Advanced Citriculture II Plant hormones and PGR effects

on fruit development

HOS 6546

L. Gene Albrigo

Lewis, L.N., R.A. Khalifah and C.W. Coggins, Jr. 1965. Seasonal changes in citrus auxin and 3 auxin antagonists as related to fruit development. Plant Physiol. 40:500-505.

• Similar auxin to IAA identified in citrus and this is a further study.

• Give reasons for thinking it was not IAA

• Purpose was to follow changes during fruit development and evaluate some anti-auxin activity.

• All tests basically biological assays

Materials & Methods

• Chromatography separation coupled with bioassay

• Seasonal sampling and analysis

Contaminant in extract?

Typical fruit

growth curve as

dry weight

Auxin conc.

Dropped off,

but per fruit

increased

starting at

June drop

Does that

matter? Maybe

depends on

where auxin is.

Dual measurements of auxin

Inhibitor

change much

stronger than

auxin change

Similar to

auxin

change

Conclusions

• Citrus auxin similar to IAA (in fact the same)

• Declined with time on concentration basis

• Inhibitor II declined with time on concentration basis, but I increased

• All increased per fruit (conc. and location important?)

Takahashi et al, 1975. Characterization of plant growth substances in

Citrus unshiu and their change in fruit development. Plant and Cell

Physiology 16: 1101-1111

• Citrus unshiu is a popular citrus species of Japan that blooms in mid-May and the fruit abscission starts ten days after full bloom

• The abscission varies every year and these physiological abscissions are considered to be controlled by the endogenous hormonal balance

• CRC in Riverside California reported a new type of non-indolic auxin “citrus auxin” and absence of indolic auxins

• Some indolic auxins were reported by Hebrew Univ, Israel

• Purpose: Hormonal changes in the development of the young fruits, the role of endogenous plant hormones in the physiological abscission of Citrus unshiu and the isolation and identification of plant growth regulators

Materials and methods • Studies were conducted from 1968-74 in Japan • Fruits were plucked and frozen for 2-3 weeks at -20oC till the

extraction • Hormonal changes with fruit development----- • Fruits were analyzed for estimation of auxin content and ABA

content on fruits harvested 5-7 days after bloom in 1968-73 • Gibberlins were not determined as they were estimated below 0.05

µg/kg in the preliminary test • Results are presented only for 1971 to 1973 • Isolation and characterization of endogenous plant growth

regulators---- • Auxins and two peptides were determined on fruits harvested 7

days after full bloom in 1969 • Neutral auxins were determined on the fruits harvested 7 days after

full bloom in 1974

Age of trees and characteristics of the fruits selected for the study are not mentioned

Results and discussion

• Total weight and number of fruits harvested at each stage in 1972 ( but 1973 in Table)

Total auxin activity

Maximum at 5 days after full bloom (DAB), suddenly started decreasing

until 20DAB, and attained another peak at 35 DAB

Neutral auxin activity: Maximum peaks at 5 DAB and 35 DAB

Acidic auxin activity: Maximum peaks at 10 and 35 DAB

Change was not dramatic as in 1972 and 1973

ABA content not given in figure 1,

but Figure caption says it does

T

Total auxin activity Maximum at 10 DAB (150µg/kg)

Neutral auxin activity: Maximum peaks at 5 DAB AND 35 DAB, like 1971

Acidic auxin activity: Maximum peaks at 10 DAB , similar to total auxin

ABA:

Maximum at 7 DAB (110µg/kg) and sharply decreased to minimum 18 DAB (3µg/kg)

and increased to another maximum of 20µg/kg again and continued increasing

Data in text do not match in the figure – above are figure data

Fig 2.

