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Papaya Ringspot Disease. Kate Stokes and Andrew Tortora. Cause. Papaya ringspot virus-type P Occurs as 2 strains Type P infects both papaya and cucurbits such as squash, pumpkin, cucumber, and watermelon Type W infects watermelon only. General Characteristics .

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papaya ringspot disease

Papaya Ringspot Disease

Kate Stokes and Andrew Tortora

cause
Cause
  • Papaya ringspot virus-type P
  • Occurs as 2 strains
    • Type P infects both papaya and cucurbits such as squash, pumpkin, cucumber, and watermelon
    • Type W infects watermelon only
general characteristics
General Characteristics
  • Member of potyvirus family
  • Long, flexous rod-shaped particles about 800-900 nm in length
  • Non-enveloped filamentous virions
  • Single-stranded linear RNA genome 12 kb total, encapsulated by a coat protein
  • 5’ terminus of RNA has VPg
symptoms
Symptoms
  • Yellowing and vein-clearing on young leaves
  • Yellow mottling of the leaves, severe blistering and leaf distortion
  • Dark-green streaks and rings in the leafstalks and stems
  • Concentric rings and spots or C-shaped markings, a darker green than the background-green fruit color
  • Can affect vigor of fruit and trees and fruit quality
distribution
Distribution
  • Occurs in nearly every region where papaya is grown except for Africa, including Hawaii, Taiwan, Brazil, Thailand, the Caribbean islands and the Philippines.
  • Particularly severe in Thailand, Taiwan, the Philippines, and the southern region China
spread
Spread
  • Carried from plant to plant by aphids during feeding probes
  • Not spread by other insects and does not survive in soil or dead plant material
  • Also spread by movement of infected papaya plants and cucurbit seedlings
  • Not usually seed-transmitted but there is one case from the Philippines
history
History
  • Brazil
    • 1969 PRSV-p found in two main

growing regions, Sao Paulo

and Rio de Janeiro

    • By 1984 73% of the

industry had moved to

remote regions to evade

the virus

history8
History
  • Hawaii
    • Severely affected the papaya industry in the 1950s. Subsequently, the papaya industry was relocated to Puna district.
    • In May 1992, PRSV was discovered in Puna, the area where 95% of Hawaii’s papaya was being grown, and was widespread throughout the growing region by 1995. Production steadily dropped from 53 million pounds in 1992 to 26 million pounds in 1998.
control
Control
  • Quarantine measures
  • Restricted distribution
  • Removal of infected plants (rouging)
  • Taiwan
    • Used protective netting against aphid vectors because the island was too small to effectively isolate plantings by moving
  • Tolerant or resistant cultivars
cross protection
Cross Protection
  • Phenomenon in which plants systematically infected with mild strain of the virus are protected against infection by a more virulent related strain
  • Used to control
    • Citrus tristeza virus
    • Tobacco mosaic virus
    • Zucchini yellow mosaic virus
  • Early attempts failed, but 2 mild strains were eventually isolated after a virulent strain PRSV HA was treated with nitrous acid
    • PRSV HA 5-1
    • PRSV HA 6-1
cross protection11
Cross Protection
  • Results
    • Delay in severe effects of the virus
    • No complete protection from the virus
  • Not Widely Accepted
    • Adverse effects of mild strain
    • Requires extra cultural management
    • Reluctance of farmers to infect their trees
pathogen derived resistance
Pathogen Derived Resistance
  • Concept conceived in 1980s
  • First demonstrated by Beachy’s group in transgenic tobacco resistant to TMV
coat protein mediated protection cpmp
Coat Protein Mediated Protection (CPMP)
  • Inhibition of disassembly in initially infected cells
    • Interferes with release of encapsidated RNA
    • Re-encapsidation
    • Overcome by inoculation with naked (+) RNA
  • Coat protein may play a role in replication and expression
    • Requires high level of expression
    • Interacts with infection cycle
  • Interference with spread of virus from cell to cell
    • Blocks movement through vascular tissue
  • Examples
    • TMV and Alfalfa mosaic virus
rna mediated resistance
RNA Mediated Resistance
  • Post transcriptional gene silencing
    • Homology dependant
    • Base pairing between the sense RNA transcript of the transgene and the negative strand of the viral RNA
    • Antisense RNA produced from the transgene could pair with the viral RNA transcript.
      • Duplex RNA is target for degradation
      • Base pairing could inhibit translation
  • Examples
    • PRSV, PVX and PVY, and all potyviruses
development of transgenic papaya
Development of Transgenic Papaya
  • Hawaiian papaya industry was in trouble
  • Dennis Gonsalves at Cornell in collaboration with Upjohn, scientists at the University of Hawaii and John Sanford at Cornell try to develop transgenic papaya resistant to PRSV
  • Target was the coat protein gene of PRSV HA 5-1
    • 97.7% identity to PRSVw from Florida
    • Gene was engineered a chimeric protein
    • 17 amino acids of CMV at the N-terminus
transformation of embryogenic tissue
Transformation of Embryogenic Tissue
  • Used gene gun newly invented by John Sanford
  • Tissue bombarded with

