Donald Thomas Wicklow, 1940–2021: Distinguished fungal ecologist and model scientist

For those of us who were fortunate enough to know him, Don Wicklow will be fondly remembered as a good-humored, intellectually adventurous person, a model scientist and colleague who overflowed with ideas and boundless energy, and a genuine lover of all things mycological. Don’s contagious enthusiasm, his congenial can-do attitude, and his encyclopedic knowledge of fungi made him not only an invaluable collaborator, but a pleasure to work with and an outstanding representative of the mycological community. In short, Don was one of a kind; science needs more remarkable people like him.

Donald Thomas Wicklow (FIGS. 1–4) was born 22 June 1940, in San Francisco, California, and died on 21 November 2021. After graduating from Abraham Lincoln High School in San Francisco in 1957, he earned B.A. (1962) and M.A. (1964) degrees in biology from San Francisco State College, where he lettered in three varsity sports (cross country, track, and soccer) and was president of the Sigma Pi Sigma social fraternity (Anonymous 2021). His initial studies as a master’s degree student with Harry D. Thiers (Thiers and Halling 2003) at San Francisco State focused on aspects of the ecology of soil fungi (Wicklow 1964). His subsequent Ph.D. research under the direction of W. F. Whittingham at the University of Wisconsin (Wicklow 1971) centered on forest microfungi. Inspired by these early studies, Don embarked on a lifelong mission, spanning five decades, to integrate mycological data with ecological theory. He continued his studies as a member of the faculty of the Department of Biology at the University of Pittsburgh, beginning in 1970. His efforts there reflected a burgeoning interest in fungal ecology, as he expanded his focus to other mycological groups, including coprophilous and carbonicolous fungi (Wicklow and Hirschfield 1979; Wicklow and Zak 1979). In 1977, he moved to the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS) Northern Regional Research Center (now the National Center for Agricultural Utilization Research, NCAUR) in Peoria, Illinois, to fill the position vacated by Dorothy Fennell (Hesseltine 1979; Raper and Fennell 1965) as curator of the Aspergilli and Penicilli in the ARS NRRL Culture Collection.

Figure 1. Don Wicklow inspecting a pure culture of Sarcocladium zeae, a protective endophyte of corn. Photograph by Scott Bauer, courtesy of the USDA Agricultural Research Service. USDA is an equal opportunity provider and employer.

Figure 2. Don Wicklow points out tan-colored sclerotia produced by a fungal culture grown on cereal grains. Photograph by Keith Weller, courtesy of the USDA Agricultural Research Service. USDA is an equal opportunity provider and employer.

Figure 3. Meredith Blackwell, George Carroll, and Don Wicklow (left to right). George invited Don and Meredith to speak at a class event, “Fungal-insect interactions: a mini-symposium,” at the University of Oregon, April–May 1987. Photograph courtesy of Meredith Blackwell.

Figure 4. Don Wicklow (back row, second from left) at his retirement home in Waukesha, Wisconsin, with family (2013). Photograph courtesy of Brandon Wicklow.

After several years in that role, he transferred to the Mycotoxin Research group at the NCAUR and spent the remainder of his professional career there, retiring in 2014. His efforts during that span focused on understanding the ecology of mycotoxin-producing fungi, with an overarching goal of controlling toxin contamination of cereal crops. Exploration of interspecific competition among fungi and other organisms was a constant theme throughout his career. Don made many significant research contributions in his studies of mycotoxigenic fungi, especially those that produce the carcinogenic aflatoxins that threaten global food safety, human health, and crop production. Important examples include elucidating the role of sclerotia in the disease cycle of aflatoxigenic Aspergillus flavus in corn (Wicklow 1987, 1989), understanding competitive interactions between A. flavus and protective endophytes that augment plant defense in corn (Wicklow et al. 1980), recognizing the significance of certain insects as vectors of A. flavus to corn (Lussenhop and Wicklow 1990), and determining how competing non-aflatoxigenic strains of A. flavus inhibit aflatoxin production (Wicklow et al. 2003). Additionally, through collaboration with coauthor Naumann, Don contributed to the molecular understanding of corn ear rots. This work showed that the corn ChitA protein is truncated by proteases secreted by diverse ear rot pathogens, including Cochliobolus carbonum (Naumann et al. 2009), Stenocarpella maydis (Naumann and Wicklow 2010), and mycotoxigenic Fusarium species (Naumann et al. 2011). Fueled by Don’s enthusiasm and knack for experimental design, this molecular interaction was shown to also be involved in fungal diseases of mustard plants, an indication that it is a general strategy used by fungi that cause plant disease (Naumann and Wicklow 2013).

