Effects of Auxins Sprays on Yield, Fruit Size, Fruit Splitting and the
Incidence of Creasing of ‘Nova’ Mandarin
J. Greenberg and I. Kaplan
M. Fainzack, Y. Egozi and B. Giladi
Ministry of Agriculture,
Mehadrin-Prior, Power center 1,
Extension Service, P. O. Box 28,
Beerot Yizhak 60905, Israel
Bet Dagan 50250, Israel
Keywords: Citrus, fruit thinning, 2,4-D, NAA, 3,5,6-TPA
abstract
Effects of the plant growth regulators (PGRs) 2,4-dichlorophenoxyacetic acid
(2,4-D, 40 mg·L-1), naphthaleneacetic acid (NAA, 300 mg·L-1) and 3,5,6-trichloro-2piridil oxyacetic acid (3,5,6-TPA, 15 mg·L-1) on yield, fruit size, fruit quality, fruit
splitting and the incidence of creasing of ‘Nova’ mandarin were studied. All PGRs
solutions were tank-mixed with ‘Bonus-npK’ fertilizer ( 5%). Sprays were applied to
whole trees at 2 dates: early spray –at 13- mm fruitlet diameter and late spray- at 26mm fruitlet diameter. Most fruit splitting occurred between the beginning of October
and the beginning of November and the total fruit drop in the unsprayed controls,
caused mainly by splitting, accumulated to 150 fruit/tree (35% of the fruit). Early
spray of 2,4-D decreased fruit splitting to 25%, increased yield to 50 kg/tree
compared to 37 kg/tree in the controls, increased fruit size and had no effect on the
incidence of creasing. Early NAA spray, thinned fruitlets, increased fruit size,
decreased splitting to 30%, decreased the incidence of creasing to 28%, compared to
36% in the controls, and had no effect on the yield. Late NAA spray did not thin fruit
and had no effect on fruit size but the number of fruit harvested and yield was
increased to 52 kg/tree due to split fruit drop reduction to 21%, and the incidence of
creasing was reduced to only 10% of the fruit. Early 3,5,6-TPA spray caused strong
fruitlets drop and only 44 fruit/tree were harvested. Late 3,5,6-TPA spray did not thin
fruit, had no effect on fruit size, reduced the incidence of creasing to 22% and reduced
fruit splitting to 17% , causing increase of the yield to 52 kg/tree. These data suggest
that sprays of auxins on fruitlets, at time when they do not affect fruit size and do not
thin fruitlets anymore, are effective for reducing fruit splitting and the incidence of
creasing of 'Nova' mandarin..
2
INRRODUCTION
‘Nova’ mandarin fruit in Israel suffer from two disorders: fruit splitting and
rind fruit creasing. Fruit splitting causes fruit abscission and loss of up to 50% of the
yield. Fruit splitting in 'Nova' has been found negatively correlated with peel
thickness and puncturing resistance of the fruit (Almela et al., 1994). In that
experiment in Spain the best reduction of splitting has been obtained by two sprays
with a mixture of GA3 and 2,4-D, 30 and 60 days before the anticipated onset of the
disorder. Also calcium nitrate sprays reduced the disorder but the sprays were
ineffective in orchards with low natural incidence of splitting (Almela et al., 1994). In
another experiment in ‘Nova’ in Spain Garcia et al., (2001) showed that two
consequent sprays of 2,4-D ( 20 mg·L-1), the first on full bloom and the second at
petal fall, reduced fruit set and reduced the percentage of splitting, while GA3 ( 20
mg·L-1) sprays at the same dates increased fruit set and had no effect on the
percentage of splitting. Spraying ‘Nova’ trees in Israel with GA3 or 2,4-D in July,
before the onset of splitting, failed to reduce the disorder ( Goren et al., 1992). Fruit
splitting in ‘Nova’ orchards in Israel was reduced slightly by successive sprays with
potassium nitrate, and better effect was obtained when 2,4-D was combined with this
fertilizer ( Lavon et al., 1992).
‘Nova’ suffers also from fruit rind creasing, that is a serious disorder in some citrus
varieties. The disorder may be reduced by GA3 sprays in late summer or autumn in
‘Valencia’ oranges (Monselise et al., 1976 ) and ‘Minneola’ tangelo (Greenberg et al.,
1992 ). In later experiments it has been found that NAA sprays on small fruitlets are
efficient for creasing reduction of ‘Valencia’ oranges (Greenberg et al., 1996 ) and
‘Newhall’ navel oranges( Greenberg et al., 2000).
