Group of emerging plant viruses causing economically significant damage to a broad range of field crops, vegetables, ornamentals, fruits, etc. Viruses can not move by themselves and they need a “safe” vehicle to spread from plant to plant one such is thrips -Naidu A. Rayapati, Presentation at CPMB, TNAU 19th,August 2009

1. Dealing with complex virus disease
problems
a case of Tospovirus Diseases in
Vegetables
Naidu A. Rayapati
Department of Plant Pathology
Washington State University
Irrigated Agriculture Research & Extension Center
Prosser, WA 99350, USA
naidu@wsu.edu

2. Topics
An overview
Thrips vectors
Tospoviruses

3. Thrips: What are they?
Thrips : Greek word for “wood worms”
Thrips : a plural noun
Each individual is “a thrips” like the word “sheep”

4. What are Tospoviruses ?
Type member: Tomato spotted wilt virus
Group of emerging plant viruses
causing economically significant
damage to a broad range of field crops,
vegetables, ornamentals, fruits, etc.

5. Thrips play a vital role in the
spread of tospoviruses
The virus disease triangle
Tospovirus
• Viruses can not move
by themselves
• They need a “safe” vehicle
to spread from plant to plant
Thrips • Thrips control strategies
Host
may be a better option to
disrupt the disease triangle

6. Thrips as vectors of viruses
• As vectors directly transmitting viruses
e.g. Tospoviruses in vegetables, field crops
and ornamentals
• As carriers of pollen containing viruses
e.g. certain other viruses (Tobacco streak virus)

7. General features of thrips
• Small size
- difficult to detect
• Polyphagous
- feed on a broad range of plant species
- feed on different parts of the plant
(pollen, flower structures, leaves, stems)
• Show habitat infidelity
- extraordinary ability to adapt
- can expand geographic range
- can spread to new crops
• Have superior reproductive output
- produce many off springs
• Have propensity to ‘overwinter’ on a
broad range of plant species
- survive through out the year
Source: Zenkoko Noson,
• Vectors of viruses
Kyoiku Kyoiku Co. Ltd, Japan. - Spread virus diseases

8. Thrips
• Approximately 5500 species of thrips
described
• About 40% known to feed on higher
plants
• The rest exploits lower plant families
(gymnosperms, ferns and fungi)
• Some species are predatory

9. Thrips species implicated in
tospovirus transmission
• 12 species in 4 genera
• About 0.16% (12/5500)
of the known Thysanoptera
Order: Thysanoptera
Family: Thripidae

10. Thrips species implicated in
tospovirus transmission
Thrips palmi Frankliniella occidentalis
T. tabaci F. fusca
T. setosus F. bispinosa
Scirtothrips dorsalis F. schultzei
Ceratothrips claratris F. intosa
F. zucchini
12 F. schultzei
species

11. Thrips species implicated in tospovirus
transmission
Frankliniella occidentalis* Thrips tabaci*
F. fusca* T. palmi*
F. bispinosa* T. setosus
F. schultzei Scirtothrips dorsalis
F. intosa Ceratothrips claratris
F. zucchini
F. schultzei
*Major vectors in the USA
*Present in the US, but vectoring capacity not clear

12. Major vector thrips in the USA
• F. occidentalis (Western flower thrips)
Polyphagous (many fruits, vegetables,
ornamentals, seed crops, cotton)
Throughout USA
• F. fusca (Tobacco thrips)
Polyphagous (common in grasslands,
peanut, tobacco, cotton)
South & Southeastern USA
• T. tabaci (Onion thrips)
Polyphagous (onion, cabbage, tobacco,
cotton, vegetables and ornamentals)
Throughout USA

13. Thrips species implicated in
tospovirus transmission
Thrips palmi* Frankliniella occidentalis**
T. tabaci* F. fusca
T. setosus F. bispinosa
Scirtothrips dorsalis* F. schultzei*
Ceratothrips claratris* F. intosa
F. zucchini
F. schultzei
*Present in Asia-Pacific Region
**Present in some countries of Asia-Pacific Region

