This document discusses the transmission of plant viruses by fungal pathogens. It notes that five species of fungi can transmit over 30 plant viruses. The fungi transmit viruses both internally, carrying the viruses within their structures, and externally, with viruses attached to the outside. This causes virus symptoms in infected plants. Several major crops are economically impacted by these soil-borne viruses. The document reviews different classes of fungi that can transmit viruses, including plasmodiophoromycetes, chytridiomycetes, and oomycetes. It provides details on the fungal pathogen Polymyxa graminis and its transmission of the Wheat spindle streak mosaic virus. Management strategies to control these soil-borne viruses transmitted by fungi include developing resistant

1. TRANSMISSSION OF PLANT VIRUS BY
FUNGAL PATHOGEN AND
MANAGEMENT AND CROPS EFFECTED

2. INTRODUCTION:
Thirty soilborne viruses or virus-like agents are transmitted by
five species of fungal vectors
 Root-infecting fungal-like organisms, the
plasmodiophoromycetes Polymyxa and Spongospora, and
the chytridiomycete, Olpidium, transmit at least 30 plant
viruses.
 Some of these viruses apparently are borne internally in,
whereas others are carried externally on the resting spores
and the zoospores of the fungi. On infection of new host
plants, the fungi introduce the virus and cause symptoms
characteristic of the virus they transmit.

3. IMPORTENCE:
 A number of plant viruses in different genera are harboured
in and transmitted through the soil.
 They are found throughout the world and several of them
cause significant economic losses to major crops.
 Vectors for spread of these viruses are fungal‐like organisms
or plant‐parasitic nematodes, but some viruses can also be
exuded from infected roots and transmitted abiotically,
without the aid of a vector.
 The long‐term persistence of these viruses in soil, often for
decades, and a lack of efficient control strategies mean that
diseases caused by these viruses are very difficult to control.
 Eradication of inoculum from infected soil is almost
impossible, particularly in those parts of the world where
highly toxic soil fumigant chemicals have been banned in
recent years. Soil‐borne viruses are difficult to study and their
biology is relatively poorly understood at present.

4. BRIEF
REVIEW

5. Different fungal vectors:
Three different classes of fungi will transmit the fungi:
MYXOMYCOTA:
CLASS:PLASMODIOPHOROMYCETES
ORDER:PLASMODIOPHORALES
FAMILY:PLASMODIOPHORACEAE
Eg : Plasmodiophora ,Polymyxa graminis, Spongospora subterranean
P. graminis : Parasitic on wheat and other cereals. Can transmit plant
viruses ( wheat mosaic)
Spongospora: S. subterranea causing powdery scab of potato tubers.

6. EUMYCOTA:
S.D : 1. MASTIGOMYCOTINA
CLASSES : 1.CHYTRIDIOMYCETES
ORDER: CHYTRIDIALES
FAMILY: SYNCHYTRIACEAE
Eg. Synchytrium endobioticum
Olphidium brassicae
Synchytrium endobioticum : Transmits Potato virus x , Potato mop top
virus
Olphidium brassicae : Transmits Tobacco necrosis virus, satellite
virus, Tobacco stunt virus, Lettuce big vein virus
2.OOMYCETES
ORDER: PERONOSPORALES
FAMILY: PYTHIACEAE
virus
Synchytrium endobioticum : Transmits Potato virus x , Potato mop top
virus
Olphidium brassicae : Transmits Tobacco necrosis virus, satellite
virus, Tobacco stunt virus, Lettuce big vein virus
Eg: Pythium ultimum transmits Pea false leaf roll

7. CLASS:PLASMODIOPHOROMYCETES
1. These are obligate endoparasites. Commonly called as endoparasitic
slime molds. Thallus is a plasmodium, Zoospores are anteriorly
biflagellte, whiplash type,unequal in size which are called as
Heterokont zoospores. After swimming for some time, the zoospore
CLASS CHYTRIDIOMYCETES:
1. Thallus
(a) primitive members - unicellular, advanced members with coenocytic
mycelium.
(b) endobiotic (fungus which lives with in the cells of host) or epibiotic
(reproductive organs of the fungus on surface of the host, part or
entire thallus with in the host cell).
(c) holocarpic or eucarpic.
2 .Zoospores are posteriorly uniflagellate whiplash type. Inside the
zoospore, around the nucleus cell ribosomes cluster together to
form a nuclear cap.
3. Asexual reproduction is by zoospores produced in zoosporangia.

