Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2005
Publication Date: 8/1/2005
Citation: Fisher, A.J., Ditomaso, J.M., Gordon, T.R. 2005. Intraspecific groups of Claviceps purpurea associated with grass species in Willapa Bay, Washington, and the prospects for biological control of invasive Spartina alterniflora. Biological Control. 34:170-179. Interpretive Summary: Spartina is an exotic cordgrass that has invaded Willapa Bay, Washington, one of the largest estuaries on the Pacific Coast of North America. Once this cordgrass becomes established it transforms tidal mudflats into grass marshes, to the detriment of birds, fish and shellfish and can change the hydrology of the estuary to the detriment of flood control programs. Hundreds of thousands of dollars from the State of Washington, and Federal sources, have been used to control this plant with herbicides and heavy machinery that cuts and crushes plant material, with limited success. We discovered a fungal pathogen in Willapa Bay that attacks Spartina flowers, preventing them from producing seed. Currently this fungus is rare in Willapa Bay, but it reaches epidemic levels in coastal England and on the Atlantic Coast of the United States. Our research shows that it may be possible to increase the incidence the fungal pathogen in Willapa Bay so that it causes significant damage to Spartina and helps reduce the spread of this aquatic invader.
Technical Abstract: Spartina alterniflora is a salt marsh halophyte introduced to the Pacific Coast of the USA, which has become a noxious weed in Willapa Bay, Washington. A sap-feeding insect has been released as part of a biological control program, and has established at multiple sites. A useful complement to this program would be a biological agent that attacks seed, to reduce expansion of the infestation by seedling recruitment. One possibility is the flower-infecting, fungal pathogen Claviceps purpurea, which causes ergot disease in grasses. This species contains three intraspecific groups, of which one is specific to salt marsh habitats, G3. Based on random amplified polymorphic DNA markers, all three groups of C. purpurea were found in Willapa Bay. The incidence of ergot on Spartina was very low, and genetic diversity was low among G3 isolates suggesting it may have been recently introduced to the region. Greenhouse tests showed S. alterniflora from Washington to be as susceptible as S. alterniflora from the Atlantic Coast, where ergot has reached epidemic levels. Neighbor-joining analysis of amplified fragment length polymorphism markers suggests that G3 C. purpurea in Washington is closely related to Southeastern USA G3. An AMOVA suggests that Willapa Bay isolates are different from all other geographic regions except Argentina. The low intensity of disease in Washington may be due, in part, to a G3 ergot population that is not well adapted to conditions in this area.