Development Of EST-SSR Markers For The Study Of Genetic Diversity In Dendrobium Genus

The Dendrobium genus is the second biggest branch of Orchidaceae family, and usually live in relatively narrow habitat with microclimate, which cause its high ecological diversity. Many of this genus are Chinese traditional precious medical herbals and valuable ornamental plants, but they're all endangered now. Thus researchers should take effective measures to study and protect Dendrobium genus.Presently research on Dendrobium genus was not in depth, our study analyzed EST-SSR from Dendrobium nobile cDNA library in several ways, aimed to assist the study of Dendrobium on genetic map, germplasm resource analysis, identification of varieties, genetic relationship, functional genomics and comparative genomics, etc.(1) 3014 EST-SSR sequences were screened and 626 EST sequences containing microsatellite were obtained, including 57 kinds of motifs. Di-nucleotide repeats and Tri-nucleotide repeats were more than other types, and the dominant type of each is AG/CT, AAG/CTT. There were 44.39% SSRs in the putative coding region (ORF), 30.1% SSRs in the 5'untranslated region,25.51% SSRs in the 3'untranslated region.(2) Among 199 pairs of primers synthesized,151 pairs of primers of them could be successfully amplified.144 EST-SSR markers were used to assess the transferability and polymorphism of the Dendrobium collections consisting of 32 accessions classified to 6 morphological groups. The average of transferability cross groups was 51.17%, the average of polymorphism was 83.43%. Otherwise, the average of transferability and polymorphism about SSRs in the putative coding region (ORF) was 58.99% and 72.09% respectively, while it was 45.91% and 75.10% in 5' untranslated region, and 52.54% and 75.55% in 3'untranslated region.(3) 31 pairs of primers were randomly selected for analyzing genetic diversity of 32 Dendrobium accessions. Totally,345 alleles were amplified, and all were polymorphic. The range of DICE similarity was 0.19-0.55,0.42 is the average. Using UPGMA to cluster, a phylogenetic tree was obtained,32 Dendrobium accessions were grouped into 5 clusters at a DICE similarity level of 0.34. This result is not completely consistent with former study, and shows EST-SSR is a strong tool to assist morphological study and correctly reveal genetic diversity and relationship cross Dendrobium genus.