Winning the battle against under-skin browning

Peter Hofman, Gavin Scurr, Ted Winston, Daryl Joyce, Andrew Macnish, PhD students

USB on ‘Honey Gold’

USB affected area

USB - under the microscope

KP

R2E2?

USB on other cultivars

Slower fruit cooling rates

Date

Mon 25 Tues 26 Wednes 27 Thurs 28

Tem

perature (o C)

10

15

20

25

30

Trt 1: tight stackTrt 2: air stackTrt 3: wrapped stack

10% affected

34% affected

52% affected

Physical injury during harvest and transport

Packaging/transport damage

Reducing transport damage - packaging

Treatment (packaging)

Inc

ide

nc

e o

f fr

uit

wit

h U

SB

(%

)

0

10

20

30

40

50 Liner (no transport)LinerLiner+wrap (fruit)Liner + sock (fruit)Wrap+pad (tray)

Fruit with any USB Fruit with USB > 3cm2

a

a

bb

bb

b

c

bc

c

USB test

The breakthrough• Lightly abrade fruit

with sandpaper• Hold at about 13°C

for at least 6 days• Ripen

Long term focus• How to produce a more robust fruit

• Harvesting• Nutrition• Irrigation• Rootstocks

Under skin browning

Harvest time

2 am 6 am 10 am 2 pm 6 pm 10 pm

% of fruit w

ith US

B>1 cm

2

10

20

30

40

50

60

70

80

average of no and 1 day delay

Harvested every 4 hrs, cooled immediately or after 1 dUSB associated with abraded sites

Under skin browning – diurnal effects

Similar diurnal effects on USB not associated with abrasion

Field treatment

Control P 200 g /tree

P 400 g /treeDouble bio gypsum

Percentage

0

10

20

30

40

50

60% abrasion sites with USB

% of f riut with USB>1 cm2 around abrasion sites

% of f ruit with USB>1 cm2 not associated with abrasion

Ca reduced USB around abrasion sites and at other positions on the fruit

Under skin browning – Ca/P

Recommendations• Reduce physical damage

– Harvest and pack carefully– Use soft liners– Reduce transport vibration/damage

• Delay cooling for at least one day• Hold above 14-16ºC

Producing more robust fruit• Harvest fruit at night

“Watch this space”• Nutrition – calcium• Irrigation

Under skin browning – so far

Acknowledgements and thanks

Funding• Pinata Farms• Horticulture Innovation Australia

• MG10009 and MG13016

• Dept Agriculture and Fisheries Qld• University of Queensland