This document provides an overview of plant viruses, including their diversity and significance. It begins with definitions of viruses and their classification. Plant viruses are obligate intracellular parasites that infect a wide variety of crop and ornamental plants, causing economic losses. Their genetic material can be RNA or DNA configured in various ways. Plant viruses are transmitted horizontally by vectors like insects or nematodes, or vertically through seeds. They cause a diversity of symptoms in infected plants. Important plant viruses discussed in more detail include Tobacco mosaic virus, Tomato spotted wilt virus, Cucumber mosaic virus. Control methods include using virus-free seeds and crops, controlling vectors, and temperature treatments. Plant viruses also play roles in cross-protection and improving host tolerance to stresses.

1. PLANT VIRUSES: overview, diversity &
significance
PRESENTED BY: Ranajit Sarmah
Roll Number 11
Department of Biotechnology, Gauhati University

2. CONTENTS
 What is a virus?
 Virus classification
 Introduction to plant viruses
 Architecture of plant viruses
 Diversity and incidence of plant viruses
 Transmission of plant viruses
 Symptoms of plant viruses
 Viral diseases in plants
 Control of viral diseases in plants
 Real Impact of Viral Diseases on Crops
 Conclusion
 References

3.  Viruses are intracellular parasites that have a set of one or more nucleic acid template molecules,
normally encased in a protective coat or coats of protein or lipoprotein, that is able to organise its own
replication only within suitable host cells
 The name is from a Latin word meaning “slimy liquid” or “poison.”
 Viral infection begins when proteins on the surface of a virion bind to specific receptor proteins on the
surface of host cells.
 Predominantly, viruses have a reputation for being the cause
of contagion. Widespread events of disease and have no doubt
bolstered such a reputation.
What is a Virus?
The outbreak
of Ebola in West Africa,
2014
The H1N1/swine
flu pandemic, 2009
The COVID 19
pandemic, 2019
Source: nature.com/articles. Ebola prepared these countries
for coronavirus — but now even they are floundering

4. Virus Classification:
Source: (1). https://www.onlinebiologynotes.com/classification-of-virus/ (2).https://ib.bioninja.com.au/standard-level/topic-5-
evolution-and-biodi/53-classification-of-biodiv/virus-classification.html
(1) (2)

5. Introduction to Plant Viruses
• Plants were the first known hosts for viruses and plant viruses have been a focus of research for nearly
120 years.
• Plant viruses are obligate intracellular parasites that do not have the molecular machinery
to replicate without a host.
• Plant viruses are a number of agents that can cause plant diseases and are of considerable economic
importance because many of them infect crop and ornamental plants.
• They are responsible for losses in crop
quality and crop yield.
• Eg: TULIPOMANIA in Netherlands, 1636-1637.
Source: https://www.apsnet.org/edcenter/disandpath/viral/introduction/PlantVirusClassification/Pages/Purpose.aspx

6. Source: thecontemporarywomen.com/2015/05/26/tulipomania-the-story-about-how-the-tulip-
became-a-distinctive-symbol-of-the-netherlands/
• Plant virus genetic material is composed of strands of RNA or DNA and be configured in any of
seven ways:

7. Architecture of plant virus:
• Knowledge of virus architecture has increased greatly with the innovation like Electron
Microscopy, optical diffraction, X-Ray crystallography procedures, mol. techniques and
chemical nature of the virus.
• The architecture of viruses is very complex, while simpler viruses seem to be composed of
protein and nucleic acid, others also contain carbohydrate and the most complex contain
materials which are indistinguishable from those found in bacteria.
• Viral Capsids:
• The capsid is the protein shell that encloses the
nucleic acid; with its enclosed nucleic acid,
it is called the nucleocapsid.
• This shell is composed of protein organized in
subunits known as capsomers.
Source: Louten J. (2016). Virus Structure and Classification. Essential Human Virology, 19–29.
https://doi.org/10.1016/B978-0-12-800947-5.00002-8

