Anti-gibberellins' effect on grapefruit size and quality


Fucik, J.E.; Swietlik, D.

Proceedings of the Plant Growth Regulator Society of America 17th Annual Meeting, St Paul, Minnesota, USA, 5-9 August 1990: 107-113

1990


Five year-old 'Rio Red' grapeCruit trees were treated with the anti-gibberellins, unlconazol(unlcon) and paclobutrazol(paclo). Treatments were: soil drenches at 10, 20, and 40 g. a.i. tree-l applied In May, 1985; trunk banding applied In an 80/20 vol-vol diesel/toluene mix of unicon at 7 rates(.062 to 2 g a.i. tree-l and paclo at .062 and 2 g. and 2 Collar sprays of 1000 ppm(Oct. 1985, Feb. 1986) and one oC 500 ppm (Feb. 1986) of both materials. Fruit size, external and juice quality were evaluated In 1987 and Crult size and juice quality In 1988. Both chemicals decreased average Crult size by Increasing the number of Crult In the smaller sb.e classes. Except Cor slightly Cewer Cruit with peel abrasions on Coliar sprayed trees the treatments did not affect the Crults' external quality. The soli drench and foliar sprays of both unlcon and paclo reduced juice quality by decreasing soluble solids, Increasing acid thus lowering sugar acid ratio and increasing the peel percentage. Trunk banding tended to Increase the percent juice and lower percent peel with the response Cor unlcon occurring the Orst and paclo the second season after treatment. Overall both antl-GA.'s appear to delay Cruit growth and maturity.

ANTI-GIBBERELLIN'S
EFFECT
ON
GRAPEFRUIT
SIZE
AND
QUALITY
JOHN
E.
FUCIK
and
DARIUSZ
SWIETLIK
,
Texas
A&I
University
Citrus
Center,
P.O.
Box
1150,
Weslaco,
TX.
78596
ABSTRACT.
Five
year-old
'Rio
Red'
grapefruit
trees
were
treated
with
the
anti-gibberellins,
uniconazol(unicon)
and
paclobutrazol(paclo).
Treatments
were:
soil
drenches
at
10,
20,
and
40
g.
a.i.
tree
'
l
applied
in
May,
1985;
trunk
banding
applied
in
an
80/20
vol-vol
diesel/toluene
mix
of
unicon
at
7
rates(.062
to
2
g
a.i.
tree'
l
and
paclo
at
.062
and
2
g.
and
2
foliar
sprays
of
1000
ppm(
Oct.
1985,
Feb.
1986)
and
one
of
500
ppm
(Feb.
1986)
of
both
materials.
Fruit
size,
external
and
juice
quality
were
evaluated
in
1987
and
fruit
size
and
juice
quality
in
1988.
Both
chemi-
cals
decreased
average
fruit
size
by
in-
creasing
the
number
of
fruit
in
the
smaller
she
classes. Except
for
slightly
fewer
fruit
with
peel
abrasions
on
foliar
sprayed
trees
the
treatments
did
not
affect
the
fruits'
external
quality.
The
soil
drench
and
foliar
sprays
of
both
unicon
and
paclo
reduced
juice
quality
by
decreasing
soluble
solids,
increasing
acid
thus
lowering
sugar
acid
ratio
and
increasing
the
peel
percentage.
Trunk
banding
tended
to
increase
the
percent
juice
and
lower
percent
peel
with
the
response
for
unicon
occurring
the
first
and
paclo
the
second
season
after
treat-
ment.
Overall
both
anti-G.A.'s
appear
to
delay
fruit
growth
and
maturity.
Both
paclobutrazol[(2RS,3RS)-1-(4-
chloropheny1)-4,4
dimethy1-2-(1,2,4-tri-
azol-1-y1)-1-pentan-3-olj
1
and
uniconazol[(E)-(p-chlorophenyl)-4,4-d
imethy1-2-(1,2,4-triazol-1-y1)-1-penten-
3-011
1
have
been
reported
to
affect
citrus
tree
growth
when
applied
as
soil
drenches
or
foliar
sprays(
Aron,
et
al.1985;
Bausher
and
Yelenosky,1986).
