Correlation of haplotypes of a fungal plant pathogen with their respective host species of origin

The anther smut fungus, Microbotryum violaceum, infects over 200 species of Caryophyllaceae (Pinks). However, limited published studies, as well as anecdotal evidence, suggest that each isolate of the fungus is restricted to one or a few species that it can productively infect. In the absence of physical differences, it would be useful to have molecular markers to identify individuals with specific host ranges prior to genetic analyses of host preference. With this purpose in mind, 17 isolates from eight different host species were characterized for differences in their respective gamma-tubulin genes. The region of the gene including the sixth and seventh introns and some surrounding coding regions was amplified and sequenced and the results were analyzed phylogenetically. Despite the small sample size and the geographical distribution of their respective host plants, isolates from the same host species showed no differences in the DNA regions examined; isolates of closely related pathovars also grouped together. In contrast, relative to the corresponding regions from other pathovars, isolates from host species that were genetically or taxonomically more distant showed a marked number of differences in both introns and in the third (wobble) position of codons in the seventh exon. Thus, DNA sequence differences in this highly conserved gene may be used to distinguish isolates from different host species. Such information may prove useful as markers for the different formae speciales in future analyses of host preference.