Thirty-five isolates of Gaeumannomyces graminis were tested
for ability to infect wheat, rye and oats, and for DNA polymorphisms
using nuclear ribosomal DNA (rDNA) RFLP patterns and RAPD analysis. In
general, the cereal-attacking isolates could be readily
assigned to the rye-attacking (R) or non-rye-attacking (N) subgroups of
var. tritici, or to var. avenae, on the basis of either
of these
molecular approaches. A small number of isolates gave anomalous rDNA RFLP
patterns, but could nevertheless be assigned to one
of the three groups by RAPD analysis. Two related G. graminis
var. tritici isolates (T1–1 and T1–2) clearly grouped
with the N
rather than the R var. tritici subgroup on the basis of molecular
analysis but were pathogenic to rye, indicating that the ability to
infect this host may have arisen more than once. An earlier phylogenetic
study of Gaeumannomyces involving DNA sequence
analysis of the internal transcribed spacers of the rDNA indicated that
several oat-infecting isolates originally classified as G. graminis
var. tritici could be grouped with var. avenae isolates.
From the rDNA RFLP and RAPD analysis described here, however, these
isolates appear to be intermediate between var. avenae and var.
tritici, although it is not clear whether they represent evidence
of
inter-varietal sexual hybridization.