Tilletia maclaganii is a pathogen of switchgrass (Panicum virgatum) and related species in North America. Switchgrass head smut is characterized by systemic infection of plants through fungal replacement of all developing ovaries on an infected panicle with a sorus of teliospores and sterile cells. Systemic infection results in significant stunting and reduction of biomass in switchgrass grown for animal forage or as a biofuel or bioproduct feedstock. It renders commercial seed production uneconomical and detracts from the aesthetic appearance of ornamental switchgrass. Teliospores germinate in less than 24 hours, when free moisture is present, to produce non-conjugating basidiospores. Seedling infection from teliospores associated with seed is documented, but little is known about other infection pathways or the multi-year survival of the fungus in infected plants or the soil. The incidence of plant infection increases with the age of switchgrass stands and there is circumstantial evidence of its spread to adjacent plants. No switchgrass cultivar or ecotype has been found to be strongly resistant to switchgrass head smut.
Tilletia maclaganii is most closely related to T. rugispora, which infects florets of Paspalum species but does not colonize its hosts systemically. Genomic analysis of T. maclaganii will provide insights into genetic diversity of this pathogen across its geographic and host range. It will also resolve phylogenetic relationships with other smut fungi and reveal genes affecting the infection processes, systemic colonization of hosts, sporulation, and survival in host plants and the environment.
