Pyrenophora Phylogenetics Inferred from ITS and Glyceradehyde-3-Phosphate Dehydrogenase Gene Sequences

The phylogeny of Pyrenophora was analyzed based on DNA sequences of two regions: the internal transcribed spacers (ITS) and a fragment (ca 600 bp) of the gpd gene coding for glyceraldehyde-3-phosphate dehydrogenase. Thirty-nine isolates of Pyrenophora/Drechslera, together with 32 isolates of five genera as outgroups were analyzed in this study. Phylogenetic analysis of the ITS and the gpd data shows that Pyrenophora is monophyletic and supports the separation of Drechslera at generic rank from other graminicolous fungi. Within the Pyrenophora clade, the sequences from multiple isolates of the same species grouped together, and asexual states clustered with their predicted sexual relatives. Overall, the relationships of most Pyrenophora/Drechslera species inferred in this study were consistent with the relationships proposed from prior morphological studies. The ITS and the gpd data sets generated in this study provided a useful database that can be used to facilitate the identification of Pyrenophora/Drechslera isolates. Eight of the 21 isolates from CBS, and three of the 17 from DOAM, labeled as Pyrenophora/Drechslera from culture collections, appeared to be misidentified. With a combination of DNA sequences and morphological data, four of these isolates were re-identified as Bipolaris species. Five isolates were re-identified within the genus Pyrenophora. One of the remaining two misidentified isolates was a Corynespora and the other remains an unidentified ascomycete. The previous transfer of Drechslera heveae and D. portulacae to Cochliobolus was supported by these molecular data.