Genetic Diversity Research Of Aquatic Plants Duckweeds In Fujian Province

Duckweeds (Lemnaceae) belong to monocotyledonous aquatic plants,and are the smallest flowering plants in the world. Their growth environments are usually the static lake, waste ponds, and rice fields. They are classified into 5 genera and 37 species. All species in the genera Wolffia and Wolffiela, as well as Lemna trisuca do not contain any roots, while other species in the genera Spirodela and Landoltia and Lemna contained only frond and root. They are mainly propagated by budding. Duckweeds growth speed is very fast when grown in nutrient-rich conditions, and can grow exponentially. Duckweeds are tolerant to sewage water with high concentrations of nitrogen and phosphorus, and purify the wastewater at the same time. Some duckweed strains contain starch content of up to 75% at certain conditions, and their biomass is easy to be converted into ethanol by fermentation due to their low content of lignin. Therefore, duckweeds are potential bioenergy crops. The genetic resources in the wild ecosystem are important basis for future utilization of these valuable plants. However, due to large scale utilization of herbicides,the natural habitat of duckweeds are becoming smaller and smaller. It is important to collect, preserve and evaluate the duckweed genetic resources before they are endangered.In this study, we focused on studying the duckweed genetic resources in Fujian Province.The main results are as follows:(1) A total of 63 duckweed populations in 53 counties of Fujian Province were studied,of which 17 population contained only one species, and other populations contained more than two species (73%). A total of 119 axentic strains were isolated. Morphological analysis showed that there are 4 genera with 4 species, which are Lemna aequinoctialis,Spirodela polyrhiza, Landoltia punctata and Wolffia globosa. Lemna aequinoctialis is the species that is most widely distributed in Fujian, Spirodela polyrhize is the second widespread, followed by Landotia punctata and Wolffia globosa.(2) The chloroplast atpF-atpH internal sequence and the rpS16 intron sequence were obtained by PCR amplification and sequencing. Phylogenetic analysis indicated that these germplams belong to four species: Landoltia punctata , Spirodela polyrhiza,Wolffia globosa, and Lemna aequinoctialis.(3) Genetic diversity analysis using DnaSP 5.10.01 software showed rich biodiversity among the germplasms, and rpS16 presented more diversity than atpF-atpH. The nucleotide diversity of atpF-atpH and rpS16 was 0.03153 and 0.05123 , respectively; the different nucleotide number per kb was 20.374 and 44.6751, respectively; the population mutation rate was 0.03640 and 0.05164, respectively, and the haplotype diversity was 0.577and 0.617, respectively. The haplotype numbers for atpF-atpH and rpS16 were 4, 2,and 2, respectively.(4) Lemna aequinoctialis contained the highest genetic diversity among the four species. The haploid type number based on atpF-atp and rpS16 sequences were 4, 2,2 and 1 for Lemna aequinoctialis, Spirodela polyrhiza, Wolffia globosa, and Landoltia punctata,respectively. Moreover, the total number of nucleotide mutations in Lemna aequinoctialis was 27 and 40 for atpF-atpH and rpS16, respectively, with SNP numbers of 27 and 40, respectively, which were the highest among the four species.(5) The genetic diversity in South Fujian was higher than that in North Fujian, and the nucleotide diversity, different nucleotide number and the population mutation rate of atpF-atpH and rpS16 in South Fujian were twice as high as those in the North.