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Improved fruit retention, yield and fruit quality in mango with exogenous application of polyamines
Scientia Horticulturae 110 (2006) 167–174 www.elsevier.com/locate/scihorti
Improved fruit retention, yield and fruit quality in mango with exogenous application of polyamines Aman Ullah Malik, Zora Singh * Horticulture, Muresk Institute, Division of Resources and Environment, Curtin University of Technology, GPO Box U 1987, Perth 6845, Australia Received 1 December 2003; received in revised form 11 May 2006; accepted 30 June 2006
Abstract Aqueous solutions (0, 0.01, 0.1, 1 mM) of PAs (putrescine, spermine, spermidine) containing a surfactant ‘Tween 20’ were sprayed onto panicles of mango (Mangifera indica L. cv. Kensington Pride) at final fruit set (FFS) stage (when all flowers abscised but remain attached to the panicle) during 1999–2001 to investigate their effects on fruit retention, yield, size, and fruit quality. The optimum time of PA application for improving final fruit retention and fruit yield was determined by spraying different concentrations (0, 0.01, 0.1, 1 mM) of spermine (SPM) containing a surfactant ‘Tween 20’ at four phenological stages including flower bud differentiation (FBD), 5–8 cm long grown panicles (GP), full bloom (FB) and at initial fruit set (IFS) stage (when 2/3rd of the flowers were abscised but attached to the panicle) during 2000. Exogenous application of PAs at FFS stage did not significantly increase fruit retention. However, compared to control (0.79 and 2.3% fruit retention), PAs treatments resulted in comparatively higher mean fruit retention (1.53 and 2.92%) during 1999–2000 and 2000–2001, respectively. Among three PAs tested, SPM was more effective in increasing mean final fruit retention. Fruit size was not significantly affected by any PA treatment. Among the four application times, SPM (0.01 mM) spray at FB stage resulted in significantly (P 0.05) greater fruit retention (4.99%) compared with control (2.1%). However, fruit yield was comparatively higher with SPM (0.01 mM) application at IFS stage or 5–8 cm GP stage compared to the control. Overall FB application was found as the optimum time of application. Application of PAs at FFS stage retarded fruit skin colour development compared to the control. Sugars and total soluble solids (TSS) were generally reduced in PA-treated fruit. Fruit acidity was increased (16.7%) with SPM, whereas it was 11% with PUT treatment as compared to the control. Total carotenoids in pulp were generally improved (49%) with PA treatments, compared to the control. Ascorbic acid concentrations were significantly reduced with spermidine (SPD) (24%) and PUT (20%) treatments, whereas higher concentrations of SPM (1 mM) tended to increase it (12.7%) compared to the control. In conclusion, application of SPM (0.01 mM) at FB stage resulted in the highest fruit retention, whereas SPM (0.01) spray at GP or IFS stage resulted in higher fruit yield. PUT application at FFS stage significantly improved fruit quality by increasing total carotenoid, while reducing acid content of ripe fruit. # 2006 Elsevier B.V. All rights reserved. Keywords: Polyamines; Fruit drop; Carotenoids; Ascorbic acid; Sugars; Colour
1. Introduction Mango (Mangifera indica L.) is a major fruit crop of the tropical regions of the world. However, its delicious taste, and unique flavour with high nutritional value have made it equally popular across the globe. Over the last decade (1991–2001), despite an increase of 42.5% in mango growing area, there has been only 1.3% increase in average fruit yield (7.5–7.6 t/ha) (FAO, 2003). Heavy fruit drop is an important factor contributing to low fruit yield in mango orchards and sometime only 0.1% of set fruit reach maturity (Chadha, 1993). Research work
* Corresponding author. Tel.: +61 8 92663138; fax: +61 8 92663063. E-mail address: [email protected] (Z. Singh). 0304-4238/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2006.06.028
implicates the role of phytohormones (Bains et al., 1999) and endogenous PAs (Malik and Singh, 2003) in fruit drop of mango. Exogenous application of various plant growth regulators have been reported to have variable success in reducing fruit drop (Chadha and Singh, 1964; Abou Rawash et al., 1998), possibly due to environmental variation and the limited understanding of the complex nature of the abscission phenomenon. On the basis that ethylene biosynthesis increases in fruitlet abscission (Malik et al., 2003), there is substantial evidence to support that ethylene is the main trigger in abscission process (Brown, 1997). Although in some cases abscission can occur without a rise in ethylene (Ruperti et al., 1998). PAs are considered as anti-ethylene substances (Apelbaum et al., 1981), being the likely competitors of precursors of ethylene (S-adenosylmethionine: SAMdc). PAs also have the properties of growth promoters (Rugini et al.,
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1986). However, their precise role and relationship with ethylene is not always clear. Exogenous application of PAs has been reported to improve fruit retention and yield in apple (Costa et al., 1986), olive (Rugini and Mencuccini, 1985), litchi (Stern and Gazit, 2000), and mango (Singh and Singh, 1995; Singh and Janes, 2000). Various reports claim that fruit retention and yield is influenced by both concentration and time of PA application. Although previous investigations did show that exogenous application of PAs increased fruitlet retention in mango, the effects of PAs applied at different times on final fruit retention, yield and fruit size of mango are yet to be investigated. Maintenance of fruit quality is critical while employing any new technology for increasing production or shelflife (Saltveit, 1999). Although a number of studies demonstrated the significance of PAs in reduing fruit drop and improving yield in various fruit crops, information on their effects on fruit quality is scant. In mango, the effects of exogenous application of PAs on fruit quality are yet to be investigated. The present study reports the effects of PAs on final fruit retention, yield, fruit size, colour and fruit quality of the Australian commercial mango cv. Kensington Pride. 2. Materials and methods Three experiments were carried out. Experiments 1 and 2 were aimed at evaluating the effects of type, concentration and time of application of PAs on final fruit retention, yield and fruit size, whereas in Experiment 3, we investigated the impact of PAs on fruit quality. 2.1. Plant materials These investigations were carried out during 1999–2001 on mango (M. indica L. cv. Kensington Pride) trees grown at commercial orchards at Gingin (longitude 1158550 E, latitude 318210 S) and at Chittering (longitude 116850 E, latitude 318250 S), Western Australia. Experiments 1 and 3 were performed on 15year-old trees at Gingin, whereas Experiment 2 was carried out on 14-year-old mango trees at Chittering. The experimental trees at both orchards were spaced at 6 m between rows and 3 m between plants. All the experimental trees received similar cultural practices during the period of investigations (Johnson and Parr, 1998) except for the experimental treatments. 2.2. Experiment 1: effects of type of polyamines on final fruit retention, yield and fruit size Efficacy of different PAs (PUT, SPD, SPM) at various concentrations (0, 0.01, 0.1, 1 mM) was tested by spraying aqueous solutions of these compounds containing a surfactant Tween 20 (0.01%) at final fruit set stage (when all flowers abscised but remained attached with the panicle) onto the panicles of whole tree to run off. Experimental lay out was randomised block design with two-factor factorial. A single tree was kept as a treatment unit with three replicates. The experiment was conducted during 1999–2001 and PAs were
sprayed on 28 November 1999 and 26 November 2000, respectively. The 2 years of data were kept separate, because the error means squares over years were heterogeneous. 2.2.1. Selection of panicles and data collection Ten uniform and healthy panicles per tree were tagged from all directions at final fruit set (FFS) stage prior to application of treatment. Total number of fruit on tagged panicles of each tree was counted before spray application and then at commercial harvest stage. Final fruit retention was expressed as per cent. Data on final fruit retention were recorded on 3 and 14 March during 2000 and 2001, respectively. 2.2.2. Fruit yield and fruit size At commercial harvest stage, the total number of fruit present on each tree was counted to record the yield. Fruit size was recorded by measuring the equatorial diameter and length of 10 uniform fruit at random on each tree and the mean values were presented as fruit volume (cm3), assuming that all fruit were similar in shape. Data on fruit yield and size were recorded on 3 and 14 March during 2000 and 2001, respectively. 2.3. Experiment 2: effects of time of spermine application on final fruit retention, yield and fruit size An aqueous solution of SPM at various concentrations (0, 0.01, 0.1, 1 mM) containing the surfactant Tween 20 (0.01%) was sprayed at four different phenological stages including flower bud differentiation (FBD), 5–8 cm grown panicles (GP), full bloom (FB) and at the initial fruit set stage (IFS) stage onto the panicles of whole tree to run off during 2000–2001. The experiment was laid out in randomised block design with twofactor factorial. A single tree was kept as a treatment unit and included three replicates. Data on final fruit retention, yield, and size were recorded on 13 March 2001 as explained in Experiment 1. 2.4. Experiment 3: effects of exogenous application of polyamines at final fruit set stage on fruit quality Uniformly mature, hard green mango fruit at commercial harvest stage (respiration 0.62 0.2 mmol kg1 h1, ethylene not detected, fruit firmness 125 5 N) were picked from mango trees sprayed with different PAs at FFS stage (Experiment 1, year 2000). Fruit were ripened at room temperature (22 1 8C). The ripe fruit at eating soft stage [softness score 4 (Shorter and Joyce, 1998)] were tested for fruit firmness, skin colour, sugars, total soluble solids (TSS), titratable acidity, TSS/acid ratio, and total carotenoids and ascorbic acid in pulp. Treatment unit comprised of 10 fruit per tree with three replicates. 2.4.1. Fruit quality parameters 2.4.1.1. Fruit firmness. At ripe stage, fruit firmness was tested with electronic pressure tester model EPT-1 (Lake City Technical Products Inc., 5-1952 Spall Road, Kelowana, BC, Canada V1Y 4R1) fitted with a plunger of 11 mm diameter. A small slice of skin was removed and fruit firmness was tested
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for two sides of individual mango fruit and expressed in Newtons (N). 2.4.1.2. Fruit colour. Skin colour of ripe fruit was measured from the opposite sides of each fruit with ColorFlex 45/0 Spectrophotometer (Hunter Associates Laboratory Inc., Reston, Virginia, USA) using the head 15-mm in diameter. The data were expressed on the Hunter scale (L, a and b), chroma (C) and ‘hue angle’ (h8). Chroma (C) and ‘hue angle’ (h8) were computed from L, a and b. In description, L represents whiteness of colour with 0 representing black and 100 representing white. The a represents red to green: a positive being an indicator of red colour, +60 being the maximum value, whilst a negative value means green colour, with 60 as the maximum. Likewise, b represents yellow to blue (+) being yellow and () being blue. Chroma [(a + b)1/2] represents colour saturation, which varies from a dull (low value) to vivid colour (high value). Hue = tan1(b/a) is like a colour wheel, with red-purple at an angle of 08, yellow at 908, bluishgreen at 1808, and blue at 2708 (McGuire, 1992). Changes in hue angle (h8), calculated as h8 = arc tan(b/a) (8) were used to indicate the colour changes from green to yellow during ripening. The ColorFlex was calibrated using the manufacturers’ standard white and black tiles. 2.4.1.3. Sugars, total soluble solids (TSS), titratable acidity (TA). Total, reducing and non-reducing sugars from the pulp of ripe fruit were analysed according to method of AOAC (1996) with some modifications (Singh et al., 2000). Total soluble solids (TSS) of juice was measured with a digital refractometer (model PR-101, Atago Co. Ltd., Itabashi-ku, Tokyo, Japan) and expressed as per cent at 20 8C. Titratable acidity was determined from fruit juice titrating against 0.1N NaOH using phenolphthalein as the indicator. The results were expressed as malic acid percentage. 2.4.1.4. Total carotenoids. Total carotenoids from pulp of ripe fruit were estimated following the method as detailed by Bhaskar (1988). Mango pulp (3–4 g) was macerated with glass powder in a glass pestle and mortar in 12% alcoholic KOH (5 ml g1). Following maceration, samples were saponified in a water bath at 37 1 8C for 30 min. From saponified samples, carotenoids were extracted in petroleum ether by vigorous shaking of the contents with a vortex mixer (Heidolph, Reax Control, Germany) and allowed to separate in two distinct layers. The top coloured phase was collected in a conical flask. The process was repeated until top layer of petroleum ether become colourless. The coloured phase of petroleum ether extract was passed through a layer of anhydrous Na2SO4 placed on glass wool to remove all moisture. The absorbance of the supernatant solution was recorded with a UV/VIS spectrophotometer (model 6405, Genway Ltd., Felsted, Dunmow, Essex CM6 3 LB, England) at 450 nm. An extinction coefficient of pure bcarotene at 450 nm, E11%cm (2500 in petroleum ether) was used in calculations. The results were expressed as mg carotenoids/100 g pulp. Since carotenoids are light sensitive, all steps of the experiments were performed in subdued light, with a 25 W red globe (Phillips Ltd., Australia).
