Mycovirus: virus that infects and replicates in fungi . They are also known as fungal virus, mycophages and virus like particles(VLPs) . During 1970s, hypovirulence in chestnut blight (Cryphonectria parasitica) led to the discovery of mycoviruses in plant pathogenic fungi.

1. WELCOME
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2. 7/6/2019 2
A Mounika
MSc.(Ag) Final Year
18412MPP001
CREDIT SEMINAR MPP-550
Department of Mycology and Plant
Pathology

3. FLOWOF SEMINAR
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INTRODUCTION
HISTORICAL HIGHLIGHTS
CHARACTERISTICS
EVOLUTION
EFFECT ON HOST PHENOTYPE
EXPLORATION OF MYCOVIRUSES IN THE MANAGEMENT
OF FUNGAL DISEASES
CASE STUDIES

4. INTRODUCTION
(Ghabrial and Suzuki, 2009)
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• Mycovirus : virus that infects and replicates in fungi
• They are also known as fungal viruses/mycophages
• Mycovirology : branch involved in study of viruses infecting
fungi

5. HISTORY
The first mycovirus was reported by Hollings in 1962 from
the cultivated mushroom (Agaricus bisporus) , that was later
known as La France disease or watery stripe disease.
Borodynko et al., concluded that La France disease was
caused by dsRNA virus i.e. La France isometric virus (LFIV)
(Son et al., 2015)
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6. GENERAL CHARACTERISTICS
25-50 nm diameter, Isometric particles
Particle weight from 6-13 x 106 Daltons
dsRNAgenomes and 30% +ssRNA
genomes.
A gemini virus-related DNA mycovirus
was also reported :i.e.,
Sclerotinia sclerotiorum hypovirulence
associated DNA virus 1 (SsHADV-1).
(Son et al., 2015)
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7. CLASSIFICATION
Mycoviruses
ds RNA
1. Totiviridae
2.Partitiviridae
3.Megabirnavirid
ae
4.Chrysoviridae
5.Reoviridae
6.Endornaviridae
7.Quadriviridae
+ss RNA
1. Alphaflexiviridae
2.Barnaviridae
3.Gammaflexivirid
ae
4.Hypoviridae
5.Narnaviridae
6. Metaviridae
7. Pseudoviridae
-ss RNA
Mymonaviridae
(Abbas, 2016)
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+ss DNA
Genomoviridae

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(Nuss, 2005)

9. EVOLUTION
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ssRNA replicon of
prokaryotic origin
Self
replicating
cellular
mRNA
Simple ssRNA
Virus
progenitor
RF
Totiviruses
Totiviruses
RF
RF
Acquire
coatprotein and
package
dsRNA/RDRP into
virions
package
RDRP into
virions
ssRNAViruses
RF
Hypoviruses
Partiviruses
La France Isometricviruses
Agaricusbisporusvirus1
Acquire genes f
pathogenicity
Coat protein
and RDRP genes
on separate
segments
Package RDRP
in virions
Loss of genes
non essential
for survival
Loss of coat
protein and
gene
rearrangement
Enclose
dsRNA/RDR
P in host
vesicles
Acquire
coatprotei
n
PossibleEvolutionarypathwaysof Mycovirusevolution
Said A. Ghabrial et al., (1998)

11. HOW DID MYCOVIRUSES EVOLVE??.
There are two major hypotheses which explain the
evolution of mycoviruses
Plant virus hypothesis
Ancient coevolution
hypothesis
Evolutionary Hypotheses of
mycovirus
(Son et al., 2015)
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12. i. Ancient coevolution hypothesis: The association
between mycoviruses and fungi is ancient and reflects
long term coevolution
Buck stated that most of the “mycoviruses evolved at a
very early stage in the phylogeny of their hosts”
i. Plant virus hypothesis: Mycoviruses originated from
plant viruses i.e., the original mycovirus was a plant
virus that moved from plant to fungus within the same
host plant
(Son et al., 2015)
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13. Use of host machinery
1. Thirty chromosomal host genes
needed for replication of killer
viruses in Saccharomyces
cerevisiae (Wickner 1996)
2. Use of host-encoded enzymes for
processing the capsid protein of
Helminthosporium victoriae virus
190S (Huang et al ., 1997)
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14. Plant virus hypothesis
1. Evidence in support of this hypothesis has come
from sequence comparisons between mycoviruses and
plant viruses.
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(Chu et al ., 2002; Linder-Basso et al ., 2005).
• CHV-CryphonectriaHypoVirus
• FgV- Fusarium graminarium
Virus
• BaMMV- Barley Yellow
Mosaic Virus

15. 2. Howitt et al. (2006) :
GVA – Garlic Virus A, GVX – Garlic Virus x, GVE – Garlic Virus E, BVX – Botrytis Virus X
15
GVX
GARLIC
GVA
GVX
GVE
BVX
B. cinerea
3. Although a small number of fungal species are known
to be vectors of plant viruses, the virions are carried on
the outside of the fungus and it is possible that a rare
event may have led to their internalization (Varga et al .,
2003).

