Abstract
Cotton root rot is an important soilborne disease of cotton and numerous dicot plants in the south-western United States and Mexico. The causal organism, Phymatotrichopsis omnivora (= Phymatotrichum omnivorum), is known only as an asexual, holoanamorphic (mitosporic) fungus, and produces conidia resembling those of Botrytis. Although the corticoid basidiomycetes Phanerochaete omnivora (Polyporales) and Sistotrema brinkmannii (Cantharellales; both Agaricomycetes) have been suggested as teleomorphs of Phymatotrichopsis omnivora, phylogenetic analyses of nuclear small- and large-subunit ribosomal DNA and subunit 2 of RNA polymerase II from multiple isolates indicate that it is neither a basidiomycete nor closely related to other species of Botrytis (Sclerotiniaceae, Leotiomycetes). Phymatotrichopsis omnivora is a member of the family Rhizinaceae, Pezizales (Ascomycota: Pezizomycetes) allied to Psilopezia and Rhizina.