Tim R. Gottwald was born in Lynwood, CA. He received a B.S. degree in botany from California State University, Long Beach, in 1975 and a Ph.D. degree from Oregon State University in 1980. He joined the USDAARS in 1980 as a research plant pathologist. For his Ph.D., Dr. Gottwald worked on eastern filbert blight in Oregon and Washington. This work led to the description of taxonomic variations in developmental schemes in the family Diaporthaceae. He described the cause of eastern filbert blight and the spread within a tree, between trees, and between orchards. Dr. Gottwald worked at the ARS Fruit and Tree Nut Research Laboratory in Bryon, GA, during his first 5 years with the USDA. His work focused on the epidemiology of fungal pathogens of pecan and peach and on the biocontrol of arboreal insect pests by entomopathogenic fungi. His significant findings that the pecan scab causal organism (Cladosporium caryigenum) was dispersed by air movement as well as by splash dispersal helped to explain the long-distance spread within and between orchards. He reclassified the scab fungus to Cladosporium caryigenum comb. novo sp. In cooperative research, he demonstrated that epizootics of the fungal parasite of insects, Beauvaria bassiana, significantly suppressed populations of the troublesome pecan weevil. He cooperated in a study to determine the effect of several diseases on the photosynthesis of pecan leaves and fruit. They found that powdery mildew was mostly a cosmetic disease and, therefore, intense measures to control mildew were not necessary. Additionally, he found that some pesticides in the standard spray schedule were largely cosmetic after a certain point in the season. His work with pecan spray programs resulted in reduced spray costs in the southeastern United States and less exposure of the environment to pesticides. Dr. Gottwald and coworkers transmitted a phytoplasma in pecans for the first time, proving that it was the causal agent of bunch disease.
At Byron, Dr. Gottwald used his engineering skills to develop a drone aircraft with an 8-foot wingspan to trap and monitor aerial populations of fungal spores and insects. He developed a new type of particle trap for this plane. For the biocontrol of insects, the plane was used to disperse small quantities of bacterial cells and fungal spores over large areas of crop canopies, which previously could not be done with conventional equipment. The project generated considerable attention from the media and even some interest from the Pest Management Board of the United States Army.
Over the years, Dr. Gottwald also developed a series of devices culminating in a sophisticated, computer-controlled, environmental chamber to study aerial release of spores of ascomycetes and hyphomycetes. The effects of relative humidity, temperature, red and infrared light, leaf wetness, vibration, and rain events can be studied with a controller and data acquisition system, all managed through computer software he developed. Dr. Gottwald also developed a noninvasive, stomatal-inoculation apparatus to evaluate different strains of bacterial pathogens on citrus. With this devise, he found that infection was not related to stomatal size, as previously suspected, and was able to demonstrate infection with single bacterial cells.
In 1985, the USDA moved Dr. Gottwald to the U.S. Horticultural Research Laboratory in Orlando, FL, to address an emerging citrus canker problem. He developed an aggressive, multifaceted research program in collaboration with other scientists. Since citrus canker was a quarantined pathogen, a great deal of innovation was required to establish field plots needed to determine the relative pathogenicity of different canker strains and their epidemiology.
Insight on movement of true citrus canker bacterium in citrus groves and nurseries was obtained through studies in Argentina. In research plots in simulated citrus nurseries near Beltsville, MD, and in north Florida, he showed that citrus bacterial spot (CBS) was not an aggressive pathogen and was unlikely to persist in commercial plantings. Dr. Gottwald and cooperators used a detached leaf assay to catalog strains of CBS for pathogenicity and to define the susceptibility of commercial citrus cultivars, rootstocks, and breeding lines to CBS and citrus canker strains. He also studied the interaction of numerous citrus cultivars and citrus relatives with the pathogens and the propagation and survival of the bacteria in situ. Dr. Gottwald used disease expression to define differences among CBS strains and between CBS and citrus canker. These findings prompted the reclassification of the CBS pathogen as a distinct pathovar and led to its deregulation by state and federal agencies. It is now considered a minor disease. His collaborative work on the etiology, epidemiology, and biology of citrus canker and CBS and the differences between these two diseases was recognized by his receipt of the Lee M. Hutchins Award in 1994 with Dr. Jim Graham. A recent outbreak of citrus canker in urban Miami has spurred new work on dispersal of citrus canker in an urban situation, in which interactions with the recently established Asian citrus leaf miner, human factors, and tropical weather events all play a role. He backtracked the spread of bacterial canker on dooryard citrus in Miami and determined that the spread of canker was primarily during major storms, spreading up to 7 miles in a single storm. Dr. Gottwald showed that windbreaks were superior to chemical or other control strategies to reduce the spread of the disease. He found that the spread of canker in citrus could be substantially slowed by the use of windbreaks and copper bactericides and that surfactants used in traditional spray programs induced stomatal flooding in citrus, enhanced infection, and intensified epidemics of citrus bacterial diseases. Innovative spatiotemporal analyses applied by Dr. Gottwald are currently being used by the Citrus Canker Eradication Agency and by the USDA/APHIS to guide eradication efforts.
Research on citrus canker stimulated Dr. Gottwald’s interest in the etiology and epidemiology of other citrus pathogens exotic to U.S. agriculture, including severe strains of Citrus tristeza virus (CTV), citrus huanglungbing (greening), and citrus variegated chlorosis. In collaboration with scientists from the United States, Taiwan, Spain, Costa Rica, Nicaragua, and the Dominican Republic, Dr. Gottwald developed the first detailed information on the spatiotemporal dynamics of CTV movement in the field. These studies contrasted the differences in disease dynamics of two CTV pathosystems characterized by the presence of different predominant aphid vectors.
In collaboration with Dr. Gareth Hughes, University of Edinburgh, Scotland, Dr. Gottwald determined that the field sampling methodologies to determine CTV incidence were inadequate. They developed a new sampling strategy for CTV based on sampling at one spatial hierarchy (group level) to predict the incidence at the individual plant level. The results of these investigations have been used by the Central California Tristeza Eradication and other programs to revise approaches on surveys for, and eradication of, CTV. Dr. Gottwald also developed quantitative models to estimate the progress of citrus greening. He demonstrated the acceleration of greening epidemics when contaminated nursery stock was used and described the dynamics of disease clustering in citrus groves as influenced by the movement of the psyllid vector. His research program also includes work on domestic diseases of citrus including citrus scab, greasy spot, and melanose. Dr. Gottwald is now considered one of the leading international authorities on spatiotemporal analyses of arboreal epidemics. He and collaborators developed software, LCORII, to perform complex, spatial, autocorrelation analyses. This software has been requested by more than 100 epidemiologists worldwide.
Dr. Gottwald has served APS as a senior editor of APS Press, as an associate editor of Phytopathology, and through participation on numerous committees. He has published over 130 papers and 80 abstracts and has been an invited participant in numerous national and international conferences and workshops.