Rust and smut fungi of Hawai'i: an annotated host index on angiosperms and ferns

Abstract

Rust and smut fungi are well-defined groups of plant pathogens. These groups generally are considered to be closely allied with one another and therefore are frequently discussed together. Both groups of fungi are known to cause major crop diseases and are well known throughout the world from the standpoint of their economic significance. These fungi occur on hosts of a variety of plant families in Hawai'i, most introduced from elsewhere, probably arriving with their hosts rather than separately via wind-borne spores. However, some species occur as apparent endemic or indigenous forms on hosts native to the Islands. Members of the grass family (Poaceae) are the most frequent hosts of both the rusts and the smuts. The rust fungi typically infect vegetative plant parts, that is, leaves and stems, where they produce abnormal growths such as witches'-brooms, galls, or raised, sporulating pustules. Because of the virulence and host specificity characteristic of the rusts in general, these fungi have received particular attention in weed biocontrol studies. The smut fungi, with some exceptions, infect reproductive parts, often destroying normal fruit and seeds and replacing these structures with masses of fungal spores. Occurrence of smut infections on economic grain crops can cause complete loss of the crop by destroying the grain kernels, while leaving the vegetative parts of the plant intact. Such severe economic losses associated with rusts and smuts are quite rare in Hawai'i, however. Endemic rusts provide interesting examples of the unusual development well known among other categories of organisms that have evolved in isolated insular systems.