M. Catherine Aime
Associate Professor of Mycology
Director of the Arthur and Kriebel Herbaria
Department of Botany & Plant Pathology
Purdue University

Topic: Uncovering Mycological “dinosaurs” in the remote jungles of Guyana's lost world

Abstract:
In terms of species numbers and ubiquity, rust fungi (Pucciniales) are an incredibly successful lineage. Together, the more than 7000 described species form the largest known monophyletic group of plant pathogens. All are obligate parasites of vascular plants including agricultural, forest and ornamental crops resulting in billions of dollars of damage worldwide each year. An intriguing aspect of rust biology is that many species are heteroecious, i.e., require alternation between two unrelated hosts in order to complete their life cycle. Whether the character of heteroecism is ancestral or derived within the rusts has never been satisfactorily resolved. Most classical treatments of rust phylogeny and classification were based on the hypothesis that “primitive” hosts (e.g., ferns) harbored “primitive” rusts (e.g., Uredinopsis, Hyalopsora) that alternate on members of the Pinaceae. However, alternative hypotheses of rust evolution have proposed various short-cycled primarily tropical rusts as ancestral, with the defining characteristic of heteroecism thus being derived within the group. Molecular studies based on rDNA genes have since disproved the fern rust hypothesis, but consensus as to what does lie at the base of the Pucciniales is still lacking. This study analyzes loci from multiple genes and taxa selected from all known families, with an emphasis on tropical species, to resolve the base of the rust fungi and infer ancestral characters including the origins of heteroecism for the order.