Submitted to: Biological Journal of the Linnean Society, London
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2013
Publication Date: 1/1/2014
Citation: Walker, D.M., Castlebury, L.A., Rossman, A.Y., Struwe, L. 2014. Host conservatism or host specialization? Patterns of fungal diversification are influenced by host specificity in Ophiognomonia (Gnomoniaceae, Diaporthales). Biological Journal of the Linnean Society, London. 111(1):1-16. Interpretive Summary: Fungi are a group of organisms that cause billions of dollars damage each year to agricultural and forest resources in the United States. One group of fungi includes the species that caused chestnut blight in the eastern United States killing all of the chestnut trees. Many additional fungi belong to the same group and cause diseases of hardwood trees in North America including butternut canker. Predicting which fungi will attack specific trees is difficult to determine. In this research a group of fungi for which species are well defined was evaluated to determine which group of hosts was attacked by each fungal species in regard to their evolutionary pathway. It was determined that within some host families it was possible to predict which fungal species would occur on hosts in that family. This paper will be used by forest pathologists and plant quarantine policy makers to determine which fungi could cause diseases of hardwood trees in the United States.
Technical Abstract: Species of Ophiognomonia (Gnomoniaceae) are perithecial fungi that occur as endophytes, pathogens, and latent saprobes on leaf and stem tissue of plants in the Betulaceae, Fagaceae, Juglandaceae, Lauraceae, Malvaceae, Platanaceae, Rosaceae, Salicaceae, and Sapindaceae. In this study host plant patterns at the order, family, genus, and species ranks were analyzed using Spatial Evolutionary and Ecological Vicariance Analysis (SEEVA) based on a multi-gene phylogeny of 45 species of Ophiognomonia. The objective of this study was to understand speciation events and host associations in Ophiognomonia. A second objective was to determine if fungal speciation events are influenced by host conservatism, specialization, or switching at different taxonomic host ranks. Host data were coded with the four variables order, family, genus, and species. Host plant differences between sister clades were interpreted using the divergence index (D), ranging from 0 for no divergence to 1 for maximum possible divergence. Several subclades showed strong patterns of order/family conservatism (D = 1.00) for hosts in the Betulaceae, Fagaceae, Juglandaceae, and Rosaceae. Trends of host specialization at the genus and species ranks (D = 1.00) were suggested within these same host families. Two independent host switches were observed at the family rank for O. clavigignenti-juglandacearum and O. pterocaryae and three host switches at the order rank for O. japonica, O. lenticulispora, and O. sassafras. Host specificity was hypothesized as a mechanism strongly contributing to speciation patterns in the genus Ophiognomonia.