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2.4.1.5. Ascorbic acid. Ascorbic acid contents from the pulp of ripe fruit were estimated following standard methods (Jagota and Dani, 1982; AOAC, 1996). Mango pulp (4–5 g) was macerated with a glass pestle and mortar using glass powder while adding 6% metaphosphoric acid solution containing 0.18% of ethylene diamino tetra acetic acid disodium salt (EDTA). After grinding and blending, the contents were transferred in a 100-ml graduated cylinder and volume was noted. Contents were centrifuged at 3000 rpm for 15 min and suspension was filtered (Whatman No. 1 filter paper). The absorbance of the filtrate was recorded using a UV/VIS spectrophotometer (model 6405, Genway Ltd., Felsted, Dunmow, Essex CM6 3 LB, England) at 760 nm and compared against a standard curve. The ascorbic acid content was expressed as mg 100 g1 pulp. 2.5. Statistical analysis The experimental data were subjected to analysis of variance (ANOVA), using Genstat release 6.1 (Lawes Agricultural Trust, Rothamsted Experimental Station, UK). The effects of various treatments and their interactions were assessed within ANOVA. Least significant difference (Fisher’s protected LSD) was calculated, following significant F-test (P 0.05). Normal probabilities plot of the residuals of the analysis of variance and a plot of residuals against predicted values were used to ensure that the assumptions of the analysis were satisfied. 3. Results 3.1. Effects of exogenous application of polyamines on final fruit retention, yield and fruit size 3.1.1. Effects of different types of polyamines Exogenous application of PAs at FFS stage did not significantly improve fruit retention (Table 1). However, mean fruit retention was increased with PAs treatments (1.53 and 2.92%) compared to the control (0.79 and 2.3%), during 1999– 2000 (off-year) and 2000–2001 (on-year), respectively. The corresponding increases in fruit yield were 63 and 4%, respectively, compared to the control. The increased fruit retention was in the order of SPM (1 mM), PUT (0.1 mM) and SPD (0.01 mM). Fruit size was not significantly affected with PA application. 3.1.2. Effects of different time of spermine application Application of SPM at different phenological stages significantly affected fruit retention and fruit yield compared to the control (Table 2). However, differences among concentrations were not significant. Spermine spray at FB or at IFS stage resulted in significantly highest mean fruit retention, whereas, mean fruit yield was comparatively higher with application at 5–8 cm GP or at IFS stage compared to the control. Interaction between concentrations and phenological stages at which treatments were applied were significant only for final fruit retention. Spray application of SPM (0.01 mM) at
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Table 1 Effect of exogenous application of polyamines at final fruit set on retention, yield and fruit size of mango Treatments
Concentration (mM)
Fruit retention (%)
Yield (number of fruit/tree)
Fruit size (cm3)
1999
2000
1999
2000
1999
2000
Control
0
2.3 1.1
0.8 0.3
204.0 21.1
18.3 7.2
92.9 3.7
79.9 5.5
Spermine
1 0.1 0.01
3.7 0.8 2.7 0.8 2.3 0.5
2.3 0.2 1.5 0.2 1.8 0.9
200.3 26.7 205.7 13.4 202.7 13.5
41.7 14.7 24.7 9.7 20.3 8.1
88.8 2.1 87.2 0.9 88.8 2.3
76.5 2.8 85.1 8.7 67.4 9.8
Spermindine
1 0.1 0.01
2.8 0.6 2.5 0.9 2.5 0.8
1.3 0.4 1.0 0.2 1.2 0.2
192.0 14.4 227.3 9.4 228.0 39.5
28.3 0.9 13.3 3.7 24.0 15.2
90.5 1.3 91.0 0.5 89.4 1.2
88.7 7.9 86.9 4.3 87.0 11.8
Putrescine
1 0.1 0.01
2.8 0.3 3.8 0.9 2.5 0.9
1.1 0.1 1.4 0.3 2.3 0.2
223.3 8.4 221.3 17.3 205.0 13.2
32.7 10.6 42.0 16.1 41.0 7.5
91.1 1.0 88.4 3.1 96.4 1.1
78.7 2.3 85.3 6.1 80.0 6.4
2.3 4.1 3.3 1.3 1.8
0.4 0.2 0.5 0.3 0.6
1.1 1.2 2.1 0.5 0.9
1.9 1.8 2.7 1.5 1.7
0.8 0.1 1.8 0.8 0.4
Source of variance
F-Values
Treatments Control vs. others Chemical (ch) Concentration (C) Ch C
0.7 1.0 0.01 0.2 1.3
n = 3 (3 replications of 10 fruit each) S.E.M., F-values without asterisks are non-significant.
FB stage exhibited 1.5-fold increase in fruit retention compared to the control (Table 2). Generally, the lowest concentration of SPM (0.01 mM) was more effective in improving fruit retention and yield. SPM application at different times did not have significant effect on fruit size compared to the control. However, trees
sprayed at flower bud differentiation stage showed significantly increase in fruit size compared to those sprayed at full bloom stage (Table 2). This is due to the fact that trees sprayed at flower bud differentiation stage had few branches damaged due to frost, resulting in a decreased number of total fruit, with larger size.
Table 2 Effects of different time of spermine application on fruit retention, yield and fruit size of mango Treatments
Concentration (mM)
Fruit retention (%)
Yield (number of fruit/tree)
Fruit size (cm3)
Control
0
2.1 0.3
141.3 28.6
94.2 0.8
Flower bud differentiation (FBD)
1 0.1 0.01
3.0 0.4 3.7 1.2 2.3 0.5
126.7 18.6 101.0 4.4 98.7 14.4
96.6 2.7 99.2 1.2 97.8 4.5
Grown panicles (GP) (5–8 cm long)
1 0.1 0.01
3.3 0.0 1.7 0.3 1.5 0.4
235.3 40.3 209.3 24.3 244.0 27.1
94.0 1.9 98.5 1.4 95.3 1.6
Full bloom (FB)
1 0.1 0.01
2.7 0.8 3.5 0.7 5.0 0.4
219.3 27.5 233.0 46.7 196.0 16.1
96.7 2.2 94.1 0.5 94.9 1.6
Initial fruit set (IFS)
1 0.1 0.01
2.1 0.5 2.6 0.4 3.5 0.9
205.3 64.3 222.0 47.0 263.0 34.4
89.5 2.4 93.9 2.4 92.7 1.6
2.9* 2.6 9.5** 0.1 0.0 0.1 0.5
1.5 0.2 4.0 * 1.1 0.4 1.9 0.7
Source of variance
F-Values
Treatments Control vs. others Stage Concentration (C) Linear Quadratic Stage C
2.5* 1.7 3.5 * 0.3 0.6 0.0 2.9 *
n = 3 (3 replications of 10 fruit each) S.E.M., * significant,
**
highly significant, F-values without asterisks are non-significant.
