Leaves of Canavalia kauensis infected with Septoria
leaf spot (left), compared with healthy leaves (right).Canavalia kauensis, a bean-like legume, was newly discovered on the island of Hawai‘i in the early 1970s. Before its discovery, this species had apparently existed for years only as dormant seeds in the rocky soil of the Ka‘u Desert region (approximately 300 m elevation) of Hawai‘i Volcanoes National Park. Elimination of extreme browsing pressure from feral goats by construction of an experimental exclosure of about 1,000 sq. m permitted a dramatic recovery of the vegetation within. The resulting alterations, especially in soil moisture, presumably were favorable for germination of the seeds of C. kauensis, along with those of other vegetation types.
A leaf spot disease, caused by a species of Septoria, appeared on C. kauensis (Gardner, 1982). For the purposes of reporting the disease, the Septoria was referred to S. molleriana, a species described from C. obtusifolia with spore measurements approximating those of the C. kauensis pathogen. Notwithstanding these similarities, S. molleriana apparently was described from Guinea in western Africa, making its occurrence on an endemic Hawaiian host difficult to accommodate. Further investigation may indicate that the pathogen represents an endemic, and therefore a new species, of Septoria.
Leaves of Canavalia kauensis infected with Septoria
leaf spot (left), compared with healthy leaves (right).
Cross section through an infected leaf showing a
pycnidium, or pycnidial conidioma (fruiting body) expelling conidia (spores).