Molecular Plant Pathology On-Line []

Relationships amongst barley and oat infecting isolates of Pyrenophora spp. based on sequences of the internal transcribed spacer regions of ribosomal DNA

Elisabeth A. Stevens, Emily J.A. Blakemore & James C. Reeves. Molecular Biology & Diagnostics Section, National Institute of Agricultural Botany, Huntingdon Road, Cambridge. CB3 0LE.

Corresponding author: Emily J.A. Blakemore E-mail:


The sequences of the internal transcribed spacers (ITS) of the rRNA genes of 21 Pyrenophora spp. isolates were determined. The size of the ITS1 region varied from 178 to 190 base pairs and the size of the ITS2 region varied from 158-161 base pairs. The results of the ITS analysis for the four barley infecting species, Pyrenophora graminea, Pyrenophora teres, Pyrenophora teres f. sp. maculata and Pyrenophora hordei, indicated that they were closely related with only one base difference in the ITS1 region separating P. graminea from the other Pyrenophora spp. The ITS sequence for the P. hordei isolate, a P. teres f. sp. teres isolate and three P. teres f. sp. maculata isolates were identical. The ITS2 was more conserved than the ITS1 region for all the isolates of Pyrenophora used in this study. There was 15.4-17% ITS1 sequence divergence between the two P. avenae isolates and the other Pyrenophora species. This was greater variation than that found between the Pyrenophora species pathogenic on barley (0.0-0.9%). There was no well-defined boundary between the interspecific and intraspecific variation of the Pyrenophora spp. pathogenic on barley. The high degree of similarity in the ITS regions for the Pyrenophora species pathogenic on barley implies that the taxonomic status of these pathogens needs to be re-evaluated for improved diagnosis and crop protection.