Their
affect
on
the
external
and
internal
quality
of
the
fruit
has
received
less
attention.
In
conjunc-
tion
with
a
previously
reported
study(
Swietlik
and
Fucik,
1988)
we
evaluated
the
size
distribution,
appearance
and
juice
quality
of
Texas
grapefruit
from
trees
treated
with
both
materials
applied
as
foliar
sprays,
soil
drenches
and
trunk
bands.
MATERIALS
AND
METHODS
Soil
drench
and
foliar
spray
experi-
ment.
Trees
of
'Rio
Red'
grapefruit
on
sour
orange
rootstock
were
planted
in
February
1980
on
a
silty
clay
soil.
Following
the
December
1983
freeze,
the
trees
were
severely
pruned
back
to
main
scaffold
limbs.
At
time
of
treatment,
canopies
were
about
1.7
m
high.
Uniconazol
(unicon)
and
paclobutrazol
(paclo)
were
used
as
10
and
50%
wettable
powders,
respectively.
Soil
drenches
and
foliar
sprays
were
applied
at
dates
and
amounts
indicated
in
Table
1.
There
were
4
replications
(trees)
in
each
treatment
arranged
in
a
completely
randomized
block
design.
107
TABLE
1.
UNICONAZOL
AND
PACLOBUTRAZOL
TREATMENTS
APPLIED
TO
RIO
RED
GRAPEFRUIT
TREES
1
Material
Application
Rate
Dates
Method
Applied
Uniconazol
Soil
Drench
Foliar
Spray
Trunk
Band
0,
10,20,40
g./tree
0,
500,
1000
ppm
0,
1/16,
1/8,
1/4,
1/2,
1
&
2
g./tree
May
1985
Oct
1985
Feb
1986
Mar
1988
Mar
1987
Paclobutrazol
Soil
Drench
Foliar
Spray
Trunk
Band
0,
20,
40
g./tree
May
1985
0,
500,
1000
ppm
Oct
1985
Feb
1988
0,
1/16,
2
g./tree
Mar
1988
Mar
1987
1
applied
in
80/20
v/v.
diesel—toluene
solution
In
the
case
of
soil
drenches,
required
amounts
of
each
chemical
were
suspended
in
8
liters
of
water
and
applied
to
basins
(1.8
m
in
diameter)
at
the
base
of
each
tree.
The
treatment
was
followed
by
11
cm
irrigation
applied
to
the
basins.
Foliar
sprays
of
unicon
and
paclo
at
1000
ppm
a.i.
were
applied
twice:
in
October,
1985
and
again
in
February,
1986.
A
foliar
spray
at
500
ppm
a.i.
was
applied
only
once,
i.e.
in
February
1986.
Unequal
number
of
sprays
was
caused
by
limited
availability
of
the
chemical
at
the
begin-
ning
of
the
experiment.
Tween
20
at
0.1%
concentration.was
added
to
the
spray
mix
as
a
wetting
agent.
Individual
trees
were
sprayed
to
run
off
with
c.a.
9.5
liters
of
water
using
a
handgun
at
0.68
MPa
pres-
sure.
Trunk
banding
experiment.Trunk
banding
treatments
were
applied
to
trees
of
'Rio
Red'
grapefruit
on
sour
orange
rootstock.
The
trees
were
selected
from
the
same
block
of
trees
in
which
the
ex-
periment
with
soil
drenches
and
foliar
sprays
was
conducted.
Required
amounts
of
unicon
and
paclo
(Table
1)
were
suspended
in
60
ml
diesel
fuel/toluene
(80/20%
v/v)
and
applied
to
the
trunks
above
the
bud
union
with
a
hand
sprayer
in
March,
1986
and
again
in
March,
1987.
Trunks
of
control
trees
were
sprayed
with
the
same
volume
of
diesel/toluene
mixture.
There
were
4
replications
(trees)
in
each
treatment
ar-
ranged
in
a
completely
randomized
block
design.
