Genetic diversity in the introduced clonal grass Poa bulbosa (Bulbous bluegrass)

Bulbous bluegrass (Poa bulbosa) is a perennial bunchgrass with a widespread distribution throughout its native range in and the Mediterranean. This grass has been introduced into North America and now occurs throughout much of the western United States. Within its native range, bulbous bluegrass reproduces mainly through sexual means; however, in North America clonal reproduction occurs primarily through the production of vegetative structures called bulblets. High chromosome counts are frequently reported for this species and suggest it is a polyploid. To assess the level and pattern of genetic diversity of bulbous bluegrass across a portion of its introduced range, a total of 10 populations from Idaho, Oregon, and Washington were analyzed by staining for 14 enzymes that were coded for by 19 genetic loci. Results indicate that bulbous bluegrass contains higher levels of genetic variation than expected for an introduced clonal plant species: 27.9% of loci are polymorphic per population, with an average of 1.54 alleles per locus, and a mean observed heterozygosity of 0.202. On average, 64% of all individuals within these populations possess three or four alleles at one or more loci; a value consistent with previous reports for autopolyploid species. A total of 84 multilocus genotypes were detected in these 10 populations, with an average of 9.6 genotypes per population. The number and complex distribution of multilocus genotypes observed in this study may be the result of multiple introductions of this species into its new range, and/or occasional sexual reproduction within introduced populations.