8. Oomycetes
(water molds, white rusts, and downy
mildews)
• Have nonseptate elongated mycelium.
Produce zoospores in zoosporangia.
Zoospores have two flagella.
• Sexual resting spores (oospores)
produced by the union of morphologically
different gametangia called antheridia
(male) and oogonia (female).

10. VIRUS TRANSMISSION THROUGH FUNGAL PATHOGENS
They are obligate parasites, live entirely within the host cells, have
similar developmental stages including a plasmodial stage, survive in
soil by formation of resting spores or cysts, and produce motile
zoospores to infect roots of the host plants (Alexopoulos et aI., 1996).
Two types of fungal transmission are distinguished based on either
the mode of acquisition or the site of virus retention (Teakle, 1983).
 In non-persistent transmission the virus particles are adsorbed to
the surface of the zoospores and are not present in the resting
spores.
 whereas in persistent transmission the virus is carried internally
into the resting spore and zoospores. In addition to the
terminology persistent and non-persistent transmission, the terms
in vivo and in vitro transmission are also still in use. Both the sets
of terms have their flaws (Campbell, 1993, 1996), but the terms
persistent/non-persistent appear to be the currently most
accepted and will therefore be used in the following section.

11. Common name Botanical name Source
Barley Hordeum vulgare Barr, 1979; Rush, 2003
Couch grass, Quackgrass Agropyron repens Barr, 1979
Millet Panicum miliaceum Rush, 2003
Rye Secale cereale Barr, 1979; Rush, 2003
Sorghum Sorghum vulgare Rush, 2003
Wheat Triticum aestivum, T. durum Barr, 1979; Rush, 2003
POLYMYXA GRAMINIS
Polymyxa graminis is an obligate root-infecting organism that was
originally described from wheat by Ledingham (1939). Barr (1979)
examined roots of common weeds for the presence of
plasmodiophoraceous fungi, but was unable to identify a natural
reservoir of host species. The recorded hosts for P. graminis are listed
as.
Recorded plant hosts of Polymyxa graminis

12. As previously stated, P. graminis is the vector for WSSMV. This fungus
is also a vector for the following viral diseases
-Aubian wheat mosaic virus
- Barley mild mosaic virus
- Barley yellow mosaic virus
- Chinese wheat mosaic virus
- Indian peanut clump virus (IPCV)
- Oat golden stripe virus
- Oat mosaic virus
- Peanut clump virus (PCV)
- Rice necrosis mosaic virus
- Rice stripe necrosis virus (RSNV)
- Soil-borne cereal mosaic virus
- Soil-borne wheat mosaic virus
- Sorghum chlorotic spot virus
- Wheat yellow mosaic virus

13. The lifecycle of P. graminis is separated into two phases,
1) the production of zoospores, and
2) the production of resting spores, with each phase initiated by
the attachment and penetration of the plant host epidermal or
root hair cells by zoospores
The zoospores form within zoosporangia located within root hairs
or epidermal cells , and the zoosporangia (resting spores) burst
open releasing the short-lived, motile zoospores into the soil
around the roots The zoospores, with the aid of their two
flagella, swim short distances through the soil moisture film
(moisture between soil particles) to infect roots . 25 fungus
invades the root hairs of young susceptible plants in the autumn
during periods of high soil moisture . The zoospore contents
enlarge within the invaded host cell and undergo several cycles of
synchronous mitotic 'cruciform' nuclear divisions and reduction in
nuclear size .

