Hormonal changes in response to paclobutrazol induced early flowering in mango cv. Totapuri

Scientia Horticulturae 150 (2013) 414–418

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Hormonal changes in response to paclobutrazol induced early flowering in mango cv. Totapuri夽 Kaushal K. Upreti a,∗ , Y.T.N. Reddy b , S.R. Shivu Prasad b , G.V. Bindu a , H.L. Jayaram a , Shailendra Rajan c a b c

Division of Plant Physiology and Biochemistry, Indian Institute of Horticultural Research, Hessaraghatta Lake Post Office, Bangalore 560 089, Karnataka, India Division of Fruit Crops, Indian Institute of Horticultural Research, Hessaraghatta Lake Post Office, Bangalore 560 089, Karnataka, India Central Institute of Sub-Tropical Horticulture, Rehmankhera, P.O. Kakori, Lucknow 227 107, Uttar Pradesh, India

a r t i c l e

i n f o

Article history: Received 12 October 2012 Accepted 27 November 2012 Keywords: Abscisic acid Cytokinins Mango Gibberellins Paclobutrazol

a b s t r a c t Paclobutrazol has been found predominantly effective in the induction of early flowering and thus finding scope for off-season production in mango. The precise physiological mechanism regulating early floral induction is meagerly understood. The objective of the study was to examine the hormonal relationships associated with floral induction in mango following paclobutrazol treatment. The paclobutrazol applied as soil drench, @ 3.0 ml/m canopy diameter during the 3rd week of August advanced fruit harvest period by 22 days as compared to untreated trees by promoting early flowering. The C:N ratio in shoots, leaf water potential ( w ) and ABA content in the paclobutrazol untreated and treated trees increased progressively as shoots approached bud break stage. There was increase in C:N ratio and leaf w , by the paclobutrazol with drastic increase at the bud break. C:N ratio in shoot was positively related to ABA content in buds. Cytokinins – zeatin (Z), zeatin riboside (ZR) and dihydrozeatin riboside (DHZR) in buds increased consistently from 30 days before bud break till floral bud initiation. In paclobutrazol treated trees, increase in ZR and DHZR contents in buds were positively related to leaf w . GA4 , GA3 , GA7 and GA1 were the prominent GAs in the leaves and buds. In buds, these gibberellins followed trends opposite to that of cytokinins. The paclobutrazol treatment declined GA4 , GA3 , GA7 and GA1 contents both in leaves and buds; with buds being more receptive to paclobutrazol treatment. These results implicated that paclobutrazol besides affecting gibberellins also increases ABA and cytokinin contents concomitant with C:N ratio and leaf w in mango buds to elicit flowering responses. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Mango is a commercially important fruit crop of India with a production of 12.54 million tonnes from 2.02 million hectares of cultivation area. It exhibits wide variations in flowering and fruiting habits due to varietal differences and diversity in agro-climatic conditions. However, availability of most of the commercial important mango varieties in markets is restricted to April–June due to short crop period and strong dependency of flowering on environment. The short period during good yielding years considerably impacts mango profitability due to price drop. One strategy to deal such problems that showed some success in Philippines and Thailand is

Abbreviations: GA, gibberellins; w , leaf water potential; PBZ, paclobutrazol. 夽 IIHR Contribution No. 72-2012. ∗ Corresponding author. Tel.: +91 080 28466420-23; fax: +91 8028466291. E-mail addresses: [email protected], [email protected] (K.K. Upreti), [email protected] (Y.T.N. Reddy), [email protected] (S.R.S. Prasad), [email protected] (G.V. Bindu), [email protected] (H.L. Jayaram), [email protected] (S. Rajan). 0304-4238/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2012.11.030

chemical manipulation of reproductive development for achieving off-season mango production. Mango induces flowering under tropical conditions during the month of October–December due to its strong dependency on cool winter temperature and the age of the flowering shoots (Davenport, 2000). The physiological mechanism underlying mango flowering suggested occurrence of constantly synthesizing florigenic promoter in leaves that moves to buds via phloem along with sugars, during cold floral inductive conditions to facilitate floral induction in growing shoots. Kulkarni (1988) suggested that the florigenic promoter of mango is graft transmissible across the cultivars. Thus success in chemical manipulations of flowering lies in altering the effects of environmental conditions, particularly of low temperature required for flowering inductions. Plant growth retardants induced manipulation in physiological activity has been considered important determinant of productivity enhancement in a number of fruit crops. Among the chemicals suggested, paclobutrazol is considered as one of important plant growth retardant which restricts vegetative growth and induce flowering in many fruit species including mango (Yadav et al., 2005). Many investigators have reported beneficial effects of

