Dr. Joyce Loper is a research plant pathologist at the USDA-ARS Horticultural Crops Laboratory located at Corvallis, OR, and a professor (courtesy) in the Department of Botany and Plant Pathology at Oregon State University. She joined ARS in 1985 as a research microbiologist with the Soilborne Diseases Laboratory in Beltsville, MD, and moved to Corvallis in 1987. Prior to joining the USDA, she served as a research scientist in the Biological Control Program of the Biotechnology Group of Chevron Chemical Company in Richmond, CA, from 1983 to 1985. As a native Californian, Joyce grew up in the San Francisco Bay area and obtained her B.S. degree in biology and her M.S. degree in plant pathology at the University of California-Davis before moving to Berkeley to obtain her Ph.D. degree in plant pathology working with Dr. Milton Schroth on the ecology of rhizosphere bacteria in 1983.
Dr. Loper is well known for her research involving the ecology of rhizosphere bacteria, with a special emphasis on biological control. Early in her career, Dr. Loper conducted research on the role of IAA production by rhizosphere bacteria on root development. In a seminal study, Dr. Loper showed how bacterial IAA production is a quantitative trait; because roots respond both positively and negatively to exogenous IAA, those bacteria that stimulated root growth produced only modest amounts of IAA, whereas strains producing higher amounts were inhibitory. This study revealed the complexity of such bacterial–root interactions and brought synthesis to a complicated literature. The work has proved useful in developing rational screens for beneficial bacteria.
Dr. Loper is perhaps most known for her detailed analysis of how iron-sequestering agents, called siderophores and produced by Pseudomonas spp. in the rhizosphere, affect iron availability to plant pathogens, leading to biological control of disease. She first genetically blocked siderophore production in mutant strains to demonstrate that these molecules contribute to a substantial part of the antagonistic effect toward pathogens such as Pythium ultimum and Fusarium oxysporum. She did more detailed analysis of the interactions between Pseudomonas biocontrol strains and plant pathogens using innovative molecular genetic techniques. She demonstrated that strains of Erwinia carotovora that were not well controlled by Pseudomonas isolates harbored genes for production of high-affinity iron uptake systems that made them insensitive to the “weaker” siderophores produced by Pseudomonas biocontrol strains. She has cloned and characterized many of the genes that are involved in siderophore production and regulation in various bacteria in natural habitats. Her group was among the first in the world to apply molecular genetic approaches to study bacterial habitats in situ by employing “biological sensors” consisting of iron-responsive promoters linked to an ice nucleation reporter gene. She has been able to show clearly that iron availability to microbes on roots varies greatly as a function of root age, soil type, plant species, and presence of other siderophore-producing bacteria. These landmark studies are at the forefront of microbial ecology and demonstrate how research in plant pathology can contribute to the broader field of microbiology. Thus, she has been able to greatly clarify the complexities of microbial iron nutrition.
Dr. Loper’s more recent work has focused on the genetics of antifungal compound production by plant-associated bacteria, particularly Pseudomonas fluorescens. She is a world leader in the use of molecular biology for studying biological control. Not only has she cloned and characterized the structural genes for several important antibiotics such as pyoluteorin and other polyketide antibiotics, but also she has made major advances in our understanding of how production of antibiotics and other antimicrobial compounds are coordinately regulated. She has identified alternative sigma factors and global regulators in Pseudomonas fluorescens and shown their importance in directing important aspects of rhizosphere interactions such as stress responses and secondary metabolite production. Dr. Loper has greatly enhanced our appreciation for the complexity of antibiosis in biocontrol organisms. She is clearly a world leader in the field of molecular microbial ecology as it applies to plant pathology, evidenced by more than 60 invited lectures she has made to national and international audiences.
Dr. Loper has an outstanding record of professional service, particularly to the American Phytopathological Society. She served on the Biological Control and Bacteriology Committees as secretary- treasurer for the APS Pacific Division from 1990 to 1993 and as a senior editor for APS Press from 1990 to 1993. She also codeveloped a slide set on biological control of plant disease for APS Press that has gained wide circulation as an important teaching tool for plant pathology and pest management courses around the world. Dr. Loper served as APS councilor-at-large from 1997 to 2000. She was selected to represent plant pathologists on the National Research Council Board on Agriculture panel that developed a position document on “ecologically based pest management.” This important document will guide pest management research in the future, and Dr. Loper’s insight will benefit many plant pathologists as we enter a new era of agricultural research priorities.
Dr. Loper has also served the field of plant pathology in many other ways, such as on the editorial committees of the Annual Review of Phytopathology (1996 to 2006) and European Journal of Plant Pathology, as an associate editor of Molecular Plant- Microbe Interactions, and on advisory boards for the NSF Center for Microbial Ecology, EPA-FIFRA, National Academy of Sciences, as well as serving on a USDA-NRI biological control grants panel. She has served the USDA as well as Oregon State University by her participation in numerous administrative and advisory committees. She has been particularly active in presenting lectures around the country as well as participating in workshops and symposia at Oregon State University on topics related to the role of women in science. It is clear from the description of her many accomplishments presented above that she is an outstanding role model for young scientists. a