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Table 3a Effect of exogenous application of polyamines at final fruit set on quality characteristics of mango fruit Treatments
Concentration (mM)
Fruit firmness (N)
TSS (8Brix)
Acidity (malic acid, %)
T. sugar (%)
R. sugar (%)
N.R. sugar (%)
Total carotenoids (mg/100g)
Vitamin C (mg/100 g)
Control
0
23.6 2.3
17.8 0.5
0.2 0.0
15.9 1.7
4.3 0.1
11.6 1.6
2.1 0.2
25.2 2.0
Spermine
1 0.1 0.01
21.5 0.2 20.9 0.2 17.9 0.3
17.6 0.3 17.0 0.2 16.9 0.1
0.2 0.0 0.2 0.0 0.2 0.0
13.3 0.3 12.3 0.5 13.0 0.3
4.5 0.1 4.5 0.1 4.6 0.1
8.9 0.2 7.8 0.4 8.4 0.2
2.4 0.1 2.1 0.5 3.0 0.2
28.3 2.0 27.5 3.2 19.9 0.5
Spermindine
1 0.1 0.01
18.5 0.3 20.0 0.4 17.3 0.2
16.7 0.2 17.4 0.2 16.8 0.4
0.2 0.0 0.2 0.0 0.2 0.0
13.9 1.2 14.8 0.7 14.4 0.8
4.5 0.1 4.5 0.1 4.1 0.1
9.5 1.1 10.3 0.6 10.3 0.8
3.4 0.2 2.4 0.1 2.7 0.1
20.2 1.1 19.2 1.2 18.0 0.7
Putrescine
1 0.1 0.01
18.9 0.3 17.6 0.2 17.8 0.3
16.2 0.4 16.7 0.5 16.1 0.2
0.2 0.0 0.2 0.0 0.2 0.0
14.6 0.5 15.6 0.1 14.5 0.5
4.2 0.0 4.1 0.2 4.3 0.1
10.4 0.4 11.5 0.2 10.2 0.6
4.1 0.3 4.4 0.3 3.8 0.1
21.2 0.9 18.5 0.3 20.4 1.1
Source of variance
F-Values
Treatments Control vs. others Chemical (ch) Concentration (C) Linear Quadratic Ch C
7.9** 36.8** 6.3** 6.9** 11.0** 2.8 2.1
3.5 * 9.2 ** 6.9 ** 1.5 0.9 2.0 1.4
4.0 ** 0.1 14.6** 0.4 0.0 0.7 1.6
2.9* 0.2 7.7** 0.2 0.4 0.1 2.6
2.0 4.8* 5.3* 0.1 0.0 0.2 0.6
2.6* 5.4* 7.6** 0.1 0.0 0.2 0.7
11.4** 16.4** 34.1** 1.1 0.5 1.6 4.0 *
6.7 ** 5.8 * 15.5** 5.2 * 10.2** 0.1 3.2 *
n = 3 (3 replications of 10 fruit each) S.E.M., TSS, total soluble solids; T. sugar, total sugar; R. sugar, reducing sugar; N.R. sugar, non-reducing sugar; * significant; ** highly-significant; F-values without asterisks are non-significant.
3.2. Effects of exogenous application of polyamines at final fruit set stage on fruit skin colour and quality Application of PAs at fruit set significantly influenced various fruit quality characteristics of ripe fruit (Tables 3a and 3b). Fruit firmness was significantly higher in untreated fruit compared to those treated with PUT and SPD. Mean fruit acidity was significantly reduced by 11% with PUT treatment, and increased by 16.7% with SPM application at final fruit set stage compared to the control. TSS was generally reduced with PA treatments (5.3%); maximum reduction (8.4%) was observed with PUT compared to the control. Sugars were generally lower in PA treated fruit as compared to the control in the reduction order of PUT < SPD < SPM. However, only SPM treated fruit showed significantly lower sugars (total sugars 18.8%, non-reducing sugars 27.8%) compared with control. Total carotenoids in the pulp were significantly improved (49%) with PAs treatments compared to control and maximum increase was observed with PUT (95%) followed by SPD (33%). Ascorbic acid concentrations were significantly
reduced with SPD (24.2%) and PUT (20.6%) treatments compared to control. Whereas higher concentrations of SPM (0.1, 1 mM) tended to increase ascorbic acid (9%, 12.7%) compared with the control. Among the interactions (chemical concentrations) effects, only total carotenoids and ascorbic acid were significantly affected (Table 3a). PUT (0.1 mM) produced fruit with maximum carotenoid content; whereas SPM (1.0 mM) treated fruit had the highest ascorbic acid concentration compared with control. Exogenous application of different PAs at FFS stage significantly maintained lower L, a, b, ‘chroma’ values and higher ‘hue angle’ of ‘Kensington Pride’ fruit at the ripe stage (Table 4). SPD treatment resulted in minimum L, a, b, ‘chroma’ values and higher ‘hue angle’ of fruit. The interactions of PAs (chemical) concentrations were also significant for L, b, and ‘chroma’ (4a). Untreated fruit exhibited the maximum values for L, a, b, and ‘chroma’, whereas treatment with the lowest concentration of SPM (0.01 mM) resulted in the minimum values for these parameters.
Table 3b Effect of exogenous application of polyamines at final fruit set on quality characteristics mango fruit Treatments
Fruit firmness (N)
Total soluble solids (8Brix)
Acidity (malic acid, %)
Non-reducing sugars (%)
Reducing sugars (%)
Total sugars (%)
Control Spermine Spermidine Putrescine
23.6 20.1 18.6 18.1
17.8 17.2 17.0 16.3
0.2 0.2 0.2 0.2
11.6 8.4 10.0 10.7
4.3 4.5 4.4 4.2
15.9 12.9 14.4 15.0
A Ba Bb Bb
A Aa Ba Bb
A Aa Ab Bc
A Bb Aa Aa
A Bc Ab Ba
A Bb Aa Aa
Means sharing common letters, or without any letter are not significantly different (P 0.05). Capital letters to compare polyamines with control, small letter to compare among polyamines.
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Table 4 Effect of exogenous application of polyamines at final fruit set on L, a, b, chroma and hue angle of ripe mango fruit Treatments
Concentration (mM)
L
a
b
Chroma
Hue angle
Control
0
57.2 0.6
7.0 0.8
27.8 0.3
28.7 0.4
76.0 1.6
Spermine
1 0.1 0.01
56.8 0.5 55.7 0.3 53.0 0.7
4.1 0.8 4.0 0.3 2.1 1.1
27.0 0.6 26.3 0.4 24.1 0.6
27.2 0.7 26.7 0.5 24.2 0.7
81.5 1.5 81.4 0.5 85.2 2.5
Spermindine
1 0.1 0.01
55.1 0.6 53.7 1.0 56.0 0.8
3.0 0.2 2.3 0.8 4.4 0.8
25.4 0.4 24.8 0.4 26.3 0.3
25.6 0.4 24.9 0.4 26.7 0.5
83.2 0.3 84.8 1.8 80.6 1.6
Putrescine
1 0.1 0.01
55.7 1.4 54.6 0.5 56.0 0.2
4.8 1.1 5.2 0.6 4.5 0.3
26.2 0.7 25.6 0.4 26.4 0.2
26.6 0.9 26.2 0.5 26.8 0.2
79.8 2.2 78.6 1.2 80.3 0.5
3.6 * 15.7** 3.9 * 0.1 0.2 0.0 2.1
5.7 ** 19.1** 1.2 1.7 2.5 0.8 6.7 **
5.4 ** 21.2** 1.7 1.1 1.8 0.4 5.4 **
3.2* 12.1** 4.3* 0.1 0.2 0.0 2.0
Source of variance
F-Values
Treatment Control vs. others Chemical (ch) Concentration (C) Linear Quadratic Ch C
3.6** 8.3* 0.4 2.6 3.0 2.3 4.6**
n = 3 (3 replications of 10 fruit each) S.E.M., * significant,
**
highly-significant, F-values without asterisks are non-significant.
