An anther-smut disease (Ustilago violacea) of fire-pink (Silene virginica): Its biology and relationship to the anther-smut disease of white campion (Silene alba)

In the southeastern United States, anther-smut disease (Ustilago violacea) was observed on the native fire pink (Silene virginica), and on the introduced white campion (Silene alba). Fungal isolates from the two host species showed fixed differences at allozyme loci, and isolates from S. alba were similar to isolates from S. alba in Europe. Fungal isolates from S. virginica did not produce disease on S. alba; crosses between fungal isolates from the two hosts showed reduced inoculation success on S. alba. Teliospores from hybrids between the isolates showed abnormal sporidial development. We conclude that the anthersmuts from each of the host species are genetically distinct and partially reproductively isolated ''host-races.'' Ustilago violacea occurs on S. virginica throughout its range, and far beyond the range of diseased S. alba. Rates of infection of healthy flowering individuals in natural populations of S. virginica were very low but a large fraction of plants were already diseased when they first flowered, suggesting disease is transmitted by spares that fall on seedlings or rosettes. There was substantial heterogeneity in disease incidence even among local populations in the same vicinity, but evidence suggests that the disease was not rapidly spreading in S. virginica.