New strategies to increase South African

citrus export volume and fruit quality

R Rosalie, OPJ Stander

J North & PJR Cronje

CRI and Department of Horticultural Science, SU

Space for More Logos

Efficient use of sun light

• The only thing free in Citriculture is sun light

+ Heat & Light are necessary for: • Color development • Carbon assimilate

accumulation - ↗Heat & Light can cause:

• Damages • Fruit growth

restrictions • Fruit drop

Mandarin cv. Nadorcott

Shade Netting in Citrusdal

• Provide 20% shade • Decrease the light damage • Increase the photoactive period • Increase the water usage

efficiency

• Completely randomized experimental design • 4 Open Blocks • 4 Net Blocks

• Growing conditions measured: • Air temperature • Soil Temperature • Soil water potential • Relative humidity

O1

O4

N1

O3

O2

N4

N2

N3

Impacts of shade netting?

• Does is decrease or increase the temperature? • On one hand shade = lower

temperature • On the other hand green-

house effect

• What is the impact on color development? • Light is necessary for

normal color development • Temperature ≥ 35°C inhibit

carotenoid synthesis

• How do the trees allocate carbon under shade netting? • More growth or better fruit

yield and quality

Reproductive Growth Vegetative Growth

Sampling

• Every months from January to June

• 5 fruits per blocks

• Types of samples: • Albedo • Flavedo • Juice

• Analyses: • Detailed sugars (HPLC) • Detailed acids (HPLC) • Total polysaccharides

Growth conditions

0

5

10

15

20

25

30

35

40

8 13 18 23 28

Tem

per

atu

re (

°C)

Week

Max. and Min. Temperature Max_Open Max_Net Min_Open

Min_Net Average_Open Average_Net

-5

0

5

10

15

20

25

30

35

40

45

0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00

Tem

per

atu

re (

°C)

Time

Summer vs winter

Open_Warm Net_Warm

Open_Cold Net_Cold

Internal fruit quality

• Carbohydrates

• Seasonal accumulation

• No Net effect

• Acids

• Seasonal decrease

• Open blocks higher until low contents

0

20

40

60

80

100

120

140

160

Jan Feb Mar Apr May Jun

Tota

l Su

gar

(mg.

ml-1

)

Juice Open Net

*

*

0

20

40

60

80

100

120

140

160

180

Jan Feb Mar Apr May Jun

Tota

l Aci

d (

mg.

ml-1

)

Juice

Rind quality - Carbohydrates

*

*

20

40

60

80

100

120

140

0

100

200

300

400

500

600

janv. févr. mars avr. mai juin juil.Suga

r co

nte

nt

(mgG

lcEq

.gD

W-1

)

Free Sugars_Open Free Sugars__Net Polysaccharides_Open Polysacchirides_Net

*

*

20

40

60

80

100

120

140

0

50

100

150

200

250

300

350

400

janv. févr. mars avr. mai juin juil.Suga

r co

nte

nt

(mgG

lcEq

.gD

W-1

)

0

20

40

60

80

100

120

140

160

Jan Feb Mar Apr May Jun

Sucr

ose

(m

g.gD

W-1

) Albedo Open Net

*

*

*

0

10

20

30

40

50

60

70

80

90

Jan Feb Mar Apr May Jun

Sucr

ose

(m

g.gD

W-1

)

Flavedo

Rind quality - Pigments

• Chlorophyll and Carotenoid contents higher under Net on young fruits

• Colour break > Net/Open effect

• No pigment differences

*

*

*

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

2

janv. mars avr. juin

Pig

men

t co

nte

nt

(µg.

gDW

-1)

Chl A - Open Chl A - Net

Chl B - Open Chl B - Net

Carotenoids - Open Carotenoid - Net

Conclusion

• Net (20%) provides:

• Lower max soil T°C in summer and higher min soil T°C

• Higher water potential

• No effect on final internal quality

• Higher sugar accumulation in rind

• No effect on pigment contents

Further work

A bigger project including:

• Horticultural aspects : • Vegetative and reproductive growth • Yields • Fruit quality • Carbon allocation

• Soil science: • Water use efficiency • Soil composition

• Anthomology: • Insect distribution

• Plant pathology: • Pathogene distribution

Fruit irradiation and cold storage • Postharvest disinfestation of citrus fruit for False Codling Moth

mostly achieved through cold treatment (Hofmeyr et al. 1998)

• Current protocol of 22/24 days <0°C detrimental to fruit quality

• Chilling injury = Temperature x Exposure time

• Need for alternative disinfestation treatments with ensured fruit quality

• Irradiation of fruit an approved practise world wide e.g.

• USDA-APHIS approved irradiation as a quarantine treatment for fruits and vegetables in Oct. 2002

Citrus fruit response to irradiation range • Establish irradiation dose threshold for adverse fruit quality effects.

• Earlier exploratory trials indicated sensitive to the range of 200 to 500 Gy.

