ECOLOGICAL GENETIC INTERACTIONS BETWEEN A CLONAL HOST-PLANT (SPARTINA-PECTINATA) AND ASSOCIATED RUST FUNGI (PUCCINIA-SEYMOURIANA AND PUCCINIA-SPARGANIOIDES)

The spatial scale of genetic diversity among patches of a host plant c ould affect the likelihood of pathogen adaptation to the host. If host patches are genetically distinct, pathogen adaptation to local host g enotypes may occur. To study this issue, we focused on the ecological and genetic interactions between two rust fungi, Puccinia seymouriana and P. sparganioides, and the clonal prairie grass, Spartina pectinata . In a field transplant experiment, disease levels differed among plan ts from different patches, suggesting variation in resistance. Over a 4.5-km scale, disease levels were not higher on plants transplanted ba ck into their source patch as opposed to other locations, providing no evidence for local adaptation in the pathogen. However, on the spatia l scales examined (ranging from 0.2 km to 120 km), there was no relati onship between the physical distance separating host patches and their similarity in isozyme banding patterns, implying that plants from mor e distant patches are not necessarily more genetically distinct than p lants from nearby patches. Plants derived from the most distant locati on had, on average, the lowest mean number of pustules at the end of t he summer, suggesting the need for reciprocal transplant studies to be performed on a larger spatial scale.