tungsten particles coated

with the engineered

DNA

resistant lines
Resistant Lines
  • Inoculation tests conducted with transgenic plants and PRSV HA
  • Line 55-1 showed resistance in greenhouse
    • female rather than hermaphrodite so progeny could not be obtained
    • Crosses with non-transgenic papaya fallowed by screening provided R1 plants resistant to PRSV
results
Results
  • Experiments showed
    • Resistance of transgenic papaya to PRSV was not correlated protein expression
    • R1 plants were highly resistant to Hawaiian strains of PRSV
    • Line 55-1 had variable levels of resistance to non- Hawaiian strains
    • Resistance due to RNA mediated mechanism rather than by coat protein
field trials
Field Trials
  • 1991 APHIS issued a permit for field trials of the new transgenic plants
  • First trails designed to asses resistance to mechanical and aphid inoculations of PRSV
  • Large Scale Tests
    • Pros
      • Industry desperate
      • Line 55-1 performed well in previous trials
      • Could be done at sufficiently isolated site
    • Cons
      • Spread of pollen to commercial plants
      • Pilferage
      • Resistant plants may become weeds
trial results
Trial Results
  • 50% of the non-transgenic control plants infected within four months
  • 100% within seven months
  • Improved performance of transgenic plants
  • Assessments of taste, production, color, size, and packing and shipping qualities were positive for the new plants
deregulation
Deregulation
  • APHIS
    • Heteroencapsidation – might lead to non-vectored virus to become vector transmissible if co-infection
    • Recombination – might lead to novel viruses
  • EPA
    • Transgenic proteins considered pesticides
  • FDA
    • Nutrition and vitamin content
    • Presence of GUS and
    • Presence of benzyl thiocynnate genes
references
References
  • Beachy, R. N., Loesch-Fries, S., Tumer, N. E., 1990. Coat Protein- Mediated Resistance Against Virus Infection. Annu. Review Phytopathol. 28:451-74
  • Tumer, N. E., Kaniewski, W., Haley, L., Gehrke, L., Lodge, J. K., Sanders, P., 1991. The second amino acid of alfalfa mosaic virus coat protein if critical for coat protein-mediated protection. Proc. Natl. Acad. Sci. USA. Vol. 88 pp 2331-2335, March 1991
  • Gonsalves, D., 1998. Control of Papay Ringspot Virus in Papaya: A Case Study. Annu. Review Phytopathol. 36:415-37
  • 2001. Chiang, C., Wang, J., Jan, F., Yeh, S., Gonsalves, D., Comparative reactions of recombinant papaya ringspot viruses with chimeric coat genes and wild type viruses on CP-transgenic papaya, Journal of general Virology. 82, 2827-2836
  • http://www.cimmvt.org/english/wpp/gen res/ringSpot.htm
  • http://www.aspnet.org/online/feature/ringspot/
  • http://dpi.qld.gov.au/horticulture/5333.html
  • http://vir.sgmjournals.org/cgi/content/full/ 82/11/2827