• 7 cultivars - export quality fruit-

• Star Ruby, Nules, Early/Late Navel, Turkey Valencia, Lemons and Nadorcott

• Exposed to 200, 300, 400 or 500 Gy

• Hepro: Cobalt irradiation source

• Cold stored at either 2 or 7°C for 40 60 d

• Evaluation for quality

• Rind disorder incidence

• Internal quality

• Taste test

Materials and methods

Results: Rind quality

05

101520253035404550

0 Gy -0.6°C

0 Gy2°C

200 Gy2°C

300 Gy2°C

400 Gy2°C

500 Gy2°C

0 Gy7°C

200 Gy7°C

300 Gy7°C

400 Gy7°C

500 Gy7°C

% P

itti

ng

Early Navel Pitting % - 40 Days

Pitting % - 60 Days

0

5

10

15

20

25

30

35

40

45

50

0 Gy -0.6°C

0 Gy2°C

200 Gy2°C

300 Gy2°C

400 Gy2°C

500 Gy2°C

0 Gy7°C

200 Gy7°C

300 Gy7°C

400 Gy7°C

500 Gy7°C

% P

itti

ng

Late Navels Pitting % - 40 d

Pitting % - 60 d

Results: Rind quality

0

5

10

15

20

25

30

35

40

45

50

0 Gy -0.6°C

0 Gy2°C

200 Gy2°C

300 Gy2°C

400 Gy2°C

500 Gy2°C

0 Gy7°C

200 Gy7°C

300 Gy7°C

400 Gy7°C

500 Gy7°C

% P

itti

ng

Star Ruby Pitting % - 40 Days

Pitting % - 60 Days

0

5

10

15

20

25

30

35

40

45

50

0 Gy -0.6°C

0 Gy2°C

200Gy 2°C

300Gy 2°C

400Gy 2°C

500Gy 2°C

0 Gy7°C

200Gy 7°C

300Gy 7°C

400Gy 7°C

500Gy 7°C

Pit

tin

g %

Turkey Valencia Pitting % - 40 d

Pitting % - 40 d

0

5

10

15

20

25

30

35

40

45

50

0 Gy -0.6°C

0 Gy2°C

200 Gy2°C

300 Gy2°C

400 Gy2°C

500 Gy2°C

0 Gy7°C

200 Gy7°C

300 Gy7°C

400 Gy7°C

500 Gy7°C

% P

itti

ng/

pet

eca

/sca

ldin

g

1st Lemon Pitting % - 40 Days Pitting % - 60 Days

Results: Rind quality

0

5

10

15

20

25

30

35

40

45

50

0 Gy -0.6°C

0 Gy2°C

200 Gy2°C

300 Gy2°C

400 Gy2°C

500 Gy2°C

0 Gy7°C

200 Gy7°C

300 Gy7°C

400 Gy7°C

500 Gy7°C

Pit

tin

g/p

etec

a/sc

ald

ing

2nd Lemons Pitting % - 40 d Pitting % - 40 d

Results: Rind quality

0

5

10

15

20

25

30

35

40

45

50

0 Gy -0.6°C

0 Gy2°C

200 Gy2°C

300 Gy2°C

400 Gy2°C

500 Gy2°C

0 Gy7°C

200 Gy7°C

300 Gy7°C

400 Gy7°C

500 Gy7°C

Pit

tin

g/st

ain

%

Nadorcott Mandarin Pitting % - 40 d

Pitting % - 60 d

0

5

10

15

20

25

30

35

40

45

50

0 Gy -0.6°C

0 Gy2°C

200 Gy2°C

300 Gy2°C

400 Gy2°C

500 Gy2°C

0 Gy7°C

200 Gy7°C

300 Gy7°C

400 Gy7°C

500 Gy7°C

% P

itti

ng

Nules Clementine Pitting % - 40 Days

Pitting % - 60 Days

Internal quality: no drastic changes expect lemons

Rind colour Juice % °Brix Cit. Acid

Star Ruby

Turkey Val

Lemon 1

Lemons 2

Navel Early

Navel Late

Nules Clementine

Nadorcott mandarin

Internal quality

0,00

0,20

0,40

0,60

0,80

1,00

1,20

1,40

1,60

1,80

0 Gy -0.6°C

0 Gy2°C

200 Gy2°C

300 Gy2°C

400 Gy2°C

500 Gy2°C

0 Gy7°C

200 Gy7°C

300 Gy7°C

400 Gy7°C

500 Gy7°C

Cit

ric

Aci

d

Turkey Valencia Citric Acid 40 days Citric Acid 60 days

4,80

5,00

5,20

5,40

5,60

5,80

6,00

6,20

6,40

6,60

0 Gy -0.6°C

0 Gy2°C

200 Gy2°C

300 Gy2°C

400 Gy2°C

500 Gy2°C

0 Gy7°C

200 Gy7°C

300 Gy7°C

400 Gy7°C

500 Gy7°C

Cit

ric

Aci

d

Lemon 1 Citric Acid Day 40 Citric Acid Day 60

0,00

1,00

2,00

3,00

4,00

5,00

6,00

7,00

0 Gy -0.6°C

0 Gy2°C

200Gy2°C

300Gy2°C

400Gy2°C

500Gy2°C

0 Gy7°C

200Gy7°C

300Gy7°C

400Gy7°C

500Gy7°C

Cit

ric

Aci

d

Lemon 2

• Only parameter effected - Citric acid in highly sensitive cultivars

• Reduction of Citric acid possibly due to increase in respiration

Conclusion and way forward

• Repeat irradiation in 2016 • Include Midknight and Nova mandarin

• Identify damaging level per cultivar group • Percentage and severity

• In general most cultivars OK <300Gy • Except Turkey<200Gy damaged • Of concern: Nadorcott and lemon

• Data will be used to motivate possible new combined protocol

Thank You

Any Questions?