Bois noir (BN) is a phytoplasma disease of grapevine spread in
the Mediterranean basin, causing relevant economic losses. BN
phytoplasma diagnosis is currently carried out by detecting the
pathogen DNA sequences in the leaf. Even if reliable and usable
in routine analyses, molecular diagnosis is nevertheless restricted
to the late summer, when BN symptoms become evident. This is
because the above methods are not enough sensitive to carry out
diagnosis in other periods of the year, when symptoms are not evident,
or on other plant organs such as roots. This consideration
suggests that more sensitive and focused detection methods for
BN would be needed. Because of the lack of diagnostic methods
for root tissues, it is not known where the pathogen overwinters
inside the host. We aim at expanding diagnosis effectiveness to
root tissues in BN-infected grapevine, to better understand phytoplasma/
grapevine interactions and to give new insights to BN
epidemiology. Different root samples from healthy, BN-infected
and recovered grapevines, have been collected and RNA was extracted.
As the low concentration of template in the host, we performed
a nested Real-Time PCR using a BN specific TaqMan
probe, following the method already described by Margaria et al.
(Plant Pathol. 58:838-845, 2009). Preliminary analyses showed
positive signal in roots of symptomatic and recovered plants,
whereas no amplification was observed in healthy samples. This
result suggests that BN phytoplasma persists in the root phloem
tissues of recovered individuals. The epidemiological significance
of this finding will be discussed.