In parallel with these studies, Don made other valuable contributions with broad significance. Much of Don’s work forecast the extraordinary biosynthetic complexity encoded in Aspergillus, Chaetomium, and coprophilous fungal genomes and our current understanding of context-dependent expression of secondary metabolism. Many researchers recognize likely connections between chemistry and ecology, but Don’s hypothesis-driven work involved efforts to actually test the application of ecological ideas in specific cases. Don’s encyclopedic knowledge of fungal lifecycle strategies led to a fruitful 30-year collaboration with coauthor Gloer, a natural products chemist, based on the rational selection of candidate fungi for chemical exploration (Wicklow et al. 1988). This collaboration, funded for nearly 25 years through a series of competitive grants from the U.S. National Science Foundation (NSF) aptly entitled “Chemistry of Fungal Antagonism and Defense,” led to discovery and characterization of over 100 novel fungal metabolites with biological activities that were targeted based at least in part on ecological considerations (Gloer 1995, 2007). His selection of fungal species for chemical investigation was based on examination of fungi with lifecycles that would naturally benefit from the production of metabolites that could afford protection from insects, inhibit competitor growth, or foster invasion or colonization of other fungi. A short list includes an array of metabolites concentrated in fungal sclerotia and ascomata with antifeedant and insecticidal activities against insect fungivores and crop pests (Gloer et al. 1988; Wang et al. 1995; Whyte et al. 1996), novel antifungal metabolites from mycoparasitic or fungicolous fungi that attack and colonize A. flavus sclerotia and other long-lived fungal structures (Angawi et al. 2003; Joshi et al. 1999; Mudur et al. 2006; Wicklow et al. 1998), compounds produced by fungi with antifungal activity against competitor fungi (Gloer 2007), production by the common corn endophyte Sarcocladium zeae of broad-spectrum antibiotics effective against corn pathogens (Wicklow and Poling 2009; Wicklow et al. 2005), and production of a potent selective inhibitor of a key heat shock protein (Hsp90) by a corn pathogen that might play a role in the disease process by subduing plant defense responses (Wicklow et al. 2009). The success and novelty of this long-term collaborative enterprise was recognized by multiple grant renewals, including an extension for Special Creativity from NSF in the 1990s, and it only ended upon Don’s retirement. Collectively, this research strongly supported the concept that secondary metabolites are commonly involved in interspecies antagonism and chemical defense among fungi and led to the identification of novel natural products from several different fungal niche groups with activities ranging from insecticidal effects to antifungal activity against medically relevant fungi. Although these kinds of results are fundamentally significant, and some of the new chemistry encountered could ultimately have practical utility, they also have relevance in a broader sense. For example, most screening programs in microbial natural product chemistry are driven strictly by bioassays, with little or no interest in exploring possible ecological implications of the chemistry they encounter. By contrast, this collaborative work showed that observations in fungal ecology can enable rational selection of candidate fungi for chemical exploration, leading to discovery of new fungal chemistry with targeted types of biological activities. This kind of research at the interface of chemistry and mycology is all too rare and provides tantalizing glimpses into natural phenomena that are still not well understood.