14. List of characterized tospoviruses
TSWV = Tomato spotted wilt virus
GRSV = Groundnut ringspot virus
TCSV = Tomato chlorotic spot virus
CSMV = Chrysanthemum stem necrosis virus
ZLCV = Zucchini lethal chlorosis virus
INSV = Impatiens necrotic spot virus
PBNV = Peanut bud necrosis virus
WSMV = Watermelon silver mottle virus
WBNV = Watermelon bud necrosis virus
CaCV = Capsicum chlorosis virus
MYSV = Melon yellow spot virus
IYSV = Iris yellow spot virus As of 2007
TYRV = Tomato yellow fruit ring virus
PYSV = Peanut yellow spot virus 16
PCFV = Peanut chlorotic fanspot virus
CCSV = Calla lily chhlrotic spot virus

15. Tospoviruses – a global view
92 TCSV
17 96 GRSV 6 viruses
viruses 100 TSWV
distributed primarily
100 CSNV
90 ZLCV in Americas
INSV
100 TYRV
IYSV
MYSV
100
100 TZSV
100 CCSV 11 viruses
74 CaCV
WSMoV
distributed primarily
100
71 WBNV in Eurasia
63 GBNV
GCFSV
100 GYSV
0.1
Some exceptions
TSWV - in Europe, Africa, Australia & Japan
IYSV - in the Americas and Australia

16. Geographic structuring of tospoviruses
within South & Southeast Asia
S. Asia Southeast
PBNV Asia
WBNV CaCV
PYSV WSMV
IYSV MYSV
PCFV

17. Thrips species implicated in
tospovirus transmission
Thrips palmi Frankliniella occidentalis
T. tabaci F. fusca
T. setosus F. bispinosa
Scirtothrips dorsalis F. schultzei
Ceratothrips claratris F. intosa
F. zucchini
12 F. schultzei
species

18. Association between tospoviruses and thrips vectors
92 TCSV
96 GRSV Group 1
100 TSWV Primary vector
CSNV
100 Frankliniella sp.
90 ZLCV
INSV
100 TYRV
IYSV
MYSV
100
100 TZSV Group 2
100 CCSV Primary vector
74 CaCV Thrips sp.
100
WSMoV
71 WBNV
63 GBNV
GCFSV Group 3
100 GYSV Primary vector
Scritothrips sp.
0.1 Phylogenetic tree - N protein

19. Peanut bud necrosis virus
a threat to tomato sustainability in India

20. Peanut bud necrosis virus (PBNV)
a major threat to tomato sustainability in India

21. Peanut bud necrosis virus
a threat to tomato sustainability in India
Healthy Infected

22. Peanut bud necrosis virus
• affects quality and shelf life
• loss of income

23. Capsicum chlorosis virus in South Asia
Symptoms mimic those produced by PBNV

24. Life stages of thrips
Larva II
♂ ♀
Prepupa
Larva I
Adult
Adult
Pupa
Egg
Western Flower Thrips
Ullman et. al., 1997
• Larvae and adults: feeding stages
• Pre-pupa and pupa: non-feeding stages
• Gender can not be determined until adult state
• Larva - adult = 15-20 days

25. Interdependency between vector life-stage
and productive virus transmission
Virus
Symptom I instar
st acquisition
by larva is crucial
expression larva
Unique among
plant viruses II nd instar
Adult
larva
Only adults
that acquire virus
as larva can transmit
Prepupa
Quiescent
Virus replicates &
Pupa
& passage occurs from
Ullman et. al., 1997 Do not feed one stage to the other

26. Tospoviruses
Tomato Peanut
• A serious threat to
vegetables, ornamentals,
food and cash crops
• ~1000 species of plants
in about 70 plant families
(dicots & monocots)
Pepper
Onion
• an estimated global yield
Tobacco losses of up to $1 billion
Ornamentals
Potato

27. Tospoviruses multiply in two disparate hosts
Thrips vector
Plants
Female
Male
Thrips
not a vector but a mobile host

28. Gender-specific differences in
virus transmission
Western flower thrips
Male Female
Transmission efficiency
Male
46%
Female
12%
Males are efficient transmitters

29. Tospoviruses have a complex structure
SDS-PAGE of
Electron micrograph TSWV particle proteins
of TSWV particles Drawing of TSWV particle TSWV Mr kDa
Replicase  150
GC  100
 75
S
M GN 
 50
L
 35
N  25
 15
Pleomorphic particles = 80-120 nm size