Fruit
quality
determinations.For
the
86/87
and
87/88
season,
the
fruit
from
each
tree
was
separated
into
6
commercial
size
classes,
p,
112,
96,
80,
70,
64
which
represent
the
number
of
fruit
that
fill
standard
field
box.
The
fruit
increases
in
size
as
the
size
class
number
decreases.
The
number
and
weight
of
fruit
in
each
class
was
determined
and
the
fruit
graded
108
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4
4
p
80
e
r
0
50
e
n
t
40
i
n
30
S
Z
20
e
a
10
0
for
peel
abrasions,
windscar
(a
scabby
blemish
caused
by
wind),
insect
and
mite
injury,
and
shape.
Because
of
labor
and
time
constrains,
the
external
quality
evaluations
were
conducted
in
one
season
only.
In
both
seasons,
a
10
fruit
sample
from
the
median
size
'lass
was
randomly
chosen
for
juicing.
Juice
analyses
consisted
of
percent
juice
(by
weight),
soluble
solids
or
sugar,
acid
and
ratio,
the
percent
soluble
solids
divided
by
the
percent
acid.
Soluble
solids
were
determined
by
a
bench
refractometer,
acid
by
titration
with
standard
base.
In
addition
the
percent
peel
(fresh)
was
ascertained
by
removing
the
pulp.
Statistical
analyses,
i.e.
ANOVA
and
regression,
were
performed
with
ap-
propriate
procedures
from
the
SAS
software,
Version
6.03.
RESULTS
AND
DISCUSSION
The
higher
percentage
of
grapefruit
in
the
112
and
smaller
size
classes
for
the
1986
season(Fig.1)
confirms
our
earlier
find-
ings
which
also
showed
unicon
elicited
a
greater
and
longer
lasting
response
than
paclo(
Swietlik
and
Fucik,
1988).
The
average
fruit
weights
of
the
control,
paclo
and
unicon
treated
fruit
were
394,
370
and
332
g,
respectively.
These
differences
were
significant
at
P
=
.001.
The
analysis
of
the
two
materials
applied
as
foliar
spray
or
trunk
banding
treatments
indicated
foliar
caused
the
greatest
reduc-
tion
in
average
fruit
weight(Table
2).
The
differences
between
paclo
and
unicon
and
the
growth
regulator
x
application
method
interaction
were
not
significant.
As
fruit
size
normally
increases
as
the
number
of
fruit
per
tree
decreases,
the
foliar
treatments'
influence
is
especially
strong
since
they
reduced
the
number
of
fruit
as
well
as
average
fruit
weight.
<
112
112
96
80
70
>
84
Grapefruit
Size
Claim
Figure
1.
The
effect
of
paclobutrazol
and
uniconazol
on
the
size
distribution
of
'Rio
Red'
grapefruit.
The
foliar
and
trunk
banding
treatments
are
combined
for
each
material.
109
Table
2.
The
Effect
of
Foliar
and
Trunk
Band
Applications
of
Paclobutrazol
and
Uniconazol
on
Yield,
Fruit
Size
and
Peel
Abrasions
of
'Rio
Red'
Grapefruit.
1
Application
Yield/Tree
2
Mean
Frt
Degrading
Peel
Method
Frt
No.
Frt
Wt(kg)
Wt(g)
Abrasions(%)
Control
183
AD
71
AB
394
c
1.8
AB
Foliar
Spray
168
A
54
A
330
A
0.7
Trunk
Band
236
s
863
372
2.4
B
1
Paolo
and
Unicon
treatments
combined
2
P
=
.01
Of
the
external
factors
evaluated,
fruit
shape,
hued
and
mite
injury,
windscar
and
peel
abrasions
only
the
latter
was
affected,
viz.
the
apparent
reduction
in
the
percent
of
fruit
with
degrading
peel
abrasions
from
the
foliar
sprays(Table
2).
We
speculate
this
could
be
due
to
greater
proctection
from
abrading
elements
by
the
denser
canopy
resulting
from
reduced
shoot
growth(Swietlik
and
Fucik,
1988).
