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Denphal-type Dendrobium is the most popular orchid for cut flower and potted plant trade. To improve commercial traits, many novel cultivars have been produced through hybridization by commercial breeders. However, the genetic relationship of most cultivars is unclear, thus hindering the progress of Denphal-type Dendrobium breeding programs. Therefore, the development of molecular markers is encouraged to identify different cultivars. In this study, based on the transcriptome database of the Denphal-type Dendrobium ‘Red Bull’, the polymorphisms expressed sequence tag-derived simple sequence repeat (EST-SSR) were developed from 100 pairs EST-SSRs that were randomly selected from the EST-SSR database. The genetic relationship of 42 Denphal-type Dendrobium cultivars was analyzed according to the developed EST-SSRs. Then, the transferability of EST-SSRs was analyzed by performing a relationship analysis of 40 Dendrobium species. The results showed that a total of 5174 potential EST-SSR markers were identified with 4486 unigene sequences, and 5289 primer pairs were successfully designed. Of the selected 100 pairs of EST-SSRs, a total of 86 pairs produced the expected polymerase chain reaction products of the primary screening, 58 pairs produced the expected fragment size, and 20 pairs showed polymorphisms. Furthermore, the dendrogram of 42 cultivars showed that at a genetic distance of 0.15, the cultivars collected were grouped into five clusters of three major clusters and two minor clusters; all these clusters had the same characters of each cluster. The transferability analysis showed that 18 of the 20 EST-SSR markers among the 40 Dendrobium species were polymorphic. Overall, this study developed EST-SSR markers and will be valuable to facilitating genetic diversity in Denphal-type Dendrobium cultivars and Dendrobium species.
Denphal-type Dendrobium is the famous cut and potted flower in the world, and most cultivated in tropical and subtropical regions. However, it often suffers from cold in winter in subtropical regions. To verify the physiological response of Denphal-type Dendrobium under low temperature in this study, the mature and young plantlets of Dendrobium Udomsri Beauty were treated under 15, 10, and 5 °C, respectively. And then the electrical conductivity (EC), soluble protein, soluble sugar, free proline, malondialdehyde (MDA), chlorophyll content, and the rate of defoliation after regrowth were measured. The results showed that both mature plant and young seedlings of Dendrobium Udomsri Beauty, the EC, soluble protein, soluble sugar, free proline, MDA content, and defoliation rate were increased with the decrease of treatment temperature and the extension of treatment times. The content of chlorophyll decreased gradually with the decrease of treatment temperature and the extension of treatment times. The correlation analysis showed that soluble sugar, free proline, MDA, chlorophyll content, and defoliation rate were significantly correlated with the semi-lethal temperature. It is indicated that the content of free proline, MDA, chlorophyll, and defoliation rate could be used as the effective indexes for the comprehensive assessment of cold tolerance of Dendrobium Udomsri Beauty.