4. Discussion 4.1. Effects of exogenous application of polyamines on final fruit retention, yield and fruit size PA applications have generally improved fruit retention and yield in mango depending upon the type and concentration of PAs and phenological stage of application. The increase in fruit retention with exogenous application of PAs may be ascribed to the increased levels of endogenous PAs in the fruitlets and pedicels, which were less prone to abscise, especially during initial 4–6 weeks of heavy fruitlet abscission. Our recent studies on cv. Kensington Pride and Glen demonstrated the association of initial fruitlet abscission with reduced levels of endogenous PAs (Malik and Singh, 2003) and increased ethylene biosynthesis (Malik et al., 2003) in mango fruitlets and their pedicels. It may also be argued that the exogenous application of PAs improved fruit retention, possibly by inhibiting endogenous ethylene biosynthesis, which is the known trigger in abscission (Brown, 1997). Different PAs did not have significant effect on fruit retention when sprayed at FFS stage (Table 1); however, SPM was comparatively more effective compared to control. Recently, we reported that SPM was the dominant PA in the intact fruitlet and their pedicels in ‘Kensington Pride’ mango at pinhead, pea and marble stages, and about-to-abscise fruitlets and their pedicels had only 10 and 19% of the mean SPM (Malik and Singh, 2003). Our experimental results suggest the optimum concentration of SPM is 0.01 mM. Highest fruit retention in litchi (Mitra and Sanyal, 1990) and apple cv. Ruby Spur (Costa and Bagni, 1983) has been achieved with a lower concentration (0.01 mM) of PUT. PA spray at FFS stage were not effective in increasing final fruit retention compared to control (Table 1), whereas during the
same year, SPM applied prior to FFS stage (FBD, GP, FB or IFS) significantly improved fruit retention (Table 2). The increased effectiveness of SPM at earlier stages (before FFS) may be due to the improved floral organ development, pollination, fertilization, and subsequent embryo and initial fruit development. Previously PUT application in olives was also not effective in reducing fruit abscission when applied at fruit set stage, however, when sprayed before anthesis or at FB it increased fruit yield (Rugini and Mencuccini, 1985). Earlier application of PUT at pre-anthesis stage in ‘Comice pear’ delayed the senescence of visible flower parts and extended the ovule longevity (Crisosto et al., 1986). It may be suggested that beside antiethylene properties, the growth promoting characteristics of PAs may have helped to improve an overall reproductive process, fruit set and embryo development, resulting in lower fruitlet abscission. Previously, when flower clusters of apple were sprayed with PAs, pistil longevity was prolonged and fruit set was improved (Wang et al., 1996). Our experimental results support the earlier report of Singh and Singh (1995) that time of PA application significantly affected the fruit set and retention in ‘Dusehri’ and ‘Langra’ mango and spray of SPM prior to anthesis, and PUT at FB were found more effective in increasing the final fruit retention, respectively. The improvement in fruit yield was the result of increased fruit retention in PA-treated trees especially with lower concentrations of SPM (0.01 mM) (Table 2). Likewise, lower concentrations (0.01, 0.1 mM) of PAs have also been reported to increase fruit yield in apple (Costa and Bagni, 1983; Costa et al., 1986) and litchi (Mitra and Sanyal, 1990). Fruit size was not significantly affected with PA sprays. The increase in fruit size with SPM application at FBD stage (Table 2) may be associated with reduced fruit yield due to frost damage, and not due to the effect of SPM. This is also supported by the fact that the treatment showing maximum number of
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fruit per tree (IFS) also had the minimum fruit size. A reduction in fruit size has been reported in ‘Hi Early’ apple as result of PUT spray, possibly at the expense of higher yield (Costa et al., 1986). 4.2. Effects of exogenous application of polyamines at final fruit set stage on fruit quality The application of PAs has varying effects on different parameters of ripe fruit. PAs generally reduced fruit firmness and sugar content, while increasing carotenoids in pulp compared to the control. PUT-treated fruit exhibited highest carotenoids, and lower ascorbic acid and TSS compared to the control. Whereas SPM treatment increased ascorbic acid content at higher concentrations and also showed higher fruit acidity. The lower sugar content in PAs treated fruit compared to control may be due to the slower conversion of starch to sugars. Generally, ripening of mango fruit has been marked by an appreciable increase in reducing and non-reducing sugars and a decrease in starch content (Lima et al., 2001). Since the predominant sugar in mango has been sucrose (Selvaraj et al., 1989), PAs may have suppressed the activities of certain enzymes such as sucrosephosphate synthase (SPS) involved in sucrose metabolism. Effects of PAs on the activities of SPS are yet to be investigated. Similarly, a reduction in sugar and TSS as a result of PUT applications at FB or 20% open flowers have also been reported in apple (Costa et al., 1986). A lower concentration (0.01 mM) of PUT applied before anthesis to litchi increased acidity and reduced total sugars and sugar acid ratio (Mitra and Sanyal, 1990). The reduction in fruit firmness with exogenous application of PAs at FFS stage warrants further investigations on their effects on the activation of enzymes involved in fruit softening. Earlier exogenous PA application in apple produced fruit with lower flesh firmness compared to the control (Costa and Bagni, 1983; Costa et al., 1986). An increase in total carotenoids contents of PA treated fruit, and the reduced levels of ascorbic acid in SPD and PUT treatment are important and yet to be investigated. Previously, transgenic tomato plants with enhanced expression of the yeast S-adenosylmethionine decarboxylase gene (ySAMdc; Spe2) had an increased conversion of PUT resulting in ripening specific accumulation of SPD and SPM leading to increased lycopene content and enhanced fruit juice quality (Mehta et al., 2002). PUT application at pre-anthesis stage has also been reported to increase anthocyanin content of litchi fruit (Mitra and Sanyal, 1990). Increased ascorbic acid content in fruit treated with a higher concentration of SPM may be ascribed to the suppression of ascorbate oxidase activities as a result of increased levels of endogenous SPM in mango fruit pulp. The effects of PAs on activities of ascorbate oxidase in mango are yet to be investigated. Higher endogenous concentration of PUT in bell pepper compared to tomato fruit has been associated with higher ascorbic acid (Yahia et al., 2001). PA treatments appeared to retard fruit skin colour development, as evident from the significantly lower L, a, b values and higher ‘hue angle’ in PA treated fruit compared with control fruit. The colour parameter b (yellowness) has been described as to best reflect the colour changes in skin tissues
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during fruit ripening (Martinez-Madrid et al., 1999). PAs may inhibit chlorophyll degradation in skin tissues, by inhibition of peroxidase activity (Ma-Jun et al., 1996). The effects of polyamines on colour retardation were in the order: SPM4+ < SPD3+ < PUT2+, following the order of their available number of cations, which has been argued as the reason for their difference in effectiveness (Valero et al., 2002). Earlier, the retardation of chlorophyll loss in muskmelon with exogenous application of PAs has been attributed to reduced hydrolytic activities acting on chloroplast thylakoid membranes (Lester, 2000). In conclusion, type and concentration of PA, and phenological stage of application influence the effects of exogenously applied PAs on fruit retention, yield, fruit skin colour and quality of mango. The application of SPM (0.01 mM) at FB stage was the most effective in increasing final fruit retention, whereas applications at 5–8 cm GP or at IFS stage had comparatively higher fruit yield. PUT application at FFS significantly improved fruit quality by increasing total carotenoids, while reducing the acid content of ripe fruit. Acknowledgements We thank Mr. M.A. Chatha for help in data collection, Dr. A. Bhaskar for technical advice on carotenoids and Vitamin C analysis, Mr. Satvinda S. Dhaliwal and Dr. Inayat, Biostatisticians for help in statistical analysis. A.U. Malik also acknowledges the financial assistance of Curtin University of Technology, Perth, Western Australia and Australian International Development Programme, for awarding International Postgraduate Research Scholarship and Australian International Development scholarship, respectively, and University of Agriculture, Faisalabad, Pakistan for granting study leave during this period. References Abou Rawash, M., Abou El Nasr, N., El Masry, H., Ebeed, S., 1998. Effect of spraying some chemical substances on flowering, fruit set, fruit drop, yield and fruit quality of Taimour [Egyptian] mango trees. Egypt. J. Hortic. 25, 83–99. AOAC, 1996. AOAC Methods. Association of Official Analytical Chemists, Washington, DC. Apelbaum, A., Burgoon, A.C., Andrew, J.D., Liberman, M., Ben-Arie, R., Matto, A.K., 1981. Polyamines inhibit biosynthesis of ethylene in higher plant tissue and fruit protoplast. Plant Physiol. 68, 453–456. Bains, K.S., Bajwa, G.S., Singh, Z., 1999. Effects of indole-3-acetic acid, gibberellic acid, and abscisic acid on abscission of mango fruitlets. Trop. Agric. 76, 88–92. Bhaskar, A.K., 1988. Studies on carotenoids in some plant foods as a source of vitamin A. Ph.D. Thesis. Osmania University, Hyderabad, India. Brown, K.M., 1997. Ethylene and abscission. Physiol. Plant 100, 567–576. Chadha, K.L., 1993. Fruit drop in mango. In: Chadha, K.L., Pareek, O.P. (Eds.), Advances in Horticulture, vol. 3. Malhotra Publishing House, New Delhi, pp. 1131–1166. Chadha, K.L., Singh, K.K., 1964. Fruit drop in mango. I. Fruit set and its retention and factors affecting it. Ind. J. Hortic. 20, 172–185. Costa, G., Bagni, N., 1983. Effect of polyamines on fruit set of apple. Hortscience 18, 59–61. Costa, G., Biasi, R., Bagni, N., 1986. Effect of putrescine on fruiting performance on apple (cv. Hi Early). Acta Hortic. 149, 189–195.
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Crisosto, C.H., Vasilakakis, M.D., Lombard, P.B., Richardson, D., Tetley, R., 1986. Effect of ethylene inhibitors on fruit set, ovule longivity, and polyamine levels in ‘Comice pear’. Acta Hortic. 179, 236–239. FAO, 2003. FAO Statistics. Retrieved on August 9, 2003, from http:// www.fao.org. Jagota, S.K., Dani, H.M., 1982. A new calorimetric technique for estimation of vitamin C using folin phenol reagent. Ann. Biochem. 127, 178–182. Johnson, P.R., Parr, D., 1998. Mango growing in Western Australia. In: Tropical and Sub-tropical Fruits. Agdex 234/01, Agriculture Bull. 4348, Western Australia. Lester, G.E., 2000. Polyamines and their cellular anti-senescence properties in ‘Honey Dew’ muskmelon fruit. Plant Sci. 160, 105–112. Lima, L.-d.-O., Chitarra, A.B., Chitarra, M.I.F., 2001. Changes in amylase activity, starch and sugar contents in mango fruit pulp of cv. Tommy Atkins with spongy tissue. Braz. Arch. Biol. Technol. 44, 59–62. Ma-Jun, Y., Zhou, R., Cheng-Bing, S., Ma, J.Y., Zhou, R., Cheng, B.S., 1996. Effect of spermine on the peroxidase activity of detached wheat leaves. J. Shandong Agric. Univ. 27, 176–180. Malik, A.U., Singh, Z., 2003. Abscission of mango fruitlets as influenced by biosynthesis of polyamines. J. Hortic. Sci. Biotechnol. 78, 721–727. Malik, A.U., Agrez, V., Singh, Z., 2003. Fruitlet abscission of mango in relation to ethylene. J. Hortic. Sci. Biotechnol. 78, 458–462. Martinez-Madrid, M.C., Martinez, G., Pretel, M.T., Serrano, M., Romojaro, F., 1999. Role of ethylene and abscisic acid in physicochemical modifications during melon ripening. J. Agric. Food Chem. 47, 5285–5290. McGuire, R.G., 1992. Reporting of objective colour measurement. Hortscience 27, 1254–1255. Mehta, R.A., Cassol, T., Li, N., Ali, N., Handa, A.K., Mattoo, A.K., 2002. Engineered polyamine accumulation in tomato enhances phytonutrient content, juice quality, and vine life. Nat. Biotechnol. 20, 613–618. Mitra, S.K., Sanyal, D., 1990. Effect of putrescine on fruit set and fruit quality of litchi. Gartenbauwissenschaft 55, 83–84. Rugini, E., Mencuccini, M., 1985. Increased yield in olives with putrescine treatment. Hortscience 20, 102–103.
