1. Potato yield variation as affected
by virus seed degeneration and
growth conditions in Tunisia
Khamassy N., Ilahy R. and Boukhris-Bouhachem S.
June 2013

2. Strategic Crop since 1984
16% of vegetable areas
3 main seasons Crop
Seed tubers Value = 40% of Crop Costs
Seed Importation Value = 23 M. US$/ year
Problems regarding Local Certified Seed
Production
Potato Crop in Tunisia
32 Kg / Capita / Year

3. WC
AC
SuC
SpC
PL
HAR
Potato Crop in Tunisia: Growing seasons
Imported
seed

4. SEEDS
1. Sources :
- Imported Seeds :
From E.U ( France, Netherlands)
- Local Seeds
• Certified seeds (20%)
• Non-certified Seeds (80%)
2. Cultivars :
• Spunta (mid early 80% of planted
area)
• Nicola, Obelix, Atlas, Mondial,
Liseta…

5. Summer C.
Autumn C.
Winter and Spring C.
Summer C.
I.S
L.S
I.S : Imported Seed
L.S: Local Seed
Seed Sources per Season Crop

6. Cultivar : Spunta
Maturity : Mid early
Tuber Shape : Long
Tuber size : Medium
Eyes Depth : Shallow
Skin Colour : Yellow
Flesh Colour : Light yellow
Average
Yield
: 30 tons/ha
Tolerance : PVY n

7. Potato Virus Y, PVY
( Spring crop and Autumn crop)
MAIN PESTS AND DISEASES

8. MAIN SEED PRODUCTION
PROBLEMS
Cold storage costs (expensive)
Diseases (viruses, fungus, bacteria)

9. Seed classes SE E A B
Viral diseases tolerance (%)
(PVY, PLRV, PVA, PVX, PVS)
0.5 2 10 -
Viruses diseases rates too low to allow a successful
local seed program
However:
Epidemiological aphids patterns
High yields were recorded from highly virus infested
seeds (non certified farmer seeds with more than 30%
infestation) in the autumnal crop
Legislation…

10. Yield reduction caused by virus diseases Yield (MT/HA) and Yield reduction (%) H.P Beukema et al, 2000
PLRV/PVYo PVYn PVX/PVSVirus
infestation
(%)
Yield
(MT/HA)
Yield
decrease
Yield
(MT/HA)
Yield
decrease
Yield
(MT/HA)
Yield
decrease
00% 25 MT (0.0%) 25 MT (0.0%) 25 MT (0.0%)
02% 24.88 (0.5%) 24.93 (0.3%) 24.98 (0.1%)
05% 24.68 (1.3%) 24.81 (0.8%) 24.94 (0.2%)
10% 24.34 (2.7%) 24.60 (1.6%) 24.86 (0.6%)
15% 23.98 (4.1%) 24.39 (2.4%) 24.79 (0.8%)
20% 23.61 (5.6%) 24.16 (3.4%) 24.72 (1.1%)
25% 23.22 (7.1%) 23.93 (4.3%) 24.64 (1.4%)
50% 20.84 (16.7%) 22.50 (10%) 24.17 (3.3%)
Some authors reported slight effect of viral
diseases on potato yields (Van der Zaag, 1987;
Beukema, 2000)

11. Objectives
Obtaining accurate data regarding the incidence
of specific viral diseases on potato yielding
Methodology:
Evaluating the potato performances of SE, E, iA,
lcA, and nc Consumption class seeds as
affected by various PVY infestation levels.

12. RESULTS AND DISCUSSION
Origin Virus
infect
ion
rates
(%)
Cover
crop
(%)
Stem
number
(m²)
Total
yield
Kg/m²
Commerc.
yield
(Kg/m²)
Tuber
weight
(g/tuber)
Commerc.
tuber
nb/m²
Non
commerc.
tuber nb/m²
2007
trials
Yield
(kg/m²)
01
(SE)
0 50 a 10.00 a 2.46 a 2.34 a 103 abc 21.20 a 4.04 b 4.24
(6%)
02
(E)
2 52 a 8.04 b 2.65 a 2.47 a 141 a 18.20 ab 4.08 b 4.44
(15%)
03
(iA)
4 48 a 8.20 b 2.42 a 2.33 a 130 ab 16.00 bc 4.00 b 4.00
(25%)
04
(lA)
8 49 a 10.08 a 1.82 b 1.71 b 85 bc 16.20 bc 5.40 b 4.24
(38%)
05
(Cons)
50 34 a 8.04 a 1.63 b 1.33 b 74 c 12.08 c 10.00 a 4.05
(90%)
Mean
trial
12.80 46.60 8.87 2.20 2.03 106 16.73 5.50 4.19