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paclobutrazol in induction flowering in different mango cultivars (Yeshitela et al., 2004; Yadava and Singh, 1998; Tongumpai et al., 1991; Kulkarni, 1988; Blaikie et al., 2004; Winston, 1992; Murti et al., 2001; Nafees et al., 2010). Inhibition in gibberellin activity following a check in the conversion of ent-kaurene to ent-kauronoic acid in the gibberellin biosynthetic pathway has been attributed as the possible primary mechanism by which paclobutrazol restricts the vegetative growth and promotes flowering. Considering that plant growth and development are not only regulated by the cellular levels of one particular phytohormone, and mutual interactions among phytohormones are well documented, the floral promotory responses of paclobutrazol could also be dependent by its effects on hormones other than gibberellins. There are enough evidences to show that the isoprenoid pathway associated with gibberellin biosynthesis also regulates partially the biosynthesis of other vital phytohormones such as abscisic acid (ABA) and cytokinins (Murti and Upreti, 2000). In the present investigation, we studied the effects of paclobutrazol on C:N ratio, leaf water potential (w ), ABA, cytokinins and gibberellins at different durations of shoot growth during inductive periods with an objective to elucidate their role on mango flowering.

2. Materials and methods 2.1. Plant material and treatments The studies were conducted at the experimental farm of Indian Institute of Horticultural Research, Hessaraghatta on 17 years old uniformly grafts of regular bearing cv. Totapuri planted at 10 m spacing during August 2010–June, 2011. Soil of the experimental site is sandy loam and average canopy diameter of the trees was 8.0 m. Recommended dosage of paclobutrazol was applied once as soil drench at a concentration 1.25 g a.i. per metre of canopy diameter by spreading the solution in a circular band of 25 cm width around the tree during 3rd week of August. Both under paclobutrazol and control, 4 trees were allotted. During the experimental period, maximum and minimum temperatures ranged between 27.6–31.2 ◦ C and 19.8–21.0 ◦ C, respectively and relative humidity was in the range of 56.7–62.8% at 1400 h and 75.7–81.1% at 0800 h. 2.2. Sampling and data collection About 100 terminal shoots measuring average length of 20 cm were tagged in four directions of the experimental trees. Observations on the response of paclobutrazol on flower induction was monitored at 15 days interval after 1 month of paclobutrazol application and number of floral buds produced were recorded to calculate average days required for 50% flowering. Observations were also recorded on days from flowering to harvest, fruit number/plant, fruit yield/plant, average fruit weight, TSS and acidity as per standard procedures. The flower induction was expressed as per cent of trees that flowered. Periodical sampling at weekly interval was made for shoots from 2nd week of September till visual indications of bud burst were evident. The analysis for C:N ratio in shoots, water potential in leaves ( w ) and phytohormones in leaves and terminal buds in the paclobutrazol untreated and treated trees were made at 30 and 15 days before bud burst and at floral bud induction stages. 2.3. Determination of C:N ratio For C:N ratio, shoots dried to constant mass at 80 ◦ C in an hot air oven were powdered in grinding mill. The contents of total C and N were determined employing CHNS Analyser (Model – Cube,