In the present study the effects of sprays, on two application dates, with 2,4-D, NAA
and 3,5,6-TPA (all combined with 'Bonus npK' fertilizer) on fruit splitting and the
incidence of creasing were examined on ‘Nova’ mandarin. Effects of the PGRs on
yield fruit size and quality were also assessed.
3
MATERIALS AND METHODS
The experiment was conducted in a 12 year old commercial plantation of
‘Nova’ mandarin grafted on sour orange ( Citrus aurantium) rootstock. Treated trees
were arranged in randomized block design with four replications of three trees each.
The diameter of 100 randomly selected fruitlets was measured at their equator at the
time of treatment and the average fruit diameter was calculated. Trees were sprayed
by handgun, as single spray of 10 L/tree, with 2,4-D (40 mg·L-1), NAA (300 mg·L-1)
and 3,5,6-TPA (15 mg·L-1) at two dates: 29 May, 2002 when average fruitlet
diameter was 13 mm or at 2 July, 2002 when average fruitlet diameter was 26 mm.
The number of split fruit per tree were counted and removed periodically. Creasing
incidence was determined on 100 randomly selected fruit on 2 dates : 8 December,
2002 and at harvest on 24 December, 2002. At harvest yield was weighed from each
replication separately. Randomly selected fruit, 100 per replication, were weighed and
their size at their equator was measured. The average fruit weight and fruit size
distribution were calculated -grading fruit into three sizes (large fruit  70 mm,
medium fruit = 61-69 mm and small fruit ≤ 60 mm). The average number of fruit per
tree was calculated by dividing the yield/tree by the average fruit weight.
The PGRs used were: NAA (The commercial preparation ‘Alphanol-super’ contains
200 g/L naphthaleneacetic acid, ‘Tapazol’, Israel), 3,5,6-TPA (The commercial
preparation ‘Tops’ contains 33 g/L 3,5,6-trichloro-2-piridil oxyacetic acid, ‘Chimac
Agriphar S.A.’ Belgium and ‘Tapazol’, Israel), and 2,4-D (the commercial
preparation ‘Hadranol’ contains 500 g/L 2,4-dichlorophenoxyacetic acid
‘Machteshim’, Israel).
All PGRs solutions were combined with ‘Bonus-npK’ fertilizer (5%), an improved
spray formulation of potassium nitrate (contains 13% N, 2% P2O and 44% K2O),
‘Haifa Agrological Power’ Israel.
Statistical analysis of the results was done using Duncan’s multiple range test at 0.05
level. Percentages were analyzed after arcsin transformation.
4
RESULTS
Effects of the treatments (with approximately the same final total fruit
number) on fruit drop (caused mainly because of fruit splitting) is shown in Fig.1.
The PGRs sprays reduced fruit drop with preference to the late TPA spray.
Fig. 2 shows the effects of the PGRs on fruit number per tree (dropped + harvested
fruit). NAA sprayed at the early date thinned fruit, while, when applied on larger
fruitlets it had no any thinning. Early 3,5,6-TPA spray caused strong fruitlets drop
and only 44 fruit/tree were harvested compared to 277 fruit/tree in the controls. Late
3,5,6-TPA spray did not thin fruit.
The effects of the treatments on splitting, expressed as percentages from total fruit
number, is shown in Table 1.The greatest splitting reduction was obtain by late NAA
and late TPA sprays: 21% and 17% of splitting, respectively, compared to 35% in the
controls.
The treatments that reduced fruit splitting increased total yield (Fig. 3). Early 2,4-D
and NAA sprays increased fruit size. Early NAA thinned friutlets and decreased total
yield, while the late NAA spray had not any thinning effect and had no effect on fruit
size ( Fig. 3).
Effects of the treatments on the incidence of creasing on two evaluation dates are
presented in Table 1. The best effects on creasing reduction were obtained by late
3,5,6-TPA and late NAA sprays, with advantage to NAA that reduced the incidence
of creasing , at the first date of evaluation, to 10% compared to 35% of creasing in the
controls.
The good treatments increased significantly the quantity of fruit without creasing,
that is suitable for export, with advantage to the late NAA spray which increased the
quantity of fruit without creasing to 41 kg/tree compared to only 22 kg/tree in the
controls (Fig. 4).
DISCUSSION
Synthetic auxin spraysfor increasing fruit size is a common cultural practice
among citrus growers in the world and their effects have been recently reviewed
(Rabe., 2000 ). Combination of the fertilizer potassium nitrate with the auxins
5
improves the effect (Erner et al., 1993 ). In the present study the auxin solutions were
combined with the improved potassium nitrate spray fertilizer- 'Bonus npK', that has
been found more effective than potassium nitrate in 'Shamouti' orange. (Greenberg et
al., 2002 ) and was more effective also in the present experiment ( data not shown).
