A simple and simultaneous detection method for two different viroids infecting chrysanthemum by multiplex direct RT-PCR

The economically important Chrysanthemum stunt viroid (CSVd) and Chrysanthemum chlorotic mottle viroid (CChMVd) were detected from infected chrysanthemum (Dendranthema grandiflorum) plants by a multiplex reverse transcription-polymerase chain reaction (RT-PCR) assay developed in this investigation. The antisense hexamer AAAGGA (5'-3') was designed. The antisense hexamer 5'AAAGGA 3' annealing at 5'TCCTTT3' is located at nucleotide positions 186-191 and 245-250 of CSVd (gb: AB006737), and 231-236 of CChMVd in their sequences. Using CSVd- and CChMVd-cDNA templates which were transcribed simultaneously by the hexamer, the following multiplex PCR could detect both viroids from doubly-infected plants without nonspecific amplification. When the hexamer was used for the RT reaction, the sensitivity of detection of CSVd or CChMVd by multiplex RT-PCR was similar to that of standard RT-PCR when each viroid was detected separately. Furthermore, multiplex RT-PCR successfully detected both CSVd and CChMVd in direct templates obtained by inserting a syringe needle into the stem, leaf, and shoot tips of infected chrysanthemum plants. The direct multiplex RT-PCR method developed in this study may reduce the cost, time, and labor required for the production of viroid-free chrysanthemum plants.