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Elementar, Germany), and C:N ratio was calculated from the respective values. 2.4. Leaf water potential Leaf  w was obtained using pressure bomb (Arimad-3000, MRC Ltd., Israel) and expressed as – MPa. 2.5. ABA and cytokinin analyses The bud and leaf samples (2 g fresh weight) were macerated in chilled 80% methanol and filtered. The filtrate was evaporated in vacuo at 35 ◦ C, the residue dissolved in water and pH was adjusted to 3.0. The aqueous acidic extract was partitioned twice against equal volumes of chilled diethyl ether. The ether phase was separated and dried over anhydrous sodium sulphate. The extract was kept overnight at 4 ◦ C, filtered and after evaporating ether, the residue was dissolved in 20 mM Tris buffer, pH 7.8 for the ABA analysis. For the cytokinin analysis, the pH of aqueous extract left after ether partitioning was adjusted to pH 8.0 and partitioned thrice with equal volumes of water-saturated n-butanol. The butanol phase was separated, evaporated in vacuo at 35 ◦ C and the residue was dissolved in Tris buffer (20 mM, pH 7.8) for cytokinin analysis. The ABA (Weiler, 1982) and the cytokinins – ZR and DHZR (Barthe and Stewart, 1985) contents were determined by ELISA using ELISA reader (Multiskan MS 352, Labsystem, Finland), employing laboratory raised polyclonal antibodies. 2.6. Gibberellins analysis Samples for GC–MS analysis using SIM were prepared according to Kaufman et al. (1976). Samples of apical buds (2 g) and leaves (5 g) were separately grounded in liquid nitrogen and extracted thrice with chilled 80% aqueous methanol (8 ml/g). Pooled filtrates were dried in vacuo, and dissolved in 10 ml of water and pH adjusted to 3.0. The aqueous acidic extract was partitioned against ethyl acetate three times and the ethyl acetate phase after separation was evaporated, redissolved in 0.1 M phosphate buffer, pH 8.0 and stirred with insoluble polyvinylpyrrolidone (2 g). After filtration, the pH was lowered to 3.0 and acid extract was partitioned thrice with ethyl acetate. After evaporating ethyl acetate, the gibberellin samples were purified on charcoal–celite (1:2 w/w, 5 g charcoal) adsorption column and silicic acid (100 mesh) partition column (Powell and Tautvydas, 1967). Gibberellins were eluted from charcoal–celite column employing 80% acetone and gradiently eluted using 30–65% ethyl acetate in n-hexane from silicic column. The purified gibberellins were passed through 0.45 um Millipore filter (Fluoropore). For GC–MS, the gibberellins samples were first methylated and further derivatized to trimethylsilyl (TMS) ether with 50 ␮l of BSTFA [bis-(trimethylsilyl) trifluoracetamide] + 1% TMCS (trimethylchlorosilane) at 60 ◦ C for 1 h. The derivatized samples were analysed on GC–MS system (Varian, USA) equipped with 3800 series gas chromatograph and 4000 series ion trap mass spectrometer. A VH-5 column (100–200 mesh, 30 m × 0.2 mm id) programmed at 100 ◦ C for 7 min followed by linear increase @ 10 ◦ C up to 200 ◦ C with 3 min hold and @ 5 ◦ C with 19 min hold (total run time of 55 min) was employed to resolve silylated gibberellins. The split ratio was 1:10. Helium gas inlet was pneumatic pressure controlled at a constant flow of 1 ml/min and injector, transfer line, source and trap temperatures were 285, 270, 210 and 200 ◦ C, respectively. The data was obtained in the full scan mode. Identification was confirmed on the basis of retention time and co-occurrence of additional ions employing NIST-2007 library. The quantification was done on the basis of peak area and the standard gibberellins (Sigma–Aldrich, USA).

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Table 1 Effects of paclobutrazol application on flowering and fruiting in mango cv. Totapuri (data represents mean ± SE, n = 4). Parameters

Untreated

Fruit no/plant Fruit yield/plant (kg/plant) TSS (◦ Brix) Acidity (%) Avg fruit weight (g) Days for 50% flowering Days from flowering to harvest

204.3 47.4 15.6 0.235 250.1 158.9 154.0

± ± ± ± ± ± ±

Paclobutrazol treated

15.2 6.58 2.33 0.04 13.68 21.44 10.23

257.8 57.5 15.5 0.235 240.7 139.6 132.1

± ± ± ± ± ± ±

17.09 8.09 1.86 0.06 19.24 16.25 17.74

Fig. 2. Effects of paclobutrazol on leaf water potential in mango cv. Totapuri (data represent mean ± SE).

Fig. 1. Effects of paclobutrazol on shoot C:N ratio in mango cv. Totapuri (data represent mean ± SE).