2,4-D and NAA are applied in Israel for increasing fruit size of some citrus varieties
(Greenberg et al., 1996; Greenberg et al., 2000). Results of the present experiment
show that when these PGRs were sprayed on small 'Nova' fruitlets ( 13 mm average
diameter), fruit size was increased (Fig. 3). Early NAA spray thinned fruitlets and
decreased yield, but NAA spray on larger fruitlets, had no thinning effect ( Fig 2).
Similar effects of time of NAA application have been found in ‘Newhall’ navel
orange ( Greenberg et al., 2000). Early 3,5,6- TPA spray had a very strong thinning
effect which caused drop of most of the fruitlets, while late spray didn’t thin fruitlets (
Fig. 2).
The main purpose of this study was to find treatments that may reduce the damages
caused to the ‘Nova’ growers by fruit splitting and creasing. Early 2,4-D spray
decreased fruit splitting (Figs 1, and. 2), as has been found by Lavon et al. (1992), but
it did not reduce the incidence of creasing (Table 1). NAA spray decreased
significantly the incidence of creasing of 'Nova' with better effect to the late
application ( Table 1). Significant reduction of the incidence of creasing by early
NAA application has been found also in ‘Valencia’ orange ( Greenberg et al., 1996 )
and ‘Newhall’ navel orange (Greenberg et al., 2000). Late 3,5,6- TPA spray had the
best effect on fruit splitting reduction ( Figs 1, and 2) and reduced significantly the
incidence of creasing (Table 1). In the present experiment, 3,5,6- TPA caused also up
to 5% decrease in the juice content of the fruit ( statistical not significant, data not
shown), a fact that has to be considered when considering its use in orchards with low
percentage of juice. However, effect on the percentage of juice inconsistent and
desires additional study.
CONCLUSIONS
Auxins sprays on small fruitlets increase the growers' returns from 'Nova' mandarin.
When fruit thinning and increase of fruit size is desired there is advantage to early
NAA spray.
6
Later sprays with the auxins NAA and 3,5,6-TPA, at time when they do not thin
fruitlets any more and do not affect fruit size, are effective for reducing fruit splitting
and reducing the incidence of fruit creasing.
Literature cited
Almela, V., S. Zargoza, E. Primo-Millo and M. Agusti. 1994. Hormonal control of
splitting in ‘Nova’ mandarin fruit. Jour. Hort. Sci. 69 (6):969-973.
Erner, Y., Y. Kaplan, A. Bracha and M. Hamon. 1993 Increasing fruit size using
auxins and potassium. Acta Hort.329:112-119.
Garcia-Luis, A.,A. M. M. Durate, M. Kanduser, and J. L. Guardiola. 2001. The
anatomy of the fruit in relation to the propensity of citrus species to split. Sci.
Hort.87:33-52.
Goren, R., M. Huberman and J. Riov. 1992. Effects of gibberellin and girdling on the
yield of ‘Nova’ (Clementine x ‘Orlando’ tangelo) and ‘Niva’(‘Valencia’ x
‘Wilking’). 1992. Proc. Int. Soc. Citriculture 493-499.
Greenberg, J., Y.Oren, G. Eshel and E.E.Goldshmidt.1992. Gibberellin A3 (GA3) on
‘Minneola’ tangelo: Extension of the harvest season and improvement of fruit
quality. Proc. VII Int. Soc. Citriculture Vol. 1: 456 –458.
Greenberg, J., G. Eshel and A. Gotfreed. 1996. Effects of NAA, 2,4-D and 2,4-DP on
yield, fruit size and creasing of ‘Valencia’ oranges. Proc.VIII Int. Soc.
Citriculture Vol 2: 934-937.
Greenberg, J., I. Mossak and I. Kaplan. 2000. Effects of NAA and 2,4-DP on fruit
size, yield and creasing of ‘Newhall’ and ‘Carter’ navel oranges. Proc. Int. Soc.
Citricult. IX Congress. 569-571.
Greenberg, J., I. Kaplan, M. Fainzack, Y. Egozi, M. Hasan, A. Hochberg and R.
Porat. 2002. Effects of 2,4-D, 2,4-DP and 3,5,6-TPA combined with 'Bonus
npK' fertilizer on 'Shamouti' orange. Et Hadr 48: 25-27 (in Hebrew).
Lavon R., S. Shapchiski. E. Mohel and N. Zur. 1992. Nutritional and hormonal
sprays decreased fruit splitting and fruit creasing of ‘Nova’. Hasadeh 72:19521257. (in Hebrew).
Monselise. S.P., M. Wieser, N. Shafir., R Goren and E.E. Goldshmidt.1976. Creasing
of orange peel-physiology and control. J. Hort. Sci. 51: 341-351.
