Intraspecific groups of Claviceps purpurea associated with grass species in Willapa Bay, Washington, and the prospects for biological control of invasive Spartina alterniflora

Spartina alterniflora is a salt marsh halophyte introduced to the Pacific Coast of the United States that has become a noxious weed in Willapa Bay, Washington. A sap-feeding insect has been released as part of a biological control program, which 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 floral-infecting, fungal pathogen Claviceps purpurea, which causes the ergot disease. This species is comprised of three intraspecific groups, of which one is specific to salt marsh habitats, G3. Based on random amplified polymorphic DNA markers, all three intraspecific groups of C. purpurea were found on grasses in Willapa Bay. The incidence of ergot on Spartina was very low over the three-year sampling period. 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 to C. purpurea 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 most closely related to Southeastern USA G3 C. purpurea. Pairwise comparisons as part of AMOVA showed that Willapa Bay isolates are different from those of 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.