13. RESULTS AND DISCUSSION
Deficient field management negatively affected crop growth:
Ground cover and stem numbers were 50% of a normal crop
growth
yield decrease was qualitatively 50% of the potential yield and
qualitatively 50% of the potential tuber weight irrespective of virus
infection rate
No significant yield decrease was observed between 0% and
4% PVY infection level.
At higher infection levels (8% and 50%), yield decreased
significantly compared to the previous infection levels.

14. y = -0,0037x + 4,7307
R
2
= 0,5051
4,3
4,4
4,5
4,6
4,7
4,8
4,9
5
0 20 40 60 80 100
Totalyield(kg/m²)
y = -0,0175x + 2,6199
R
2
= 0,6354
0
0,5
1
1,5
2
2,5
3
0 10 20 30 40 50 60
Totalyield(kg/m²)
y = -0,0103x + 3,2491
R
2
= 0,1125
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
0 20 40 60 80 100
Viral infection (%)
Totalyield(kg/m²)
Suitable agricultural management
Deficient agricultural management
Suitable agricultural management
Physiologically aged seeds
(non published data)
Effect of virus infection level on potato
yield under different growing conditions

15. CONCLUSION
Based on these actual results:
PVY incidence on potato yield loss seems to be not
relevant, at least if crop management and seed ageing
factors are respected.
The viral disease tolerance standards must be reviewed
when at least it deals with PVY and Spunta cultivar.
In Tunisia, already the standards of viruses tolerance are as
following (BS 0%; SE 2%; E 5%, A 10% and B 15%)
Crop management is more determinant than PVY infection
rates on yield (Q&Q). When crop management is deficient,
the effect of viruses on yield reduction is economically
significant.

16. MNT (0%)
SE (2%)
E (5%)
A (10%)
B/C (15%)
(CAS)
Seed Class
Yield Reduction
(%)
Yield/20T
(0%viruses)
E (10%v.) -1.26% (A) 19.7 T/ha
A (20%v.) -3.4% (B/C) 19.3 T/ha
B/C (50%v.) -10% 18 T
G1
G2
G4
G3
Applied schema for
Local Seed production
program since 2009
Certified
seed

17. Further studies have to be made before generalising
such assumption. (defining virus resistance levels of all the
cultivars registered in the National Official Catalogue).
PERSPECTIVES
Accurate data regarding the number of
multiplication cycles to adopt in a local
seed program.

19. Yield reduction caused by virus diseases Yield (MT/HA)
and Yield reduction (%)
H.P Beukema et al, 2000
PLRV/PVYo PVYn PVX/PVSVirus
infestation
(%)
Yield
(MT/HA)
Yield
decrease
Yield
(MT/HA)
Yield
decrease
Yield
(MT/HA)
Yield
decrease
00% 25 MT (0.0%) 25 MT (0.0%) 25 MT (0.0%)
02% 24.88 (0.5%) 24.93 (0.3%) 24.98 (0.1%)
05% 24.68 (1.3%) 24.81 (0.8%) 24.94 (0.2%)
10% 24.34 (2.7%) 24.60 (1.6%) 24.86 (0.6%)
15% 23.98 (4.1%) 24.39 (2.4%) 24.79 (0.8%)
20% 23.61 (5.6%) 24.16 (3.4%) 24.72 (1.1%)
25% 23.22 (7.1%) 23.93 (4.3%) 24.64 (1.4%)
50% 20.84 (16.7%) 22.50 (10%) 24.17 (3.3%)

20. (1): E importée (2): E locale (3): A importée (4): A locale
(1) (2)
(3)(4)
Récolte 25-06-05
CS 2005: Etat de la culture au 30 JAP

21. Récolte 26-01-05

22. mars avril mai
0
5
10
15
20
25
30
9 10 11 12 13 14 15 16 17 18 19 20 21 22
Batan
Bousalem
Sidi M
Douala
Population dynamic of aphid vectors related
to potato development in Tunisia
Period of susceptibility
Boukhris-Bouhachem S (2007)