Changes in

auxin and

ABA levels

(1972)

Total auxin activity

Maximum at 6DAB (800µg/kg)

Neutral auxin activity:

Maximum peaks at 6 (70µg/kg)

and 32 DAB (20µg/kg)

Acidic auxin activity: Maximum peak at 6 DAB

Only traces of endogenous

auxins in two month old fruits

ABA: Maximum at 7 and 35 DAB and

continued to gradually increase

Fig. 3. Changes in auxin and

ABA content (1973)

•The increase of abscission peak started about 10 days after the

maximum peak of auxins. Maximum peak of abscission was attained

10-15 days after the minimum auxin content, just before the second

auxin peak.

•The second peak was 15 days after the second maximum of auxins

Fig. 4 Abscission of fruit

at various developmental

stages in 1973

Isolation of endogenous plant

Growth regulators

IAA was identified in fraction A

IAM was identified in fraction C

and D

Two peptides from fraction D

(unidentified)

IAA-Me from fraction B

Conclusions

• Acidic auxin varied over the years • Maximum peak was always observed in the very early

developmental stage of fruits( 5-10 DAB) reaching a maximum and suddenly decreasing

• Neutral auxin similar every year • Two peaks at 7 and 35 DAB • ABA peak in very early stage • Hormonal balance may affect the physiological abscission

of fruits • Sudden decrease of the auxin content from its maximum

peak as well as appearance of the BA peak play an important role in the fruit abscission?

• The occurrence of indole auxins was confirmed, while citrus auxin could not be detected

• Young fruits harvested 5-7 DAB contained IAA as an acidic auxin, IAA-Me and IAM as neutral auxins

Overview

• Introduction and objectives are well defined

• Materials and methods are detailed for the procedures but the characters of trees or fruits used are not mentioned

• The auxin activity shows large variations in different years, but no supportive data for this variation is mentioned like climate or methodology

• Age of trees and characteristics of the fruit selected for the study are not mentioned

• Some typing mistakes • Data in text do not match in the figure (ABA in text higher) • Results are not supported with suitable references

Goldschmidt, E.E., S.K. Eilati and R. Goren. 1970. Increase in ABA-like growth inhibitors and decrease in gibberellin-like substances during ripening and senescence of citrus fruits. Plant Growth Substances 1970:612-617

• Citrus is non-climacteric (slow changes) but peel color does change

• Understanding mature versus senescent would have value in handling fresh fruit

• Purpose: Determine GA-ABA balance based on color changes

Materials and Methods

• Mature (?) but green Shamouti oranges were sampled and then held up to 9 days at 25 oC in dark

• Flavedo, albedo and segments separated at each sample time

• Extracts tested by bioassay for GA- and ABA-like substances

ABA-like growth inhibitors, 0.5 to 1.0 Rf

Increase in ABA-like activity after 10 days (180, 130 and 213 %

increases)

Inhibitors in

extract

GA levels after storage show decreases with least change in BA

treated

Conclusions

• ABA-like materials increased and GAs decreased over 9 days post harvest in flavedo

• Did not measure GA in other tissues

• Changes in storage for 9 days not a true measure of senescence (need long period in field)

Hofman, P.J. 1990. Abscisic acid and gibberellins in the fruitlets and leaves of ‘Valencia’ orange in relation to fruit growth and retention. Scientia Hort. 42:257-267

• In South Africa they deal with poor fruit size

• Note that fruit near new leaves grow better than if near old leaves (carbs?)

• PGRs influence fruit size and could be involved as hormonal levels change

• Purpose: Monitor GA and ABA status during fruit growth

Materials and Methods

• Fruit growth and retention measured on 12 year-old ‘Valencia’ trees

• Hormones GA and ABA monitored

Leafy exceed leafless

particularly after May-June

drop

Better retention of leafy

fruitlets, note change is at

40 days

GA/gm all over the board,

but per fruit better in leafy

Free ABA also higher in

leafy which were more

likely to set

Bound ABA also higher in

leafy fruitlets

GA much higher in mature

leaves. No break at 40 days

ABA also higher in mature

leaves both free and

bound. No statistics, but

minimum in mature leaves

at 40 days?

