Description:
<jats:title>Abstract</jats:title><jats:p> <jats:italic>Puccinia graminis</jats:italic> subsp. <jats:italic>graminicola</jats:italic> has caused economically important losses of tall fescue (<jats:italic>Festuca arundinacea</jats:italic> Schreb.) in North America. This rust infects leaves, culms, and spikelets of the host. Initital symptoms consist of very small, chlorotic flecks, followed by long, narrow lesions. Invasive hyphae were diffuse and filamentous, changing to dense and blocky with the formation of hymenia. Tissues were extensively colonized, including development caryopses. Seedborne infection consisted of mycelium within the embryo and urediniospores carried on both surfaces of the glumes. It is not known whether caryopses that are internally infected can germinate to produce infected individuals, but this could be an important quarantine consideration. Although, at the ultrastructural level, urediniospore development in this fungus is similar to that of other rusts, we detected an additional layer at the interface of the urediniospore and its pedicel. This layer may play a role in the, release of urediniospores from their pedicels.</jats:p>