Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2006
Publication Date: 4/15/2007
Citation: Fisher, A.J., Ditomaso, J.M., Gordon, T.R., Aegerter, B.J., Ayres, D.R. 2007. Salt marsh Claviceps purpurea in native and invaded Spartina marshes in Northern California. Plant Disease. 91:380-386. Interpretive Summary: The San Francisco Bay, one of the largest estuaries on the Pacific Coast of North America, contains populations of native and invasive Spartina cordgrasses. Invasive cordgrasses are detrimental to the health of the estuary because they out compete the native in areas where they co-exist, and transform tidal mudflats into grass marshes, which change the hydrology of the estuary to the detriment of flood control programs. We have identified a fungal pathogen that infects both native and invasive cordgrasses, however the native sustains high rates of fungal infection in marshes north of the San Francisco Estuary and invasive cordgrasses are virtually disease free. Fungal infection reduces seed production in native cordgrass populations by 40-70%. The fungal epidemic on native cordgrasses north of the San Francisco Estuary further reduces the meager competitive ability of this declining native plant species.
Technical Abstract: The fungal pathogen Claviceps purpurea (subgroup G3) has a worldwide distribution on salt marsh Spartina species. In Northern California (US), native S. foliosa sustains high rates of infection by G3 C. purpurea in marshes north of the San Francisco Estuary. Invasive populations of S. alterniflora and S. alterniflora x foliosa hybrids are virtually disease-free in the same estuary, although S. alterniflora is host to G3 C. purpurea in its native range (Atlantic Coast of the US). Greenhouse inoculation experiments showed no differences in susceptibility among S. foliosa, S. alterniflora and Spartina hybrids. Under field conditions, S. foliosa sustained a higher incidence of disease in coastal marshes than in marshes within the bay. This geographic effect may be attributable to environmental differences between the coast and the bay proper, with the former being more conducive to infection by C. purpurea. Seed set of S. foliosa spikelets was 40-70% lower on infected than on uninfected inflorescences, but seed germination was not affected. The C. purpurea epidemic on S. foliosa on the coast north of the San Francisco Estuary further reduces the meager competitive ability of this declining native plant species.