Page 4 - Volume 2,Issue 2, July 2009

© Benaki Phytopathological Institute
Van der Vlugt 48
bearing S. tuberosum spp., causing mostly a
symptomless systemic infection or mild mo-
saic symptoms. However, in two local Pe-
ruvian S. tuberosum cultivars and S. stolon-
iferum PI 230557 the virus caused a severe
systemic necrosis (Jones et al., 1980). The vi-
rus was shown to be transmitted through
tubers.
Several weed hosts were also found to
be infected with PepMV. Jones et al. (1980)
reported Datura stramonium, Nicandra ph-
ysaloides and Physalis peruvianum as weed
hosts in Peru. Studies on material sampled
from the mainland of Spain and the Ca-
nary Islands (Jordá et al., 2001) showed a
large number of weed species being latent-
ly infected (i.e. showing no symptoms) with
PepMV: Amaranthus sp., Malva parviflora,
Nicotiana glauca, Solanum nigrum, Sonchus
oleraceus , Bassia scoparia, Calystegia sepium,
Chenopodium murale, Convolvulus althae-
oides , C. arvensis, Conyza albida, Coronopus
sp., Diplotaxis erucoides, Echium creticum, E.
humile, Heliotropium europaeum, Moricandia
arvensis , Onopordum sp ., Piptatherum multi-
florum, Plantago afra, Rumex sp ., Sisymbrium
irio , Sonchus tenerrimus, and Taraxacum vul-
gare . However, the following species were
found not to be infected with the virus: Cap-
sicum annuum, Cucumis sativus, Chenopo-
dium amaranticolor, C. quinoa, Petunia x hy-
brida , Phaseolus vulgaris, Physalis floridana,
Nicotiana rustica, N. tabacum, Polypogon
monspeliensis and Senecio vulgaris.
In the initial PepMV report, the typi-
cal symptom caused by the virus was a dis-
tinct yellow mosaic on young leaves of pep-
ino. Most of the infected plants also showed
dark green enations on the lower surface
of some leaves. In Lycopersicon spp. the vi-
rus caused a symptomless systemic infec-
tion, which became apparent only by back-
inoculation on susceptible indicator plants,
such as Nicotiana glutinosa. Only Datura me-
tel, D. stramonium and some Nicotiana spp.
showed distinct symptoms upon systemic
infection. The virus failed to infect 13 plant
species belonging to six other families.
The virus was found in 1999 in commer-
cial tomato crops in the UK and The Nether-
lands causing more pronounced symptoms.
However, symptoms may depend on the
PepMV strain, the tomato cultivar, the age of
the plant when first infected and the envi-
ronmental conditions. Generally symptoms
include yellow leaf spots, yellow-green mo-
saic, mottle on the older leaves and/or slight
curling of the top leaves (nettle head symp-
tom) or a grayish appearance of the top of
the plant (Figure 1a, b & c). Fruit symptoms
range from alteration in colour, in some cas-
es sever yellow/orange mottling (Figure 1d)
and uneven ripening to netting and crack-
ing and shape distortion (Spence et al., 2006;
Hanssen et al., 2008). Particular isolates cause
leaf and stem necrosis. Fruit symptoms, such
as uneven ripening, marbling or even crack-
ing, may affect fruit quality resulting in dif-
ferent levels of economic damage. Environ-
mental conditions are reported to affect
symptom expression with low temperatures
and low light conditions favouring the ap-
pearance of more pronounced symptoms.
Symptoms are also reported to change dur-
ing the growing season when environmen-
tal or growing conditions change. Especial-
ly plant stress appears to promote symptom
expression. Initially it was thought that the
different virus strains induced different
symptoms, but isolates belonging to the
same strain (i.e. EU-tomato or Chile-2) may
also differ greatly in the severity of symp-
toms they cause in a tomato crop ranging
from only a few yellow spots to severe ne-
croses on stems and leaves or very severe
symptoms on fruit. Inoculation studies on
sets of indicator plants confirmed these dif-
ferences between different isolates.
Virion properties
PepMV is a potexvirus and as such, has typ-
ical filamentous particles with a normal
length of 510 nm. Particles are comprised of
a single capsid protein (CP) of approximately
26 kDa. In ultrathin sections of infected leaf
material inclusions consisting of arrays of
filamentous virus-like particles may be ob-
served.