8. Viral capsids:
Helical capsid proteins wind
around the viral nucleic acid
to form the nucleocapsid.
An icosahedron is a geometric shape
with 20 sides, each composed of an
equilateral triangle.
Source: Louten, Jennifer. “Virus Structure and Classification.” Essential Human Virology (2016): 19–29. doi:10.1016/B978-0-12-800947-5.00002-8

9. Diversity and incidence of plant viruses:
• Viruses are abundant in wild plants, from the tropics to Antarctica, with infection incidence
as high as 60% based on current and older technologies, and most are turning out to be
novel.
• In addition to wild plants, plant virus like nucleic acids have been found in numerous aquatic
environments and in feces from humans and other animals.
• This remarkable diversity, most of which is probably still unknown based on the current rate
of novel findings, implies important roles for viruses in the evolution and ecology of their
hosts.
Source: Roossinck, M. J. (2015). Plants, viruses and the environment: ecology and
mutualism. Virology, 479, 271-277.

10. Transmission of plant viruses:
• There are main two types of transmission:
1. Horizontal Transmission- Through “Vectors”.
Because plant viruses have no legs, wings, tails, or cilia, they reach plants with the aid of
carriers (also called “vectors”) and other mechanisms.
Viruses can be transmitted through living organisms (e.g., insects, nematodes, mites, and soil
microorganisms).
The principal virus-carrying insects are about 200 species of aphids, which transmit
mostly mosaic viruses, and more than 100 species of leafhoppers, which carry yellows-
type viruses.
2. Vertical Transmission- Through “parent plant”.
It occurs when a plant gets it from parent plant, either by vegetative reproduction, seed
transmission.

11. Source: UGA Cooperative Extension Bulletin 1507 • Whitefly-Transmitted Plant Viruses in
Southern Georgia
Whitefly-vectored viruses are semi-persistent or persistent. Semi-persistent viruses reach
the foregut and can be transmitted immediately after acquisition. Persistent circulative
viruses move from the midgut into the hemocoel (primary body cavity) and to the salivary
gland before they can be inoculated, so they generally have latent periods of multiple
hours to days.

12. Symptoms of plant viruses:
Source: apsnet.org/edcenter/disandpath/viral/introduction/PlantVirusClassification/Pages/Purpose

13. TobaccoMosaic
Virus(TMV):
 It was the first plant virus isolated in the history (1892).
 Tobacco mosaic virus (TMV) infects the leaves of tobacco,
tomato, bean, and pepper plants and is an example of a
helical, rigid rod virus.
 TMV is made up of a piece of nucleic acid, about 5% (ribonucleic
acid; RNA) and a surrounding protein coat, 95%.
 Once inside the plant cell, the protein coat falls away and regular
replication occurs.
Viral diseases in plants:

14.  Tobacco mosaic virus is very stable, so stable
that it can survive for years in cigars and
cigarettes made from infected leaves.
 TMV particle is about 300 nanometers (nm) in
length and 18 nm in diameter.
 TMV can also survive outside the plant in sap
that has dried on tools and other surfaces.

15. Source:Heinlein, M. (2002). The spread of tobacco mosaic virus infection: insights into the
cellular mechanism of RNA transport. Cellular and Molecular Life Sciences CMLS, 59(1), 58-82.
Stages of TMV infection:

16. Tomato spotted wilt virus (TSWV):
• The "spotted wilt" disease of tomato was first described in
Australia in 1915 and was determined to be of viral etiology
in 1930.
• The Tomato spotted wilt virus (genus Tospovirus;
family Bunyaviridae) (TSWV) now contains TSWV as the
type member and more than a dozen other distinct viruses
whose identification has been facilitated by the use of
serological and molecular techniques.
• The tospoviruses are transmitted by thrips
(Thysanoptera: Thripidae) and replicate in both the thrips
vectors and the plant hosts.
• The virus is found in temperate, sub tropical and
tropical regions of the world.

