Host Specialization and Fungal Speciation in Ceratocystis

Iowa State University, Ames IA

Investigators

Abstract

0128104 Harrington Studies of fungal species, their reproductive strategies, how they evolve, and how humans influence their evolution and distribution are needed. This need is particularly acute for plant pathogenic fungi because humans unwittingly move cryptic species of fungi around the world on their crops (mostly on plant propagative materials such as seeds and cuttings) and plant products (such as logs, wood chips, packing materials, etc.), often with devastating consequences. Introductions of invasive fungal species and changes in fungal populations frequently frustrate disease control strategies, reduce food and fiber productivity, and threaten forest ecosystems. Ceratocystis species, which are primarily found in the Americas, have been particularly damaging when introduced into new ecosystems or when introduced plant hosts come into contact with indigenous pathogen populations. The research of Dr. Thomas Harrington at Iowa State University focuses on how new species arise in the Ceratocystis fimbriata complex, which contains some of the most aggressive pathogens in the genus Ceratocystis. Although currently considered one species, it is actually a complex of many species that share morphological similarities but infect different hosts in different parts of the world. Dr. Harrington will use a variety of modern molecular and traditional tools to delimit species within the complex and infer their evolutionary history. Particular emphasis will be given to the host range (which hosts the pathogen can infect) of each of the delimited species. DNA fingerprinting markers will be used to study the diversity of populations and trace the suspected spread of host-specialized species by human activity. Recently derived populations should have low levels of genetic diversity and have limited geographic ranges, except where the geographic range has been extended by humans. Older lineages are hypothesized to have more genetic diversity and broader geographic ranges. Also, the hypothesis that older lineages are more restricted in their host ranges will be tested. These studies will build a foundation for a taxonomic treatment of this ecologically and economically important genus. Where and how populations of C. fimbriata were introduced by humans will also be determined, and this information will be particularly important because of the increasing movement of plant pathogens on logs, wood chips and crating material. The studies will allow for a better understanding of how ecological niche affects speciation and will lead to a more practical definition of species in the fungi. The definition of a species continues to be among the most controversial issues in basic biology, but the practical implications for plant pathology, particularly for quarantine concerns, are immediate. Concerns over invasive species, including plant pathogens, have been heightened by the globalization of our economies, and the simple concept of a species continues to be of pivotal importance to the prevention of introductions and management of introduced pests.