Discussion
Paspalum vaginatum is a promising new genomic model system for
the study of salt tolerance in cereals and other plant species. Our
population genomic analyses, using new wild samples collected widely
throughout the southern US, and without a bias toward turf-like
(fine-textured) ecotypes, has allowed us to make several key insights
into the genetic diversity, population structure and genomic composition
of this species, with broader implications for mechanisms of salinity
adaption in widespread species. Our findings include the following: 1)
Clonal propagation occurs extensively in both P. vaginatumecotypes, as well as in the non-halophytic sister species P.
distichum (Table 1; Table S1); 2) Clones of the coarse-textured ecotype
are more widely distributed than the fine-textured ecotype, both
geographically and with respect to the environment (Fig. 1; Fig. 2),
suggesting a “general purpose genotype” adaptive strategy for the
former and a “frozen niche” strategy for the latter; 3) The system is
characterized by extensive ploidy variation, including diploids and
allotriploids that vary in their subgenome composition (Table 1; Fig.
S5, S6); and 4) Increasing number of P. vaginatum subgenomes
within a genotype are associated with occurrence in more saline
environments (Fig. 5), suggesting a direct effect of the halophytic
species’ genome on salinity adaptation. Collectively these findings
suggest that both clonal propagation and hybridization-associated ploidy
variation play key roles in the ability of this species to grow widely
across environments of varying salinity.