3. Results and discussion Paclobutrazol treatment induced profuse early flowering in Totapuri trees. As a result of paclobutrazol treatment, days for 50% flowering were advanced by 19.3 days, the days from flowering to fruiting reduced by 22 days (Table 1). The increased flowering in mango by paclobutrazol is reported in mango cvs Alphonso (Burondkar et al., 2000), Khiew Sawoey (Tongumpai et al., 1996), Carabao (Protacio et al., 2000), Dashehari (Karki and Dhakal, 2003) and Kensington Pride (Winston, 1992). Early flowering is speculated as the consequences of changes induced by paclobutrazol on overall physiology of mango trees viz., improved nutrient uptake, rapid and enhanced photosynthate re-allocation, altered hormonal balance and modifications in plant water balance. In addition to effects on flowering, paclobutrazol treatment produced 26.2% more fruit number which resulted in 21.3% increase in fruit yield. Fruit weight and fruit quality parameters such as TSS and acidity were unaffected by paclobutrazol treatment (Table 1). Paclobutrazol application resulted increase in shoot C:N ratio progressively from 29.5 to 52.4 in the untreated trees to 51.2–67.6 from 30 days before flowering to bud break. Both in paclobutrazol untreated and treated trees, there was high ratio at bud break stage (Fig. 1). C:N is considered as an important factor in the regulation of flowering in fruit crops. A high ratio has been postulated

promotory to flowering whereas opposite beneficial for vegetative growth (Corbesier et al., 2002). The increase in C:N ratio is ascribed as the consequence of increased carbohydrate availability as suggested by Ito et al. (2004), which is necessary for the induction of flowering. Thus maintenance of high C:N ratio may be one of important characteristic associated with the paclobutrazol for the floral bud induction in mango. Paclobutrazol induced enhancement in C:N ratio has been reported in pommelo (Phadung et al., 2011), and mango (Subhadrabandhu et al., 1997). Leaf water potential ( w ) of the untreated trees ranging between 0.753 and 0.474 (−) MPa was increased by 14.1–18.7% following paclobutrazol application at stages coinciding 30 and 15 days before bud break and at bud break, and the increase was pronounced at the stage preceding bud break (15 days before) (Fig. 2). In both paclobutrazol untreated and treated trees, the w values in general, were high at bud break stage. w is illustrative of the water status of plants. An increase in w as evident in the present study depicted inductance of water stress tolerance, which could be vital for the formation of floral buds in mango. The paclobutrazol induced increase in w is speculated as the result of increased root hydraulic conductivity or reduced transpiration. However, it is unclear whether increase in w was a result of either of or both. Abdul Jaleel et al. (2007) reported decline in transpiration rate by paclobutrazol. The w values in paclobutrazol treated trees showed positive relationship with C:N ratio (R2 = 0.784, p < 0.05) In the paclobutrazol untreated trees, the ABA content was 85.7–106.3 ng/g and 52.3–65.5 ng/g in the buds and leaves, respectively (Table 2). Following paclobutrazol application, the ABA content increased by 54.2–91.9% and 64.1–98.3% in buds and leaves, respectively and increase was drastic at the bud break stage. With respect to stages, the ABA content was recorded high in buds and leaves at 15 days before flowering in the paclobutrazol untreated trees and at bud burst in the paclobutrazol treated trees. The role of high ABA content in the induction of floral bud formation has been reported by Chacko (1986) in mango and by Hou et al. (1987) in litchi. Paclobutrazol induced increases in ABA is in agreement with the earlier reports of induction in ABA biosynthesis as a result

Table 2 Effects of paclobutrazol (PBZ) on abscisic acid (ABA) and cytokinin contents in buds and leaves of cv. Totapuri (data represent mean ± SE; n = 4). Phytohormones

ABA (ng/g) −PBZ +PBZ Zeatin (pg/g) −PBZ +PBZ ZR (pg/g) −PBZ +PBZ DHZR (pg/g) −PBZ +PBZ