Conclusions

• No apparent relationship of GA to fruit growth except that leafy, = more retention, had more GA but also had more ABA

• Perhaps auxins, cytokinins and carbohydrates more related to early fruit growth and retention than GA or ABA

Structural materials did decrease over time.

Ali Dinar, H.M. and A.H. Krezdorn. 1976. Extending the grapefruit harvest season with growth regulators. Proc. Fla. State Hort. Soc. 89:4-6

• Economically desirable to delay harvest of grapefruit

• Peel condition and seed germination undesirable in late harvested fruit

Materials & Methods

• GA and 2, 4-D sprays applied on Nov. 17th after about 35 % of crop removed (larger sized fruit

• Fruit drop evaluated throughout test period

• Many parameters measured over time

• Pull force-rind puncture and seed germination measured once.

Fruit drop and yield

2, 4-D reduced fruit drop

Higher number (to 4) = more green

Color index

This result has not been reproduced

Little influence on internal quality

Fruit size not affected

Conclusions

• 2, 4-D reduced fruit drop

• GA3 treated fruit greener (fresher) than controls, no 2, 4-D effect

• Peel tougher (both PGRs ?) and pull force greater (less drop) with 2, 4-D

• Seed germination less (never repeated)

• Internal quality not affected

• Fruit size not affected

grapefruit. Proc. Fla. State Hort. Soc. 95:242-245

GA DELAYED FIRMNESS LOSS AND

COLOR CHANGE, 2, 4-D DELAYS

ABSCISSION AND BUTTON LOSS

Guardiola, J.L., M.T. Barres, C. Albert and A. Garcia-Luis. 1993. Annals Bot. 71:169-

176

Effects of exogenous growth regulators on fruit

development in Citrus unshiu

Introduction

• Seedlessness is favorable trait, but parthenocarpic varieties show lower fruit set and fruit size than seeded cultivars

• Treatment with plant hormones have been used to improve both traits in these varieties

• The application of either gibberellins and cytokinins at or shortly after flower opening enhances fruitlet growth

• The early application of synthetic auxins increase the final fruit size more consistently, although these don’t increase early fruitlet growth

• Auxin effect on fruit growth could be due to their effect on phloem formation in the pedicel

• Purpose: Characterization of the response to the application of exogenous growth regulators by the ovaries and developing fruitlets of the highly parthenocarpic Satsuma mandarin

Methodology • Trees used: 20 year old Satsuma Mandarin • Single flowered leafy inflorescences tagged at anthesis (15 May) were

used • Treatments • Gibberellic acid (GA) --20gm-3 • Benzyladenine (BA) -- 20gm-3

• 2,4,5-Tricholorophenoxyacetic acid, isobutyl eater (2,4,5-T) -- 10gm-3

• Control- solution of wetting agent in the distilled water • Application day diameter of ovary or fruitlet (mm) • 0 (Anthesis) 3.8 • 11 8.0 • 21 10.0 • 30 12.7 • 42 17.2 • Number of fruits/ treatment=60 • Measurements: Fruit dry weight, phloem and xylem cross sectional area in

the pedicel, specific mass transfer in the pedicel • In vitro growth conditions: • 25 explants per treatment cultured for 35 days • Growth hormone concentration from 10-5 to 10-8 M in the presence of 2, 4-

D • Measurements: Response of the explants in GA and BA

Flower opening showing empty locules with ovules Juice sac primordia differentiating

in the inner epidermis of the pericarp

30 DAAJuice vesicles showing sig.

growth due to meristematic activity

55 DAA juice vesicles filled the locules

Callus formation in explants of 30 day old fruitlets

in the presence of growth regulators +10% orange juice

Juice sac enlargement without callus formation

in 55 days old fruitlets after 35 day

•Hormonal treatment did not effect

fruit set (data not given)