17. Symptoms and Signs of TSWV:
• Stunting is a common symptom of TSWV infection, and is
generally more severe when young plants are infected.
(a) necrotic lesions in leaf
(b) veinal necrosis
(c) stem necrosis
(d) chlorotic lesions in cowpea
(e) Chenopodium amaranticolor
(f) necrotic ring-spots in Solanum lycopersicum
(g) necrotic lesions in Nicotiana glutinosa
(h) white necrotic rings in Datura stramonium
(i) The vector of TSWV, Frankliniella occidentalis
adult in chrysanthemum
• Although TSWV is not seed transmitted, it may cause the
discoloration of seed produced on infected hosts
Source: Mandal, B., Gawande, S. J., Renukadevi, P., Holkar, S. K., Krishnareddy, M., Ravi, K. S., & Jain, R. K. (2017). The occurrence, biology,
serology and molecular biology of tospoviruses in indian agriculture. In A century of plant virology in India (pp. 445-474). Springer, Singapore.

18. Life Cycle of TSWV:
Source: (https://www.sciencedirect.com/science/article/pii/B0122276205001804)

19.  Historically, Cucumber mosaic virus (CMV) was first described in detail
in 1916 on cucumber (simultaneously by Doolittle and Jagger) and
other cucurbits.
 It is now known to occur worldwide in both temperate and tropical
climates, affecting many agricultural and horticultural crops.
 On the basis of different criteria (e.g., serological typing, peptide
mapping of the coat protein, sequence similarity of their genomic RNA)
CMV isolates can be classified into two major subgroups, now named
subgroup I and subgroup II.
 The host range of the collective isolates of CMV is over 1300 species in
more than 500 genera of over 100 families, with new hosts reported
each year.
Cucumber
Mosaic Virus
(CMV)

20.  CMV has icosahedral particles 29 nm in diameter.
 CMV moves cell to cell via plasmodesmata between
cells until it reaches the vasculature,
 CMV appears to move between epidermal cells as well
as from epidermal cells down to mesophyll cells toward
vascular cells.
Symptoms and Signs of TSWV:
1. Stunting
2. mosaic pattern of light and dark green (or yellow and green) on
the leaves.
3. malformation of leaves or growing points
4. yellow streaking of leaves (especially monocots)
5. yellow spotting on leaves
6. ring-spots or line patterns on leaves or fruit lower color breaking
distinct yellowing only of veins

21. Top 10 plant viruses in molecular plant pathology:
Source: Scholthof, K. B. G., Adkins, S., Czosnek, H., Palukaitis, P., Jacquot, E., Hohn, T., ... & Foster, G. D.
(2011). Top 10 plant viruses in molecular plant pathology. Molecular plant pathology, 12(9), 938-954.

22. CONTROL OF PLANT VIRAL DISEASES:
• Selection of viral disease free seeds from
the disease free regions.
• Application of Soil Fumigation for
Nematodes transmitted viruses to control
nematodes.
• Destruction of weeds that serve as host
for virus causing viral disease in plants
• Application of temperature treatment Ex.
Sugarcane mosaic can be destroyed or
reduce by hot water treatment 520 C for
30 minutes.

23. PRODUCTS THAT CONTROL VIRUSES:
 Aphids- UPL Phoskill Insecticide, Active Gold Neem Oil, Azaal Neem Oil,
Jashn Insecticide, Koranda 505 Insecticide.
 Nematode - FMC Furadan Insecticide
 Leafhoppers- UPL Phoskill Insecticide
 White flies- Anant Insecticide, Active Gold Neem Oil, Azaal Neem Oil
 Virus- V-Bind Viricide

24. What is the Real Impact of Viral Diseases on Crops?
• Virus diseases in different crops cause enormous losses all over the world in terms of quantity
and/or quality of products.
• Strains of Cassava mosaic begomoviruses cause more than 25 million tons of losses per year in
Africa, India, and Sri Lanka
• Viruses affecting rice cultures result in yield losses estimated at more than $1.5 billion in South-
East Asia alone
• Moreover, virus-associated losses in fields are highly under-estimated as some viral infections are
asymptomatic alone.
• More importantly, viruses have been described causing half of the reported emerging infectious
diseases from plants

