APS Abstracts of Presentations

Molecular phylogeny of Phymatotrichopsis omnivora
Presenter: S. Marek, Oklahoma State University, Stillwater, OK, USA
Phytopathology 95:S65

The persistent soilborne disease Phymatotrichum root rot (= cotton root rot or Texas root rot) is caused by the fungus Phymatotrichopsis omnivora (Duggar) Hennebert and severely limits alfalfa (Medicago sativa L.) and cotton (Gossypium hirsutum L.) production in southern Oklahoma, Texas, and Arizona. This fungus has one of the broadest host ranges of any plant pathogen, infecting numerous dicot crops (e.g. peanuts, pecans, fruit trees, grapes, and vegetable crops). No practical disease management strategy currently exists. The anamorphic causal fungus has been affiliated with polypore fungi of the Basidiomycota, but its taxonomy has remained uncertain. Several isolates of P. omnivora collected from Texas and Oklahoma were used to construct phylogenetic trees based on the amplified DNA sequences of the nuclear ribosomal DNA repeat (SSU-ITS1-5.8S-ITS2-LSU), and RNA polymerase II subunit 2 (RPB2) and beta-tubulin genes. All trees indicated P. omnivora should be placed in the Order Pezizales (operculate discomycetes) within the Ascomycota, and, based on rDNA sequences, was most similar to Rhizina undulata Fr. in the monotypic family Rhizinaceae. However, an unambiguous familial assignment could not be made due to the incomplete availability of RPB2 and beta-tubulin gene sequences from taxa of the Pezizales.

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