Application at 0 day flower opening: -GA and BA enhanced ovary growth

-Maximum difference in fruitlet diameter

compared with control were recorded

30 days after hormonal application (DAH)

and decreased afterwards

-2,4,5 T resulted in reduction of growth

Application at 11 day -No growth enhancement due to GA and BA

-2,4,5 T resulted in reduction of growth

Application at 21 day Sensitivity of fruitlets decreased with age

0 day

11 day

21 days

No data at 30 and 42 days

•Fruit diameter increased with GA and BA, while decreased with 2,4,5 T

•Radial and dorsal length of the locule as well as the cross sectional area of

the pericarp increased by the GA and BA application and was reduced by

2,4,5,T

• Similar was the effect in pericarp thickness and the cross sectional area

• Pericarp cell number increased with GA and BA showing the effect of BA and

GA on pericarp growth and therefore was due to increased cell division

• Not affected by 2,4,5 T showing the depressing effect was due to

reduction in cell expansion

•The rate of phloem formation was low

during early fruit growth, increased to

-maximum value between days 30-75

-continued until maturity at smaller rate

•Specific mass transfer per unit of phloem

cross sectional area increased from

flowering

reached maximum at 47 day (1 g/cm2/hr)

and then falling to< 0.4 g/cm2/hr until

maturity

•Accumulation of fruit dry matter

was very small initially and increased to

maximum by 41 day and remained

constant till maturity

Hormone effects on the development of

vascular system in the pedicel

Pedicel cross sectional area was

-Increased by all the hormones until

53rd day

Phloem Formation

-Increased with all the hormones

-BA and GA effect was up to 30 days

and did not last after 30 days

-2,4,5, T effect was maintained from 31-

53 days

-Xylogenesis:

-Enhanced by GA showing clear effect

by 30 days but disappeared by 53rd day

-No effect of BA and 2,4,5, T (Water uptake

not as important after initial fruit set?)

Mesocarp explants • showed little growth irrespective of fruitlet age

•Addition of 10% juice had no effect on this behavior except for

5 day old fruilets (2.7 times)

Endocarp explants: Growth was weak, but increased with fruitlet age at abscission up to 50 days

Final weight had nearly doubled at 60 days, but a loss compared to 50 days

(No without juice data)

Growth of fruit tissue in vitro

Fig 4 A: 5 days

-Growth enhancement was bigger

for BA than GA or 2,4,5-T

-The effect was more

pronounced with higher

Concentration (10-5 to 10-6 )

2,4,5-T showed depressive effect

at high conc.

Fig 4 B: 30 days

-Similar trend of growth

enhancement as at 5 days

-The effect was pronounced at

with lower (10-8) conc.

-Higher conc. proved excessive

-Fig 4 C: 50 days

-Much smaller effect on growth

enhancement

-Fig 4 D: 60 days

-Growth was markedly stimulated

by 2,4,5,-T and was more

effective than GA

5 days 30 days

50 days 60 days

GA

BA

2, 4, 5

TP

•-There was an initial increase in

weight followed by a period of slow

growth

•A marked increase in the growth

rate after 21 days

•Most of the initial increase in weight

was completed after 24 hrs of

incubation (data not shown)

•Sigmoid growth curve

The time course of growth of the explants

•No sig. difference of GA and BA on final fruit size was observed

•The application of 2,4,5,-T showed no immediate effect in fruitlet growth

•Growth response decreased with the earliness of application

•The fruilets treated at 11 day had smaller diameter than control

•For 42 day old fruits, increased fruit size at maturity

Effect of hormone

treatments on final fruit size

Conclusions

• The application of GA or BA at flower opening caused a transient increase in cell division in the ovary wall but had no significant effect on final fruit size

• Late fruit growth and final fruit size was increased by application of synthetic auxin 2,4,5,-T that had a specific effect on the enlargement of juice vesicles

• The 3 growth regulators enhanced vascularization in the pedicel but the growth effects observed were unrelated to their influence on the transport capacity of the phloem, but caused by their direct effects on the fruit tissues

• The sensitivity of the fruit tissues to the applied growth regulators changed markedly during early fruit development

Overview • Introduction, objectives and methodology were adequately

explained and suitable to the study

• Data not shown for many discussed aspects

• Results were thoroughly discussed and supported with suitable references

• Overall the paper was well summarized

Agusti, M., V. Almela, S. Zaragoza, E. Primo-Millo and M. El-Otmani. 1996. Proc.

