The society grants this honor to a current APS member in recognition of distinguished contributions to plant pathology or to The American Phytopathological Society. Fellow recognition is based on significant contributions in one or more of the following areas: original research, teaching, administration, professional and public service, and/or extension and outreach.
Dr. Steven J. Klosterman was born in St Marys, Ohio, and earned his B.S. in biology from Wright State University (1996) and a Ph.D. (2002) in plant pathology from Washington State University. Following a postdoctoral fellowship at the University of Georgia, he joined the USDA ARS in 2006, in Salinas, California, where he is currently a Research Molecular Biologist.
Dr. Klosterman is known for his stellar work on both Verticillium wilt and downy mildews. Just as he transitioned from his postdoctoral project into the ARS position, he was drafted to lead an international team of collaborators that secured USDA/NSF funding to decipher and characterize the first genomes of Verticillium dahliae and V. alfalfae. This research led to new theories regarding the genetics of pathogenesis and niche adaptation of Verticillium spp. into the host xylem. He identified four lineage-specific (LS) regions or “genome islands” on two chromosomes in V. dahliae, and hypothesized that plasticity and transposon-enrichment within these regions has driven niche adaptation and host range expansion. It also provided the first evidence of cross-kingdom horizontal gene transfer from bacteria to Verticillium spp. The resulting publication in PLoS Pathogens has been cited >550 times and became a cornerstone of all subsequent genomic studies on V. dahliae. The resulting insights and genome resources have been used worldwide to identify genetic components of Verticillium spp. and virulence.
Dr. Klosterman then elucidated the genetic bases for production of microsclerotia and melanin in V. dahliae. The mechanisms underpinning melanin production presented an intriguing opportunity since fungal dihydroxynaphthalene (DHN) melanin synthesis was originally characterized in V. dahliae in the 1960s and 1970s. Armed with the newly generated genome resources, he identified a gene cluster responsible for pigment production in V. dahliae and showed that two of the genes within this cluster are critical for survival against UV irradiation and elevated temperatures. He was a pioneer in directing high-throughput RNA-sequencing to identify genes differentially expressed during microsclerotial development and collaborated on the development of a widely used technique to more efficiently elucidate the function of V. dahliae genes governing survival, morphogenesis, and virulence. These studies were instrumental in understanding the role of DHN melanin in survival and virulence of V. dahliae. His collaborative work subsequently clarified the genetic basis of the defoliation phenotype and the avirulence gene marker for race 3 of V. dahliae. These findings are used to discern V. dahliae defoliating from nondefoliating, and define race pathotypes worldwide. Dr. Klosterman played a major mentoring role with collaborators from the Beijing Forestry University, Chinese Academy of Agricultural Sciences (CAAS), and Northwest A & F University. For his mentoring role, he was appointed as Distinguished International Supervisor and Distinguished Professor by CAAS.
While pursuing these seminal studies on V. dahliae, Dr. Klosterman also began researching downy mildews of spinach and lettuce caused by Peronospora effusa and Bremia lactucae, respectively. Even though most of his research until then was in the laboratory and greenhouse, Dr. Klosterman reoriented his program for field research. He acquired these skills quickly and achieved uncommon expertise. Using a clever combination of aerobiology and molecular quantification, he demonstrated the year-round inoculum availability for both pathogens in the Salinas Valley of California. Though these pathogens are nearly universally present, quantification from spore trap samples revealed times of increased spore dispersal. This vital information was then used to schedule preventative fungicide applications.
Germination of the oospores of P. effusa was last described in the literature in 1919 by the Swedish scientist Dr. Jakob Eriksson. Dr. Klosterman replicated the finding of oospore germination in 2019 and demonstrated the role of seed and soilborne oospores as primary inoculum for initiating spinach downy mildew. Additionally, he developed accurate and sensitive quantitative PCR assays to consistently detect V. dahliae levels in commercial spinach seed lots by incorporating an innovative technology to homogenize the recalcitrant spinach seeds. He directed a workshop so that all seed producers and marketers employ this method. His work to detect latent infections of P. effusa in spinach leaves is novel and has also been adapted to determine whether to harvest crops early or to apply fungicides on conventional spinach production fields. He also quantified seedborne oospores of P. effusa in commercial spinach seed lots and developed methods to test their viability. The industry currently uses these methods to limit the oospores on seeds.
Dr. Klosterman’s work in the epidemiology/diagnosis of spinach downy mildew led to keynote addresses at International Spinach Conferences. His leadership of Verticillium comparative genomics garnered invitations as a plenary speaker at the International Symposium on Verticillium (IVS) in Corfu, Greece, keynote presentations at the IVS Symposium in Ljubljana, Slovenia and the Chair of the Dez Barbara Memorial Session at the IVS in Gottingen, Germany. He was invited to write three different reviews in the Annual Review of Phytopathology. He has hosted several outstanding visiting scientists in his laboratory.
Dr. Klosterman has been the recipient of many competitive grants totaling $5.4 million to support his research on Verticillium wilt and downy mildew. In all, he has 114 peer-reviewed publications.
As a staunch advocate of APS, Dr. Klosterman has been a member or Chair of several APS subject matter committees, has co-organized eight special sessions at APS meetings, and has served as an Associate and Senior Editor in Phytopathology. His exemplary service as the inaugural Senior Editor for Reviews in Phytopathology led to monthly reviews as a regular feature, a first for the journal. He has served on the APS journals task force and played a critical role in the establishment of the new, niche-filling APS journal PhytoFrontiers, where he served as the inaugural Associate Editor-in-Chief and then as its Editor-in-Chief, supervising an Editorial Board of 70 Senior and 27 Associate Editors. PhytoFrontiers is an established APS journal now. He has also served as interim Research Leader of the ARS Unit in Salinas. His contributions to the science/mission of plant pathology, including solving problems for growers and industries, and a record of stellar service to APS eminently qualify Dr. Klosterman as an APS Fellow.
