THE INFECTION OF FESTUCA-ARUNDINACEA BY PUCCINIA-GRAMINIS SUBSP GRAMINICOLA

Puccinia graminis subsp, graminicola has caused economically important losses of tall fescue (Festuca arundinacea Schreb.) in North America. This rust infects leaves, culms, and spikelets of the host. Initial s ymptoms consist of very small, chlorotic flecks, followed by long, nar row lesions. Invasive hyphae were diffuse and filamentous, changing to dense and blocky with the formation of hymenia. Tissues were extensiv ely colonized, including development caryopses. Seedborne infection co nsisted of mycelium within the embryo and urediniospores carried on bo th 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 si milar to that of other rusts, we detected an additional layer at the i nterface of the urediniospore and its pedicel. This layer may play a r ole in the release of urediniospores from their pedicels.