14.  The Polymyxa cytoplasm becomes an irregularly shaped
multinucleate sac (plasmodium),which develops into a
zoosporangium, separated from the host cytoplasm by a distinct
cell wall . The secondary zoospores are cleaved apart, become
rounded when they mature, and the septa between zoosporangial
segments disintegrate later developing into resting spore clusters
(Ward et al).
 The fungus forms dark clusters of resting spores in the cortical
tissues within the infected root . These spore balls are released
into the soil when the roots decay , and the fungus survive as
clusters of thick-walled resting spores within the soil for more than
15 years in the absence of access to susceptible hosts . The cycle is
restarted when the resting spores germinate to each produce one
biflagellate zoospore , which, in turn, will infect the root epidermal
cells of a suitable plant host , and behaving in the same manner as
zoospores derived from zoosporangia

16. Transmission of Wheat spindle streak mosaic virus by
Polymyxa graminis
 WSSMV particles are thought to be present in viruliferous P.
graminis resting spores and zoospores.
 Driskel et al. produced direct evidence that WSSMV is internalised
by P. graminis, as WSSMV coat protein was detected in the resting
spores using immunofluorescence
 WSSMV cannot be removed from zoospores by washing, or
inactivated by application of antiserum.
 P. graminis resting spores remain viruliferous after treatments with
diluted NaOH and HCl (Kanyuka et al., 2003).
 The precise mechanism of virus uptake and transfer is unknow, and
it is also not known whether WSSMV is able to replicate within P.
graminis, although indirect evidence suggests that it does not
Zoospores released from viruliferous P. graminis isolates grown in
virus-resistant host plants no longer contain WSSMV, or loose the
ability to transmit the virus .

17. I. Plant resistant varieties.
II. Postpone fall planting
operations past the Hessian
fly-free date, until mid-
October or later. This delay in
planting means that wheat
seedlings will emerge in
cooler soils that are less
favorable to P. graminis
activity and, thus, conditions
will be less favorable for
infection by WSSMV.
III. Improve internal and
surface drainage of fields
where problems exist.
IV. • Avoid crop production
practices that encourage soil
compaction.
 Crop rotation as a management
tool to reduce the incidence of
disease
 Manipulation of planting dates,
irrigation schedules and paddock
drainage by avoiding exposure of
crops to high risk low-lying wet
areas could reduce virus
incidence .
 although many sources of
resistance to WSSMV have been
identified in commercial wheat
varieties and in wild Triticum
species, with the resistance trait
being highly heritable
Polymyxa graminis
wheat spindle streak mosic
virus

18.  Peanut Clump virus transmission by Polymyxa graminis under
controlled conditions.
Dieryck B1, Weyns J, Van Hese V, Bragard C, Legrève A.
Author information
Abstract
More than fifteen soil-borne viruses belonging to the Beny-, Bymo-,
Furo- or Pecluvirus, causing diseases on cereals and groundnut, are
transmitted by the soil-borne protist root endoparasite Polymyxo
graminis.
 Barley yellow mosaic virus is plant pathogenic virus that causes
the yellow mosaic disease of barleyThe virus is transmitted
via Polymyxa graminis, which is a plasmodiophorid protist,
through the resting spores that survive in the soil, and
eventually zoospores.[2]

19. Spongospora subterranea
Spongospora subterranea is the causal agent of powdery scab on
potato. Though this disease can reduce yield somewhat, the true
economic effect is due to the unmarketable, scabbed appearance
Host range and distribution
Spongospora subterranea can be found worldwide, wherever
potatoes are consistently grown. Other than potato
(Solanum tuberosum), few hosts have been reported. But it is
assumed that solanaceous plants are susceptible including reports
of tomato (Lycopersicon esculentum) and
other Solanumsp. such as nightshade
(S. demissum). Nasturtium sp. has also been reported as a host

20. Ecology and life cycle
 Starting with a biflagellate, uninucleate zoospore (n) there are two
paths possible. The zoospore can directly infect the root, encyst, and
form a uninucleate plasmodium which will multiply and develop into
a multinucleate plasmodium, though all nuclei will remain identical
(n). The plasmodium will develop into a thin-walled zoosporangium
containing many new zoospores, all identical .
 Resting spores can persist in the soil for up to ten years. The cell
walls contain three layers, aiding in the spore’s longevity. Zoospores
swim through water films and therefore require free water in order
to infect. After emergence, they swim to a host but only survive for
about two hours. Infected seed tubers are a source of inoculum as
well as infested soils where the organism persists for long periods of
time. Symptomatic tubers will, therefore, not be accepted for seed

