Anther smuts of Silene acaulis and S. uniflora in the Outer Hebrides, including an assessment of ITS genotypes of Microbotryum silenes-acaulis

Abstract

Anther smuts on Silene acaulis and S. uniflora from the Outer Hebrides, Scotland, UK), are analysed using morphological and molecular techniques, and found to represent Microbotryum silenes-acaulis and M. silenes-inflatae, respectively. This is the first identification of caryophyllaceous anther smuts in the Outer Hebrides according to modern species concepts and the first report of Microbotryum silenes-acaulis confirmed by molecular analysis from the British Isles. Additionally, the genetic structure of Microbotryum silenes-acaulis, based on all currently available ITS sequences, is analysed and discussed. Seven ITS genotypes are determined for Microbotryum silenes-acaulis, including three genotypes in North America and four genotypes in Europe. Compared to European accessions, all North American accessions share specific nucleotides and are genetically divergent.

Keywords: Basidiomycota; Microbotryum; Ustilaginales; arctic and alpine fungi; genotypes; molecular phylogenetics; plant pathogens.

Fig. 1.

Distributions of Silene acaulis and S. uniflora in the Outer Hebrides based on all records from any date. Localities mentioned in the text are named.

Fig. 2.

Microbotryum silenes-acaulis on Silene acaulis. A. The habitat at Loch a’ Bheannaich, Lewis. B. Infected and uninfected flowers at the same locality. Note that this is a female tussock, but the fungus has induced infected flowers to produce stamens. (Corresponds to TUB 019585; scale bar approx 1 cm).

Fig. 3.

Distribution of Microbotryum silenes-acaulis on Silene acaulis in the Outer Hebrides.

Fig. 4.

Bayesian inference of phylogenetic relationships between the sampled Microbotryum species: Markov chain Monte Carlo analysis of an alignment of concatenated ITS + LSU base sequences using the GTR+I+G model of DNA substitution with gamma distributed substitution rates and estimation of invariant sites, random starting trees, and default starting parameters of the DNA substitution model. A 50 % majority-rule consensus tree is shown computed from 75 000 trees that were sampled after the process had reached stationarity. The topology was rooted with Microbotryum scabiosae. Numbers on branches before slashes are estimates for a posteriori probabilities; numbers on branches after slashes are ML bootstrap support values. Branch lengths were averaged over the sampled trees. They are scaled in terms of expected numbers of nucleotide substitutions per site. The colour dots refer to ITS genotypes of Microbotryum silenes-acaulis (see also Fig. 5). D. = Dianthus, M. = Microbotryum, S. = Silene.

Fig. 5.

Nucleotide differences between aligned ITS sequences, and the geographical distribution of corresponding specimens of Microbotryum silenes-acaulis. Locations depicted with a question mark are not precise as they were included in GenBank as Alaska and Canada, respectively. Colours refer to ITS genotypes (see also Fig. 4).

Fig. 6.

Records of Microbotryum silenes-inflatae on Silene uniflora from the Outer Hebrides since 2008.

Fig. 7.

Microbotryum silenes-inflatae on Silene uniflora from the Outer Hebrides. A. The habitat at Loch Eirearaigh, Lewis. B. Infected flower at the same locality (corresponds to KRAM F-59027; scale bar approx 1 cm). C–D. Spores seen by LM, median and superficial views (TUB 019588). E–F. Spores seen by SEM (KRAM F-59020). Bars: C–D = 10 μm, E = 5 μm, F–G = 4 μm.