Claviceps phalaridis in Australia: biology, pathology and taxonomy with a description of the new genus Cepsiclava (Hypocreales, Clavicipitaceae)

Abstract

Claviceps phalaridis is a native systemic grass endophyte known only from southeastern Australia. It renders its annual and perennial hosts sterile, producing deciduous sclerotia in all florets of infected plants and occurring at a low level on its four known native hosts (species of Austrodanthonia, Austrostipa, Elymus and Microlaena). Introduced pooid grasses in the genera Bromus, Dactylis, Holcus, Hordeum, Phalaris, Lolium and Vulpia are commonly infected. Occasional infection in crops of oats and barley (Avena sativa, A. strigosa, Hordeum vulgare) has occurred. Sclerotia are composed of fungal and host floret tissues (stamens, ovary, styles and stigmas) and can germinate immediately. In the field, production of ascostromata from sclerotia is synchronised with autumn seed germination of its grass hosts and seedling infection is suspected. Two conidial anamorphs are produced, one with dry unicellular conidia developing from enteroblastically proliferating conidiophores on the apex of maturing sclerotia, the other two-celled and with apical branched appendages, arising sympodially from germinating unicellular conidia and ascospores, and in culture. The morphological and biological characteristics of C. phalaridis are distinct from those of the genus Claviceps. Of species currently placed in Claviceps, it is most similar to C. diadema and related Central and South American taxa on panicoid hosts. These species have sclerotia including host tissue but they have a sphacelial anamorph characteristic of Claviceps. It differs from Neoclaviceps, recently described parasitising ovaries of a panicoid host in Costa Rica, in producing a discrete Sclerotium, a unicellular anamorph and in having mainly pooid hosts. Comparison with other genera of plant-parasitic Clavicipitaceae shows that it cannot be included in them. It is unique amongst these genera in invading male floret organs (stamens) before female organs (ovaries). The new genus Cepsiclava is established for it and the term pseudoergot proposed for the fungus and the disease it causes.