How to deal with complex virus disease problems

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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

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  • Thrips have different developmental stages
  • How to deal with complex virus disease problems

    1. 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. 2. TopicsAn overview Thrips vectors Tospoviruses
    3. 3. Thrips: What are they?Thrips : Greek word for “wood worms”Thrips : a plural nounEach individual is “a thrips” like the word “sheep”
    4. 4. What are Tospoviruses ?Type member: Tomato spotted wilt virusGroup of emerging plant virusescausing economically significantdamage to a broad range of field crops,vegetables, ornamentals, fruits, etc.
    5. 5. Thrips play a vital role in the spread of tospovirusesThe 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. 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. 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 yearSource: Zenkoko Noson, • Vectors of virusesKyoiku Kyoiku Co. Ltd, Japan. - Spread virus diseases
    8. 8. Thrips• Approximately 5500 species of thripsdescribed• About 40% known to feed on higherplants• The rest exploits lower plant families (gymnosperms, ferns and fungi)• Some species are predatory
    9. 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. 10. Thrips species implicated in tospovirus transmissionThrips palmi Frankliniella occidentalisT. tabaci F. fuscaT. setosus F. bispinosaScirtothrips dorsalis F. schultzeiCeratothrips claratris F. intosa F. zucchini 12 F. schultzei species
    11. 11. Thrips species implicated in tospovirus transmissionFrankliniella occidentalis* Thrips tabaci*F. fusca* T. palmi*F. bispinosa* T. setosusF. schultzei Scirtothrips dorsalisF. intosa Ceratothrips claratrisF. zucchiniF. schultzei *Major vectors in the USA *Present in the US, but vectoring capacity not clear
    12. 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. 13. Thrips species implicated in tospovirus transmissionThrips palmi* Frankliniella occidentalis**T. tabaci* F. fuscaT. setosus F. bispinosaScirtothrips 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. 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. 15. Tospoviruses – a global view 92 TCSV 17 96 GRSV 6 virusesviruses 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. 16. Geographic structuring of tospoviruses within South & Southeast Asia S. Asia Southeast PBNV Asia WBNV CaCV PYSV WSMV IYSV MYSV PCFV
    17. 17. Thrips species implicated in tospovirus transmissionThrips palmi Frankliniella occidentalisT. tabaci F. fuscaT. setosus F. bispinosaScirtothrips dorsalis F. schultzeiCeratothrips claratris F. intosa F. zucchini 12 F. schultzei species
    18. 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. 19. Peanut bud necrosis virusa threat to tomato sustainability in India
    20. 20. Peanut bud necrosis virus (PBNV)a major threat to tomato sustainability in India
    21. 21. Peanut bud necrosis virusa threat to tomato sustainability in India Healthy Infected
    22. 22. Peanut bud necrosis virus • affects quality and shelf life • loss of income
    23. 23. Capsicum chlorosis virus in South Asia Symptoms mimic those produced by PBNV
    24. 24. Life stages of thrips Larva II ♂ ♀ Prepupa Larva I Adult Adult PupaEgg 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. 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 virusas larva can transmit Prepupa Quiescent Virus replicates & Pupa & passage occurs from Ullman et. al., 1997 Do not feed one stage to the other
    26. 26. TospovirusesTomato 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 yieldTobacco losses of up to $1 billion Ornamentals Potato
    27. 27. Tospoviruses multiply in two disparate hosts Thrips vector Plants Female Male Thripsnot a vector but a mobile host
    28. 28. Gender-specific differences in virus transmissionWestern flower thrips Male Female Transmission efficiency Male 46% Female 12% Males are efficient transmitters
    29. 29. Tospoviruses have a complex structure SDS-PAGE ofElectron micrograph TSWV particle proteinsof TSWV particles Drawing of TSWV particle TSWV Mr kDa Replicase  150 GC  100  75 S M GN   50 L  35 N  25  15Pleomorphic particles = 80-120 nm size
    30. 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. 31. A tospovirus can be transmitted by more than one thrips vectorVirus Thrips vectorTomato spotted wilt virus Frankliniella occidentalis F. fusca F. intosa F. bispinosa F. schultzei Thrips tabaci T. setosusImpatiens necrotic spot virus F. occidentalis F. fusca F. intosa F. schultzei
    32. 32. A single species of thrips vector can transmit more than one tospovirusThrips vector VirusF. occidentalis Tomato spotted wilt virus Impatiens necrotic spot virus Tomato chlorotic spot virus Groundnut ringspotvirus Chrysanthemum stem necrosis virusT. 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. 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. 34. Viruses and insects do not carry passports • virus vectors introducedGlobal village in to new areas • viruses introduced in to new areas by land, sea and air, via international trade or accidentallyThe planetary ecosystem has changed !!!
    35. 35. Challenges in controlling tospovirus diseases Tospoviruses• broad host range• multiple vector species• evolution of new strains• ability to overcome host plant resistance
    36. 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. 37. Challenges in controlling tospovirus diseases Host plant resistance Resistance only against TSWV• Sw-5 resistance gene in tomatoagainst TSWV• Tsw resistance gene in Capsicumagainst TSWV
    38. 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 inCapsicum 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. 39. Challenges in controlling tospovirus diseases Host plant resistance• virus-specific• no ‘one-size-fits all’ approach
    40. 40. Durable resistance is difficult to achieve due to rapid evolution ofresistance-breaking virus strains K.S. Ravi, Mahyco, India
    41. 41. Crop Improvement against tospovirusesbiologic chess game !!!
    42. 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. 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. 44. Project Goal“minimize crop losses due to thrips-bornetospoviruses in smallholder vegetablefarming systems in South and SoutheastAsia through new science and technologiesand multidisciplinary global partnerships,and improve nutritional status of peopleincluding women and children”
    45. 45. Project Objectives1. Conduct strategic research on tospoviruses and thrips vectors2. Carryout applied and adaptive research to deploy ‘eco-friendly’ IPM strategies to control tospovirus diseases3. Strengthening institutional capacities within host countries to conduct problem-oriented research on virus diseases (short- and long-term training)
    46. 46. Thank You

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