Int. Soc. Citriculture 1996; 922-928

Recent findings on the mechanism of action of the synthetic auxins

used to improve fruit size of citrus

Introduction

• In Spain in the Mediterranean basin, since the crop is mainly for fresh consumption, fruit size represents one of the main quality factors

• Factors controlling citrus fruit size are well known

• Techniques such as girdling and the application of fruit thinning agents are used

• It has been a topic of interest in separating the indirect effect of fruit abscission and the direct effect on size, in order to make proper use of the synthetic auxins as fruit size enhances without reducing the crop

• Purpose:

• Report recent findings for the mechanism of action of the synthetic auxins as fruit enhancers and their effect on the development on fruit tissues

Methodology • Period of study 1988-95 for 8 years • In the Valencia citrus area in Spain on Mandarin and Orange varieties • Various auxins used: • IZAA, ethylclozate • NAA, ethyl ester • 3-CPA, • 4-CPA, • 2,4,-D, isopropanol ester, • 2,4,5-T, isobutyl ester, • 2,4,-DP butyl glycol ester, • MCPA- Thioethyl, phenothiol and • 3,5,6-TPA free acid and isopropyl ester • Applications were made to entire trees and locally to tagged 15-20mm diameter

fruitlets from single flowered leafy inflorescence • 5 fruitlets /tree and at least 10 trees were used were treated with each auxin and

concentration • Treatments were applied at two dates for Clementine mandarins: • Date I: -During the natural physiological fruit drop when mean fruit diameter was 11-15mm • Date II: -After the fruit drop when fruit diameter was 15-20 mm

Methodology Contd.. • Satsuma mandarin (at 20-25mm) and sweet oranges (at 25-30mm)

were treated on date II

• Measurements:

• Clementine Mandarin, diameter of tagged fruit (25) were measured periodically until maturity, abscised fruit / tree were counted 15 day after treatment, yield was determined

• Average fruit size, % abscission, and % fruit retention relative to the control trees were determined

• These were used to estimate treatment effects on fruit thinning

• Fruit characteristics were studied on 20 fruit/tree

• Histological studies were made on the fruit harvested 20 days after

treatments

• Experimental design: RBD

• Replications: 2 tree plots and 4 replications

•There was an inverse relationship between daily fruit growth and per cent

abscission (???)

•Auxins increased the sink capacity of leaves that in turn reduces transport

of metabolites to the fruits, as a consequence fruit daily growth rate is

reduced (???) but some auxins increase growth rate

•The degree of reduction depends upon the auxin type, formulation and

concentration applied

Thinning effect

Fig 2 A

-The % of fruit thinned due to treatment,

increased with applied concentration

-The increase in fruit diameter reached a

maximum at 20 mg/l

Direct effects

Fig 2B:

-In the absence of thinning larger fruit diameter

was obtained for fruits treated after the natural

fruit drop

-Maximum diameter was obtained at same

concentration regardless of the date of

application

•Auxin treatments failed as fruit thinners when they were applied after the

natural physiological fruit drop with the exception of 3,5,6,TPA ester (all do)

• The absence of the transient depressive effect for the majority of the synthetic

auxins applied at date II has been suggested as the primary cause of their

failure as thinners

•After 20 days of treatment

Differences of

•Fruit size affected sig

•Peel wt increased sig.

•Peel thickness not affected

•Locule size increased sig.

•Juice vesicles per locule

was not altered

-cell size is sig. increased

-Vesicles- length, width fresh

weight, dry weight increased sig.