25. SIGNIFICANCE OF PLANT VIRUSES:
1. Virus infection improves host tolerance to various stresses:
• RNA viruses improve plant tolerance to abiotic stress, indicating a conditional mutualistic
relationship which helps host to survive in adverse conditions.
Four different viruses namely Brome mosaic virus (BMV), Cucumber mosaic virus
(CMV), Tobacco mosaic virus (TMV) and Tobacco rattle virus (TRV) were inoculated
on beet, pepper, watermelon, cucumber, tomato, zucchini, rice, tobacco, Chenopodium
amaranthicolor, Nicotiana benthamiana and N. tabacum.
After infection, drought stress orWD was imposed.
It was found that CMV infection improved the drought tolerance in the inoculated
plants and enhanced freezing tolerance in beet plants.
Xu,
P.,
Chen,
F.,
Mannas,
J.
P.,
Feldman,
T.,
Sumner,
L.
W.,
&
Roossinck,
M.
J.
(2008).
Virus
infection
improves
drought
tolerance.
New
Phytologist,
180(4),
911-921.

26. 2. Plant viruses in cross protection:
• The phenomena in which a mild viral strain (not causing yield loss) is used to prevent disease
caused by related severe viral strain is called cross protection.
• This phenomenon was first described by McKinney (1926) in two genotypes of Tobacco mosaic
virus (TMV, Genus Tobamovirus).
• Tobacco plants infected with green mosaic strain remained protected against yellow mosaic
symptoms on subsequent inoculation with TMV yellow mosaic strain.
• The first commercial use of this phenomenon was reported with Citrus tristeza virus (CTV:
Genus Closterovirus).

27.  Citrus crop is well known to be infected by CTV around world. CTV is one of the
most complex and largest known plant viruses, which belongs to family
Closteroviridae and is phloem limited virus
 Another important crop in which cross protection phenomenon was used is papaya.
Papaya ring spot virus (PRSV) causes papaya ringspot disease in this crop.
 Using chemical mutagenesis, two milder strains named as PRSV-HA 5-1 and
PRSV-HA 6-1 were synthesized from severe Hawaii strain (PRSV-HA).
 These mild strains were used in different parts of Taiwan and Hawaii to protect
against PRSV disease with varied success

28. 3. Viruses and their role in plant biology
• Viruses act as catalyst to understand host biology specially to understand host defense network which
leads to development of strategies to counter pathogenic viruses.
• These studies lead to understand the host innate defense system i.e. RNA silencing or RNA interference
(RNAi) in a better way.
• Also, studies on viruses leads to development of virus-based tools by modifying viral genome i.e. virus
induced gene silencing (VIGS).
• Both of these i.e. RNAi and VIGS contribute significantly to understand the plant biology and leads the
way to develop new strategies for controlling pathogenic viruses.

29. Pasin,
Fabio;
Menzel,
Wulf;
Daròs,
José-Antonio
(June
2019).
"Harnessed
viruses
in
the
age
of
metagenomics
and
synthetic
biology:
an
update
on
infectious
clone
assembly
and
biotechnologies
of
plant
viruses".
Plant
Biotechnology
Journal.
17
(6):
1010–1026.

30. CONCLUSION!!
 Viruses have a great deal of potential for the benefit of agriculture, but this will require that we let go
of our almost ubiquitous bias about the negative nature of viruses.
 With our changing environment, lack of adequate water and loss of arable lands, which are
concurrent with ever-increasing human populations, we need to make use of every possible tool at
our disposal to enhance agricultural production without further compromising the environment.
 Viruses hold the potential for safe, inexpensive and nondestructive improvements to cropping
practices that need to be taken seriously by horticulturists, crop scientists and plant pathologists.

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mechanism of RNA transport. Cellular and Molecular Life Sciences CMLS, 59(1), 58-82.
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