Reverse transcription--polymerase chain reaction (RT-PCR) assays were developed for the detection of Citrus tristeza virus (CTV; genus Closterovirus) and Citrus psorosis virus (CPsV; genus Ophiovirus) in citrus trees. Real-time TaqMan RT-PCR was also developed for the detection of CTV. Three different sample preparation methods were compared. The total RNA extraction method by Qiagen was found to be more reliable than the other two methods consisting of crude plant sap extraction and total nucleic acid trapping on a silica bed. Of 287 samples tested for CTV, 210 samples tested positive by RT-PCR and 198 samples by enzyme-linked immunosorbent assay (ELISA). Furthermore, the results from monthly tests of a selected number of field-grown CTV-infected trees showed that RT-PCR detected the virus in 100% of the infected trees in winter and summer, whereas ELISA did not. The one-tube RT-PCR detection was developed for CPsV and was more sensitive than ELISA. Notably, three of 10 CPsV isolates were not detected by ELISA. As demonstrated here, our approach allows the efficacious detection of different viruses in citrus plants using a minimal amount of tissue during all seasons. The molecular methods described could be used in citrus certification programs and to test trees in nurseries and commercial orchards.
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