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.
Emily J.A. Blakemore E-mail: email@example.com
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.