The
foliar
sprays
again
produced
the
greatest
and
most
consistent
effect
on
juice
quality
and
the
percent
peel(Table
3).
In
both
cases,
the
resultant
increase
in
percent
acid
and
peel
and
decrease
in
per-
cent
soluble
solids(sugar)
and
ratio,
must
be
considered
undesirable
in
that
all
these
factors
suggest
delayed
maturity.
The
regressions
of
both
materials
applied
as
soil
drenches
revealed
much
the
same
results
except
that
the
drench
responses
were
manifested
the
second
season
after
application(Table
4).
Although
Bausher
and
Yelenosky(1986)
showed
greater
responses
to
soil
drenches
Figure
2.
Curves
of
soil
drench
application
of
uniconazol
on
the
percent
soluble
solids
(sugar),
acid
and
sugar/acid
ration
of
'Rio
Red'
grapefruit
juice.
These
curves,
typical
of
the
responses
of
both
paclobutrazol
and
uniconzol,
indicate
both
materials
were
most
effecive
at
low
rates
with
the
higher
rates
giving
little
additional
affect.
P
10
e
a
8
R
a
t
I
0
1
%
Soluble
Solidi
mi"'
Ratio
%
Acid
10
20
30
Rate
of
Unicon
Soil
Drench
1.6
-
1.4
-
1.2
-
1.0
O
0.8
-
0.6
-
0.4
0.2
0.0
40
P
e
0
n
t
r
d
110
Table
3.
The
Effect
of
Foliar
Spray
Rates
on
'Red
Rio'
Grapefruit
Juice
Quality.
1
Quality
Factor
Concentration
(ppm)
0
500
1000
%
Juice
58
b
58
to
56
a
.05
%
Soluble
Solids
8.9
8.4
8.5
n.s.
%
Acid
1.09
A
1.08
I
1.20
B
.01
Ratio
8.1
B
7.8
B
7.0
A
.01
%
Peel
23.8
ab
22.4
a
25.1
b
.05
1
-
Paclo
and
Unicol
treatments
combined.
Table
4.
Summary
of
the
Ragressions
of
Paclobutrazol
and
Uniconazol
Soil
Drench
and
Trunk
Band
Applications
on
'Rio
Red'
Grapefruit
Juice
Quality.
1
Application
Method
Samson
Juice
X
Quality
Factor
e
Ratio
X
PEEL
X
Soluble
Solid
X
Acid
X
Soil
19841-87
n.e. n.e. n.e.
.58•
.81••
(-)
(+)
Drench
1087-88
n.s.
.70"
.58•
.89••
n.s.
PACLO-
(-)
(+)
(-)
BUTRAZOL
Trunk
1988-87
n.s.
n.s.
n.s.
n.s.
n.s.
Band
1087-88
n.s.
n.s.
n.s.
.59•
(+)
(-)
Soil
19841-87
n.s.
n.e.
n.s.
n.e.
Drench
1987-88
n.s.
.55•
.74••
.73"
n.s.
UNICONAZOL
(-)
(+)
(-)
Trunk
1988-87
.40•
n.s.
n.s.
n.s.
.54••
(+)
(-)
Band
1987-88
n.s.
.42•
n.e.
n.s.
n.e.
(-)
1
-
P
level
of
r
=
n.s.
(not
significant).
(.05).
••
(.01)
2
-
Materials
decreased(-)
or
inoreased(+)
the
factor
A.
controls
111
of
paclo
compared
to
foliar
sprays
they
were
using
potted
citrus.
The
delayed
response
in
the
field
may
be
an
indirect
one
exerted
through
a
growth
reduction
and
change
in
morphology
of
the
root
system
as
reported
by
these
same
re-
searchers.
Trunk
banding
produced
the
only
positive
responses,
namely
an
increase
in
the
per-
cent
juice
and
a
decrease
in
percent
peel(Table
4).
While
the
two
materials
produced
similar
effects,
they
differed
in
timing.
Unicon
treated
trees
responded
the
first
season
after
treatment
compared
to
the
second
season
for
the
paclo
trees.
