papaya ring spot 2005

8/8/2019 Papaya Ring Spot 2005

1/23

Kate Stokes and AndrewKate Stokes and AndrewKate Stokes and Andrew

TortoraTortoraTortora

Papaya RingspotPapaya RingspotPapaya Ringspot

DiseaseDiseaseDisease


2/23

Cause

Papaya ringspot virus-type P

Occurs as 2 strains

Type P infects both papaya and cucurbits suchas squash, pumpkin, cucumber, and watermelon

Type W infects watermelon only


3/23

General Characteristics

Member ofpotyvirus 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


4/23

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 orC-shaped

markings, a darker green than the background-green fruit color

Can affect vigor of fruit and trees and fruitquality

SymptomsSymptomsSymptoms


5/23

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 thesouthern region China

Distribution


6/23

Spread

Carried from plant to plant by aphidsduring feeding probes

Not spread by other insects and doesnot survive in soil or dead plantmaterial

Also spread by movement of infected

papaya plants and cucurbit seedlings Not usually seed-transmitted but

there is one case from the Philippines


7/23

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


8/23

History

HawaiiHawaii 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 areawhere 95% of Hawaiis 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.


9/23

Control Quarantine measures

Restricted distribution

Removal of infected plants (rouging)

Taiwan

Used protective netting against aphid vectors

because the island was too small to effectivelyisolate plantings by moving

Tolerant or resistant cultivars


10/23

Cross Protection

Phenomenon in which plants systematicallyinfected with mild strain of the virus are protectedagainst 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 wereeventually isolated after a virulent strain PRSVHA was treated with nitrous acid

PRSV HA 5-1

PRSV HA 6-1


11/23


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13/23

Coat Protein Mediated

Protection (C

PMP) 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


14/23

RNA Mediated

Resistance Post transcriptional gene silencing

Homology dependant

Base pairing between the sense RNA transcript of thetransgene and the negative strand of the viral RNA

Antisense RNA produced from the transgene could pairwith the viral RNA transcript.

Duplex RNA is target for degradation

Base pairing could inhibit translation

Examples

PRSV, PVX and PVY, and all potyviruses


15/23

Development ofTransgenic Papaya

Hawaiian papaya industry was in trouble

DennisGonsalves at Cornell in collaboration withUpjohn, scientists at the University of Hawaii andJohn Sanford at Cornell try to develop transgenicpapaya 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


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Transformation of

Embryogenic Tissue

Used gene gun newly invented by John

Sanford Tissue bombarded with

tungsten particles coated

with the engineeredDNA


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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 fallowedby screening provided R1 plants resistant to

PRSV


18/23


19/23

Field Trials

1991 APHIS issued a permit for field trials of thenew 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


20/23

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


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Deregulation

APHIS

Heteroencapsidation might lead to non-vectored virusto become vector transmissible if co-infection

Recombination might lead to novel viruses EPA

Transgenic proteins considered pesticides

FDA

Nutrition and vitamin content Presence ofGUS and

Presence of benzyl thiocynnate genes


22/23

References

Beachy, R. N., Loesch-Fries, S., Tumer, N. E., 1990. Coat Protein- MediatedResistance 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 forcoat 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 CaseStudy. Annu. Review Phytopathol. 36:415-37

2001. Chiang, C., Wang, J., Jan, F., Yeh, S.,Gonsalves, D., Comparativereactions of recombinant papaya ringspot viruses with chimeric coat genes andwild 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


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