PHYTO MEDIZIN Mitteilungen der Deutschen ... - Die DPG

esults. The real-time RT-PCR protocol developed by Boonham et al. (Journal
of Virological Methods 116, 139146, 2004) performed extremely well in
a recent ring test, comparing different PSTVd detection methods in several
laboratories. In addition, real-time PCR technology has proved suitable for
highthroughput testing. Therefore, this method was chosen as the starting
point for the development of a protocol for the large-scale testing of potato.
The initial experiments focused on the specificity of the primers and probes
with regard to different isolates of PSTVd and other (pospi-) viroids. Further
experiments performed with leaf material concerned sampling position,
growing-on temperature and bulking rate. In addition, different grinding and
nucleic-acid extraction methods were compared. To monitor false negatives
and positives, different controls were included. The final protocol was tested
using a hundred samples from the Dutch potato monitoring programme. Future
plans include the development of a protocol for direct tuber testing and
inter-laboratory ring testing of the protocols.
Multiple infections of commercial Poinsettia
H Jeske, M aus dem Siepen, B-J Koo, JO Pohl and C Wege; Institute of Biology,
Department of Plant Molecular Biology and Virology, University of Stuttgart
Commercial Poinsettia (Euphorbia pulcherrima Willd.) are frequently infected
by three agents, a beneficial phytoplasm and two viruses which were
formerly named Poinsettia mosaic virus (PnMV) and Poinsettia cryptic virus,
and classified as tymo- and cryptic virus, respectively. The sequence analysis
of both viruses requires a revision of the taxonomy now which may have
important implications for quarantine measures in greenhouse propagation of
Poinsettia. PnMV is more closely related to marafiviruses than to tymoviruses.
The second virus (now named Poinsettia Latent virus, PnLV) showed
an unprecedented hybrid genome structure combining the first two thirds of a
polerovirus - providing functions for replication - and one third of a sobemovirus
coding for the coat protein. The extreme 5’ and 3’ ends which harbour
the putative origins of replication resemble those of poleroviruses.
Whereas marafiviruses are transmitted by leafhoppers, sobemoviruses may
be spread via soil and watering, a route which would explain the frequent reoccurence
of the Poinsettia viruses in plant material that had been tested
virus-free before. Under these perspectives much more care should be taken
in greenhouses to prevent mechanical dissemination than with the assumption
of a cryptic virus. Since PnMV frequently re-occurred together with PnLV -
even in quarantine facilities – it may be interesting to search for a genetic
dependence of both viruses in future.
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