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A taxonomic re-examination of Ceratocystis fimbriata, the causal agent of Ceratocystis canker of almond in California

Leslie Holland: Department of Plant Pathology, University of California, Davis

<div><em>Ceratocystis fimbriata sensu lato </em>is an important fungal pathogen worldwide, causing various wilt and canker diseases in a wide range of hosts. In California, <em>C. fimbriata</em> infections are associated with tree wounds made by mechanical harvesting equipment and cause cankers in almond trees. The genus <em>Ceratocystis </em>is divided into four, distinct clades, the African, Asian, Latin American (LAC) and North American (NAC) clades. Recently, fungal isolates recovered from almond in California were classified as <em>C. variospora</em> in the NAC, along with isolates recovered from <em>Quercus</em> spp. and other woody hosts in the U.S. and abroad. However, phylogenetic analyses suggest that <em>C. variospora </em>is a paraphyletic taxon comprising multiple species. The objectives of this study were to revisit the taxonomy of<em> Ceratocystis </em>spp. from almond in California and to resolve cryptic species in the NAC. Multi-locus sequencing of five loci (β-tubulin, TEF1-α, 60S, MCM7 and Cerato-platanin genes) were used to characterize representative isolates. Results of the multi-locus phylogenetic analyses indicated several monophyletic groups of undescribed <em>Ceratocystis</em> species within <em>C. variospora</em>, including a single, novel and well-supported <em>Ceratocystis</em> species from California almond. This work demonstrated that there is a greater diversity of species in the NAC of <em>C. fimbriata sensu lato </em>than previously known.</div>