Photo courtesy of W. E. Fry.
Sporangium of Phytophthora infestans.
Fungi represent the second largest group of organisms, next to the insects. Application of molecular and genomic tools to trace life histories has revealed that the Oomycetes, traditionally studied with the Fungi, are Stramenopiles in the Chromista. The study of these organisms has a special place in the history of plant pathology because they were the first described plant pathogens; today we know that phytopathogens from these groups cause the majority of plant diseases. The ability to be pathogenic is relatively rare, however, despite the abundance of fungal species; what distinguishes pathogens from non pathogens, and symbionts from pathogens or non-pathogens is the focus of our contemporary research in plant pathology. This endeavor is facilitated, enormously, by the availability of molecular genetic, genomic and phylogenomic resources. Insights into fungal and oomycete biology can have broad impact in the life sciences. For example, the quest to discover what makes a pathogen a pathogen overlaps with the study of reproductive strategies, since both are fundamentally recognition issues. For pathogenic symbiotic, or mutualistic associations, the issue is how cells of different organisms communicate with each other to effect their partnership or cause disease; for reproduction, the question is how cells of the same organism recognize self from non-self. Both forms of recognition allow one cell to form an intimate association, or to fuse with, another. Of practical importance, is the fact that fungi and oomycetes travel in the field by spore dissemination, thus, complete understanding of the spore developmental pathway provides an avenue for design of global solutions for preventing plant disease.
The Fungal and Oomycete Biology Program has three activity areas, which are described below.
Genetics and Genomics
Our faculty pilot or are allied with genome projects involving diverse fungi that are representative of broad phylogenetic groupings, including the cereal phytopathogens, Cochliobolus heterostrophus, Fusarium graminearum, and Magnaporthe grisea, the cosmopolitan pathogen of dicots, Alternaria brassicicola, the Chestnut blight fungus, Cryphonectria parasitica, the saprobe Neurospora crassa, and the mycorrhorizal symbiont, Glomus intraradices (See the Plant-Microbe Biology research area for more genome projects). In addition, several faculty exploit genomic resources available for Oomycete phytopathogens, such as Phytophthora infestans. Representative areas of investigation include: 1) genome wide discovery and functional analysis of general, specific, and unique virulence factors in pathogen genomes, 2) genomic comparisons among saprobes, symbionts, and pathogens to appreciate seminal differences between these lifestyles, 3) phylogenomic and functional genomic approaches to understanding the role(s) of natural product metabolites in the fungal lifecycle, 4) population level epidemiological studies of fungi and oomycetes, 5) genetic requirements for vegetative incompatibility, and 6) role of natural variation in the circadian clock.
Cell and Developmental Biology
We seek to understand the biochemical activities and cellular locations of virulence factors and small molecules, and the molecular bases for movement of these molecules as they are deployed within fungal cells or as they exit and interact with other fungal cells or with plants. We also study basic fungal and oomycete development, particularly asexual and sexual spore production as these stages of development are key to understanding mechanisms of proliferation in the field. Representative questions include: are AM fungi able to reproduce only clonally and if so, why are they able to survive as asexual organisms? what is the suite of genes required for sexual development of incompatible (heterothallic) versus compatible (homothallic) fungi and where are the corresponding products deployed in the fungal cell? what benefit do fungal small molecules have in fungal cells themselves (separate from obvious effects on other organisms, e.g., as antibiotics as medicinals, as toxins, as biocontrol agents) and what cellular effect does absence of a small molecule metabolite have on fungal cell development?
Systematics, Ecology and Evolution
Our faculty use molecular genetic, genomic and phylogenomic approaches as well as classical genotypic and phenotypic approaches to understand fungal relationships and to make inferences about evolution of fungal speciation and of genes associated with pathogenicity to plants or insects. Similar approaches are applied to understanding fungal life histories and evolution of fungal and oomycete developmental programs such as asexual and sexual reproduction. Some faculty focus on alpha-taxonomy, the branch of systematics in which organisms are described for the first time, given names, and placed on their rightful branches in the tree of life. Others consider the evolution of arbuscular mycorrhiza (AM) fungi, and their mutualistic symbiosis with the majority of land plants, including many crop species. Still others explore the ecology and rhizobiology of soil borne oomycetes such as Pythium ultimum and the epidemiology of Phytophthora infestans.
Faculty affiliated with the Fungal and Oomycete Biology program
Gary Bergstrom—Biology, epidemiology, and integrated management of diseases of wheat, corn, soybean, forage legumes, and biofuel feedstock crops.
Donna M. Gibson—Discovery of microbial metabolites and the roles they may play in pathogenicity, virulence, defense, or growth and development (Adjunct Faculty, USDA -ARS)
William Fry—Biology of oomycetes and management of disease they cause (with emphasis on Phytophthora infestans).
David M. Geiser—Molecular evolutionary genetics and systematics of fungi, especially /Fusarium/ and /Aspergillus/
Maria Harrison—The arbuscular mycorrhizal symbiosis and phosphate acquisition in plants. (Adjunct Faculty, BTI)
Kathie Hodge—Systematics and ecology of pathogenic and symbiotic fungi, especially those that are pathogens of insects. Director of the Cornell Plant Pathology Herbarium.
Richard A. Humber—Biology, systematics/taxonomy, and biocontrol uses of fungal pathogens from arthropods and other invertebrates. Curates ARSEF, the world's largest, most diverse culture collection for fungal pathogens affecting invertebrates.
Michael Milgroom—Population biology and evolution of plant pathogens; the integration of population biology and plant disease epidemiology.
Eric Nelson—Ecology and development of oomycetes in the spermosphere and rhizosphere with special emphasis on plant pathogenic Pythium species. Of special interest is understanding how microbial interactions and plant associations influence Pythium development and pathogenesis.
Rebecca Nelson—The genetics of quantitative disease resistance; international agriculture. We currently focus on two diseases of maize that are important both in the US and in Africa: northern corn leaf blight and gray leaf spot.
Teresa Pawlowska—Biology and evolution of arbuscular mycorrhizal (AM) fungi (phylum Glomeromycota)
Richard C. Staples—Physiology, metabolism, and cell biology of fungi, experience focused on the rust fungi. (Adjunct Faculty, BTI)
Gillian Turgeon—Genetics and molecular biology of fungal pathogens.
Thomas Zitter and Helen Griffiths—Identification of effective methods to control diseases caused by Phytophthora erythroseptica and Pythium species in potato.