Rugini, E., Bongi, G., Mencuccini, M., 1986. Effect of putrescine, L. arginine and cobalt on fruit set, ethylene content and apparent parthenocarpy in olives (Olea europea L.). Acta Hortic. 179, 365–368. Ruperti, B., Bonghi, C., Tonutti, P., Ramina, A., 1998. Ethylene biosynthesis in peach fruitlet abscission. Plant Cell Environ. 21, 731–737. Saltveit, M.E., 1999. Effect of ethylene on quality of fresh fruits and vegetables. Postharvest Biol. Technol. 15, 279–292. Selvaraj, Y., Kumar, R., Pal, D.K., 1989. Changes in sugars, organic acids, amino acids, lipid constituentsand aroma characteristics of ripening mango (Mangifera indica L.) fruit. J. Food Sci. Technol. 26, 308–313. Shorter, A.J., Joyce, D.C., 1998. Effect of partial pressure infiltration of calcium into Kensington mango fruit. Aust. J. Exp. Agric. 38, 287–294. Singh, Z., Singh, L., 1995. Increased fruit set and retention in mango with exogenous application of polyamines. J. Hortic. Sci. 70, 271–277. Singh, Z., Janes, J., 2000. Regulation of fruit set and retention in mango with exogenous application of polyamines and their biosynthesis inhibitors. Acta Hortic. 509, 675–680. Singh, Z., Janes, J., Tan, S.C., 2000. Effect of different surfactants on calcium uptake and its effect on fruit ripening, quality and postharvest storage of mango under modified atmosphere packaging. Acta Hortic. 509, 413– 417. Stern, R.A., Gazit, S., 2000. Application of the polyamine putrescine increased yield of ‘Mauritius’ litchi (Litchi chinensis Sonn.). J. Hortic. Sci. Biotechnol. 75, 612–614. Valero, D., Martinez Romero, D., Serrano, M., 2002. The role of polyamines in the improvement of the shelflife of fruit. Trends Food Sci. Technol. 13, 228– 234. Wang, S., Song, C., Li, L., Zhang, Y., Wang, S.P., Song, C.B., Li, L.C., Zhang, Y.M., 1996. Physiological function of polyamines during blossoming and fruit setting in apple. Acta Hortic. Sin. 23, 319–325. Yahia, E.M., Contreras Padilla, M., Gonzalez Aguilar, G., 2001. Ascorbic acid content in relation to ascorbic acid oxidase activity and polyamine content in tomato and bell pepper fruits during development, maturation and senescence. Lebensm. Wiss. Technol. 34, 452–457.
Improved fruit retention, yield and fruit quality in mango with exogenous application of polyamines Aman Ullah Malik, Zora Singh * Horticulture, Muresk Institute, Division of Resources and Environment, Curtin University of Technology, GPO Box U 1987, Perth 6845, Australia Received 1 December 2003; received in revised form 11 May 2006; accepted 30 June 2006
Abstract Aqueous solutions (0, 0.01, 0.1, 1 mM) of PAs (putrescine, spermine, spermidine) containing a surfactant ‘Tween 20’ were sprayed onto panicles of mango (Mangifera indica L. cv. Kensington Pride) at final fruit set (FFS) stage (when all flowers abscised but remain attached to the panicle) during 1999–2001 to investigate their effects on fruit retention, yield, size, and fruit quality. The optimum time of PA application for improving final fruit retention and fruit yield was determined by spraying different concentrations (0, 0.01, 0.1, 1 mM) of spermine (SPM) containing a surfactant ‘Tween 20’ at four phenological stages including flower bud differentiation (FBD), 5–8 cm long grown panicles (GP), full bloom (FB) and at initial fruit set (IFS) stage (when 2/3rd of the flowers were abscised but attached to the panicle) during 2000. Exogenous application of PAs at FFS stage did not significantly increase fruit retention. However, compared to control (0.79 and 2.3% fruit retention), PAs treatments resulted in comparatively higher mean fruit retention (1.53 and 2.92%) during 1999–2000 and 2000–2001, respectively. Among three PAs tested, SPM was more effective in increasing mean final fruit retention. Fruit size was not significantly affected by any PA treatment. Among the four application times, SPM (0.01 mM) spray at FB stage resulted in significantly (P 0.05) greater fruit retention (4.99%) compared with control (2.1%). However, fruit yield was comparatively higher with SPM (0.01 mM) application at IFS stage or 5–8 cm GP stage compared to the control. Overall FB application was found as the optimum time of application. Application of PAs at FFS stage retarded fruit skin colour development compared to the control. Sugars and total soluble solids (TSS) were generally reduced in PA-treated fruit. Fruit acidity was increased (16.7%) with SPM, whereas it was 11% with PUT treatment as compared to the control. Total carotenoids in pulp were generally improved (49%) with PA treatments, compared to the control. Ascorbic acid concentrations were significantly reduced with spermidine (SPD) (24%) and PUT (20%) treatments, whereas higher concentrations of SPM (1 mM) tended to increase it (12.7%) compared to the control. In conclusion, application of SPM (0.01 mM) at FB stage resulted in the highest fruit retention, whereas SPM (0.01) spray at GP or IFS stage resulted in higher fruit yield. PUT application at FFS stage significantly improved fruit quality by increasing total carotenoid, while reducing acid content of ripe fruit. # 2006 Elsevier B.V. All rights reserved. Keywords: Polyamines; Fruit drop; Carotenoids; Ascorbic acid; Sugars; Colour
1. Introduction Mango (Mangifera indica L.) is a major fruit crop of the tropical regions of the world. However, its delicious taste, and unique flavour with high nutritional value have made it equally popular across the globe. Over the last decade (1991–2001), despite an increase of 42.5% in mango growing area, there has been only 1.3% increase in average fruit yield (7.5–7.6 t/ha) (FAO, 2003). Heavy fruit drop is an important factor contributing to low fruit yield in mango orchards and sometime only 0.1% of set fruit reach maturity (Chadha, 1993). Research work
* Corresponding author. Tel.: +61 8 92663138; fax: +61 8 92663063. E-mail address: [email protected] (Z. Singh). 0304-4238/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2006.06.028
implicates the role of phytohormones (Bains et al., 1999) and endogenous PAs (Malik and Singh, 2003) in fruit drop of mango. Exogenous application of various plant growth regulators have been reported to have variable success in reducing fruit drop (Chadha and Singh, 1964; Abou Rawash et al., 1998), possibly due to environmental variation and the limited understanding of the complex nature of the abscission phenomenon. On the basis that ethylene biosynthesis increases in fruitlet abscission (Malik et al., 2003), there is substantial evidence to support that ethylene is the main trigger in abscission process (Brown, 1997). Although in some cases abscission can occur without a rise in ethylene (Ruperti et al., 1998). PAs are considered as anti-ethylene substances (Apelbaum et al., 1981), being the likely competitors of precursors of ethylene (S-adenosylmethionine: SAMdc). PAs also have the properties of growth promoters (Rugini et al.,
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1986). However, their precise role and relationship with ethylene is not always clear. Exogenous application of PAs has been reported to improve fruit retention and yield in apple (Costa et al., 1986), olive (Rugini and Mencuccini, 1985), litchi (Stern and Gazit, 2000), and mango (Singh and Singh, 1995; Singh and Janes, 2000). Various reports claim that fruit retention and yield is influenced by both concentration and time of PA application. Although previous investigations did show that exogenous application of PAs increased fruitlet retention in mango, the effects of PAs applied at different times on final fruit retention, yield and fruit size of mango are yet to be investigated. Maintenance of fruit quality is critical while employing any new technology for increasing production or shelflife (Saltveit, 1999). Although a number of studies demonstrated the significance of PAs in reduing fruit drop and improving yield in various fruit crops, information on their effects on fruit quality is scant. In mango, the effects of exogenous application of PAs on fruit quality are yet to be investigated. The present study reports the effects of PAs on final fruit retention, yield, fruit size, colour and fruit quality of the Australian commercial mango cv. Kensington Pride. 2. Materials and methods Three experiments were carried out. Experiments 1 and 2 were aimed at evaluating the effects of type, concentration and time of application of PAs on final fruit retention, yield and fruit size, whereas in Experiment 3, we investigated the impact of PAs on fruit quality. 2.1. Plant materials These investigations were carried out during 1999–2001 on mango (M. indica L. cv. Kensington Pride) trees grown at commercial orchards at Gingin (longitude 1158550 E, latitude 318210 S) and at Chittering (longitude 116850 E, latitude 318250 S), Western Australia. Experiments 1 and 3 were performed on 15year-old trees at Gingin, whereas Experiment 2 was carried out on 14-year-old mango trees at Chittering. The experimental trees at both orchards were spaced at 6 m between rows and 3 m between plants. All the experimental trees received similar cultural practices during the period of investigations (Johnson and Parr, 1998) except for the experimental treatments. 2.2. Experiment 1: effects of type of polyamines on final fruit retention, yield and fruit size Efficacy of different PAs (PUT, SPD, SPM) at various concentrations (0, 0.01, 0.1, 1 mM) was tested by spraying aqueous solutions of these compounds containing a surfactant Tween 20 (0.01%) at final fruit set stage (when all flowers abscised but remained attached with the panicle) onto the panicles of whole tree to run off. Experimental lay out was randomised block design with two-factor factorial. A single tree was kept as a treatment unit with three replicates. The experiment was conducted during 1999–2001 and PAs were
