Low level of genetic variation and restricted gene flow in water lily Nymphaea tetragona populations from the Amur River

Nymphaea tetragona is the most widely distributed water lily in China. It is also an important ornamental plant. However, with the degradation and fragmentation of wetlands in China, populations of N. tetragona have shrunken rapidly in recent decades. Genetic variation and population structure of eight N. tetragona populations from the Amur River basin in northeastern China were assessed by inter-simple sequence repeat (ISSR) markers. Thirteen primers produced a total of 289 unambiguous bands of which 234 (81.0%) were polymorphic. N. tetragona appeared to possess a low level of gene diversity within the population (Pp = 43.3%, HE = 0.151 and I = 0.226). The main factors responsible for that were the annual life history and inbreeding reproductive system (FIS = 0.261 or 0.344) of the plant, and recent genetic bottlenecks in populations due to degrading habitats. The F statistics calculated by different approaches consistently revealed a high genetic differentiation among populations, with the proportion of genetic differentiation among populations accounting for >35% of the total genetic diversity (GST = 0.367, θB = 0.371 and F = 0.410). The evident population structure of N. tetragona could be due to self-fertilizing reproduction, restricted gene flow (Nm = 0.424, M = 0.376) and genetic drift. These results are discussed in relation to both in situ and ex situ efforts to conserve this species.