Dealing with complex virus disease problems

a case of Tospovirus Diseases in Vegetables

Naidu A. RayapatiDepartment of Plant PathologyWashington State UniversityIrrigated Agriculture Research & Extension CenterProsser, WA 99350, USAnaidu@wsu.edu

An overview

Thrips vectors

Tospoviruses

Topics

Thrips : Greek word for “wood worms”

Thrips : a plural noun

Each individual is “a thrips” like the word “sheep”

Thrips: What are they?

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.

Thrips play a vital role in the spread of tospoviruses

Tospovirus

Thrips Host

The virus disease triangle

• Viruses can not move by themselves

• They need a “safe” vehicle to spread from plant to plant• Thrips control strategies may be a better option to disrupt the disease triangle

Thrips as vectors of viruses

• As vectors directly transmitting virusese.g. Tospoviruses in vegetables, field crops

and ornamentals

• As carriers of pollen containing virusese.g. certain other viruses (Tobacco streak virus)

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

• Vectors of viruses- Spread virus diseases

Source: Zenkoko Noson, Kyoiku Kyoiku Co. Ltd, Japan.

• 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

Thrips

• 12 species in 4 genera

• About 0.16% (12/5500) of the known Thysanoptera

Family: Thripidae

Order: Thysanoptera

Thrips species implicated in Thrips species implicated in tospovirus transmissiontospovirus transmission

Thrips species implicated in Thrips species implicated in tospovirus transmissiontospovirus transmission

Frankliniella occidentalisFrankliniella occidentalisF. fuscaF. fuscaF. bispinosaF. bispinosaF. schultzeiF. schultzeiF. intosaF. intosaF. zucchiniF. zucchiniF. schultzeiF. schultzei

Thrips palmiThrips palmiT. tabaciT. tabaciT. setosusT. setosusScirtothrips dorsalisScirtothrips dorsalisCeratothrips claratrisCeratothrips claratris

12 species

Thrips species implicated in tospovirus Thrips species implicated in tospovirus transmissiontransmission

Frankliniella occidentalis*Frankliniella occidentalis*F. fusca*F. fusca*F. bispinosa*F. bispinosa*F. schultzeiF. schultzeiF. intosaF. intosaF. zucchiniF. zucchiniF. schultzeiF. schultzei

Thrips tabaci*Thrips tabaci*T. palmi*T. palmi*T. setosusT. setosusScirtothrips dorsalisScirtothrips dorsalisCeratothrips claratrisCeratothrips claratris

*Major vectors in the USA*Present in the US, but vectoring capacity not clear

• 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

Major vector thrips in the USA

Thrips species implicated in Thrips species implicated in tospovirus transmissiontospovirus transmission

Frankliniella occidentalisFrankliniella occidentalis****F. fuscaF. fuscaF. bispinosaF. bispinosaF. schultzeiF. schultzei**F. intosaF. intosaF. zucchiniF. zucchiniF. schultzeiF. schultzei

Thrips palmiThrips palmi**T. tabaciT. tabaci**T. setosusT. setosusScirtothrips dorsalisScirtothrips dorsalis**Ceratothrips claratrisCeratothrips claratris**

*Present in Asia-Pacific Region**Present in some countries of Asia-Pacific Region

TSWV = Tomato spotted wilt virusGRSV = Groundnut ringspot virusTCSV = Tomato chlorotic spot virusCSMV = Chrysanthemum stem necrosis virusZLCV = Zucchini lethal chlorosis virusINSV = Impatiens necrotic spot virusPBNV = Peanut bud necrosis virusWSMV = Watermelon silver mottle virusWBNV = Watermelon bud necrosis virusCaCV = Capsicum chlorosis virusMYSV = Melon yellow spot virusIYSV = Iris yellow spot virusTYRV = Tomato yellow fruit ring virusPYSV = Peanut yellow spot virusPCFV = Peanut chlorotic fanspot virusCCSV = Calla lily chhlrotic spot virus

List of characterized tospoviruses

As of 2007

16

6 virusesdistributed primarily

in Americas

11 virusesdistributed primarily

in Eurasia

TCSV GRSV

TSWV CSNV

ZLCV INSV

TYRV IYSV MYSV TZSV CCSV

CaCV WSMoV WBNV

GBNV GCFSV GYSV100

9296

90

100

100

100

100100

100

74

6371

100

0.1 Some exceptionsTSWV - in Europe, Africa, Australia & JapanIYSV - in the Americas and Australia

Tospoviruses – a global view

17 viruses

Southeast Southeast AsiaAsia

CaCVCaCV WSMVWSMV MYSVMYSV PCFVPCFV

Geographic structuring of tospoviruseswithin South & Southeast Asia

S. AsiaPBNVWBNVPYSVIYSV

Thrips species implicated in Thrips species implicated in tospovirus transmissiontospovirus transmission

Frankliniella occidentalisFrankliniella occidentalisF. fuscaF. fuscaF. bispinosaF. bispinosaF. schultzeiF. schultzeiF. intosaF. intosaF. zucchiniF. zucchiniF. schultzeiF. schultzei

Thrips palmiThrips palmiT. tabaciT. tabaciT. setosusT. setosusScirtothrips dorsalisScirtothrips dorsalisCeratothrips claratrisCeratothrips claratris

12 species

TCSV GRSV

TSWV CSNV

ZLCV INSV

TYRV IYSV MYSV TZSV CCSV

CaCV WSMoV WBNV

GBNV GCFSV GYSV100

9296

90

100

100

100

100100

100

74

6371

100

0.1

Group 1Primary vector

Frankliniella sp.