sprayed on 28 November 1999 and 26 November 2000, respectively. The 2 years of data were kept separate, because the error means squares over years were heterogeneous. 2.2.1. Selection of panicles and data collection Ten uniform and healthy panicles per tree were tagged from all directions at final fruit set (FFS) stage prior to application of treatment. Total number of fruit on tagged panicles of each tree was counted before spray application and then at commercial harvest stage. Final fruit retention was expressed as per cent. Data on final fruit retention were recorded on 3 and 14 March during 2000 and 2001, respectively. 2.2.2. Fruit yield and fruit size At commercial harvest stage, the total number of fruit present on each tree was counted to record the yield. Fruit size was recorded by measuring the equatorial diameter and length of 10 uniform fruit at random on each tree and the mean values were presented as fruit volume (cm3), assuming that all fruit were similar in shape. Data on fruit yield and size were recorded on 3 and 14 March during 2000 and 2001, respectively. 2.3. Experiment 2: effects of time of spermine application on final fruit retention, yield and fruit size An aqueous solution of SPM at various concentrations (0, 0.01, 0.1, 1 mM) containing the surfactant Tween 20 (0.01%) was sprayed at four different phenological stages including flower bud differentiation (FBD), 5–8 cm grown panicles (GP), full bloom (FB) and at the initial fruit set stage (IFS) stage onto the panicles of whole tree to run off during 2000–2001. The experiment was laid out in randomised block design with twofactor factorial. A single tree was kept as a treatment unit and included three replicates. Data on final fruit retention, yield, and size were recorded on 13 March 2001 as explained in Experiment 1. 2.4. Experiment 3: effects of exogenous application of polyamines at final fruit set stage on fruit quality Uniformly mature, hard green mango fruit at commercial harvest stage (respiration 0.62 0.2 mmol kg1 h1, ethylene not detected, fruit firmness 125 5 N) were picked from mango trees sprayed with different PAs at FFS stage (Experiment 1, year 2000). Fruit were ripened at room temperature (22 1 8C). The ripe fruit at eating soft stage [softness score 4 (Shorter and Joyce, 1998)] were tested for fruit firmness, skin colour, sugars, total soluble solids (TSS), titratable acidity, TSS/acid ratio, and total carotenoids and ascorbic acid in pulp. Treatment unit comprised of 10 fruit per tree with three replicates. 2.4.1. Fruit quality parameters 2.4.1.1. Fruit firmness. At ripe stage, fruit firmness was tested with electronic pressure tester model EPT-1 (Lake City Technical Products Inc., 5-1952 Spall Road, Kelowana, BC, Canada V1Y 4R1) fitted with a plunger of 11 mm diameter. A small slice of skin was removed and fruit firmness was tested
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for two sides of individual mango fruit and expressed in Newtons (N). 2.4.1.2. Fruit colour. Skin colour of ripe fruit was measured from the opposite sides of each fruit with ColorFlex 45/0 Spectrophotometer (Hunter Associates Laboratory Inc., Reston, Virginia, USA) using the head 15-mm in diameter. The data were expressed on the Hunter scale (L, a and b), chroma (C) and ‘hue angle’ (h8). Chroma (C) and ‘hue angle’ (h8) were computed from L, a and b. In description, L represents whiteness of colour with 0 representing black and 100 representing white. The a represents red to green: a positive being an indicator of red colour, +60 being the maximum value, whilst a negative value means green colour, with 60 as the maximum. Likewise, b represents yellow to blue (+) being yellow and () being blue. Chroma [(a + b)1/2] represents colour saturation, which varies from a dull (low value) to vivid colour (high value). Hue = tan1(b/a) is like a colour wheel, with red-purple at an angle of 08, yellow at 908, bluishgreen at 1808, and blue at 2708 (McGuire, 1992). Changes in hue angle (h8), calculated as h8 = arc tan(b/a) (8) were used to indicate the colour changes from green to yellow during ripening. The ColorFlex was calibrated using the manufacturers’ standard white and black tiles. 2.4.1.3. Sugars, total soluble solids (TSS), titratable acidity (TA). Total, reducing and non-reducing sugars from the pulp of ripe fruit were analysed according to method of AOAC (1996) with some modifications (Singh et al., 2000). Total soluble solids (TSS) of juice was measured with a digital refractometer (model PR-101, Atago Co. Ltd., Itabashi-ku, Tokyo, Japan) and expressed as per cent at 20 8C. Titratable acidity was determined from fruit juice titrating against 0.1N NaOH using phenolphthalein as the indicator. The results were expressed as malic acid percentage. 2.4.1.4. Total carotenoids. Total carotenoids from pulp of ripe fruit were estimated following the method as detailed by Bhaskar (1988). Mango pulp (3–4 g) was macerated with glass powder in a glass pestle and mortar in 12% alcoholic KOH (5 ml g1). Following maceration, samples were saponified in a water bath at 37 1 8C for 30 min. From saponified samples, carotenoids were extracted in petroleum ether by vigorous shaking of the contents with a vortex mixer (Heidolph, Reax Control, Germany) and allowed to separate in two distinct layers. The top coloured phase was collected in a conical flask. The process was repeated until top layer of petroleum ether become colourless. The coloured phase of petroleum ether extract was passed through a layer of anhydrous Na2SO4 placed on glass wool to remove all moisture. The absorbance of the supernatant solution was recorded with a UV/VIS spectrophotometer (model 6405, Genway Ltd., Felsted, Dunmow, Essex CM6 3 LB, England) at 450 nm. An extinction coefficient of pure bcarotene at 450 nm, E11%cm (2500 in petroleum ether) was used in calculations. The results were expressed as mg carotenoids/100 g pulp. Since carotenoids are light sensitive, all steps of the experiments were performed in subdued light, with a 25 W red globe (Phillips Ltd., Australia).
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2.4.1.5. Ascorbic acid. Ascorbic acid contents from the pulp of ripe fruit were estimated following standard methods (Jagota and Dani, 1982; AOAC, 1996). Mango pulp (4–5 g) was macerated with a glass pestle and mortar using glass powder while adding 6% metaphosphoric acid solution containing 0.18% of ethylene diamino tetra acetic acid disodium salt (EDTA). After grinding and blending, the contents were transferred in a 100-ml graduated cylinder and volume was noted. Contents were centrifuged at 3000 rpm for 15 min and suspension was filtered (Whatman No. 1 filter paper). The absorbance of the filtrate was recorded using a UV/VIS spectrophotometer (model 6405, Genway Ltd., Felsted, Dunmow, Essex CM6 3 LB, England) at 760 nm and compared against a standard curve. The ascorbic acid content was expressed as mg 100 g1 pulp. 2.5. Statistical analysis The experimental data were subjected to analysis of variance (ANOVA), using Genstat release 6.1 (Lawes Agricultural Trust, Rothamsted Experimental Station, UK). The effects of various treatments and their interactions were assessed within ANOVA. Least significant difference (Fisher’s protected LSD) was calculated, following significant F-test (P 0.05). Normal probabilities plot of the residuals of the analysis of variance and a plot of residuals against predicted values were used to ensure that the assumptions of the analysis were satisfied. 3. Results 3.1. Effects of exogenous application of polyamines on final fruit retention, yield and fruit size 3.1.1. Effects of different types of polyamines Exogenous application of PAs at FFS stage did not significantly improve fruit retention (Table 1). However, mean fruit retention was increased with PAs treatments (1.53 and 2.92%) compared to the control (0.79 and 2.3%), during 1999– 2000 (off-year) and 2000–2001 (on-year), respectively. The corresponding increases in fruit yield were 63 and 4%, respectively, compared to the control. The increased fruit retention was in the order of SPM (1 mM), PUT (0.1 mM) and SPD (0.01 mM). Fruit size was not significantly affected with PA application. 3.1.2. Effects of different time of spermine application Application of SPM at different phenological stages significantly affected fruit retention and fruit yield compared to the control (Table 2). However, differences among concentrations were not significant. Spermine spray at FB or at IFS stage resulted in significantly highest mean fruit retention, whereas, mean fruit yield was comparatively higher with application at 5–8 cm GP or at IFS stage compared to the control. Interaction between concentrations and phenological stages at which treatments were applied were significant only for final fruit retention. Spray application of SPM (0.01 mM) at
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Table 1 Effect of exogenous application of polyamines at final fruit set on retention, yield and fruit size of mango Treatments
Concentration (mM)
Fruit retention (%)
Yield (number of fruit/tree)
Fruit size (cm3)
1999
2000
1999
2000
1999
2000
Control
0
2.3 1.1
0.8 0.3
204.0 21.1
18.3 7.2
92.9 3.7
79.9 5.5
Spermine
1 0.1 0.01
3.7 0.8 2.7 0.8 2.3 0.5
2.3 0.2 1.5 0.2 1.8 0.9
200.3 26.7 205.7 13.4 202.7 13.5
41.7 14.7 24.7 9.7 20.3 8.1
88.8 2.1 87.2 0.9 88.8 2.3
76.5 2.8 85.1 8.7 67.4 9.8
Spermindine
1 0.1 0.01
2.8 0.6 2.5 0.9 2.5 0.8
1.3 0.4 1.0 0.2 1.2 0.2
192.0 14.4 227.3 9.4 228.0 39.5
28.3 0.9 13.3 3.7 24.0 15.2
90.5 1.3 91.0 0.5 89.4 1.2
88.7 7.9 86.9 4.3 87.0 11.8
Putrescine
1 0.1 0.01
2.8 0.3 3.8 0.9 2.5 0.9
1.1 0.1 1.4 0.3 2.3 0.2
223.3 8.4 221.3 17.3 205.0 13.2
32.7 10.6 42.0 16.1 41.0 7.5
91.1 1.0 88.4 3.1 96.4 1.1
78.7 2.3 85.3 6.1 80.0 6.4
2.3 4.1 3.3 1.3 1.8
0.4 0.2 0.5 0.3 0.6
1.1 1.2 2.1 0.5 0.9
1.9 1.8 2.7 1.5 1.7
0.8 0.1 1.8 0.8 0.4
Source of variance
F-Values
Treatments Control vs. others Chemical (ch) Concentration (C) Ch C
0.7 1.0 0.01 0.2 1.3
n = 3 (3 replications of 10 fruit each) S.E.M., F-values without asterisks are non-significant.
