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Verticillium-wilt (Verticillium albo-atrum)
on Medicago sativa (alfalfa) in Iran
M. Ghalandar1*, E. Clewes2, D.J. Barbara2,
R. Zare3 and A. Heydari3
1 Agricultural Research Centre of Markazi Province,
P.O. Box 889, Arak, Iran
2 Warwick HRI, Wellesbourne, Warwickshire, CV35 9EF, UK
3 Plant Pests and Diseases Research Institute, P.O. Box
1454, Tehran 19395, Iran
*mghalandar@yahoo.com
Accepted for publication 24/5/04
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Figure 1a: Symptoms of Verticillium-wilt in naturally
infected alfalfa plants from Markazi Province, Iran: whole plant
with desiccated leaves on many stems.
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An outbreak of a wilt-like disease of
alfalfa (lucerne) in the Markazi Province of Iran was
investigated. Field symptoms during early growth stages typically
consisted of V-shape orange-pinkish necrotic areas on the
leaflets. On severely affected shoots of more mature plants,
leaflets were usually desiccated and twisted, forming spirals.
Vascular browning could be seen in stem sections. Diseased stems
remained erect and did not themselves become chlorotic, until
after all the leaves had lost their chlorophyll. New shoots on
infected plants appeared normal at first but showed symptoms as
they approached physiological maturity. These symptoms are very
similar to those reported for Verticillium-wilt in alfalfa (Leath
& Pennypacker, 1990). Verticillium albo-atrum was isolated
from field collected plant samples by plating surface-sterilised
stem tissue onto water agar. V. albo-atrum was confirmed as
the causal agent of the disease by inoculating lucerne plants by
root dipping into conidial suspensions. Symptoms on inoculated
plants were similar to those described above for field infections.
Following amplification by PCR, the sequences of the complete
ITS1/5.8S/ITS2 regions of the rRNA gene repeats for
three isolates (GenBank Acc. Nos AY536044-6) were identical to
that previously reported for the lucerne (L) pathotypes of V.
albo-atrum (Barbara & Clewes, 2003). Although generally
similar morphologically to V. albo-atrum, the resting
mycelium produced in culture was paler than expected and without
the torulose cells described previously (Hawksworth & Talboys,
1970). The source of the outbreak is unknown but V. albo-atrum
is known to be seed-borne in alfalfa (Leath & Pennypacker,
1990) and may have been introduced to Iran by this means.
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Figure 1b: Symptoms of Verticillium-wilt in naturally infected
alfalfa plants from Markazi Province, Iran: the vascular browning
typically associated with infection by Verticillium (left: infected
plant; right: uninfected).
As compared to the non-lucerne pathotype, the L pathotype of V.
albo-atrum has a restricted host range and geographic distribution
and generally causes only mild diseases in hosts other than alfalfa
(Leath & Pennypacker, 1990). Verticillium-wilt of alfalfa was first
reported in Europe but has since been reported from the Unites States,
Canada, New Zealand and Japan (Pegg & Brady, 2002). This is the
first reported occurrence of Verticillium-wilt disease of alfalfa in
Iran, or indeed anywhere in continental Asia. Verticillium-wilt can be a
severe disease in alfalfa and should it become widespread in Iran, it
could cause significant crop loss.
Figure 2: Cladogram showing relationship of the Iranian isolates
(Ir1-3) to other isolates of V. albo-atrum and closely related
species, based on sequences of the rRNA ITS1 and 2 regions and the 5.8S
RNA. V. albo-atrum NL and L are non-lucerne and lucerne
pathotypes respectively. Sequences other than those of the Iranian
isolates taken from published sources (Barbara & Clewes, 2003).
References
Barbara DJ, Clewes E, 2003. Plant pathogenic Verticillium
species: how many of them are there? Molecular Plant Pathology 4,
297-305.
Hawksworth DL, Talboys PW, 1970. Verticillium albo-atrum.
CMI Descriptions of Pathogenic Fungi and Bacteria. No. 255.
Wallingford, UK: CABI Publishing.
Leath KT, Pennypacker BW, 1990. Verticillium wilt. In: Stuteville DL,
Erwin DC, eds. Compendium of Alfalfa Diseases. St Paul, MN, USA:
APS Press, 39-41.
Pegg GF, Brady BL, 2002. Verticillium wilts.
Wallingford, UK: CABI Publishing.
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