A new genus and species for the globally important, multihost root pathogen Thielaviopsis basicola

The plant pathogenic asexual fungus Thielaviopsis basicola (Ascomycota) causes black root rot on many important agricultural and ornamental plant species. Since its first description in 1850, this species has had a tumultuous taxonomic history, being classified in many different genera. Thus far, DNA ‐based techniques have not played a significant role in identification of T. basicola and have been used only to confirm its placement in the Microascales. This investigation reconsidered the phylogenetic placement of T. basicola , using DNA sequence data for six different gene regions. It included 41 isolates identified as T. basicola from 13 geographical locations worldwide. Phylogenetic analyses showed that these isolates grouped in a well‐supported lineage distinct from other genera in the Ceratocystidaceae, here described as Berkeleyomyces gen. nov. The data also provided robust evidence that isolates of T. basicola include a cryptic sister species. As a result, this report provides a new combination as B. basicola comb. nov. and introduces a new species as B. rouxiae sp. nov.