Hybridization, polyploidy and clonality influence geographic patterns of
diversity and salt tolerance in the model halophyte seashore paspalum
(Paspalum vaginatum)
Abstract
Seashore paspalum (Paspalum vaginatum Swartz) is a halophytic
turfgrass and emerging genomic model system for the study of salt
tolerance in cereals and other grasses. Despite recent interest and an
increase in available tools, little is known about the diversity present
in wild populations of P. vaginatum and its close relative
P. distichum. Variation in ploidy, clonal propagation,
hybridization, and subgenome composition appear to occur in the wild and
may interact to influence geographic patterns of adaptation,
particularly in response to environmental salinity levels. Using 218
accessions representing >170 wild collections from
throughout the coastal southern United States plus existing USDA
germplasm, we employed genotyping-by-sequencing, cpDNA sequencing and
flow cytometry to identify genetic differentiation and ploidy variation.
Within P. vaginatum, there are two morphologically distinct
ecotypes: the fine-textured ecotype is diploid and appears to reproduce
in the wild both sexually and by clonal propagation; in contrast, the
coarse-textured ecotype consists largely of clonally-propagating
triploid and diploid genotypes. The coarse-textured ecotype appears to
be derived from hybridization between fine-textured P. vaginatum
and an unidentified Paspalum species. These clonally propagating
hybrid genotypes are more broadly distributed than clonal fine-textured
genotypes and may represent a transition to a more generalist adaptive
strategy. The triploid genotypes vary in whether they carry one or two
copies of the P. vaginatum subgenome, indicating multiple
evolutionary origins. This variation in subgenome composition shows
associations with local ocean salinity levels across the sampled
populations and may play a role in local adaptation.