Genetic diversity of the submerged macrophyte Hydrilla verticillata (L. f.) Royle in a river system in Japan

The genetic diversity of Hydrilla verticillata was studied in the Kako River system, Hyogo Prefecture, southwestern Japan, including some of its tributaries. Sex expression (monoecy or dioecy), ploidy level (diploid or triploid), and isoenzyme phenotypes were investigated for plant samples collected from 51 sites along the water course. Monoecious plants occurred at 10 sites and dioecious plants at 47 sites. Among dioecious plants, diploid and triploid plants occurred at 1 and 46 sites, respectively. Seven multienzyme phenotypes (MEPs) were recognized by electrophoretic analysis among dioecious triploid plants. The distribution pattern of nine biotypes based on sex expression, ploidy level, and MEPs suggested the possibility of ecological differentiation among different biotypes. The implications of genetic diversity demonstrated in this study were discussed in relation to the conservation strategy of biodiversity in a river system.