Genetic diversity within tall form Spartina alterniflora Loisel.: Along the Atlantic and Gulf coasts of the United States

Spartina alterniflora is the dominant flowering plant of regularly flooded salt marshes along the Atlantic and Gulf coasts of the United States. Studies have suggested that there may be a genetic basis for the morphological, physiological, and phenological differences observed in plants sampled over a broad geographic range. Randomly amplified polymorphic DNA (RAPD) analysis was employed to assess the genetic variability in tall form S. alterniflora from the Atlantic and Gulf coasts. Twenty-nine RAPD primers produced 300 scoreable electrophoretic bands, of which 225 were polymorphic (75%). An UPGMA (unweighted pair-group method using an arithmetic average) phenogram based on Jaccard's genetic distances showed three clusters of plants: New England/New Jersey, North Carolina/South Atlantic, and Gulf coast. Analysis of molecular variance (AMOVA) was used to estimate how genetic variability is partitioned among regions, areas, and individuals. The resulting variance components were highly significant at all hierachical levels for the sampling regime employed. The correlation between genetic and estimated coastal geographic distance was positive and highly significant based on Mantel's non-parametric test. Although direct gene flow among plants from geographically separate areas is not probable due to differences in flowering phenology, a total barrier to the exchange of genetic information is not likely. Present data and results of previous studies suggest a genetic continuum for this species rather than discrete, isolated populations.