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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
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