•Epidermal cells per vesicle

-Number of rows was not

affected

•The effect of auxins on fruit

development was based on

greater cell expansion than the

cell division due to increase in

cell vacuolization that increased

vesicle size, locular dimensions

and final fruit size

Auxin treatments affected only juice vesicles weight, with

vesicles of treated fruits accumulating higher amount of dry matter

•Individual fruit size ,peduncle diameter and phloem development increased with

auxins

• There was an increase in fruit sink capacity

Application of auxins to individual fruit

Fruit size was increased on the average with a significant shift of whole crop

to the larger sizes that are more valuable commercially.

Conclusions

• The effect of auxins on fruit development is based on greater cell expansion rather than cell division

• Auxins increases generalized growth of all fruit tissues

• Some synthetic auxins promote fruit development through reduction of competition between fruits (thinning)

• Except for IAA and 3,5,6-TPA, auxin treatments failed as fruit thinners when applied after the natural physiological fruit drop

• Thinning doesn’t increase fruit size except if the magnitude of thinning takes away at least 60% of the developing fruitlets but this represents serious reduction in yield, therefore it is more appropriate to use auxin’s direct effect without fruit thinning

Overview

• Age of the trees not mentioned

• The data was summarized from previous trials conducted from 1988-95, the data of which should have been included to make the results more explicit

• The dates I and II are not mentioned

De Almeida, I.M.L., J.D. Rodrigues and E.O.

Ono. 2004. Brazilian Arch. Biol. & Technology

47:511-520

Application of plant growth regulators

at pre-harvest for fruit development of

“PERA” oranges

Introduction • The size of the fruit is important not only because it is a component of

productive yield, but also determines the acceptance by the consumer

• The harvest of Navel oranges begins in August and natural dropping begins in May and can last several months with summer and preharvest drop

• Spraying of auxins prevented the dropping of fruit preharvest by maintaining the cells at the zone of abscission

• The use of 2,4-D as a growth regulator promotes size and reduces leaf and fruit drop

• Combined application of GA3 and 2,4-D reduces the precocious drop of fruit through the action of auxin and retards the softening and senescence of the peel

• 2,4-D is rapidly excreted unchanged and is not stored in tissues of mammals

• Purpose:

• Evaluation of the effects of auxins and gibberellins when applied pre-harvest for the development of the fruit and for the rate of drop to determine the possibility of retarding harvest of cv Pera citrus fruit

Methodology • Study on Citrus sinensis cv Pera • Foliar treatments-10 and Replications: 6 • GA3 12.5 mg L -1 + 2,4-D 12.5 mg/ L-1 , • GA3 25 mg L -1 + 2,4-D 25 mg L-1, • GA3 37.5 mg L -1 + 2,4-D 37.5 mg L-1, • GA3 12.5 mg L -1 + NAA 12.5 mg L-1, • GA3 25 mg L -1 + NAA 25 mg L-1 , • GA3 37.5 mg L -1 + NAA 37.5 mg L-1, • NAA 12.5 mg L -1 + 2,4-D 12.5 mg L-1 , • NAA 25 mg L-1 + 2,4-D 25 mg L-1, • NAA 37.5 mg L -1 + 2,4-D 37.5 mg L-1 , • Control (Water)

• Applications dates 3 times • 1. May24 Change in fruit color • 2. 45 days later • 3. 45 days after 2. • Measurements: fruit length, diameter, fresh fruit weight , rate of natural fall

of fruit was evaluated in 7 periods. • Statistical analysis: multi-varied model

Age of trees not given

The sign. effects of the treatments on the length were not observed

But sign. effects of measurement time were observed

Among the periods of measurement sign. differences could be observed from

the first to the 4th period, demonstrating that fruit length increased up until the