FB stage exhibited 1.5-fold increase in fruit retention compared to the control (Table 2). Generally, the lowest concentration of SPM (0.01 mM) was more effective in improving fruit retention and yield. SPM application at different times did not have significant effect on fruit size compared to the control. However, trees
sprayed at flower bud differentiation stage showed significantly increase in fruit size compared to those sprayed at full bloom stage (Table 2). This is due to the fact that trees sprayed at flower bud differentiation stage had few branches damaged due to frost, resulting in a decreased number of total fruit, with larger size.
Table 2 Effects of different time of spermine application on fruit retention, yield and fruit size of mango Treatments
Concentration (mM)
Fruit retention (%)
Yield (number of fruit/tree)
Fruit size (cm3)
Control
0
2.1 0.3
141.3 28.6
94.2 0.8
Flower bud differentiation (FBD)
1 0.1 0.01
3.0 0.4 3.7 1.2 2.3 0.5
126.7 18.6 101.0 4.4 98.7 14.4
96.6 2.7 99.2 1.2 97.8 4.5
Grown panicles (GP) (5–8 cm long)
1 0.1 0.01
3.3 0.0 1.7 0.3 1.5 0.4
235.3 40.3 209.3 24.3 244.0 27.1
94.0 1.9 98.5 1.4 95.3 1.6
Full bloom (FB)
1 0.1 0.01
2.7 0.8 3.5 0.7 5.0 0.4
219.3 27.5 233.0 46.7 196.0 16.1
96.7 2.2 94.1 0.5 94.9 1.6
Initial fruit set (IFS)
1 0.1 0.01
2.1 0.5 2.6 0.4 3.5 0.9
205.3 64.3 222.0 47.0 263.0 34.4
89.5 2.4 93.9 2.4 92.7 1.6
2.9* 2.6 9.5** 0.1 0.0 0.1 0.5
1.5 0.2 4.0 * 1.1 0.4 1.9 0.7
Source of variance
F-Values
Treatments Control vs. others Stage Concentration (C) Linear Quadratic Stage C
2.5* 1.7 3.5 * 0.3 0.6 0.0 2.9 *
n = 3 (3 replications of 10 fruit each) S.E.M., * significant,
**
highly significant, F-values without asterisks are non-significant.
A.U. Malik, Z. Singh / Scientia Horticulturae 110 (2006) 167–174
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Table 3a Effect of exogenous application of polyamines at final fruit set on quality characteristics of mango fruit Treatments
Concentration (mM)
Fruit firmness (N)
TSS (8Brix)
Acidity (malic acid, %)
T. sugar (%)
R. sugar (%)
N.R. sugar (%)
Total carotenoids (mg/100g)
Vitamin C (mg/100 g)
Control
0
23.6 2.3
17.8 0.5
0.2 0.0
15.9 1.7
4.3 0.1
11.6 1.6
2.1 0.2
25.2 2.0
Spermine
1 0.1 0.01
21.5 0.2 20.9 0.2 17.9 0.3
17.6 0.3 17.0 0.2 16.9 0.1
0.2 0.0 0.2 0.0 0.2 0.0
13.3 0.3 12.3 0.5 13.0 0.3
4.5 0.1 4.5 0.1 4.6 0.1
8.9 0.2 7.8 0.4 8.4 0.2
2.4 0.1 2.1 0.5 3.0 0.2
28.3 2.0 27.5 3.2 19.9 0.5
Spermindine
1 0.1 0.01
18.5 0.3 20.0 0.4 17.3 0.2
16.7 0.2 17.4 0.2 16.8 0.4
0.2 0.0 0.2 0.0 0.2 0.0
13.9 1.2 14.8 0.7 14.4 0.8
4.5 0.1 4.5 0.1 4.1 0.1
9.5 1.1 10.3 0.6 10.3 0.8
3.4 0.2 2.4 0.1 2.7 0.1
20.2 1.1 19.2 1.2 18.0 0.7
Putrescine
1 0.1 0.01
18.9 0.3 17.6 0.2 17.8 0.3
16.2 0.4 16.7 0.5 16.1 0.2
0.2 0.0 0.2 0.0 0.2 0.0
14.6 0.5 15.6 0.1 14.5 0.5
4.2 0.0 4.1 0.2 4.3 0.1
10.4 0.4 11.5 0.2 10.2 0.6
4.1 0.3 4.4 0.3 3.8 0.1
21.2 0.9 18.5 0.3 20.4 1.1
Source of variance
F-Values
Treatments Control vs. others Chemical (ch) Concentration (C) Linear Quadratic Ch C
7.9** 36.8** 6.3** 6.9** 11.0** 2.8 2.1
3.5 * 9.2 ** 6.9 ** 1.5 0.9 2.0 1.4
4.0 ** 0.1 14.6** 0.4 0.0 0.7 1.6
2.9* 0.2 7.7** 0.2 0.4 0.1 2.6
2.0 4.8* 5.3* 0.1 0.0 0.2 0.6
2.6* 5.4* 7.6** 0.1 0.0 0.2 0.7
11.4** 16.4** 34.1** 1.1 0.5 1.6 4.0 *
6.7 ** 5.8 * 15.5** 5.2 * 10.2** 0.1 3.2 *
n = 3 (3 replications of 10 fruit each) S.E.M., TSS, total soluble solids; T. sugar, total sugar; R. sugar, reducing sugar; N.R. sugar, non-reducing sugar; * significant; ** highly-significant; F-values without asterisks are non-significant.
3.2. Effects of exogenous application of polyamines at final fruit set stage on fruit skin colour and quality Application of PAs at fruit set significantly influenced various fruit quality characteristics of ripe fruit (Tables 3a and 3b). Fruit firmness was significantly higher in untreated fruit compared to those treated with PUT and SPD. Mean fruit acidity was significantly reduced by 11% with PUT treatment, and increased by 16.7% with SPM application at final fruit set stage compared to the control. TSS was generally reduced with PA treatments (5.3%); maximum reduction (8.4%) was observed with PUT compared to the control. Sugars were generally lower in PA treated fruit as compared to the control in the reduction order of PUT < SPD < SPM. However, only SPM treated fruit showed significantly lower sugars (total sugars 18.8%, non-reducing sugars 27.8%) compared with control. Total carotenoids in the pulp were significantly improved (49%) with PAs treatments compared to control and maximum increase was observed with PUT (95%) followed by SPD (33%). Ascorbic acid concentrations were significantly
reduced with SPD (24.2%) and PUT (20.6%) treatments compared to control. Whereas higher concentrations of SPM (0.1, 1 mM) tended to increase ascorbic acid (9%, 12.7%) compared with the control. Among the interactions (chemical concentrations) effects, only total carotenoids and ascorbic acid were significantly affected (Table 3a). PUT (0.1 mM) produced fruit with maximum carotenoid content; whereas SPM (1.0 mM) treated fruit had the highest ascorbic acid concentration compared with control. Exogenous application of different PAs at FFS stage significantly maintained lower L, a, b, ‘chroma’ values and higher ‘hue angle’ of ‘Kensington Pride’ fruit at the ripe stage (Table 4). SPD treatment resulted in minimum L, a, b, ‘chroma’ values and higher ‘hue angle’ of fruit. The interactions of PAs (chemical) concentrations were also significant for L, b, and ‘chroma’ (4a). Untreated fruit exhibited the maximum values for L, a, b, and ‘chroma’, whereas treatment with the lowest concentration of SPM (0.01 mM) resulted in the minimum values for these parameters.
Table 3b Effect of exogenous application of polyamines at final fruit set on quality characteristics mango fruit Treatments
Fruit firmness (N)
Total soluble solids (8Brix)
Acidity (malic acid, %)
Non-reducing sugars (%)
Reducing sugars (%)
Total sugars (%)
Control Spermine Spermidine Putrescine
23.6 20.1 18.6 18.1
17.8 17.2 17.0 16.3
0.2 0.2 0.2 0.2
11.6 8.4 10.0 10.7
4.3 4.5 4.4 4.2
15.9 12.9 14.4 15.0
A Ba Bb Bb
A Aa Ba Bb
A Aa Ab Bc
A Bb Aa Aa
A Bc Ab Ba
A Bb Aa Aa
Means sharing common letters, or without any letter are not significantly different (P 0.05). Capital letters to compare polyamines with control, small letter to compare among polyamines.
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Table 4 Effect of exogenous application of polyamines at final fruit set on L, a, b, chroma and hue angle of ripe mango fruit Treatments
Concentration (mM)
L
a
b
Chroma
Hue angle
Control
0
57.2 0.6
7.0 0.8
27.8 0.3
28.7 0.4
76.0 1.6
Spermine
1 0.1 0.01
56.8 0.5 55.7 0.3 53.0 0.7
4.1 0.8 4.0 0.3 2.1 1.1
27.0 0.6 26.3 0.4 24.1 0.6
27.2 0.7 26.7 0.5 24.2 0.7
81.5 1.5 81.4 0.5 85.2 2.5
Spermindine
1 0.1 0.01
55.1 0.6 53.7 1.0 56.0 0.8
3.0 0.2 2.3 0.8 4.4 0.8
25.4 0.4 24.8 0.4 26.3 0.3
25.6 0.4 24.9 0.4 26.7 0.5
83.2 0.3 84.8 1.8 80.6 1.6
Putrescine
1 0.1 0.01
55.7 1.4 54.6 0.5 56.0 0.2
4.8 1.1 5.2 0.6 4.5 0.3
26.2 0.7 25.6 0.4 26.4 0.2
26.6 0.9 26.2 0.5 26.8 0.2
79.8 2.2 78.6 1.2 80.3 0.5
3.6 * 15.7** 3.9 * 0.1 0.2 0.0 2.1
5.7 ** 19.1** 1.2 1.7 2.5 0.8 6.7 **
5.4 ** 21.2** 1.7 1.1 1.8 0.4 5.4 **
3.2* 12.1** 4.3* 0.1 0.2 0.0 2.0
Source of variance
F-Values
Treatment Control vs. others Chemical (ch) Concentration (C) Linear Quadratic Ch C
3.6** 8.3* 0.4 2.6 3.0 2.3 4.6**
n = 3 (3 replications of 10 fruit each) S.E.M., * significant,
**
highly-significant, F-values without asterisks are non-significant.
