Sess10 3 chris visser and dirk bellstedt – potato virus y in south africa – isolate...
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Transcript of Sess10 3 chris visser and dirk bellstedt – potato virus y in south africa – isolate...
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Departement Biochemie ● Department of Biochemistry
Potato virus Y in South Africa: Isolate characterization and
assessment of potato cultivar resistance
Chris Visser and Dirk BellstedtDepartment of BiochemistryUniversity of Stellenbosch
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Introduction
• Only PVYN and PVYO with classic symptoms and yield losses occurred in South Africa before 1995
• After 1995 mosaic leaf symptoms became less prominent
• Tuber necrosis (PTNRD) observed for the first time in 2005 - associated with severe yield and quality losses for the potato producer
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Changes in symptom development
Mild mosaic symptoms PTNRD
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Project goals
• Characterize South African PVY isolates to understand changed symptom expression
• Establish speed of spread and PTNRD symptom development in local cultivars in order to assess cultivar resistance to PVY infection
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Approach for strain characterization
• Use CP gene sequencing and differential RT-PCR for strain identification - 2004 to 2008
• Use whole genome sequencing of representative PVY strains for full characterization - 2009 to 2011
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Results of CP gene sequencing and differential RT-PCR
133 PVY isolates characterized:• PVYO isolates (7.5%)
– 10 PVYO strains
• PVYN isolates (20.3%)– 22 PVYN strains
– 4 PVYNE-11 from China
– 1 SASA-61 from Scotland
• Recombinant strains (72.2%)– 34 PVYN-Wilga strain (25.6%)(1 PTNRD phenotype)
– 62 PVYNTN strain (46.6%)(20 PTNRD phenotype)
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Approach for strain characterization
• Use CP gene sequencing and differential RT-PCR for strain identification - 2004 to 2008
• Use whole genome sequencing of representative PVY strains for full characterization - 2009 to 2011
![Page 8: Sess10 3 chris visser and dirk bellstedt – potato virus y in south africa – isolate characterization and assessment of potato cultivar resistance](https://reader035.fdocuments.us/reader035/viewer/2022062307/55569579d8b42afd768b45bd/html5/thumbnails/8.jpg)
Whole genome sequencing results
4 PVYN
1 SASA-61
1 PVYNE-11
15 PVYNTN
4 PVYN-Wilga
2 PVYO
Diagram showing recombination patternsNo of isolates
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Whole genome sequencing results
Phylogenetic analysis of the whole genome sequence data indicates that some PVYNTN
and PVYN-Wilga were imported via tissue culture material from Europe:
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Project goals
• Characterize South African PVY isolates to understand changed symptom expression
• Establish speed of spread and PTNRD symptom development in local cultivars in order to assess cultivar resistance to PVY infection
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Biological characterization • Small scale greenhouse trial• 4 cultivars, 7 isolates• Mechanical infection• Viral spread monitored by
qRT-PCR• Tubers inspected for
PTNRD
Point of mechanical
infection
Monitored byqRT-PCR
here
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Isolate
Cultivar
Z001 Z16 SS607 31 Z14 NTN OVS GP
Hermes
Sifra
Mondial
Fabula
0
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 5
** *
Number of weeks Number of weeks Number of weeks Number of weeks Number of weeks Number of weeks
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
0
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 5
* * *Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Number of weeks Number of weeks Number of weeks Number of weeks Number of weeks Number of weeks
0
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 5Number of weeks Number of weeks Number of weeks Number of weeks Number of weeks Number of weeks
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
0
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 50
1
2
1 2 3 4 5
* *
0
1
2
1 2 3 4 5
*
** * *
Number of weeks Number of weeks Number of weeks Number of weeks Number of weeks Number of weeks
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Num
ber o
f pla
nts
Spread rate of PVYNTN isolates in 4 cultivars
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Z001
NTN-OVS
Z14
SS607(31) Z16 GP
00: No symptoms observedND: Not done
Z001 Z16 SS607 31 Z14 NTN-OVS GPHermes 100.00 80.00 26.47 25.00 2.73 0.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
% T
uber
s di
spla
ying
PTN
RD
Hermes
Tuber necrosis assessment
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Z001
NTN-OVS
Z14
SS607(31) Z16 GP
0
0: No symptoms observedND: Not done
Z001 Z16 SS607 31 Z14 NTN-OVS GPSifra 33.33 40.63 5.56 13.64 0.00 5.66
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
% T
uber
s di
spla
ying
PTN
RD
Sifra
Tuber necrosis assessment
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Z001
NTN-OVS
Z14
SS607(31) Z16 GP
0
0: No symptoms observedND: Not done
Z001 Z16 SS607 31 Z14 NTN-OVS GPMondial 16.95 2.54 14.00 8.57 0.00 20.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
% T
uber
s di
spla
ying
PTN
RD
Mondial
Tuber necrosis assessment
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Z001
NTN-OVS
Z14
SS607(31) Z16 GP
0
0
0
0: No symptoms observedND: Not done
Z001 Z16 SS607 31 Z14 NTN-OVS GPFabula 0.00 4.88 6.58 0.00 0.00 9.68
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
% T
uber
s di
spla
ying
PTN
RD
Fabula
Tuber necrosis assessment
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Conclusions
• PVYN and PVYO have been replaced with PVYNTN and PVYN-Wilga strains
• Some virus isolates spread rapidly in the potato plant and induce tuber necrosis
• Some potato cultivars only allow slower viral spread and exhibit less tuber necrosis
• Together viral spread and ability to induce tuber necrosis give an indication of potato cultivar resistance
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Future work• Assess rate of viral spread and tuber
necrosis formation in 20 of the most planted cultivars in South Africa
• Use rate of viral spread and PTNRD symptom development data to establish the levels of PVY resistance in cultivars planted in South Africa
• Advise farmers to plant resistant cultivars to improve yields
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Acknowledgements• APA 2013 conference organizers
• Coral de Villiers, Wiets Roos, University of Stellenbosch
• Anel Espach, Potato Certification Services
• Dr Ben Pieterse, former research manager, Potatoes South Africa
• Dr Fienie Niederwieser, research manager, Potatoes South Africa
• Potatoes SA for funding
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Thank you for your attention