4th measurement period, right after which length stabilized

•No Sign. difference in diameter were observed in 1st period

•Sign. differences were observed in the 2nd period

- Control different from GA3 25 mg L -1 + 2,4-D 25 mg L-1,

GA3 37.5 mg L -1 + 2,4-D 37.5 mg L-1 and GA3 37.5 mg L -1 + NAA 37.5 mg L-

1

The differences were observed at different measurement periods

Significant effect of treatments in 2nd period were observed

The treatments of GA3 25 mg L -1 + 2,4-D 25 mg L-1,

GA3 37.5 mg L -1 + 2,4-D 37.5 mg L-1 and GA3 37.5 mg L -1 + NAA 37.5 mg L-1

presented sign. differences from the control to increase fresh fruit mass

•Sign. effects of measurement times were observed

•Increase of mass was observed up to the 4th period

•Starting with the 5th period pronounced decrease in fruit mass was

observed , which may be due to water loss due to unusually low rainfall in

that month

The profiles of the 10 treatments were similar

Treatments 1,2,3 (GA3+2,4,D) coincided, but were different than

control thus leading to lowest rate of fall

There was no interaction between time and treatment observed

Rates of drop increased with time, for all the treatments

All the treatments containing plant growth regulators were effective

in controlling fall of fruit, but at different levels

The largest reduction was with GA3 and 2,4,D combination

Conclusions

• The plant growth regulators had no influence on the development of the fruit, as fruit length, diameter and mass

• These treatments effectively inhibit the natural fall of the fruit , permitting the prolongation of the harvest season

• Treatments that contain auxins presented the highest fall, other than the control

• None of the treatments promoted fruit growth, but only reduced the natural fall rate

Overview

• All treatments are only combinations of the auxins and GA’s, the inclusion of individual treatments should have been included to make the comparisons

• Age of the trees not mentioned

• Results are not in agreement to the other similar studies

• There are more parameters (treatment) in figures, which make them difficult to interpret or should have given the values in tabular form

• Translation to English left many things confusing? Are we talking about true harvest period or major part of growth period? Wouldn’t get this much fruit size increase if harvest period?

Stewart, I. and T.A. Wheaton. 1971. Effects of ethylene and

temperature on carotenoid pigmentation of citrus peel. Proc.

Fla. State Hort. Soc. 84:264-266

• Ethylene at high temperature breaks down chlorophyll in mature fruit but does not increase orange-red pigments

• Robinson tangerine did have increased red-orange pigments when treated with ethylene at color break but not other cultivars

• Purpose: Test ethylene & cool temp. together to enhance color after storage

Materials and Methods

• Ethylene tested in degreening rooms OR

• Large jars were used to control ethylene and these were placed in temperature controlled rooms

• Color was monitored

I, J, K and L not

shown on graph

North side, shade & less direct sunlight, had better color

Best color at

moderate

temperature

Major effect

until 7th day

at 75 C

Ethylene treatment at 75 C doubled the cryptoxanthin

similar to at 85 C but B-citraurin was raised 3 times the

temperature alone value at 75 C

No time interval for this test mentioned

Conclusions

• For short time period, 75 C with ethylene can cause significant rise in color

• One week plus changes during transit time very effective

• From practical side, decay losses of normally harvest and treated fruit too high

Overall conclusions

• Hormonal balance may affect the physiological abscission of fruits

• Indole auxins have been identified in citrus • The application of GA at flower opening caused a

transient increase in cell division in the ovary wall but had no significant effect on final fruit size

• 2, 4-DP has effect on final fruit size due to cell expansion • The effect of auxins on fruit development is based on

greater cell expansion rather than cell division & is in vesicles

• Auxins increase generalized growth of all fruit tissues if applied at higher concentrations

• Interaction of GA and 2, 4-D at lower concentrations promote fruit growth

Overall conclusions

• 2,4-D effectively reduces preharvest drop

• GA reduces peel color changes and apparently aging (peel firmness)

• Still not good understanding of mechanisms

• Ethylene at high temperatures promotes degreening, at moderate temperature promotes carotenoid production