Molecular Phylogeny of the Peronosporomycetes (Oomycota or Heterokonta)

Northern Illinois University, Dekalb IL

Investigators

Abstract

0213076 Hudspeth Phylogenetic relationships within the Peronosporomycetes, a diverse group of economically important fungal-like protists often referred to as oomycetes, are poorly understood. In this study the primary goal is to establish an extensive DNA database derived from mitochondrial and nuclear genes of a diverse selection of these organisms. The resultant database is then to be used to infer evolutionary relationships of major, understudied, and newly identified genera. With the development of peronosporomycete specific DNA primers this study emphasizes both obligate and opportunistic parasites of plants, algae, and terrestrial and marine animals. The resulting inferred phylogeny is expected to provide new insight into evolutionary relationships and trends within the Peronosporomycetes, and to identify anomalously placed taxa for reevaluation using morphological and biochemical data. The broader impact of this study stems from the inclusion in the Peronosporomycetes of a significant number of pathogenic organisms. Hosts include representatives from all eukaryotic kingdoms. Plant pathogens encompass a spectrum of cereal and leguminous crops, rosaceous fruit trees, forest trees, and ornamental plants as hosts. The societal impact of the downy mildews Plasmopara and Peronospora (responsible for the decimation of the French wine and Cuban tobacco industries) and of Phytophthora infestans, the causative agent of late blight of potato (famines in Ireland in the mid-1840's and World War I Germany), is part of the historical record. Currently, the worldwide economic impact of these and other peronosporomycete genera amounts to tens of billions of dollars in crop losses and disease control. The newly identified Phytophthora ramorum (causative agent for sudden oak death) with its broad host range currently threatens large stands of trees in the western U.S., and aggressive hybrid variants of other "phytophthoras" with their expanding host ranges are emerging as additional threats. In the rapidly expanding area of aquaculture, peronosporomycete animal "mycoses" affecting roe, fingerlings, molluscans, and crustaceans are currently being identified. Even the incidence of mammalian "pythiosis" (Pythium isidiosum) in an increasing number of hosts, including man, is being recognized. Establishing a molecular database for this group provides both a resource for the early and rapid molecular identification of pathogens, and a significant step in understanding the evolutionary history and trends of the Peronosporomycetes.