Molecular Detection and Characterization of Citrus Viroids

Total RNA was isolated from the phloem of young shoots and retro-transcripted to cDNA by reverse transcriptase- polymerase chain reaction (RT-PCR) with specific primers; the amplified cDNA fragments were sequenced for identification of subtypes. In this study, an effective RT-PCR technique was established for detecting citrus viroids, and three citrus viroids were recognized, namely, CEVd, CVd-II, and CVd-III. The latter two were identified for the first time in China. The sequences of CVd-II were different from all the three subtypes reported in the GenBank and seemed to be a new subtype. CVd-IIIb detected in the present study could be further developed as a dwarfing agent.