Identification of Dendrobium species by dot blot hybridization assay

A method was developed for rapid identification of Dendrobium species by a dot blot hybridization assay. The dot blot system is based on species-specific amplified fragments derived from the internal transcribed spacer (ITS) region of different Dendrobium species as target DNA, which were blotted as dots on the nylon membrane. A small aliquot of the ITS amplified product from a selected species or mixed ITS DNA from several species was labeled by peroxidase and used as a probe for hybridization to the dot blot membrane. Simply visualizing the positive hybridization reaction between the probe DNA and the target DNA could identify the selected species. The D. officinal-specific and D. nobile-specific ITS-based probes could separately identify D. officinal and D. nobile. Eight Dendrobium species, including D. salaccense, D. brymerianum, D. ellipsophyllum, D. chrysanthum, D. officinale, D. thyrsiflorum, D. nobile and D. chrysotoxum could be simultaneously detected using their complex ITS amplified products as a probe, and the ITS DNA probe amount for detection by the dot blot membrane is very small, just 2.5 ng. The assay can also be used to identify the resource species of Fengdou Shihu and Huangcao Shihu from the commercial market. The identification based on the ITS sequence was superior to the conventional approaches in speed, sensitivity, and specificity. Therefore, the polymerase chain reaction (PCR)-dot blot hybridization assay can be considered a reliable method for general identification of commercial Shihu.