Pathovars or formae speciales of Microbotryum violaceum differ in electrophoretic karyotype

Isolates of the basidiomycete phytopathogen, Microbotryum violaceum (Pers.: Pers.) Deml & Oberw. (Ustilago violacea [Pers.] Roussel), are restricted in their host range to one or a few species of Caryophyllaceae (Pinks). Thus, the 200-plus species that serve as hosts for M. violaceum define pathovars or formae speciales of the fungus. For both a(1) and a(2) sporidial mating-type strains of different formae speciales of M. violaceum electrophoretic karyotypes and chromosomal polymorphisms were examined using CHEF gel analysis and 12-15 distinct bands were visualized. The bands, representing intact chromosomes, ranged in size from ca. 0.97 to 5.7 megabase pairs (Mb) for the pathovar that infects Silene latifolia. Their chromosome numbers were consistent with the numbers of linkage groups (14-20) identified by genetic analysis. Several size polymorphisms were detected within this forma specialis, and some dramatic polymorphisms were observed between different formae speciales. Southern analyses with the genes for M. violaceum gamma-tubulin and TATA-box binding protein (TFIID) as probes confirmed the size polymorphisms among the respective karyotypes of the strains.