Page 19 - Volume 1, Issue 1, January 2008
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New plant pathogens in Greece
17
toms appeared in early September, 40
days after defoliation of the plants and
became more serious after storage. The
virus variant responsible for PTNRD was
called PVY
NTN
and formed a distinct PVY
N
subgroup, in which high variability was
observed. Most recent molecular detec-
tion methods of NTN isolates rely on the
recombination event between PVY
O
and
PVY
N
groups, usually (but not always) oc-
curring on the coat protein gene. Late-
ly, it was further shown that probably all
PVY
N
isolates could produce some necrot-
ic symptoms on tubers of sensitive vari-
eties and that it may be necessary to set
a cultivar-specific Disease Index thresh-
old to separate PVY
N
from PVY
NTN
. It is also
noteworthy that all recently obtained po-
tato isolates were of PVY
NTN
-like type. This
virus type was isolated from most areas of
the country, showing a tendency to pre-
dominate (Varveri, 2006).
Another type of new virus variant iso-
lates is the PVY
N
W type recently recorded
in Greece. These isolates are also recom-
binant, biologically resembling PVY
N
iso-
lates but serologically the PVY
O
ones, and
are considered to be particularly infec-
tious in potato (Varveri, 2006).
3.2.2. Transmitted by whiteflies
Beet pseudo-yellows virus
(BPYV, genus
Crinivirus
)
,
Cucurbit yellow stunting dis-
order virus
(CYSDV, genus
Crinivirus
)
The last fifteen years, two whitefly-
transmitted criniviruses that elicit identical
symptoms of interveinal chlorosis (yellow-
ing) were identified in greenhouse- and
field-grown cucurbits: BPYV which is trans-
mitted by
Trialeurodes vaporariorum
(West-
wood) and CYSDV transmitted by
Bemisia
tabaci
(Gennadius)
(Livieratos
et al
., 1998).
In 2000-2003 a survey was carried out in
glasshouse and occasionally open field cu-
cumber and melon crops all over the coun-
try. In most cases disease incidence ranged
from 50 to 80%. Application of molecular
diagnosticmethods showed that BPYVwas
predominant in cucumber (68%) and mel-
on (80%) crops, whereas CYSDV, reported
for the first time in Greece, was isolated
only in three regions of Southern Greece
(Rhodes, Crete, Arkadia) at a lower inci-
dence (cucumber 32%; melon 20%) (Bou-
bourakas
et al
., 2006a, Katis
et al
., 2006).
Tomato infectious chlorosis virus
(TICV,
genus
Crinivirus
)
,
Tomato chlorosis virus
(ToCV, genus
Crinivirus
)
Since 1997, a yellowing disease has been
observed in greenhouse tomato (
Lycopersi-
con esculentum
Mill.) in Southern Greece
and the island of Crete. By 2001, the disease
was widespread including also open field
tomato crops and in most cases the inci-
dence was 80 to 90% or even 100%. Epi-
demics in glasshouses were always associat-
ed with high populations of the whiteflies
T.
vaporariorum
and
B. tabaci
,
the major white-
fly pests in vegetable crops in Greece. Affect-
ed plants exhibited a generalized interveinal
bright yellowing of leaves, were less vigor-
ous and underwent severe yield losses due
to reduced fruit size and delayed ripening.
Molecular analysis revealed infection with
the phloem restricted criniviruses TICV (87%)
and ToCV (16%). TICV is transmitted by
T. va-
porariorum
and ToCV by
B. tabaci
,
T. vaporari-
orum
and
T. abutilonea
(Haldeman) (Dovas
et
al
., 2002) in a semi-persistent manner.
Tomato yellow leaf curl virus
(TYLCV,
genus
Begomovirus
)
,
Tomato yellow leaf
curl Sardinia virus
(TYLCSV, genus
Bego-
movirus
)
In 2000, tomato crops grown under
greenhouses in Crete (Ierapetra, Tym-
paki) and Southern Peloponnese (Lako-
nia) showed severe symptoms of Toma-
to yellow leaf curl disease (TYLCD), one
of the most devastating tomato diseases
in the Mediterranean basin. The disease
is caused by a complex of closely related
whitefly persistently transmitted bego-
moviruses. Immunological, molecular and
biological techniques confirmed TYLCV
