**4. Conclusion**

Our results showed that the modified CTAB-B method promoted here was of high quality, purity and yield and was suitable for downstream molecular assays. Based on a CTAB method, the protocol has been improved as follows: the more volume of extraction buffer was used to completely break down the cell walls; the samples were ground with PVPP to effectively inhibit the oxidation of phenolics; during the extraction, 3 mol/L sodium acetate (NaAc) was added to reduce markedly the co-precipitation of polysaccharides with the nucleic acids; contaminating RNA was removed with RNase I; acid phenol extraction (phenol: chloroform: isoamylal alcohol (PCI)=25:24:1) was used to effectively removes the residual proteins and inhibitors in the RNase reagent. Thus, despite the high levels of secondary metabolites in the leaves of *R soongorica*, the high quality DNA is isolated from the nuclei without interference. Moreover, the new protocol is also suitable for isolating genomic DNAs from other desert plant species and tissues that are rich in secondary metabolites.

### **5. Acknowledgments**

This study was supported by the National Key Technologies R&D Program: The Integration and Experiment Demonstration of Ecological Restoration Technology in Loess Hills-Sand Areas (2011BAC07B05) and by the Ministry of Forestry Commonweal Special Project: Monitoring and Assessment Technologies for Hydrological Regulation Function of Desert Ecosystem (201004010-05).
