Manifestations of the Septoria
leaf spot disease of Rumex compared with a healthy leaf (right). The
disease causes chlorosis and defoliation.Rumex skottsbergii and R. giganteus (Polygonaceae), both known by the common name "pawale," are shrubs endemic to Hawai‘i. These species are morphologically variable and apparently closely allied to one another. As generally recognized, R. giganteus is an understory component of mesic to wet forests on the islands of Moloka‘i, Maui, and Hawai‘i, whereas R. skottsbergii occurs on the island of Hawai‘i, where it colonizes dry, open lava fields.
A leaf spotting disease occurs on these Rumex species, and is particularly severe on a population of R. skottsbergii colonizing a recent cinder deposit in Hawai‘i Volcanoes National Park (Gardner 1997a). The disease usually is evident as few to several scattered lesions visible on both leaf surfaces. On heavily infected leaves, spots coalesce into necrotic blotches while the surrounding leaf tissue dies and the leaf is shed. The disease is associated with a fungus of the genus Septoria, which I recently described as a new species, as S. vulcani (Gardner 1997a). Fruiting bodies of the fungus, viewed microscopically, are scattered within infected tissue, exuding spores when fresh under humid conditions.
Manifestations of the Septoria
leaf spot disease of Rumex compared with a healthy leaf (right). The
disease causes chlorosis and defoliation.
A pycnidium (or pycnidial conidioma, a flask-shaped fruiting body)
embedded in infected leaf tissue producing spores of S. vulcani.
Thread-like spores (condia) of S. vulcani. Viewed with
the high power objective (left) and the oil immersion objective (right).