Study On Genetic Diversity Of Mangrove Species From China In The Genus Sonneratia

The genetic diversity and genetic structure of six mangrove species of the genusSonneratia distributed in China were assessed by means of inter-simple sequence repeats (ISSR)markers. The correlation between population genetic diversity and environmentall factors wereanalyzed through correlation analysis. Additionally, inter-simple sequence repeats (ISSR)DNA polymorphisms were utilized to distinguish taxa and relationships within thegenus Sonneratia. The main results obtained from the dissertation study are asfollows.1. Leaf samples of eighty-six individuals from three Sonneratia caseolaris natural populations, as well as one introduced population in Hainan Island, China were collected. Eleven ISSR primers gave rise to 239 discernible DNA fragments of which 194 (81.17%) were polymorphic. The percentage of polymorphic bands at the population level was from 40.59% to 50.21%, 45.71% on average. The Nei's gene diversity and Shannon's information index were 0.2103 and 0.3256 respectively at the species level, 0.1468 and 0.2210 respectively at the population level. Based on Nei's Gst value, 69.83% genetic variance was resided among individuals within populations, 30.17% genetic variance was resided among populations. The genetic identity between populations was 0.9011 on average. UPGMA cluster analysis based on Nei's genetic distance divided the populations into two main groups: Wanning population (WN) and Qionghai population (QH) formed one group, Hengshan population (HS) and Dongzhai Harbor population(DZG) were in the other group. The Mantel test showed that genetic distance was correlated positively with geographical distance, but not significantly. The correlation analysis showed that no significant relation was observed between population genetic diversity level and environmental factors.2. Leaf samples of fifty-seven individuals from three Sonneratia paracaseolaris natural populations, as well as three introduced populations in Hainan Island, China were collected. Eleven ISSR primers gave rise to 161 discernible DNA fragments of which 131 (81.37%) were polymorphic. The percentage of polymorphic bands at the population level was from 19.25% to 71.43%, 40.58% on average. The Nei's gene diversity and Shannon's information index were 0.2081 and 0.3501 respectively at the species level, 0.1340 and 0.2023 respectively at the population level. Based on Nei's Gst value, 64.37% genetic variance was resided among individuals within populations, 35.63% genetic variance was resided among populations. The genetic identity between populations was 0.8982 on average. UPGMA cluster analysis based on Nei's genetic distance divided the populations into two main groups: Dongge population (DG) and Qionghai population (QH) formed one group, Linjiawan population (LJW),Miaopu population (MP),Sanjiang population (SJ) and Touwan population (TW) were in the other group. The Mantel test showed that genetic distance was not correlated with geographical distance. The correlation analysis showed positive relations between populaton genetic diversity level and soil pH value and soil conductivity; negative correlations between population genetic diversity level and soil total nitrogen, total phosphorous, and extractable phosphorous, but none is significantly.3. Leaf samples of one hundred indidivuduals from four Sonneratia alba natural populations, as well as one introduced population in Hainan Island, China were collected. Eleven ISSR primers gave rise to 133 discernible DNA fragments of which 103 (77.44%) were polymorphic. The percentage of polymorphic bands at the population level was from 51.88% to 65.41%, 57.74% on average. The Nei's gene diversity and Shannon's information index were 0.2271 and 0.3489respectively at the species level, 0.1837 and 0.2775 respectively at the population level. Based on Nei's Gst value, 81.02% genetic variance was resided among individuals within populations, 18.98% genetic variance was resided among populations. The genetic identity between populations was 0.9342 on average. UPGMA cluster analysis based on Nei's genetic distance divided the populations into two main groups: Sanya population (SY) and Lingshui population (LS) formed one group, Qionghai population(QH),Wenchang population(WC) and Dongzhai Harbor population(DZ) were in the other group. The Mantel test showed that genetic distance was significantly correlated with geographical distance. The correlation analysis showed a significant positive relation between population genetic diversity level and soil pH value, and no significant relation was observed between the population genetic diversity level and other environmental factors.4. Leaf samples of thirty-nine individuals from two Sonneratia hainanensis natural populations, as well as two introduced populations in Hainan Island, China were collected. Eleven ISSR primers gave rise to 166 discernible DNA fragments of which 142 (85.54%) were polymorphic. The percentage of polymorphic bands at the population level was from 14.46% to 80.12%, 46.24% on average. The Nei's gene diversity and Shannon's information index were 0.2329 and 0.3619 respectively at the species level, 0.1538 and 0.2317 respectively