30. Tospoviruses have a complex genome
Organization
Replicase
L-RNA 8.9 kb
NSm GN/GC N GC Replicase
M-RNA 4.8 kb GN
NSs N
S-RNA 2.9 kb
L-RNA = negative sense
M- & S- RNA = Ambisense
• Tri-partite genome: three genomic segments
• Hybrid particles: virus-encoded and host-derived

31. A tospovirus can be transmitted by
more than one thrips vector
Virus Thrips vector
Tomato spotted wilt virus Frankliniella occidentalis
F. fusca
F. intosa
F. bispinosa
F. schultzei
Thrips tabaci
T. setosus
Impatiens necrotic spot virus F. occidentalis
F. fusca
F. intosa
F. schultzei

32. A single species of thrips vector
can transmit more than one tospovirus
Thrips vector Virus
F. occidentalis Tomato spotted wilt virus
Impatiens necrotic spot virus
Tomato chlorotic spot virus
Groundnut ringspotvirus
Chrysanthemum stem necrosis virus
T. palmi Peanut bud necrosis virus
Watermelon silver mottle virus
Watermelon bud necrosis virus
Melon yellow spot virus
Capsicum chlorosis virus
Tomato spotted wilt virus ??

33. Geographic expansion of thrips vectors
Western flower thrips (WFT)
(Frankliniella occidentalis)
• A native to the
southwestern USA
• Spread through global trade
in ornamental greenhouse
plants around the world
from mid-1980s
Melon thrips (Thrips palmi)
• A native to Southeast Asia
• Expanded its geographic
range in 1970s and 80s
Source: www.eppo.org

34. Viruses and insects
do not carry passports
• virus vectors introduced
Global village in to new areas
• viruses introduced in to
new areas
by land, sea and air, via
international trade or
accidentally
The planetary ecosystem has changed !!!

35. Challenges in controlling
tospovirus diseases
Tospoviruses
• broad host range
• multiple vector species
• evolution of new strains
• ability to overcome
host plant resistance

36. Challenges in controlling
tospovirus diseases
Vector thrips
• polyphagous & show habitat infidelity
• has superior reproductive output
• has propensity to ‘overwinter’ on a
broad range of plant species
• develop resistance against pesticides

37. Challenges in controlling
tospovirus diseases
Host plant resistance
Resistance only against TSWV
• Sw-5 resistance gene in tomato
against TSWV
• Tsw resistance gene in Capsicum
against TSWV

38. Challenges in controlling
tospovirus diseases
Host plant resistance
• No broad-spectrum resistance
e.g. CaCV overcame the Sw-5 resistance gene
in tomato
e.g CaCV overcame TSWV resistance in
Capsicum chinense accessions PI 152225,
PI 159236 and AVRDC 00943
• Resistance to ‘Asian’ tospoviruses
not yet known
e.g. is there resistance to PBNV in tomato ?

39. Challenges in controlling
tospovirus diseases
Host plant resistance
• virus-specific
• no ‘one-size-fits all’ approach

40. Durable resistance is difficult
to achieve
due to rapid evolution of
resistance-breaking virus strains
K.S. Ravi, Mahyco, India

41. Crop Improvement against
tospoviruses
biologic chess game !!!

42. Management of tospovirus
diseases:
an IPM approach
• Knowledge about the virus & vector
• Diagnostic tools
• Ecology and epidemiology
• Thrips vector management options
• Altering cropping patterns
• Deploying tolerant/resistant cultivars
• Capacity building

43. Integrated Management of Thrips-borne Tospoviruses
in Vegetable Cropping Systems
in South Asia and Southeast Asia Region
Funded by
Integrated Pest Management Collaborative Research
Support Program (IPM CRSP) of USAID
Global IPM Theme: Insect-transmitted viruses

44. Project Goal
“minimize crop losses due to thrips-borne
tospoviruses in smallholder vegetable
farming systems in South and Southeast
Asia through new science and technologies
and multidisciplinary global partnerships,
and improve nutritional status of people
including women and children”

45. Project Objectives
1. Conduct strategic research on tospoviruses
and thrips vectors
2. Carryout applied and adaptive research to
deploy ‘eco-friendly’ IPM strategies to control
tospovirus diseases
3. Strengthening institutional capacities within
host countries to conduct problem-oriented
research on virus diseases
(short- and long-term training)

46. Thank You