If
the
anti-G.A.'s
could
have
influenced
cambium
cell
growth
and
expansion,
phloem
tissues
may
have
been
restricted
sufficiently
to
simulate
girdling.
The
in-
crease
in
juice
content
and
decrease
in
peel
might
be
manifestations
of
this
effect.
The
usual
increase
in
juice
sugar
and
con-
comittant
reduction
in
acid
accompanying
girdling
might
be
offset
by
the
apparent
maturity
delaying
action
of
the
two
materials
cited
above.
The
variability
in
response
time
might
be
another
indication
of
the
greater
potency
of
unicon
vs.
paclo
indicated
above.
While
Wang
and
Blessington
(1990)
showed
varied
responses
to
unicon
and
paclo
soil
drenches
and
foliar
sprays
by
4
different
tropical
foliage
plants,
the
ef-
fects
of
both
materials
on
fruit
size
and
juice
quality
are
very
similar
to
those
reported
for
paclo
on
'Delicious'
ap-
ples(Greene,
1986)
which
were
also
inter-
preted
as
maturity
delaying
responses.
In
view
of
the
similar
results
across
a
wide
range
of
species,
the
decrease
in
low
temperature
injury
by
uniconazole-
treated
cucumbers
could
be
of
great
inter-
est
to
citrus
growers(Upadhyaya,
et
al.,1989).
CONCLUSIONS
On
Texas
'Rio
Red'
grapefruit:
1.
Both
paclo
and
unicon
by
whatever
method
applied
increased
the
percentage
of
small
sized
fruit
thereby
reducing
the
average
fruit
weight.
2.
Except
for
reducing
peel
abrasions
none
of
the
treatments
affected
the
other
exter-
nal
quality
factors
evaluted.
3.
Both
paclo
and
unicon
lowered
juice
quality
by
increasing
acid
and
decreasing
soluble
solids
and
the
sugar/acid
ratio.
These
responses
were
most
evident
and
consistent
in
the
soil
drench
and
foliar
spray
treatments.
4.
Applying
the
anti-G.A.'s
by
trunk
banding
produced
the
only
apparent
though
minor
beneficial
reponse
of
in-
creasing
the
percent
juice
and
decreasing
the
percent
peel.
5.
The
higher
rates
of
either
material
produced
very
little
additional
response
above
the
lowest
rate.
The
general
response
of
grapefruit
to
both
materials
suggested
a
retarding
of
both
fruit
growth
and
maturation.
Trunk
band-
ing
may
have
restricted
phloem
tissues
sufficiently
to
induce
a
girdling
effect
manifested
by
an
increase
in
the
fruit's
juice
content
and
lower
peel
percentage.
LITERATURE
CITED
Bausher,M.
and
G.
Yelenosky.
1986.
Sen-
sitivity
of
pottted
citrus
plants
to
top
sprays
and
soil
applications
of
paclobutrazol.
Hortscience
21(1):141-
43.
112
Green,D.
1986.
Effect
of
paclobutrazol
and
analogs
on
growth,
yield,
fruit
quality,
an
storage
potential
of
'Delicious'
apples.
J.
Amer.Soc.
Hort
Sci.
111(3):
328-332.
Swietlik,
D.
and
J.
Fucik.
1988.
Responses
of
field-grown
grapefruit
trees
to
XE
1019
and
paclobutrazol.
In:
R.
Goren
and
K.
Mendel(Eds),Proc.
Sixth
Inter-
national
Citrus
Congress.
Balaban
Publishers,
Philadelphia,
PA.
Upadhyaya,A.,
T.
Davis,
R.
Walser,
A
Galbraith
and
N.
Sankhla.
1989.
Uniconazole-induced
alleviation
of
low-temperature
damage
in
relation
to
antioxidant
activity.
Hortscience
24(6):
955-957.
Wang,
Y.T.
and
T.
Blessington.
1990.
Growth
of
four
tropical
foliage
species
treated
with
paclobutrazol
or
uniconazole.
Hortscience
25(2):202-
204.
113