at the population level. Based on Nei's Gst value, 75.89% genetic variance was resided among individuals within populations, 24.11% genetic variance was resided among populations. The genetic identity between populations was 0.9253 on average. UPGMA cluster analysis based on Nei's genetic distance divided the populations into two main groups: two natural populations, Dongge population (DG) and Touwan population (TW), formed one group, two artificial populations, LJW and SJ, were in the other group. The Mantel test showed that genetic distance was significantly correlated with geographical distance. The correlation analysis showed the population genetic diversity level of S.hainanenais had negative correlations with the content of total soil nitrogen, the content of soil organicmatter and logitude significantly, and no significant relation was observed between the population genetic diversity level and other environmental factors.5. Leaf samples of thirty-nine individuals from three Sonneratia ovata populations in Hainan Island, China were collected. Eleven ISSR primers gave rise to 185 discernible DNA fragments of which 127 (68.65%) were polymorphic. The percentage of polymorphic bands at the population level was from 36.76% to 54.95%, 47.21% on average. The Nei's gene diversity and Shannon's information index were 0.1411 and 0.2292 respectively at the species level, 0.1209 and 0.1910 respectively at the population level. Based on Nei's Gst value, 87.58% genetic variance was resided among individuals within populations, 12.42% genetic variance was resided among populations. The genetic identity between populations was 0.9709 on average. The correlation analysis showed the population genetic diversity level of S.ovata had a negative correlation with the soil conductivity significantly. On the contrary, it had a significant positive correlation with the content of total soil phosphorous. No significant relation was observed between the population genetic diversity level and other environmental factors.6. Leaf samples of forty-five individuals from two Sonneratia apetala populations in Hainan Island and Shenzhen, China were collected. Eleven ISSR primers gave rise to 196 discernible DNA fragments of which 128 (65.31%) were polymorphic. The percentage of polymorphic bands at the population level was 48.47% on average. The Nei's gene diversity and Shannon's information index were 0.1556 and 0.2441 respectively at the species level, 0.1403 and 0.2142 respectively at the population level. Based on Nei's Gst value, 90.15% genetic variance was resided among individuals within populations, 9.85% genetic variance was resided among populations. The genetic identity between populations was 0.9645 on average. The gene flow was 2.2872.7. Genetic relationships in the genus Sonneratia were analyzed using ISSR markers. Sixty-six individuals, representing six taxa of S.caseolaris, S.paracaseolaris, S.alba, S.hainanensis, S.ovata, S.apetala, were sampled in this study. The resultshowed that the biggest genetic distance was 0.3879 between S.caseolaris and S.alba, the smallest genetic distance was 0.1617 between S.ovata and S. hainanensis. UPGMA cluster analysis based on Nei's genetic distance divided the 6 species of Sonneratia into three main groups: Group A contained S.caseolaris, Group B contained S.apetala, and Group C included 4 species: S.paracaseolaris, S.alba, S.hainanensis, S.ovata. Group C could be divided into two subgroups, C1: S.paracaseolaris, S.alba and C2: S.hainanensis, S.ovata. UPGMA cluster analysis based on Nei and Li similarity coefficient divided the six species of Sonneratia into two groups: Group A included S.caseolaris, S.paracaseolaris and S.alba; Group B included S.ovata, S.hainanensis and S.apetala. The result is simialr to Ko's (1993) phylogenetic analysis based on the presence or absence of petals.8. The additivity of ISSR bands in S.paracaseolaris with its putative parents S.alba and S.caseolaris was 57.8%, verifying that S.paracaseloaris is a hybrid at the molecular level. The additivity of ISSR bands in S.hainanensis with its putative parents S.alba and S.ovata was 23.9%, indicating that S.hainanensis is possibly also a species of hybridization origin.9. According to IUCN, S.hainanensis, S. paracaseolaris and S.ovata are all endangered species in China, S.alba is a threatened species. The reaon that has rusulted them into endangered status is mainly people's economic activities, especially fish-pond and shrimp-pond operations. Furthermore, the lower pollen stainability and lower seed goodness of S.paracaseloaris and S. hainanensis are also reasons for their endangerment. From the study, higher genetic diversity level were detected in the Sonneratia species, so the factors threatened the survival of endangered Sonneratia species are not associatied with their genetic diversity level.10. In that the individual numbers of S. hainanensis, S.paracaseloaris and S.ovata are all rare in the field, so every individual should be protected. Great genetic differentiation has happened among S.paracaseolaris populations, so sampling from more populations is the conservation sample strategy at ex situ conservation. Most genetic variance of S. alba was resided among individuals within...