sess07 3 khamassy n., ilahy r. & boukhris bouhachem s. - potato yield variation as affected by...
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Potato yield variation as affected by virus seed degeneration and
growth conditions in Tunisia
Khamassy N., Ilahy R. and Boukhris-Bouhachem S.
June 2013
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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
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WCAC
SuCSpC
PL
HAR
Potato Crop in Tunisia: Growing seasons
Imported seed
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SEEDS1. 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…
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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
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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
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Potato Virus Y, PVY
( Spring crop and Autumn crop)
MAIN PESTS AND DISEASES
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MAIN SEED PRODUCTION PROBLEMS
Cold storage costs (expensive)
Diseases (viruses, fungus, bacteria)
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Seed classes SE E A BViral 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 infestedseeds (non certified farmer seeds with more than 30%infestation) in the autumnal crop
Legislation…
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Yield reduction caused by virus diseases Yield (MT/HA) and Yield reduction (%) H.P Beukema et al, 2000
PLRV/PVYo PVYn PVX/PVS Virus infestation
(%) Yield
(MT/HA)Yield
decreaseYield
(MT/HA)Yield
decreaseYield
(MT/HA)Yield
decrease00% 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 viraldiseases on potato yields (Van der Zaag, 1987;Beukema, 2000)
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ObjectivesObtaining 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 asaffected by various PVY infestation levels.
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RESULTS AND DISCUSSION
Origin Virus infection 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 trialsYield (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
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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.
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y = -0,0037x + 4,7307R2 = 0,5051
4,3
4,4
4,5
4,6
4,7
4,8
4,9
5
0 20 40 60 80 100
Tota
l yie
ld (k
g/m
²)
y = -0,0175x + 2,6199R2 = 0,6354
0
0,5
1
1,5
2
2,5
3
0 10 20 30 40 50 60
Tota
l yie
ld (k
g/m
²)
y = -0,0103x + 3,2491R2 = 0,1125
00,5
11,5
22,5
33,5
44,5
5
0 20 40 60 80 100
Viral infection (%)
Tota
l yie
ld (k
g/m
²)
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
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CONCLUSION
Based on these actual results:
PVY incidence on potato yield loss seems to be notrelevant, at least if crop management and seed ageingfactors are respected.
The viral disease tolerance standards must be reviewedwhen at least it deals with PVY and Spunta cultivar.
In Tunisia, already the standards of viruses tolerance are asfollowing (BS 0%; SE 2%; E 5%, A 10% and B 15%)
Crop management is more determinant than PVY infectionrates on yield (Q&Q). When crop management is deficient,the effect of viruses on yield reduction is economicallysignificant.
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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
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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.
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Yield reduction caused by virus diseases Yield (MT/HA) and Yield reduction (%)
H.P Beukema et al, 2000
PLRV/PVYo PVYn PVX/PVS Virus infestation
(%) Yield
(MT/HA)Yield
decreaseYield
(MT/HA)Yield
decreaseYield
(MT/HA)Yield
decrease00% 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%)
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(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
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Récolte 26-01-05
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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)