The Population Biology of a Smut Fungus, <i>Ustilago spinificis</i> Ludw. I. Geographic Distribution and Abundance.

Abstract

Ustilago spinificis, a floral smut of Spinifex hirsutus and S. sericeus, was collected across southern Australia from Yanchep, W.A. on the west coast to Seaspray, Vic, on the south-eastern coast and from the North Island of New Zealand. The host plants are most abundant on beaches with extensive sand dunes and the smut is common in regions where the host is abundant. The distribution limits for the smut are set by the replacement of S. hirsutus by a non-host, S. longifolius, north of Perth on the west coast; by the absence or rarity of host plants on rocky coastlines across the Great Australian Bight and in the SE. and SW. corners of Australia; and by the limited occurrence of host plants on the east coast of Australia. Spinifex inflorescences were sampled on 33 beaches and on the 29 beaches where smut was found the mean frequency of smutted inflorescences was 22%. These high infection rates represent a natural epidemic of a plant disease and data on other natural populations of smut fungi are presented to show that these results are not exceptional.