16. Mycoviruse
s
Chitridiomyco
ta
Zygomycota
Ascomycota
Deuteromycota
Basidiomycot
a
Host rangeof mycoviruses
(Son et al., 2015)
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18. TRANSMISSIONOF MYCOVIRUSES
Intercellular transmission of mycoviruses is mainly by
two ways:
i. Horizontally via protoplasmic fusion (Hyphal
anastomosis)
ii. Vertically by sporulation
Transmission by anastomosis Transmission by spores
(Kumar et al.,2016)
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19. MOVEMENTOF MYCOVIRUSES WITHINFUNGI
• Virus dissemination in mycelial networks via septa
• They move forward by plasma streaming and extend into
new hyphae.
(Son et al.,2015)
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20. Mycoviruses can alter phenotypes of infected fungi, such
as reduced growth, pigmentation and lack of sporulation.
Latent and persistent infections.
7/6/2019 Cho et al. 2012
A- Virus free colony B- Virus infected colony
Fusarium graminearum virus 1-DK21 infection
IMPACT ON HOST PHENOTYPE

21. Phenotypic effects
Advantageous effects Deleterious effects
(Son et al., 2015)
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1. Hypovirulence
2. Diseases :
La France’ disease of Agaricus bisporus
d² - Ophiostoma ulmi
1. Killer strains
2. Thermostat :
Curvularia thermal
tolerance virus (CThTV)
The mycoviruses confer a range of phenotypes in their fungal
hosts, both advantageous and deleterious, but many of them
appear Cryptic.

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KILLER STRAINS
Some strains of S. cerevisiae and Ustilago maydis (corn smut
fungus) secrete extracellular toxins that either kill or suppress
the growth of same or related fungal species but each killer
strain is immune to its own toxin.
PAUL A. ROWLEY, 2016

23. EXPLORATION OF MYCOVIRUSES IN THE
MANAGEMENT OF FUNGAL DISEASES
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24. HYPOVIRULENCE
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Hypovirulence is the advantageous infection of viruses
which decrease the pathogenicity of plant pathogenic
fungi.
“Will the blight end the chestnut?
The farmers rather guess not. It keeps smolderingat the
roots And sending up newshoots Till another parasite Shall
come to end the blight.”
- Robert Frost

25. •Chestnut cankers were first reported in US
in 1904 on American chestnut trees.
•By 1950, the blight had devasted 9 million
acres of forests by killing several billion
American chestnut trees.
•During 1965, “Jene Grente” reported
hypovirulent strains of the blight fungus
from Italy and use of these strains in a
successful biological control of chestnut
blight.
(Kumar et al.,2016)
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Hypovirulence against Cryphonectria parasitica
( Chestnut blight)

26. Mechanism of hypovirulence
The mechanism of hypovirulence is still not clear, but
various hypothesis were given by different workers, such as
 RNA silencing of the fungus and counter silencing
mechanism by the hypovirus (Nuss,2011)
 There are various other mechanisms, which are reported
such as mitochondrial mutations and nuclear mutations have
been or may be associated with hypovirulence.
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The mechanism of hypovirulence is still not clear, but
various hypothesis were given by different workers, such
as
Possible interference of virus infection with G-protein
signalling(Nuss, 1996)
 Different elements of signal transduction, mostly those
involving kinase proteins (Kim et al., 2006).
 RNA silencing of the fungus by the hypovirus (Nuss,
2011)

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Fungus Disease
Virus
Genus
Mangaporthe oryzae Rice blast MoV1 and MoV2 Totivirus
Rhizoctonia solani Sheath blight
Rhizoctonia virus
M2
Mitovirus
Sclerotinia sclerotiorum White mold SsDRV Alfaflexivirus
Cryphonectria parasitica Chestnut blight CHV1 Hypovirus
Ophiostoma novo-ulmi Dutch Elm disease
Ophiostoma
mitovirus
Mitovirus
Diaporthe ambigua Canker on Rosaceae DaRV Carmovirus
Fusarium graminearum Head blight
Fusarium poae
virus
Partitivirus
Botrytis cinerea Grey mold BVF and BVX Mycoflexivirus
Yadav et al., (2015)
FUNGAL PATHOGENS AND THEIR ASSOCIATED MYCOVIRUSES

28. The advantages of using mycoviruses in fungal
disease management
Once hypovirulence-associated mycoviruses are
transmitted to a virulent fungal strain, they quickly
inhibit lesion extension
The fitness of a hypovirulent strain on crop plants is
not likely to be a problem
Hypovirulent strains share a similar niche with
virulent strains and so hypovirulent strains can grow
well on hosts
(Xie et al., 2014)
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29. The disadvantage of using mycoviruses to control fungal
diseases of crop
Vegetative incompatibility operates widely in filamentous
fungi, which restricts the transmission of virulence-
attenuating hypoviruses in the fungus
(Xie et al., 2014)
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30. Objective: To investigate the effect of mycovirus FodV1 on the plant
colonization pattern of its fungal host
CASE STUDY 1
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31. External colonization of carnation roots by the virus-free (V−)
and the virus-infected (V+) GFP-strains of Fusarium oxysporum f.
sp. dianthi isolate 77
(Torres-Trenas et al., 2019)
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External colonization of carnation roots by the virus-free (V−) and the virus-
infected (V+) GFP-strains of Fusarium oxysporum f. sp. dianthi isolate 77. (A,B)
Superficial colonization of adventitious roots by the virus-free (A) and the virus-
infected (B) strains showing single and germinating conidia (arrowed). (C) Event
of penetration of the root epidermis cells showing the formation of apressoria (ap)
on the cell surface, and haustoria (ha) inside the epidermal cell. Scale bar = 50