21. LIFE CYCLE OF SPONGOSPORA

22. MODE OF TRANSMISSION OF POTATO MOP TOP VIRUS BY
SPONGOSPORA:
 Zoospores of Spongospora subterranea introduce the virus into the
potato plant when they infect the roots, stolons and/or young tubers.
 Systemic movement of the virus within the plant is generally slow and
erratic. The critical period for infection and development of powdery
scab on tubers is early in the growth cycle, at stolon formation and
tuber set, a period that lasts about 3-4 weeks. Tubers which have
matured beyond this period are resistant to infection by zoospores.
 Little or no spread occurs in areas where soil temperatures are above
20°C, or where moisture is lacking. When PMTV-infected tubers are
planted as seed, the virus is passed on as a secondary infection to
only limited numbers of progeny tubers (30 - 50%). Therefore, spread
via the obligate vector, powdery scab is the most important means of
transmission.

23. Resistance and control
 Varietal susceptibility of potatoes to powdery scab varies
considerably but no varieties are immune to either powdery
scab or PMTV.
 Resistance to powdery scab and to PMTV are genetically
independent traits. , control of PMTV is generally directed at
its vector,Spongospora subterranea.
 Using clean seed and minimising the spread of soil and other
forms of contamination restricts spread of the pathogen.
 Infection may be reduced by environmental control such as
improved drainage, reduced irrigation during early tuber
development, delayed planting until soils are warmer or drier
and crop rotation with brassicas and other crops.
 Seed and soil treatments may also help reduce the spread of
the pathogen from infected seed and reduce numbers of viable
spores.

24. Potato scab
Spongospora subterranea
Potato mop-
top virus
(PMTV)

25. Table 2. Major examples of plant viruses that can be vectored by
zoospores
Virus name Virus host Vector
Tobacco necrosis group (isometric)
Tobacco necrosis
virus
Many hosts O. brassicae
Cucumber necrosis
virus
Cucumber Olpidium sp.
Melon necrotic spot
virus
Melon, cucumber Olpidium radicale
Tobacco stunt type (rigid tubular; double-stranded RNA)
Tobacco stunt virus Nicotiana Olpidium brassicae
Lettuce big vein

26. Barley yellow mosaic group (filamentous)
Barley yellow
mosaic virus
Hordeum spp. Polymyxa graminis
Wheat spindle
streak mosaic
virus
Triticum spp. P. graminis
Oat mosaic virus Avena spp. P. graminis
Wheat yellow
mosaic virus
Triticum spp. P. graminis
Rice necrotic
mosaic virus
Oryza spp. P. graminis
Virus host vector

27. Furovirus group (Fungally transmitted rod-shaped viruses; single-stranded
RNA)
Soil-borne wheat
mosaic virus
Triticum spp. Polymyxa graminis
Beet necrotic
yellow vein virus
Beta spp. Polymyxa betae
Potato mop top
virus
Solanum spp. Spongospora subterranea
Oat golden stripe
virus
Avena spp. P. graminis
Peanut clump virus Peanut P. graminis
Broad bean
necrosis virus
Broad bean P. graminis

28. Olpidium brassicae
Morphology and biology:
 Olpidium brassicae Vegetative body is
ameboid, turning into zoosporangium
inside host plant cells.
 In host plant the cell can form to 12
zoosporangia. In the spring the zoospores
go to the surface of host plant through
aerotropical channels. Zoospores are
spherical, 3 microns in diameter.
 This cycle of asexual reproduction takes
several days. When the sexual reproduction
is taking place, the zoospores leaving
different zoosporangia merge in pairs,
forming biflagellate zygote that fastens to
surface of a host cell after a dormant
period, crusts and turns into cyst.

