Published Date: 2007-06-24 23:50:00
Subject: PRO/PL> Viruses, sweet potato - worldwide: synergism
Archive Number: 20070624.2042
VIRUSES, SWEET POTATO - WORLDWIDE: SYNERGISM
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Fri Jun 2007
Source: The American Phytopathological Society, Plant Disease [edited]
Untiveros M et al: Synergistic interaction of _Sweet potato chlorotic
stunt virus_ (_Crinivirus_) with carla-, cucumo-, ipomo-, and
potyviruses infecting sweet potato. Plant Disease 91(6): 669-676.
Co-infection of _Sweet potato chlorotic stunt virus_ (SPCSV, genus
_Crinivirus_) with _Sweet potato feathery mottle virus_ (SPFMV, genus
_Potyvirus_) results in sweet potato virus disease (SPVD), a
synergistic disease that is widely distributed in the sweet potato
(_Ipomoea batatas_) growing regions of the world.
Since both SPCSV and SPFMV are common and often detected as part of
multiple co-infections of severely diseased plants, the occurrence of
synergistic interactions with other viruses often found in sweet
potato was investigated. Data from this study show that SPCSV, but
not SPFMV, can cause synergistic diseases in sweet potato with all
viruses tested, including members of the genera _Potyvirus_ (_Sweet
potato latent virus_, _Sweet potato mild speckling virus_),
_Ipomovirus_ (_Sweet potato mild mottle virus_), _Cucumovirus_
(_Cucumber mosaic virus_), and putative members of the genus
_Carlavirus_ (Sweet potato chlorotic fleck virus and C-6 virus).
The synergism was expressed as an increase in the severity of
symptoms, virus accumulation, viral movement in plants, and as an
effect on yield of storage roots. The presence of a third different
virus in plants affected with SPVD increased the severity of symptoms
even further compared with SPVD alone. There was a positive
correlation between increase in virus accumulation and symptom
expression in double and triple SPCSV-associated co-infections.
Epidemiological implications of these results may also be expected.
[Multiple viral infections are common in field plants with the
potential for synergism (symbiotic enhancement) or cross-protection
(competitive suppression, used in disease management). So far,
cooperation has more often been found to be the case for unrelated
viruses, competition more often for similar ones [an exception being
the ACMV strains mentioned in the next para.].
Synergistic virus diseases have been descr
ibed in different plants. Most of them involve a potyvirus and a virus
in a different family resulting in normal replication of the potyvirus
and enhanced replication of the partner virus. SPVD (see ProMED-mail
post 20070420.1291) is an example of such a potyviral synergism.
Non-potyviral synergism is characterised by a dramatic increase in
both symptom severity and DNA amounts of both of the virus partners.
An example is cassava mosaic disease (CMD; see ProMED-mail post
20070529.1737) due to co-infection of different strains of _African
cassava mosaic virus_ (ACMV).
In addition to SPVD, synergistic interactions of both types are
reported here. These results are remarkable because it is the
non-potyviral partner (SPCSV) of SPVD forming these associations, and
because synergistic relationships of more than 2 viruses were also
identified leading to increasingly severe symptoms.
Worldwide, at least 19 different viruses have been described in sweet
potato, a vitally important food source in many poor regions. Not all
of them, including 'Sweet potato chlorotic fleck virus' and 'C-6
virus') have been recognised by the International Committee on
Taxonomy of Viruses (ICTV) as yet. Even more can be expected to exist
due to the predominantly vegetative propagation of this crop, which
increases the risk of a build-up of viruses. A yield increase of up to
40 percent was reported from tested virus-free cultivars.
The epidemiology of the synergistic viruses and their respective
vectors will necessarily be highly complex. The genus _Crinivirus_
(_Closteroviridae_) is whitefly-transmitted; the genus _Potyvirus_
(_Potyviridae_) is transmitted by aphids and mechanical means; the
genus _Ipomovirus_ (_Potyviridae_) is transmitted by white flies,
mechanical means, and grafting; the genus _Cucumovirus_
(_Bromoviridae_) is aphid-transmitted; and the genus _Carlavirus_
(_Flexiviridae_) is mostly aphid-transmitted and can be spread
Sweet potato virus disease:
SPFMV symptoms on cassava:
ACMV symptoms on cassava:
Descriptions of all ICTV-recognised viruses via:
_Sweet potato chlorotic fleck virus_ taxonomy:
List of sweet potato viruses:
Background on virus symbiosis and competition (review):
Further information on synergism:
Implications of synergism on disease epidemiology:
Potyviral genes in synergism:
Synergism in mosaic disease of cassava:
List of strains of ACMV:
<http://gemini.biosci.arizona.edu/viruses/acmv/index.htm>. - Mod.DHA]