Construction Of Pyropia Haitanensis Core Ger Mplasm Repositories

Pyropia haitanensis is distributed widely along the southeastern coast of China and is one of the most important artificially cultivated algae species.The economic development and the growth in the demand for its consumption,have promoted the development of the Pyropia cultivation industry in China.Therefore,the preservation of Pyropia germplasm and breeding projects have become increasingly important.A number of wild P.haitanensis populations are distributed along China's southeastern coast.These populations contain abundant germplasm resources.In recent years however,environmental pollution has caused significant damage to this source of wild germplasm.To save and use these wild P.haitanensis germplasm resources effectively,the construction of a core collection has become a top priority.In this study,molecular systematics principles and methods were used to select simple sequence repeat(SSR)molecular markers,which combined with traditional phenotypic methods were used to analyze the genetic diversity in 77 P.haitanensis germplasm strains.The construction of a core collection of P.haitanensis germplasm based on phenotypic data,SSR molecular markers,and a combination of phenotypic and SSR marker data is described.The results will be of great significance to the protection of P.haitanensis germplasm resources for use in future breeding projects.The main results are described below.1.Phenotypic traits,such as length,width,thickness,and color of the 73 P.haitanensis germplasm strains from laboratory breeding and wild collections were investigated and recorded.Weight showed one of the largest variations among the phenotypic traits studied,while thickness of the tip showed the least variation.All the variation coefficients were over 10%,except the coefficients for thickness.The average of the differentiation coefficient for each trait was 92.96%,which indicated genetic diversity was abundant.The analysis of variance showed that the variance components between strains were 77%.The strain variation was only 5.8%,machine error was about 17.3%,and genetic variation between strains was greater than the variations within strains.2.The genetic diversity among 77 P.haitanensis germplasm strains was analyzed using 30 SSR primers.A total of 134 sites were amplified,of which 126 were polymorphic;the percentage of polymorphic sites was 94%.The observed number of alleles was 1.9310,the effective number of alleles was 1.5393,Nei's genetic diversity degree was 0.2963,and Shannon's information index was 0.4473.All these values are high,implying that the P.haitanensis genetic diversity was high.3.Based on the phenotypic data of 73 P.haitanensis germplasm strains,a method to construct a core collection of P.haitanensis germplasm strains was developed.The merits of using Mahalanobis distance and Euclidean distance to construct the core collection were considered and,finally,Euclidean distance combined with three different sampling methods and five sampling ratios was selected to construct 15 core collections.The core collections were evaluated using principal component analysis to ensure its representativeness.We found that when the sample size was 25%,using Euclidean distance in the random sampling strategy to build the core collection of P.haitanensis produced the most representative results.The final optimal solution generated a core collection that contained 18 germplasm strains.4.Based on the SSR marker data of 77 P.haitanensis germplasm strains,we explored ways to build a second P.haitanensis core collection.Using three different genetic distances,two sampling methods,and five sample sizes a core collection that contained 30 germplasm strains was constructed and evaluated using principal component analysis.The results showed that the optimal solution was to use the preferred sampling sites with a sampling ratio of 15% in the SM genetic distance to construct the core repositories.The final optimal solution generated a core collection that contained 12 germplasm strains.5.Based on the 73 P.haitanensis germplasm strains phenotype and SSR molecular data,we built a third P.haitanensis core collection.Using the phenotypic data to cluster the strains according to the molecular data,we calculated the effective number of alleles,and used allele preferred sampling method to take samples.Five different sample sizes were used to cluster and compress the data,and five pre-selected core germplasm collections were obtained.After their evaluation and validation,under a sampling ratio at 20%,we obtained a core collection that contained 15 germplasm strains.6.The three core collections of germplasm strains that were selected based on phenotypic data,SSR marker data,and phenotypic data combined with SSR data were evaluated and compared.By taking both environmental and genetic interaction effects into account,we choose the core collection that contained the 15 germplasm strains that were selected based on the combined phenotypicand SSR maker data as the most representative P.haitanensis core germplasm collection.