29. Hosts Infects cabbage and other cruciferous species, and also flax,
cucumbers, tomato, salad, tobacco, and other plants.
Olphidium transmitted viral diseases:
Introduction Olpidium brassicae is a root-infecting plant parasite
and widespread in temperate areas of the world. It was reported
to cause a damping-off disease of cabbage, but the disease may
be caused by other pathogens. O.brassicaes.l. is economically
important because O.brassicaes transmits several destructive plant
viruses, such as Tobacco necrosis virus, Tobacco stunt virus, Tulip
mild mottle mosaic virus, Lettuce big-vein associated virus
(LBVaV)(syn.＝Lettucebig-veinvirus), Mirafiori lettuce big-vein
virus

30. cucumber systemic
necrosis virus
lettuce with big-vein symptomsTOBACCO NECROSIS VIRUS

31. MANAGEMENT : control of Olpidium brassicae, the vector of
cucumher systemic necrosis and bean stipple streak virus diseases
 Under laboratory conditions cucumber systemic necrosis virus
(CSNV) and bean stipple streak virus (BSSV) were controlled by
fumigation of soils naturally infected with the vector Olpidium
brassicae, using methyl bromide at 9.76 kg/100 m, steam, or an
air-steam mixture.
 CSNV and BSSV were not effectively controlled with the soil
fumigants chloropicrin and dazomet.Incorporation of the
fungicides benomyl, captan, and zineb into naturally infected soil
gave some control at high rates of application; copper oxychloride
in the soil had no effect on disease incidence.
 Methyl bromide fumigation of naturally infected soils with 12.20
kg/100 m and 14.64 kg/100m eradicated CSNV and BSSV from
commercial glasshouses.

33. SYNCHITRIUM ENDOBIOTICUM
synchytrium is a large genus of plant pathogens within the phylum Chytridiomycota.
Species are commonly known as false rust or wart disease. Approximately
200 species are described
Lifecycle
S. endobioticum is an obligate parasite which does not produce hyphae, but
sporangia containing 200-300 motile zoospores. In the spring, at temperatures
above 8°C and given sufficient moisture, the winter (i.e. long-lived) sporangium in
decaying warts in the soil germinates and releases uninucleate zoospores. The latter
possess a single flagellum enabling them to move in soil water and reach the living
host.
zoospore penetrates the host cell. This becomes greatly enlarged and the enclosed
fungus forms a short-lived, quickly reproducing stage, the summer sporangium,
Under certain conditions of stress, such as water shortage, the zoospores may fuse
in pairs to form a zygote; the host cell in which it forms does not swell but divides.
The host cell wall remains closely attached, forming an outer layer to the resistant,
thick-walled winter sporangium. This matures and is released into the soil from
rotting warts. Winter sporangia can remain viable for at least 30 years and are found
at depths of up to 50 cm.

34. Lifecycle OF SYNCHITRIUM ENDOBIOTICUM

35. Potato virus x and synchytrium endobioticum :
 Both the virus and fungus are presumably of long association with the potato plant
, since both are present in the Andes of south America, the probably home of this
plant ,as well as in many other countries. However the evidence implicating S.
endobioticum as a vector of potato virus x is derived from laboratory studies in
Europe only.
 Nienhus and stille found the zoospore suspension taken from potato plant
onfected by both the wart fungus and potato virus x transmitted the virus to shoot
of healthy tubers. No transmission of the virus was achieved if zoospores are
inactivated before testing, or if zoospores from virus free plants were mixed with a
potato virus x suspension.
 These results indicate that the virus may be thallus acquired by the potato wart
fungus and carried internally in the zoospores. The soil borne tobamoviruses and
potyvirus which have this relationship can persist in the resting spores of their
vectors of years. Such a persistant relationship would have a useful function in the
soil survival of the rather unstable particles of potato virus x , although the
common carry-over of the virus in the tubers would reduce the importence of this

36. MANAGEMENT
Control Tomato varieties with resistance to PVX (and ToMV) are
available. Consult with your local extension agent to determine
those suitable in your region. Avoid growing tomatoes near potato
fields. Workers who handle potato plants or tubers should change
clothes and wash thoroughly with soap and water before working
with tomatoes. Similarly, tools and equipment used with potatoes
should be thoroughly cleaned before being used in tomatoes.
PVX

