Sess07 3 khamassy n., ilahy r. & boukhris bouhachem s. - potato yield variation as affected by virus seed degeneration and growth conditions in tunisia

Potato yield variation as affected by virus seed degeneration and

growth conditions in Tunisia

Khamassy N., Ilahy R. and Boukhris-Bouhachem S.

June 2013

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

WCAC

SuCSpC

PL

HAR

Potato Crop in Tunisia: Growing seasons

Imported seed

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…

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

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

Potato Virus Y, PVY

( Spring crop and Autumn crop)

MAIN PESTS AND DISEASES

MAIN SEED PRODUCTION PROBLEMS

Cold storage costs (expensive)

Diseases (viruses, fungus, bacteria)

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…

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)

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.

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

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.

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

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.

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

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.

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%)

(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

Récolte 26-01-05

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)