Dr. Richard D. Berger, Emeritus Professor of Plant Pathology at the University of Florida (UF), passed away on December 22, 2011, after a long illness. His colleagues and former students remember him as a friendly, quiet and dedicated researcher and teacher, with a unique sense of humor and a tremendous historical knowledge of the development of epidemiological concepts and applications. Dr. Berger voiced and published many original, innovative and sometimes controversial ideas about temporal and spatial dynamics of plant diseases. He trained six M.S. and eight PhD students the principles and practice of plant disease epidemiology in addition to teaching an introductory course in Plant Disease Control and a course in Epidemiology at the graduate level.
Dr. Berger was born in Pennsylvania in 1934, grew up on a farm, and received his B.S. degree from Kutztown State College, PA, in 1955. He then served in the U.S. Army as research assistant doing research on rice blast in the biological warfare laboratories in Frederick, MD. There, he developed an interest in and understanding of plant disease epidemiology, so that he continued with graduate studies in Plant Pathology at the University of Wisconsin, where he earned the PhD degree in 1962. His first position in Plant Pathology was that of Extension Plant Pathologist at the Pennsylvania State University. Next, he became assistant and later associate professor at the Everglades Research and Education Center of UF in Belle Glade, Fl. In 1976, he and his family moved to the main campus of UF in Gainesville, Fl., where he taught the epidemiology course, maintained a successful research program, and mentored graduate students for many years. An interest unrelated to epidemiology was his fascination of Cercospora taxonomy. For a few years, Dr. Berger was also the interim Department Chair for the Department of Plant Pathology.
Dr. Berger retired in 2003, but continued to teach epidemiology until 2006.
Dr. Berger was an active member of the American Phytopathological Society, serving as Chair or member of the Epidemiology, the IPM and the Crop Loss Committees. He was also a member of the Florida State Horticultural Society and of the American Peanut Research and Education Association. He was Senior and Associate Editor of Phytopathology, Assigning and Senior Editor of Plant Disease, Associate Editor of Phytoprotection, and served on the Editorial Committee of the Annual Review of Phytopathology.
He attended numerous scientific meetings worldwide and was a regular participant in the International Epidemiology Workshops. He also gave many invited presentations at various conferences. Dr. Berger spent several study leaves abroad, among others in the Netherlands, Brazil, Puerto Rico and Mexico. For these tremendous contributions Dr. Berger received two awards from horticultural organizations in Florida and two awards (Campbell award and Fellow award) from the American Phytopathological Society.
Contributions to Science
Dr. Berger’s research interest was in quantitative epidemiology, particularly the intensification of disease in time and space. He worked on many pathosystems, including leaf spots on beans, soybeans, celery, citrus, roses, turf grass, sweet corn and oats, root and bulb pathogens on onions or garlic to weed pathogens that could be used as biological control agents. Dr. Berger and his graduate students developed models and simulators to help interpret the peculiarities of natural epidemics, and these models were used to devise ways to better manage plant diseases. They used a wide array of experimental techniques, including electronic probes to measure micro- and macroclimate variables, light interception, infra-red reflection, leaf area meters and video imagery to assess effects of the environment on disease development and the amount of host stress caused by disease and other factors.
Dr. Berger published about 100 scientific papers, mostly in APS journals. His most important contributions to epidemiology were: improved disease assessments by partitioning the crop canopy and designing interpolative disease rating scales (1973); the development of disease forecasting systems for early blight on celery and Northern leaf blight on corn, widely used by growers (1973-1976); prediction of final disease and crop loss from average epidemic rates (1974); the realization that disease develops in temporal ‘waves’ at the beginning of the epidemic, which can only be observed when observations are made daily (1975); utilization of isopaths to describe the spread of plant diseases in time and space (1979); demonstration of the superiority of the Gompertz equation over the logistic equation for many disease progress curves (1981); coupling of models for pest and disease development to growth simulators to predict yield loss (1983); the development of a general model for disease progress with functions for variable latency and lesion expansion on growing host plants (1985); development, with Paul Waggoner, of the concepts of healthy leaf area duration (HAD) and healthy leaf area absorption (HAA) , the latter being the integration of the incident insolation absorbed by the healthy leaf area over the season, to predict crop yield (1987 and 1995); the development of a simulation model for bean rust (1995); the importance of lesion expansion for epidemic development, especially in (sub)tropical climates (1997); introduction of the area under the disease gradient curve (AUDGC) as alternative to fitting various models to disease gradients (1999); modification of the HAA concept to photosynthesizing leaf area index absorption (PAA) to account for large ‘virtual lesion’ areas (2001); and the realization that a biotrophic pathogen has a less damaging effect on physiological processes of the remaining green leaf area than a hemibiotrophic pathogen (2002).
The later contributions resulted from collaborative research with Brazilian epidemiologists (L. Amorim, R.B. Bassanezi, A. Bergamin and L.A. Maffia). In addition to his Brazilian colleagues, Dr. Berger had a wide network of other collaborators, in particular, in Germany (B. Hau, G.E. Weber and J. Kranz), the Netherlands (J.C. Zadoks), and the U.S. (P. Waggoner). In Dr. Berger’s own words: “International projects provide an added stimulus to study epidemiology under different sets of host-pathogen-environmental conditions.”
Contributions to teaching
Dr. Berger developed and taught primarily the graduate course "Epidemiology of Plant Disease". This course consisted of lectures on the theory of epidemiology, various computer exercises, and also hands-on laboratory and field sections, including disease assessment, quantification of inoculum and inoculation of plants, and monitoring a field epidemic in space and time. Students often thanked him for the lessons learned in the field plots as the most valuable part of their training in plant pathology. Through computer exercises the students learned sampling techniques, analysis of experimental data, curve fitting of epidemics in space and time, and simulation modeling. The students got acquainted with classical simulation models like EPIDEM of P. Waggoner as well as Dr. Berger’s own model CERCOS (for Cercospora blight on celery). His lectures reflected his research interests next to giving an overview of epidemiological concepts. For example, he showed students that disease progress occurs in waves in the early stages of epidemic development. [I remember vividly that Dr. Berger presented a lecture on this topic at Wageningen University, when I was an M.S. student in the 1970s!!]. He also discussed the controversy surrounding the relationship between inoculum density and disease incidence (ID:DI) based on the rhizosphere-rhizoplane models presented by R. Baker (1967 and 1972). To quote Dr. Berger: “There has been controversy about the “I” and the “D” in inoculum density AND the “D” and the “I” in disease intensity. The only part of the ID:DI relationship that was non-controversial was the colon “:” !!”. Other lecture topics included spatial distribution and spread, disease forecasting, components of resistance and gene deployment; and finally, systems analysis, modeling, yield and crop loss. Dr. Berger summarized his approach to teaching as follows: “This systems philosophy permeates most of my activities. It has really changed the way how I look at plant pathological problems. Before my indoctrination, I visualized our science as thousands of bits and pieces, unique for every pathosystem. Now, I look for patterns, generalizations, commonalities, etc.; the holistic view.”
Dr. Berger is missed by epidemiologists worldwide, plant pathologists in the USA, and colleagues, students and growers in Florida. However, he left behind an important legacy of theoretical concepts, practical information and excellent lecture notes, which will be used for many years to come.
Dr. Berger is survived by his wife Joyce, son Dan and daughter Tina, a sister and two brothers, and four grandchildren.
Author: Ariena van Bruggen, professor of plant disease epidemiology, Dept. of Plant Pathology and Emerging Pathogens Institute, University of Florida, Gainesville, FL. With special thanks to Larry Madden and Terry Davoli for corrections in the text.