32. Colonization of the root crown by the virus-free (V−) and the
virus-infected (V+) GFP- strains of F. oxysporum f. sp. dianthi
isolate 77
(Torres-Trenas et al., 2019)
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(A) Longitudinal and (C) transversal root crown sections of plants inoculated
with the virus-free strain V− (green) 14 days after inoculation. (B)
Longitudinal and (D) transversal root crown sections of plants inoculated with
the virus-infected strain V+ (green) 21 days after inoculation. Scale bar = 50

33. Internal colonization of stem internodes after inoculation of carnation plants with the
virus-free (V−) and the virus-infected (V+) GFP-strains of F. oxysporum f. sp. dianthi
isolate 77
(Torres-Trenas et al., 2019)
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Transversal sections of the internodes (I) were obtained at 14, 21, 28, and 35
days post inoculation (dpi).presence of hyphae and colonization patterns were
detected. Arrows indicate the presence of hyphae (green). vt, vascular tissue.

34. Objective: To demonstrate extracellular transmission of SsHADV-1 and its use
in biological control of Sclerotinia sclerotiorum stem rot disease in Rapeseed
CASE STUDY 2
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35. Extracellular application of purified particles of
SsHADV-1 to intact hyphae of Sclerotinia sclerotiorum
grown on PDA plates
(Yu et al., 2012)
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(A) Sectoring in a colony of strain Ep-1PNA367 at 2 dpi (B) Colony morphology of newly
infected strain Ep-1PNA367; colony morphology of the virus-free stain Ep-1PNA367 and the
virus-infected strain DT-8 (C) Electrophoretic profiles of genomic DNA extracted from the
cultures shown in B are shown Lane M: λ-Hind III-digested DNA marker. Lanes 1–3, DNA
samples of isolates Ep-1PNA367, virus infected Ep-PNA367, and strain DT-8, respectively.

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(A) Four isolates cultured on the same potato dextrose agar (PDA) plate showing
incompatibility reaction zones. One randomly selected isolate (RL6) was dual-cultured in one
PDA plate to show compatible reaction. (B) Suppression of S. sclerotiorum (strain Ep-
1PNA367) lesion development on detached Arabidopsis thaliana leaves previously treated
with virus particles and isolation of virus-infected colonies from such abnormal lesions. The
wildtype strain and virus-infected isolates were incubated on PDA plates for 7 d at 20 °C. (C)
Lanes 1 and 2; 3 and 4; 5 and 6; and 7 and 8 indicate the wild-type and virus-infected isolates

37. (Yu et al., 2012)
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At 8dpi,pathogengrowth extended to the stem of PBSbuffer-treated plants. Although pathogen
growth might rarely extend to the stem of virus-treated plants, only small lesions on the stem could
be observed, and all plants remained standing and were not killed. Weakened inoculated leaves of
virus-treated plantsand detached. At 12 dpi, only three of 16 virus-treated plants were killed by S.
sclerotiorum, but all PBS-treated plants were killed. The therapeutic activity of SsHADV-1 is
comparable to that of Carbendazim, a widely used fungicide. At 15 dpi, only two of eight
Suppression of lesion expansion induced by sclerotinia
sclerotiorum by the application of SsHADV-1

38. CONCLUSION
The majority of mycoviruses have dsRNA genome and 20% of
mycoviruses have +ss RNA genome and are prevalent in major
phyla of fungal kingdom
The mycoviruses confer a wide range of phenotypic effects on
their host ranging from deleterious diseases to beneficial killer
strains and thermal tolerance.
 Co-evolution and Plant virus hypothesis suggest their
evolutionary pathways which is still a matter of mystery
Hypovirulence, an important phenomenon that forms the basis
for exploration of these mycoviruses for biological control.
Many economically important plant pathogenic fungi have
been reported to have mycoviruses which requires further
studies for their successful role in biological control.
The success of Mycoviruses in biological control is limited due
to limited mode of transmission i.e., Hyphal anastomosis.
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39. Future Prospects
 Molecular mechanisms of host-mycovirus interactions.
As genome sequences become available our understanding
of phylogenetic relationships and ultimately mycovirus
evolution will improve.
Perhaps the biggest opportunity for mycovirus research is to
develop them further as biocontrol agents, to assist in the
control of plant pathogens.
a complementary approach to biological control might be the
use of mycoviruses as gene vectors
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40. References
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962–965.
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Florida, pp 1–84.
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119–131
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41. • Xie, J., Wei, D., Jiang, D., Fu, Y., Li, G., Ghabrial, S. and Peng, Y. (2006)
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