A comparison of the extent of genetic variation in the endangered Sagittaria natans and its widespread congener S. trifolia

Genetic variation and clonal diversity of 14 populations of the endangered clonal herb Sagittaria natans and its widespread congener S. trifolia were investigated using inter-simple sequence repeat (ISSR) markers. Using nine effective ISSR primers, a total of 92 DNA fragments were generated with 54 (percentage of polymorphic loci, PPL: 58.7%) being polymorphic. A higher level of genetic diversity among populations was found in S. natans (PPL: 48.9%) than S. trifolia (PPL: 32.6%). Analysis of molecular variance (AMOVA) showed that in each species a similar proportion of the total genetic variation resided within and among populations, and that between species there was a moderate genetic differentiation (Gst: 0.601). With the use of 54 polymorphic ISSR markers, we identified 116 genets among 138 samples from five S. natans populations, and 93 genets among 215 samples from nine S. trifolia populations. The proportion of distinguishable genets (PD: mean 0.82) and Simpson's diversity index (D: mean 0.95) for S. natans exhibited higher degree of clonal diversity compared to S. trifolia (PD: mean 0.42; D: mean 0.89). Sexual reproduction might have been played an important role in maintaining and increasing the clonal diversity in both species. Recent and on-going decimation of S. natans populations in the region appear not to have had a major impact on genetic diversity in this rare plant.