen from his long-term, meticulous studies of the epiphytic microbiology of pear and apple flowers in relation to fire blight. Evaluation of populations in the field and use of innovative reporter genes to quantify microbial interactions on flower surfaces enabled Johnson and his colleagues at Oregon State University and USDA-ARS to determine that bees can be used to deliver biological control agents to the floral stigmata; antibiosis is an important mechanism of biological control of fire blight; apple and pear flowers represent an iron-limited environment; certain combinations of biocontrol agents are mechanistically incompatible, while mixtures or sequences composed of compatible biocontrol agents can suppress disease more effectively than individual agents; and Erwinia amylovora modifies the epiphytic habitat presented by the stigma through a pathogenesis-related process, which provides it an advantage over nonpathogenic bacteria residing on the same surface. While investigating these fundamental interactions, Johnson and his colleagues developed successful integrated control programs in response to increased susceptibility in deployed apple cultivars and in frequency of antibiotic resistance in the E. amylovora population. More recent work has resulted in the development of a rapid molecular scouting protocol that uses loop-mediated isothermal amplification (LAMP) to detect DNA of epiphytic E. amylovora on samples of pear and apple flowers, as well as to quantify seedborne Xanthomonas hortorum pv. carotae, an important pathogen of carrot seed crops in Oregon. Johnson and colleagues also have recently sequenced the genome of X. hortorum pv. carotae, demonstrating the potential for improved molecular diagnostics, and identified type III effectors that may allow for resistance gene-mediated control of the pathogen.
While running an internationally recognized research program, Johnson also has made substantial teaching contributions. He taught introductory plant pathology at both the graduate and undergraduate levels at Oregon State University and currently teaches a combined undergraduate/graduate course. This course continues to grow in popularity and now serves 80–100 students annually. He has trained 13 graduate students and advises 12–15 undergraduate botany majors annually.
Johnson has provided significant service to his department and his profession. He has served on and/or chaired most of the important committees within his department and has served on several important committees at the college level. He has served APS as associate editor and senior editor of Phytopathology, senior editor of Plant Health Instructor, member and chair of both the Epidemiology Committee and the Disease Losses Committee, and member of the Phyllosphere Microbiology, Strategic Planning, and Plant Pathology 2000 Committees. He has been a member of the Epidemiology Committee of the International Society for Plant Pathology and active in organizing scientific conferences internationally. He has served on an impressive number of grant panels of both fundamental and applied nature and is a popular speaker at both scientific and grower meetings. He previously received the Ciba Geigy and Lee Hutchins Awards from APS and several research awards from Oregon State University.
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