Group 2Primary vector

Thrips sp.

Group 3Primary vectorScritothrips sp.

Phylogenetic tree - N protein

Association between tospoviruses and thrips vectors

Peanut bud necrosis virus a threat to tomato sustainability in India

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

Healthy Infected

Peanut bud necrosis virus a threat to tomato sustainability in India

• affects quality and shelf life

• loss of income

Peanut bud necrosis virus

Capsicum chlorosis virus in South Asia

Symptoms mimic those produced by PBNV

Life stages of thrips

Egg

Lar

va I

Lar

va I

I

Pre

pu

pa

Pu

pa

Ad

ult

Ad

ult

• 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

Western Flower Thrips

Ullman et. al., 1997

♀♂

Unique among plant viruses II nd instar

larva

Quiescent&

Do not feed

Only adults that acquire virus

as larva can transmit

Symptom expression

Prepupa

Pupa

Adult

Virus acquisition

by larva is crucial

Interdependency between vector life-stage and productive virus transmission

Ist instar larva

Virus replicates & passage occurs from one stage to the otherUllman et. al., 1997

Tospoviruses• A serious threat to vegetables, ornamentals,

food and cash crops

• ~1000 species of plants in about 70 plant families (dicots & monocots)

• an estimated global yield losses of up to $1 billion

Tomato Peanut

Tobacco

Pepper

Potato

Ornamentals

Onion

Thrips vector

Tospoviruses multiply in two disparate hosts

Plants Male

Female

Thrips not a vector but a mobile host

Western flower thrips

Male FemaleMale46%

Female12%

Transmission efficiency

Gender-specific differences in virus transmission

Males are efficient transmitters

SDS-PAGE ofTSWV particle proteinsElectron micrograph

of TSWV particles

GC

N

GN

TSWV MrDrawing of TSWV particle

150

100

75

50

35

25

15

kDa

M S

L

Tospoviruses have a complex structure

Pleomorphic particles = 80-120 nm size

Replicase

Tospoviruses have a complex genome

Organization

L-RNA = negative senseM- & S- RNA = Ambisense

NSs N

NSm GN/GC

Replicase8.9 kb

4.8 kb

2.9 kb

L-RNA

S-RNA

M-RNA GC N

GN

• Tri-partite genome: three genomic segments• Hybrid particles: virus-encoded and host-derived

Replicase

Virus Thrips vectorTomato spotted wilt virus Frankliniella occidentalis

F. fuscaF. intosaF. bispinosaF. schultzeiThrips tabaciT. setosus

Impatiens necrotic spot virus F. occidentalisF. fuscaF. intosaF. schultzei

A tospovirus can be transmitted by more than one thrips vector

A single species of thrips vector can transmit more than one tospovirus

Thrips vector VirusF. occidentalis Tomato spotted wilt virus

Impatiens necrotic spot virusTomato chlorotic spot virusGroundnut ringspotvirusChrysanthemum stem necrosis virus

T. palmi Peanut bud necrosis virusWatermelon silver mottle virusWatermelon bud necrosis virusMelon yellow spot virusCapsicum chlorosis virusTomato spotted wilt virus ??

Western flower thrips (WFT)(Frankliniella occidentalis)

Melon thrips (Thrips palmi)

Source: www.eppo.org

• A native to the southwestern USA• Spread through global trade

in ornamental greenhouse plants around the world from mid-1980s

• A native to Southeast Asia• Expanded its geographic

range in 1970s and 80s

Geographic expansion of thrips vectors

• virus vectors introduced in to new areas

• viruses introduced in to new areas by land, sea and air, via

international trade or accidentally

Viruses and insects do not carry passports

The planetary ecosystem has changed !!!

Global village

Challenges in controlling tospovirus diseases

Tospoviruses

• broad host range• multiple vector species• evolution of new strains• ability to overcomehost plant resistance

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

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

Challenges in controlling tospovirus diseases

Host plant resistance

• No broad-spectrum resistancee.g. CaCV overcame the Sw-5 resistance gene in tomatoe.g CaCV overcame TSWV resistance in

Capsicum chinense accessions PI 152225, PI 159236 and AVRDC 00943

• Resistance to ‘Asian’ tospoviruses not yet knowne.g. is there resistance to PBNV in tomato ?

Challenges in controlling tospovirus diseases

Challenges in controlling tospovirus diseases

Host plant resistance

• virus-specific• no ‘one-size-fits all’ approach

Durable resistance is difficult to achieve

due to rapid evolution of resistance-breaking virus strains

K.S. Ravi, Mahyco, India

biologic chess game !!!

Crop Improvement against tospoviruses

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

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

“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”

Project Goal

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)

Project Objectives

Thank You