Systemic spread of viroid infection and
bioamplification of viroid RNA in the tomato cv. ‘Micro-
Tom’ grown in the temperature of 20–25°C was very
slow. The presence of viroid infection by RT-PCR was
hardly detectable on 21 dpi. Better results were obtained
using RNA extracted on day 30 dpi. However, the viroid
titers obtained were highly variable among the plants,
in contrast to the titers of plant ribosomal RNA used
as an internal control (Pic. 1). Variation in viroid titers
could be caused by different viroid concentration in the
inoculum.