37. Pythium ultimum
Pythium ultimum is a plant pathogen. It causes the damping-off and root rot
diseases of hundreds of diverse plant hosts including corn, soybean, potato, wheat,
fir, and many ornamental species.
Ecology and lifecycle
P. ultimum can grow saprophytically and survive as resistant resting structures in
the soil and in root residues. When conditions are favorable, the fungi begin to
infect the seeds and/or root tips of plants. Vegetative hyphae can directly penetrate
plant cells. Mycelial growth and the movement of zoospores can facilitate the
spread of P. ultimum to other susceptible plants. P. ultimum can reproduce both
sexually and asexually. For asexual reproduction, sack-like sporangia will be formed .
Sporangia can directly germinate as hyphae. For sexual reproduction,
an oogonium and a club-shaped antheridium) will be produced. When they contact
with each other, the nuclei of this two structures will form a zygote, then a thick-wall
oospore will be formed. Both sporangia and zoospores are short-lived in soils, while
oospores can be survived in the soil for longer periods. For example, sporangia of P.
ultimum were found to remain viable for 11 months in the, while oospores can
survive in the soil for nearly 12 years.

38. Pea False Leaf Roll and Pythium ultimum
 This suspected virus is unusual is being reported to be
transmissible by sap, seed, Myzus persicae and Pythium ultimum (
Thottappilly and schmutterer, 1968)
 When the mixture of healthy and diseased seed was planted in the
same pot, the disease incidence was increased from 10-12 % to 50-
60%.
 Replanting infested soil without prior steaming resulted in 40%
disease incidence , compared with no infection in steamed soil.
 Seed treatment with certain fungicide greatly reduce the spread of
the disease.
 The disease spread from diseased to healthy pea seedlings placed
iin water on opposite sides of a petri dish.
 Pythium ultimum caused the disease when its mycelium infected
healthy seedlings.

39. Pythium ultimum LIFECYCLE

40. Management of disease is challenging but focuses on
sanitation, fungicides, and biological control.
 Fungicides include mefenoxam, thiadiazole, etridiazole,
propamocarb, dimethomorph, and phosphonates.
 Biological control agents include the bacteria Bacillus subtilis,
Streptomyces griseoviridis, and the fungi Candida oleophila,
Gliocladium catenulatum, Trichoderma
harziamum, and Trichoderma virens.
 Effective resistance in the plant host is generally not available.
Sanitation is very important since the pathogen can be easily
introduced into pasteurized soil or even soil-free potting
mixes on dirty tools or pots.
 Especially in greenhouses, fungus gnats may also help move
the pathogen from place to place.

41. Pythium transmits PEA FALSE LEAF ROLL VIRUS:

42. Acknowledge
I acknowledge the scientists who spent valuable time in
generating information on various aspects of plant pathology
and displayed the same on internet for use by teachers and
researchers.
CONCLUSION:
By understanding the different viruses are transmitted by
fungi we recommend the proper chemical to control fungi and
vectors in crop management there by increasing yield and
income
we concluded that research on fungi which transmit viruses is
not sufficient to identify the correct symptoms of disease and
favourable conditions. We need study on the soil born viruses
which are transmitted by fungi

43. REFERENCE:
 HANDBOOK OF PLANT VIROLOGY – Jawaid A.Khan, Jeanna Dijkstra
 PLANT VIRUS VECTORS, EPIDEMELOGY AND MANAGEMENT-S.Mukhopadhyay
 link.springer.com/chapter/10.1007%2F978-3-540-78826-3_24
 www.sipav.org/main/jpp/volumes/0305/030501.pdf
 hillagric.ac.in/.../Lect.%207%20Pl%20Path%20502%20Plant%20virus%...
 www.annualreviews.org › ... › List of Issues › Volume 34, 1996
 onlinelibrary.wiley.com/doi/10.1002/9780471729259.../pd
 Vectors of Plant Pathogens
edited by Kerry F. Harris, Karl Maramorosch
 MOLECULAR BIOLOGY OF PLANT VIRUSES edited by c. L. Mandahar Botany
Department Panjab University, India
 COMPARATIVE PLANT VIROLOGY SECOND EDITION
ROGER HULL Emeritus Fellow Department of Disease and Stress Biology