| Ceratopteris pteridoides (Hook.) Hieron. is an annual aquatic homosporous fern(2n=28),belonging to Ceratopteris, Parkeriaceae. It always distributes in tropical and subtropical regions in China including Hunan province, Hubei province, Anhui province, Jiangsu province, Guangxi province and Yunnan province. Fresh leaves of C. pteridoides can be eaten. Also it can be used as medicinal and ornamental plants and regarded as model plant for the study of sex determination, molecular biology, gamete morphology, biochemistry, genetics, cell biology and other disciplines for plants.The numbers and populations of C. pteridoides had declined sharply in China, due to human activities. It has been listed among the second category of Protected Wild Plants in China. Mating system is the most critical factors on the study of plant genetic diversity, genetic structure, spatial distribution of genotype and gene flow. Therefore, it is necessary to study the mating system of endangered plants, for exploring the mechanism of endangered species and biodiversity.In this study, we use the AFLP (amplified fragment length polymorphism) technology, gametophyte development and self-test experiments in order to quantitative analysis the mating system of C. pteridoides. We hope this will be considered as basic theory in order to formulate rational conservation strategies. The main conclusions are as follows:(1) Thirteen selected AFLP primers amplified475reproducible bands, with143of them being polymorphic. A low level of genetic diversity was found at the species level (percentage of polymorphic loci Pp=30.11%, Nei’s genetic diversity index H=0.081and Shannon diversity index1=0.136). However, Clonal diversity and clones richness of populations (Simpson diversity index D=0.99, Fager index E=0.99) were very high, which is closely related to sexual reproduction;(2) Analysis of molecular variance (AMOVA) showed that53.27%of the total genetic diversity was attributable to among-population, coinciding with genetic differentiation coefficient(Gst=0.5036) at population level. It might be speculated that habitat fragmentation led to the decrease of Nm among populations (Nm=0.4876), forcing selfing behavior within populations, and the level of genetic differentiation within populations becomes lower. Mantel test showed no significantly correlation between their geographic distance and genetic distance(r=0.3872, p=0.9798).(3) Gametophyte development and selfing experiments showed a lower germination rate of C. pteridoides spores, suggesting more stringent requirements on the growth environment. Cultured under suitable conditions, gametocytes are more likely to develop into hermaphrodite and the survival rate is more than72.9%after isolation culture, detecting a certain level of self-potential.(4) The analysis of mating system showed that multilocus outcrossing rate (tm) and multilocus outcrossing rate (ts) values were all above0.863, inbreeding index (tm-ts) value is0.136and the level of inbreeding coefficient F is0.507, each population is smaller, detecting that outcrossing is dominated in C. pteridoides. And the value of outcrossing leve among parents (rp(s)-rp(m)) is-0.078, suggesting that parents have a lower level of correlation.(5) When carrying out in-situ conservation, one of the most effective measures is to protect its habitat and reduce human activities. Many protected locations would be established. Considering that C. pteridoides tends to outbreeding and genetic diversity is in low level, we had better to mix populations form different areas as much as possible when carrying out ex-situ conservation.Thus, the chance of inbreeding will decrease, the level of gene flow will increase, genetic diversity will be enriched and the effective number of population will be bigger. |
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