Keywords: 
• tropical fruits tree /
• DNA extraction /
• modified CTAB method /
• Southern blot analysis

Abstract: Tissues of most tropical fruit trees contain polysaccharide and polyphenolics that restrict the extraction of high-quality genomic DNA for further molecular biology analysis. This experiment was conducted to develop a simple, universal and effective modified CTAB method for genomic DNA extraction from tissues of tropical fruit trees for southern blot analysis. This optimized procedure includes two steps. First, before the DNA was extracted, the polysaccharide and polyphenolics were pre-removed through the STE lysis buffer by centrifugation. In addition, possible contamination by secondary metaboliates could be avoided by picking up the cotton-shaped genomic DNA floccules resuspended in liquid at the DNA precipitation step with ethanol. With the modified CTAB method, high-quality DNAs were extracted from young leaves of the three representative tropical fruit trees, banana （Musa spp.）, papaya （Carica papaya L.） and longan （Dimocarpus longan Lour.）. After digested with different restriction enzymes, fragments of banana ethylene receptor gene （GenBank accession No. AF113748）, papaya phytoene desaturase gene （DQ779922） and longan flowering-related LEAFY homologous gene （DQ160214） were used as probes for further Southern blot analysis, respectively. The hybridization bands were clear with high background. The results indicate that the modified CTAB method, with pre-treated conjugation by DNA pick-up, is a simple and effective protocol for genomic DNA isolation from tropical fruit trees, which produces high-quality genomic DNA available for further Southern blot analysis and other tests in molecular biology.