Pathogenic Microfungi Associated with Spartina in Salt Marshes

Abstract

Diebacks associated with disease in salt marshes are not as frequently observed as in terrestrial systems. However, when they do occur, the ecological costs to the marsh system can vary from devastation, in the case of Sudden Vegetation Dieback, to a minor cost, as in the case of Spartina rust outbreaks. All major diebacks of Spartina alterniflora have occurred along its native range in the western Atlantic and Gulf Coast. Fungi, herbivores, and abiotic stressors are frequently associated with the dieback. Many dieback/disease events have occurred as a result of fungal pathogens being introduced on invasive S. alterniflora. The dieback of the native common reed grass Phragmites australis in Shanghai, China, was found to be associated with F. palustre being vectored on S. alterniflora where it spread onto Phr. australis. Another example was where S. alterniflora presumably introduced the Spartina strain of ergot (Claviceps purpurea) to Europe where it increased on Spartina anglica. Although ergot was already present on the native Spartina foliosa in the eastern Pacific Coast marshes, the more resistant and robust hybrids that resulted between the invasive S. alterniflora and native S. foliosa were selectively favored over the native S. foliosa, thus advancing the dominance of the hybrids in these marshes. The incidence of Spartina rust incited by Puccinia sparganioidis is frequently seen in the marsh, but the rust is not considered to have a significant ecological cost to the marsh. The main economic concern is the disfigurement it can cause to its alternate host, ash (Fraxinus spp.). The last fungus discussed (Phaeosphaeria spartinicola) did not incite disease, but was highlighted due to its important function as a saprobe and in its facultative, mutualistic relationship with the herbivorous periwinkle snail. During periods of drought, these two organisms interacted in a way that led to massive dieback. Given the resilience of Spartina spp., it is surprising when these fungi cause significant damage. Most disease problems, however, tend to be associated with global spread of S. alterniflora into nonnative habitats.