Three decades after directing Don’s M.S. studies, and after his retirement, Harry Thiers worked with Don at the NCAUR collecting fungicolous and mycoparasitic fungi in central Illinois that were screened for biologically active compounds. This project led to the discovery of a new mycophilic species of Pencillium, assigned the name P. thiersii (Peterson et al. 2004), that produces new compounds that they named thiersinines, along with other novel antiinsectan diterpenoids (Li et al. 2002, 2005). Harry likely had a profound impact on Don’s career because they were remarkably similar in their enthusiastic approach to and deep love of mycological research. Don was quite pleased to work once again with his former advisor and to honor his contributions.

Don demonstrated outstanding, consistent productivity over the course of his nearly 50-year research career and made contributions in a wide array of different aspects of mycology, ranging from the applied and practical to the fundamental and philosophical. This is readily evident from his publication record, which is impressive in both number and scope. Don’s great legacy of scholarly work is represented by over 200 peer-reviewed publications, 24 book chapters, 12 patents, and 36 invited presentations at national or international meetings on subjects pertaining to fungal ecology, plant pathology, and mycotoxins. His research over the years was supported in large part by the USDA ARS’s mycotoxin research program at the NCAUR, and by funding from the National Science Foundation (1973–1984; 1989–2013), the National Institutes of Health (2004–2008), Biotechnology Research and Development Corporation (1990–2002), and other sources. Alongside these many research achievements, Don co-edited “The Fungal Community: Its Organization and Role in the Ecosystem” (1981) and a subsequent second edition (1992) with George Carroll of the University of Oregon (Carroll and Wicklow 1992; Wicklow and Carroll 1981). These influential, ground-breaking volumes traversed many topics related to fungal ecology and were innovative in their efforts to interface mycological data with ecological theory. Their stated objective was to gather data on ecological studies with fungi into a coherent whole within the broader framework of general ecology. The series they started has continued as the field has progressed with more recent further editions (Dighton and White 2017; Dighton et al. 2005).

Don was very active in the Mycological Society of America (MSA), from 1964 to the time of his death in 2021, and was a generous supporter of the travel fund. He received the C. J. Alexopoulous Prize from the MSA in 1980, awarded annually to an outstanding mycologist early in their career. The same year, he was elected to a term as MSA Councilor for Ecology-Pathology (1980–1983) and then served as a member of the Ecology Committee (1992–1995). In 2016, the MSA honored Don with its highest award, Distinguished Mycologist, based on the quality, originality, and quantity of his scholarly fungal ecological studies, especially on the nature and role of fungal secondary compounds, and on his service to the MSA (Anonymous 2016). In 2010, a freshwater fungal species representing a new genus (Wicklowia aquatica) was named in his honor “for outstanding studies of the nature and role of fungal secondary compounds” (Raja et al. 2010) and was more recently classified as the first member of a new family (Wicklowiaceae) (Calabon et al. 2020). Don was active in several other scientific societies, including the American Phytopathological Society (1996–2021), American Society for Microbiology (1988–2021), British Mycological Society (1968–2021), Ecological Society of America (1966–1980), and Mycological Society of Japan (1988–2021). In 1988, Don was elected as a Fellow in the American Academy of Microbiology, an honorific leadership group within the American Society for Microbiology. He was elected as a Centenary Fellow (Honorary Life Member) in the British Mycological Society in 1996.

Don was a wonderful representative of the mycological community and a model of an ideal collaborator. His enthusiasm was boundless, contagious, and inspirational. He had a remarkable flair for recognizing connections between biological phenomena and chemistry, and his profound love of mycology was always evident, as was his great respect for his peers and awareness of their work. He had an amazingly keen eye for detail and for homing in on central, cross-disciplinary issues and clever ways of how to address them. He is deeply missed.

ACKNOWLEDGMENTS

We thank Brandon Wicklow and Cameron Wicklow for reading a draft of the manuscript.

DISCLOSURE STATEMENT

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Additional information

Funding

This research was supported in part by the U.S. Department of Agriculture Agricultural Research Service National Program for Food Safety.