4. Discussion 4.1. Effects of exogenous application of polyamines on final fruit retention, yield and fruit size PA applications have generally improved fruit retention and yield in mango depending upon the type and concentration of PAs and phenological stage of application. The increase in fruit retention with exogenous application of PAs may be ascribed to the increased levels of endogenous PAs in the fruitlets and pedicels, which were less prone to abscise, especially during initial 4–6 weeks of heavy fruitlet abscission. Our recent studies on cv. Kensington Pride and Glen demonstrated the association of initial fruitlet abscission with reduced levels of endogenous PAs (Malik and Singh, 2003) and increased ethylene biosynthesis (Malik et al., 2003) in mango fruitlets and their pedicels. It may also be argued that the exogenous application of PAs improved fruit retention, possibly by inhibiting endogenous ethylene biosynthesis, which is the known trigger in abscission (Brown, 1997). Different PAs did not have significant effect on fruit retention when sprayed at FFS stage (Table 1); however, SPM was comparatively more effective compared to control. Recently, we reported that SPM was the dominant PA in the intact fruitlet and their pedicels in ‘Kensington Pride’ mango at pinhead, pea and marble stages, and about-to-abscise fruitlets and their pedicels had only 10 and 19% of the mean SPM (Malik and Singh, 2003). Our experimental results suggest the optimum concentration of SPM is 0.01 mM. Highest fruit retention in litchi (Mitra and Sanyal, 1990) and apple cv. Ruby Spur (Costa and Bagni, 1983) has been achieved with a lower concentration (0.01 mM) of PUT. PA spray at FFS stage were not effective in increasing final fruit retention compared to control (Table 1), whereas during the
same year, SPM applied prior to FFS stage (FBD, GP, FB or IFS) significantly improved fruit retention (Table 2). The increased effectiveness of SPM at earlier stages (before FFS) may be due to the improved floral organ development, pollination, fertilization, and subsequent embryo and initial fruit development. Previously PUT application in olives was also not effective in reducing fruit abscission when applied at fruit set stage, however, when sprayed before anthesis or at FB it increased fruit yield (Rugini and Mencuccini, 1985). Earlier application of PUT at pre-anthesis stage in ‘Comice pear’ delayed the senescence of visible flower parts and extended the ovule longevity (Crisosto et al., 1986). It may be suggested that beside antiethylene properties, the growth promoting characteristics of PAs may have helped to improve an overall reproductive process, fruit set and embryo development, resulting in lower fruitlet abscission. Previously, when flower clusters of apple were sprayed with PAs, pistil longevity was prolonged and fruit set was improved (Wang et al., 1996). Our experimental results support the earlier report of Singh and Singh (1995) that time of PA application significantly affected the fruit set and retention in ‘Dusehri’ and ‘Langra’ mango and spray of SPM prior to anthesis, and PUT at FB were found more effective in increasing the final fruit retention, respectively. The improvement in fruit yield was the result of increased fruit retention in PA-treated trees especially with lower concentrations of SPM (0.01 mM) (Table 2). Likewise, lower concentrations (0.01, 0.1 mM) of PAs have also been reported to increase fruit yield in apple (Costa and Bagni, 1983; Costa et al., 1986) and litchi (Mitra and Sanyal, 1990). Fruit size was not significantly affected with PA sprays. The increase in fruit size with SPM application at FBD stage (Table 2) may be associated with reduced fruit yield due to frost damage, and not due to the effect of SPM. This is also supported by the fact that the treatment showing maximum number of
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fruit per tree (IFS) also had the minimum fruit size. A reduction in fruit size has been reported in ‘Hi Early’ apple as result of PUT spray, possibly at the expense of higher yield (Costa et al., 1986). 4.2. Effects of exogenous application of polyamines at final fruit set stage on fruit quality The application of PAs has varying effects on different parameters of ripe fruit. PAs generally reduced fruit firmness and sugar content, while increasing carotenoids in pulp compared to the control. PUT-treated fruit exhibited highest carotenoids, and lower ascorbic acid and TSS compared to the control. Whereas SPM treatment increased ascorbic acid content at higher concentrations and also showed higher fruit acidity. The lower sugar content in PAs treated fruit compared to control may be due to the slower conversion of starch to sugars. Generally, ripening of mango fruit has been marked by an appreciable increase in reducing and non-reducing sugars and a decrease in starch content (Lima et al., 2001). Since the predominant sugar in mango has been sucrose (Selvaraj et al., 1989), PAs may have suppressed the activities of certain enzymes such as sucrosephosphate synthase (SPS) involved in sucrose metabolism. Effects of PAs on the activities of SPS are yet to be investigated. Similarly, a reduction in sugar and TSS as a result of PUT applications at FB or 20% open flowers have also been reported in apple (Costa et al., 1986). A lower concentration (0.01 mM) of PUT applied before anthesis to litchi increased acidity and reduced total sugars and sugar acid ratio (Mitra and Sanyal, 1990). The reduction in fruit firmness with exogenous application of PAs at FFS stage warrants further investigations on their effects on the activation of enzymes involved in fruit softening. Earlier exogenous PA application in apple produced fruit with lower flesh firmness compared to the control (Costa and Bagni, 1983; Costa et al., 1986). An increase in total carotenoids contents of PA treated fruit, and the reduced levels of ascorbic acid in SPD and PUT treatment are important and yet to be investigated. Previously, transgenic tomato plants with enhanced expression of the yeast S-adenosylmethionine decarboxylase gene (ySAMdc; Spe2) had an increased conversion of PUT resulting in ripening specific accumulation of SPD and SPM leading to increased lycopene content and enhanced fruit juice quality (Mehta et al., 2002). PUT application at pre-anthesis stage has also been reported to increase anthocyanin content of litchi fruit (Mitra and Sanyal, 1990). Increased ascorbic acid content in fruit treated with a higher concentration of SPM may be ascribed to the suppression of ascorbate oxidase activities as a result of increased levels of endogenous SPM in mango fruit pulp. The effects of PAs on activities of ascorbate oxidase in mango are yet to be investigated. Higher endogenous concentration of PUT in bell pepper compared to tomato fruit has been associated with higher ascorbic acid (Yahia et al., 2001). PA treatments appeared to retard fruit skin colour development, as evident from the significantly lower L, a, b values and higher ‘hue angle’ in PA treated fruit compared with control fruit. The colour parameter b (yellowness) has been described as to best reflect the colour changes in skin tissues
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during fruit ripening (Martinez-Madrid et al., 1999). PAs may inhibit chlorophyll degradation in skin tissues, by inhibition of peroxidase activity (Ma-Jun et al., 1996). The effects of polyamines on colour retardation were in the order: SPM4+ < SPD3+ < PUT2+, following the order of their available number of cations, which has been argued as the reason for their difference in effectiveness (Valero et al., 2002). Earlier, the retardation of chlorophyll loss in muskmelon with exogenous application of PAs has been attributed to reduced hydrolytic activities acting on chloroplast thylakoid membranes (Lester, 2000). In conclusion, type and concentration of PA, and phenological stage of application influence the effects of exogenously applied PAs on fruit retention, yield, fruit skin colour and quality of mango. The application of SPM (0.01 mM) at FB stage was the most effective in increasing final fruit retention, whereas applications at 5–8 cm GP or at IFS stage had comparatively higher fruit yield. PUT application at FFS significantly improved fruit quality by increasing total carotenoids, while reducing the acid content of ripe fruit. Acknowledgements We thank Mr. M.A. Chatha for help in data collection, Dr. A. Bhaskar for technical advice on carotenoids and Vitamin C analysis, Mr. Satvinda S. Dhaliwal and Dr. Inayat, Biostatisticians for help in statistical analysis. A.U. Malik also acknowledges the financial assistance of Curtin University of Technology, Perth, Western Australia and Australian International Development Programme, for awarding International Postgraduate Research Scholarship and Australian International Development scholarship, respectively, and University of Agriculture, Faisalabad, Pakistan for granting study leave during this period. References Abou Rawash, M., Abou El Nasr, N., El Masry, H., Ebeed, S., 1998. Effect of spraying some chemical substances on flowering, fruit set, fruit drop, yield and fruit quality of Taimour [Egyptian] mango trees. Egypt. J. Hortic. 25, 83–99. AOAC, 1996. AOAC Methods. Association of Official Analytical Chemists, Washington, DC. Apelbaum, A., Burgoon, A.C., Andrew, J.D., Liberman, M., Ben-Arie, R., Matto, A.K., 1981. Polyamines inhibit biosynthesis of ethylene in higher plant tissue and fruit protoplast. Plant Physiol. 68, 453–456. Bains, K.S., Bajwa, G.S., Singh, Z., 1999. Effects of indole-3-acetic acid, gibberellic acid, and abscisic acid on abscission of mango fruitlets. Trop. Agric. 76, 88–92. Bhaskar, A.K., 1988. Studies on carotenoids in some plant foods as a source of vitamin A. Ph.D. Thesis. Osmania University, Hyderabad, India. Brown, K.M., 1997. Ethylene and abscission. Physiol. Plant 100, 567–576. Chadha, K.L., 1993. Fruit drop in mango. In: Chadha, K.L., Pareek, O.P. (Eds.), Advances in Horticulture, vol. 3. Malhotra Publishing House, New Delhi, pp. 1131–1166. Chadha, K.L., Singh, K.K., 1964. Fruit drop in mango. I. Fruit set and its retention and factors affecting it. Ind. J. Hortic. 20, 172–185. Costa, G., Bagni, N., 1983. Effect of polyamines on fruit set of apple. Hortscience 18, 59–61. Costa, G., Biasi, R., Bagni, N., 1986. Effect of putrescine on fruiting performance on apple (cv. Hi Early). Acta Hortic. 149, 189–195.
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