Ploidy Level and Genetic Diversity in the Genus Paspalum, Group Disticha

The importance of the warm-season grass Paspalum vaginatum Sw. lies in its salt tolerance and its ability to serve as forage, ground cover for erosion control, and turf for sport surfaces in vulnerable areas in the tropics and subtropics. We conducted DNA content measurements using flow cytometry and diversity analyses using 43 simple sequence repeat (SSR) markers in a set of 97 Paspalum group Disticha accessions to resolve the relationship between the two group Disticha species, P. vaginatum Sw. and P. distichum L., and determine their ploidy level, genetic diversity, population structure, and distribution history. Using glume pubescence as a distinguishing characteristic, P. vaginatum accessions were largely diploid and P. distichum accessions largely polyploid, although exceptions were identified in both species. Transferability of genomic P. vaginatum SSRs to P. distichum confirmed the close genetic relationship between the two species. Similarity in SSR allele sizes between the two species may be an indication of gene flow. Population structure analyses grouped the germplasm into three subpopulations. One subpopulation consisted of accessions with mixed leaf texture, mixed glume pubescence phenotypes, and mixed ploidy levels. The other two subpopulations contained only diploid members with a typical P. vaginatum turf phenotype. Our data bring into question the distinguishing characteristics of P. distichum and P. vaginatum and whether they should be considered the same species. We also make some strategic recommendations for new collections and accession maintenance.