Rabe, E. 2000. Fruit thinning for enhanced fruit size: an overview of strategies. Proc.
Int. Soc. Citricult. IX Congress. 595-601.
7
Table 1. Effects of the treatments on the percentage of splitting and the percentage of creasing
on 2 dates of evaluation.
treatmentu
Control
Split fruit (%)
35 ax
Incidence of creasing (%)
Dec. 8
Dec. 24
35 ab
41 ab
Early 2,4-D
25 b
44 a
54 a
(40 mg·L-1)z
Early NAA
30 ab
28 ab
38 ab
-1 z
(300 mg·L )
Late NAA
21 bc
10 c
19 b
-1 y
( 300 mg·L )
Late 3,5,6- TPA
17 c
22 b
30 ab
-1 y
(15 mg·L )
u
Treatment solutions contained 'Bonus npK' (5%).
z
Early spray- applied on 29 May 2002, to fruitlets 13 mm in diameter.
y
Late spray- applied on 7 July 2002, to fruitlets 26 mm in diameter .
x
Mean separation within columns by Duncan's multiple range test, P ≤ 0.05.
Percentages were analyzed after arcsin transformation.
8
Cumulative drop ( fruit/tree)
160
140
120
Control
Early 2,4-D
Late NAA
Late TPA
a
ab
100
bc
80
c
60
40
20
0
Sept. 17
Oct. 8
Oct. 29
Nov.13
Dec. 5
Fig. 1. Effects of 2,4-D (40 mg·L-1), NAA ( 300 mg·L-1) and 3,5,6-TPA ( 15 mg·L-1) sprays on
the cumulative fruit drop ( mainly due to splitting). Early spray- applied on 29 May
2002, to fruitlets 13 mm in diameter. Late spray- applied on 7 July 2002, to fruitlets 26
mm in diameter . Treatment solutions contained 'Bonus npK' (5%). Mean separation on
the 5 Dec. results, by Duncan's multiple range test, P ≤ 0.05.
9
500
Harvested
Split
No. fruit/tree
400
300
ab
a
b
a
ab
b
c
a
200
100
a
0
c
d
c
ol
tr
on
C
D
PA
PA
AA
AA
,4T
T
N
N
2
y
rly
ate
ate
rly
arl
a
L
a
L
E
E
E
TREATMENT
Fig. 2. . Effects of 2,4-D (40 mg·L-1), NAA ( 300 mg·L-1) and 3,5,6-TPA ( 15 mg·L-1) sprays
on fruit number (split + harvested fruit). ). Early spray- applied on 29 May 2002, to
fruitlets 13 mm in diameter. Late spray- applied on 7 July 2002, to fruitlets 26 mm in
diameter . Treatment solutions contained 'Bonus npK' (5%). Mean separation among
split fruit and harvested fruit separately, by Duncan's multiple range test, P ≤ 0.05.
01
60
a
a
Yield (kg/tree)
50
40
b
a
Small
Medium
Large
b
30
20
c
10
b
0
a
a
b
b
b
ol
C
tr
on
D
PA
PA
AA
AA
,4T
T
N
N
2
te
rly
rly
ate
a
rly
a
a
L
a
L
E
E
E
TREATMENT
Fig 3. Effects of 2,4-D (40 mg·L-1), NAA ( 300 mg·L-1) and 3,5,6-TPA ( 15 mg·L-1) sprays on
yield and fruit size distribution. Early spray-applied on 29 May, 2002 to fruitlets 13 mm
in diameter. Late spray- applied on 7 July, 2002 to fruitlets 26 mm in diameter.
Treatment solutions contained 'Bonus npK' (5%). Mean separation among the total and
the large fruit yield, by Duncan's multiple range test, P ≤ 0.05.
00
60
Total yield
Without creasing
40
a
a
b
a
b
30
20
a
a
b
b
b
Yield (kg/tree)
50
10
0
t
P
eT
La
A
te
La
A
NA
Ea
rl
AA
N
y
D
,42
y
rl
Ea
Co
ol
r
t
n
Fig. 4. Effects of 2,4-D (40 mg·L-1), NAA ( 300 mg·L-1) and 3,5,6-TPA ( 15 mg·L-1) sprays on
the total yield and the yield without creasing at the late harvest date (Dec. 24). Early
spray- applied on 29 May 2002, to fruitlets 13 mm in diameter. Late spray- applied on 7
July 2002, to fruitlets 26 mm in diameter . Treatment solutions contained 'Bonus npK'
(5%). Mean separation was done separately to the total yield and the yield without
creasing, by Duncan's multiple range test P≤ 0.05.