Head Smut

Ustilago bullata , the causal organism of head smut of grasses, is a highly polymorphic species that can attack several genera of grass hosts. It is a seedling-infecting pathogen that grows systemically in host vegetative tissues, then preempts fl owering tissue for its own reproduction. In most cases, particularly in annual hosts, successful infection by this pathogen completely prevents seed production.

The life cycle of the pathogen in an annual plant is matched to that of its host, with a single generation per year (i.e., a monocyclic life cycle). According to early studies, race-specifi c resistance at the species level is the norm for host response to U. bullata.

In addition, pathogen races defi ned on the basis of a series of host differential species were often complex genetic entities made up of multiple avirulence genotypes, with contrasting patterns of race-specifi c resistance on different populations within native grass species