RESULTS
Biological indexing
Three months after inoculation, 20 samples grafted on
citron plants showed mild epinasty and leaf roll
symptoms, and the remaining samples have no typical
of citrus viroid infection. 58 samples induced typical
symptoms of stunting and epinasty on the indicators
one year after inoculation, whereas the rest 7 samples
did not induce symptoms on indicator plants.
One-step RT-PCR assay for detection and
characterization of citrus viroids
Amplified fragments specific to each of the target pathogens
were obtained from tested field samples, whereas
no nonspecific band was detected in healthy citrons.
Fig.1 shows the amplification results of 5 citrus viroids
whole genome by uniplex RT-PCR. The size (bp) of
the amplified products for each viroid was 371 for
CEVd; 318 for CBLVd; 302 for HSVd; 294 for CVdIII,
and 284 for CVd-IV, respectively. Sequencing confirmed
that these amplicons corresponded to full-length
sequences of those viroids.
To differentiate cachexia variants and non-cachexia
variants of HSVd isolates, the same RT-PCR procedures
have been performed using two discriminating
primer pairs designed by Bernad and Duran-Vila (2006).
PCR yielded 220 bp amplicon (primer pair: HSVd-R2/
HSVd-F2´) only with samples infected by non-cachexia
variants of HSVd, whereas yielded 283 bp amplicon
(primer pair: HSVd-R2/HSVd-F2) only with samples
infected by cachexia isolates (Fig.2). To date, only one
cachexia variants of HSVd from Newhall navel orange
collected from Guizhou Province has been identified
by RT-PCR for strain characterization.
One-step multiplex RT-PCR assay for
simultaneous detection of citrus viroids
In the present study we have developed a one-step
multiplex RT-PCR for the simultaneous detection of
CEVd, CBLVd, HSVd, CVd-III, and CVd-IV, plus an
internal control, and meanwhile, amplified fragments
can easily be differentiated by agarose gel electrophoresis
because of redesigning partial primer sets.
Fig.3 shows the amplified fragments by one-step multiplex
RT-PCR from extracts of 7 infected samples and