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Sweet potato is not often affected by serious fungal disease in the Pacific Islands. On Nendo Island Temotu Province, Solomon Islands, Athelia rolfsii is a problem, although restricted to one farm. It was fairly dry (for a place that gets 4000 mm plus rain a year) up till Christmas and then wet. After a week of rain, the disease ran rampant and large areas are now affected with the fast growing mycelium, rotting vines and killing the plants. It looked like Athelia rolfsii, but sclerotia (the small white round structures that occur on stems of beans, tomatoes. etc., at soil level) were not found.
Landcare, New Zealand, has looked at a specimen and confirms that mycelial characteristics (hyphal size, pattern of branching, and presence of a few clamp connections) all fit with the description of A rolfsii.
Palau reported a similar condition on sweet potato grown in poorly drained fields in the past 2 years of very rainy (La Nina) weather. The plants produced few or no sweet potatoes in these fields. The vines appeared to outgrow it, so it was not apparent at first that there was disease, but when checked for root development the vines were rotting away at the base. The symptoms were as illustrated.
It was pointed out by Solomon Islands that A rolfsii has been observed affecting sweet potato on a minor scale for quite a while. In most cases, newly planted sweet potato vines are attacked at the base where the mycelia and brownish sclerotia can be seen. Replanting sweet potato on the same land is not recommended, but other crops like cassava are tolerant.
The preferred name is Corticium rolfsii Curzi (the teleomorph form). Synonyms are A rolfsii and Sclerotium rolfsii. More information on the fungal pathogen is available in EcoPort: www.ecoport.org/ep.exe$EntPage.
However, Landcare accepted that the name Athelia rolfsii is the correct one for the common soil fungus on taro and many other crops.
Tu and Kimbrough (1978) made the new combination of A rolfsii, based on the basionym Corticium rolfsii. Both the genera Corticium and Athelia are basidiomycetous fungi (i.e. teleomorph). The asexual or imperfect stage (anamorph) of A rolfsii is Sclerotium rolfsii.
Athelia rolfsii is accepted as the ‘correct’ name by USDA and CBS (a Dutch Mycological Institute). Although the CABI Crop Protection Compendium, 2nd edition uses Corticium rolfsii, the mycologists at CABI use Athelia rolfsii as the preferred name (in, for example, their Index of Fungi).