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Kenneth B. Johnson

Kenneth B. Johnson obtained his B.S. degree in plant health technology in 1979 from the University of Minnesota and an 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 and continued as a postdoctoral associate and lecturer until 1988. Subsequently, he joined the faculty of the Department of Botany and Plant Pathology at Oregon State University, where he is an associate professor.

Dr. Johnson has distinguished himself as a productive member of APS, through outstanding, pioneering research on potato and deciduous tree fruit and nut crop diseases. His research focuses on the areas of quantitative epidemiology, integrated control, and application of epidemiological principles for enhancing biocontrol.

Dr. Johnson’s contributions to plant pathology began with his graduate work, which centered on understanding the mechanistic basis of pest- and disease-induced crop loss in potato. He not only developed a conceptual framework to study the effects of multiple pest/pathogens on potato, but also provided experimental data to support the concept. Prior to this work the effects of plant disease epidemics on crop productivity generally were studied with single pathogens/pests. Dr. Johnson hypothesized that pathogens/pests affect crop productivity either by reducing the photosynthetic area, in turn affecting solar radiation interception, or by interfering with radiation use efficiency. He demonstrated that early blight and Verticillium wilt reduce radiation interception by causing premature senescence of older leaf tissues and that feeding by the potato leafhopper reduces radiation use efficiency in photosynthetically active tissues, the latter of which exerted a greater net effect on crop yield. This information was coupled with a potato growth simulation model to study yield losses in different environments and with other variables.

In his current position, Dr. Johnson has made outstanding contributions on two host-pathosystems: eastern filbert blight of European hazelnut caused by Anisogramma anomala and fire blight of pear and apple caused by Erwinia amylovora. With colleagues, Dr. Johnson ascertained how and when A. anomala gains entry into a hazelnut tree and showed that only immature tissues near the apical meristem are susceptible to infection. He further determined optimal inoculum densities and conditions for infection and developed fungicide application schedules for immediate disease management. Dr. Johnson also has collaborated to develop resistant hazelnut clones and techniques to rapidly screen hazelnut for disease resistance. In fire blight research, Dr. Johnson studied efficiency of pollinator bees as vectors of bacterial antagonists of E. amylovora. The bees delivered the antagonists to sites on open blossoms where they suppressed epiphytic growth of E. amylovora, showing the potential for honey bees to disperse biocontrol bacteria in a manner compatible with conventional orchard management practices. Dr. Johnson and colleagues have examined the population dynamics of bacterial antagonists in antibiotic-sprayed and unsprayed orchards, showing that by delaying antibiotic sprays until 7 days after the application of the antagonists, their population can be maintained at high levels, paving the way for integration of chemical and biological approaches to fire blight management.

Dr. Johnson also developed a conceptual framework to study doseresponse relationships in biological control of plant disease. Because of the potential practical implications, his development of a theory defining epidemiological parameters that govern the efficacy of biological control of plant disease is a major breakthrough. His model states that the degree of disease control obtained with a biocontrol agent depends on the density of the agent, the density of the pathogen, how efficiently individual agents render units of the pathogen ineffective, and the proportion of the pathogen population potentially affected by the agent. Evaluation of these parameters for different host-pathosystems will clearly identify ways to improve the efficacy of biological control.

Dr. Johnson has been an outstanding teacher and faculty member in the Department of Botany and Plant Pathology at Oregon State University. He teaches graduate courses on plant pathology and disease management that are consistently rated highly by students. He has overseen the research of five M.S. and two Ph.D. students. Oregon State University’s College of Agriculture has recognized his achievements by conferring three awards: the Briskey Award for Faculty Excellence; the Oldfield/Jackman Team Award, recognizing his collaborative efforts; and the Savary Outstanding Young Faculty Member Award.

Dr. Johnson has served APS as member and chair of the Plant Disease Losses and Epidemiology committees, as a member of the Adhoc Committee for Plant Pathology 2000, and as associate and senior editor of Phytopathology. He also has been active in the IPPC Epidemiology Committee.