1. Departement Biochemie ● Department of Biochemistry
Potato virus Y in South Africa:
Isolate characterization and
assessment of potato cultivar
resistance
Chris Visser and Dirk Bellstedt
Department of Biochemistry
University of Stellenbosch

2. 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

3. Changes in symptom development
Mild mosaic symptoms PTNRD

4. 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

5. 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

6. 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)

7. 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

8. Whole genome sequencing results
4 PVYN
1 SASA-61
1 PVYNE-11
15 PVYNTN
4 PVYN-Wilga
2 PVYO
Diagram showing recombination patterns
No of isolates

9. 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:

10. 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

11. 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 by
qRT-PCR
here

12. Isolate
Cultivar
Z001 Z16 SS607 31 Z14 NTN OVS GP
Hermes
Sifra
Mondial
Fabula
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
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
Numberofplants
Numberofplants
Numberofplants
Numberofplants
Numberofplants
Numberofplants
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
* * *
Numberofplants
Numberofplants
Numberofplants
Numberofplants
Numberofplants
Numberofplants
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 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5Number of weeks Number of weeks Number of weeks Number of weeks Number of weeks Number of weeks
Numberofplants
Numberofplants
Numberofplants
Numberofplants
Numberofplants
Numberofplants
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
1
2
1 2 3 4 5
0
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
Numberofplants
Numberofplants
Numberofplants
Numberofplants
Numberofplants
Numberofplants
Spread rate of PVYNTN isolates in 4 cultivars

13. Z001
NTN-OVS
Z14
SS607(31) Z16 GP
0
0: No symptoms
observed
ND: Not done
Z001 Z16 SS607 31 Z14 NTN-OVS GP
Hermes 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
%TubersdisplayingPTNRD
Hermes
Tuber necrosis
assessment

14. Z001
NTN-OVS
Z14
SS607(31) Z16 GP
0
0: No symptoms
observed
ND: Not done
Z001 Z16 SS607 31 Z14 NTN-OVS GP
Sifra 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
%TubersdisplayingPTNRD
Sifra
Tuber necrosis
assessment

15. Z001
NTN-OVS
Z14
SS607(31) Z16 GP
0
0: No symptoms
observed
ND: Not done
Z001 Z16 SS607 31 Z14 NTN-OVS GP
Mondial 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
%TubersdisplayingPTNRD
Mondial
Tuber necrosis
assessment

16. Z001
NTN-OVS
Z14
SS607(31) Z16 GP
0
0
0
0: No symptoms
observed
ND: Not done
Z001 Z16 SS607 31 Z14 NTN-OVS GP
Fabula 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
%TubersdisplayingPTNRD
Fabula
Tuber necrosis
assessment

17. 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

18. 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

19. 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

20. Thank you for your attention