Study On Genetic Diversity And Genetic Structure Of Guava Germplasm Resources In China

Guava(Psidium guajava)belongs to the Psidium genus,it has its origin in the America tropics and is today widely distributed in tropical and subtropical regions.At about 17 th century in China,guava was introduced,which is now mainly cultivated in southern China,Fujian,Taiwan,and has wild distribution in the southwest China includes Sichuan,Yunnan,Guizhou.Guava tree has great tree has a great economic value,and its fruit can use both as food and medicine.Nowadays,with the long-term and continuous collection of germplasm collection,many provinces and autonomous regions in China have established corresponding guava germplasm resources.Due to the lack of systematic and perfect methods of variety identification in the process of collection,confusion of varieties resulted in the occurrence of multiple homonyms and different homonyms,which caused great losses to guava breeding and industrial development.In the early stage of the study,the genetic diversity of 45 guava varieties(lines)were analyzed by morphological markers combined with SSR markers,and in the middle and late stages,the 131 guava germplasm resources in different germplasm resource nurseries or places in China were collected,and a variety of molecular markers were used to comprehensively analyze and investigated the genetic relationship and genetic structure of our country guava germplasm resources.The research results are as follows:Using 45 guava varieties(lines)as test materials,19 phenotypic traits were used for correlation and principal component analysis,and 15 pairs of SSR primers were analyzed with diversity and clustering.The results showed that there were significant genetic variations in phenotypic traits of guava materials,and the variation coefficient of quality traits was less than that of quantitative traits,with the largest variation coefficient of peel color and fruit weight respectively.The fruit weight was significantly positively correlated with leaf length,fruit longitudinal,fruit transverse diameter,fruit cavity longitudinal,fruit cavity transverse diameter,and meat thickness.Fruit firmness was significantly positively correlated with total soluble solids(TSS),and negatively correlated with leaf width and fruit transverse diameter.Six principal components with eigenvalues greater than 1 were extracted by principal component analysis,and the cumulative contribution rate was 73.37%.The contribution rate of fruit weight factor was the highest,which was 23.867%.A total of 65 polymorphic loci were detected by 15 pairs of polymorphic SSR primers with 97.01% ratio of polymorphic loci,the 0.60 of average PIC,the 0.29 of Nei's gene diversity and the 0.44 of Shannon's index.Compared with morphological markers,SSR marker cluster analysis can completely distinguish seedlings from cultivars.Based on phenotypic and SSR molecular markers,it is revealed that 45 guava varieties(lines)were rich in genetic diversity,and can be selected to guide breeding according to different needs of high-quality traits such as fruit quality,plant growth,appearance color and waterlogging tolerance.A total of 131 guava populations were collected from China,and a total of 21 pairs of primers with clear and highly polymorphic bands were screened from 23 pairs of primers for genetic diversity and population structure analysis through optimized SSR reaction system.A total of 124 loci were detected in 21 pairs of SSR primers,and the polymorphic loci were 120.The percentage of polymorphic loci was 96.77%,and the average PIC was 0.6.AMOVA showed that 81% of the genetic variation came from the population,and the variation between the populations was 19%,the genetic distance between populations was 0.028 and 0.200,and the gene flow(Nm)was 1.07.Both principal coordinate analysis and UPGMA clustering classified 131 guava materials into three groups,the genetic similarity coefficient ranged from 0.429 to 0.997,most of the germplasms were not clustered according to their origin.Structure software classified 131 guava materials into three groups: red,blue and green,and clearly identified the pedigree composition among individuals.Twenty-four pairs of polymorphic primers were screened out from 30 pairs of SRAP primers through the optimized SRAP reaction system.318 loci were amplified from 131 guava germplasms,with 304 polymorphic loci and 95.60% polymorphic loci.AMOVA analysis showed that 92% of genetic variation was mainly from within population and 8% from among population.The genetic distance between populations ranged from 0.018 to 0.067,and the gene flow(Nm)was 2.885.UPGMA clustering divided 131 guava germplasms into three groups,which were consistent with SSR markers,and the genetic similarity coefficient ranged from 0.378 to 0.998.Seventeen polymorphic SCoT primers were screened out from 36 single SCoT primers through the optimized SCoT reaction system.131 loci were amplified from 131 guava germplasms,with 125 polymorphic loci and 95% polymorphic loci ratio.AMOVA analysis showed that genetic variation was 87% in the population,the variation among population was 13%.Genetic distance was between 0.017 and 0.075,and gene flow(Nm)was 1.645.131 guava germplasms were clustered into 2 groups and 7 subgroups by UPGMA method,with genetic similarity coefficient ranging from 0.438 to 0.994.The detection efficiency of SSR,SRAP and SCoT markers in 131 guava germplasm genetic diversity was high,indicating that the genetic diversity of guava germplasm resources was rich.The results of mantel correlation analysis showed that the genetic distance between the three markers was significantly irrelevant and supplemented with each other in revealing genetic information.Population clustering results showed that the genetic distances between Brazilian germplasm(BX)and the other six populations were the farthest.The genetic distances of Guangxi Resource Nursery(GX),Fujian Resource Nursery(FJ)and Zhanjiang Resource nursery(ZJ)were relatively close,indicating that the genetic relationships among the three populations were relatively close,and the genetic variation mainly occurred within the population.UPGMA cluster analysis of 131 guava germplasms by three method such as SSR markers alone,SRAP markers alone and combining three markers,classified them into three groups,and clearly distinguish the genetic differences among related species,local species and homologous and heteronymous species.