30 days before bud break

15 days before bud break

At bud break

Buds

Buds

Leaves

Buds

Leaves

Leaves

85.68 ± 6.53 135.41 ± 12.25

52.33 ± 6.31 89.35 ± 10.25

106.28 ± 8.85 163.88 ± 16.25

74.62 ± 8.82 122.37 ± 13.35

97.27 ± 7.36 186.67 ± 23.33

65.52 ± 7.07 129.88 ± 8.08

465.21 ± 23.22 593.37 ± 35.11

218.55 ± 17.41 233.63 ± 26.64

557.36 ± 42.21 714.85 ± 55.65

196.36 ± 22.37 208.08 ± 14.22

607.44 ± 71.21 836.95 ± 56.64

125.4 ± 13.39 117.4 ± 12.22

684.71 ± 30.14 789.96 ± 22.27

369.94 ± 14.42 397.77 ± 24.28

754.11 ± 45.05 907.09 ± 61.24

303.96 ± 27.72 339.55 ± 35.05

824.22 ± 62.22 1109.94 ± 85.65

257.7 ± 26.52 229.8 ± 20.09

221.48 ± 38.74 268.94 ± 12.24

108.87 ± 11.62 95.58 ± 6.58

369.87 ± 19.82 515.56 ± 33.63

196.96 ± 26.11 145.83 ± 17.07

391.08 ± 22.08 576.64 ± 45.56

802.4 ± 47.71 923.3 ± 63.39

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Table 3 Effects of paclobutrazol (PBZ) on gibberellin contents in buds and leaves of cv. Totapuri (data represent mean ± SE; n = 4). Gibberellins

30 days before flowering Buds

GA1 (ng/g) −PBZ +PBZ GA3 (ng/g) −PBZ +PBZ GA4 (ng/g) −PBZ +PBZ GA5 (ng/g) −PBZ +PBZ GA7 (ng/g) −PBZ +PBZ GA9 (ng/g) −PBZ +PBZ GA13 (ng/g) −PBZ +PBZ GA25 (ng/g) −PBZ +PBZ

15 days before flowering Leaves

Buds

At flowering Leaves

Buds

Leaves

51.26 ± 3.21 38.51 ± 2.08

23.36 ± 3.18 17.17 ± 2.19

42.32 ± 5.16 23.35 ± 2.44

28.23 ± 2.09 12.21 ± 1.35

31.25 ± 2.66 17.35 ± 1.84

19.24 ± 2.11 11.26 ± 1.63

395.55 ± 21.22 306.63 ± 29.81

224.08 ± 19.03 182.24 ± 14.89

301.41 ± 25.08 168.24 ± 11.14

168.68 ± 17.76 152.25 ± 14.42

231.41 ± 15.37 114.62 ± 10.85

136.63 ± 12.08 132.33 ± 14.07

625.41 ± 19.95 511.32 ± 31.26

369.63 ± 23.08 311.22 ± 18.08

532.69 ± 31.24 387.74 ± 16.57

304.41 ± 21.07 223.37 ± 18.91

426.62 ± 32.14 286.66 ± 21.14

256.66 ± 8.07 206.61 ± 11.15

ND 3.04 ± 0.05

7.47 ± 1.04 ND

4.22 ± 0.08 2.36 ± 0.03

12.31 ± 0.93 9.63 ± 1.02

6.35 ± 4.17 4.61 ± 3.55

9.06 ± 1.41 6.08 ± 0.08

204.07 ± 15.07 162.25 ± 12.32

85.08 ± 7.07 71.22 ± 6.36

165.74 ± 13.38 122.24 ± 9.92

64.07 ± 5.51 51.33 ± 4.38

133.64 ± 9.09 89.07 ± 7.72

52.09 ± 7.94 40.14 ± 3.39

25.63 ± 3.69 21.24 ± 2.55

10.24 ± 1.34 8.56 ± 1.62

19.14 ± 2.33 15.28 ± 1.62

8.08 ± 1.02 7.14 ± 0.04

16.01 ± 1.38 13.35 ± 1.04

6.36 ± 0.07 6.07 ± 0.04

3.041 ± 1.91 3.214 ± 1.08

2.147 ± 3.07 1.954 ± 1.54

2.212 ± 0.07 1.435 ± 0.08

1.524 ± 1.69 1.335 ± 1.49

2.011 ± 0.09 1.124 ± 0.05

0.953 ± 1.12 ND

23.34 ± 2.85 19.22 ± 2.05

12.32 ± 1.41 10.11 ± 0.08

16.05 ± 1.22 12.32 ± 1.06

10.32 ± 1.27 8.07 ± 0.09

18.62 ± 1.25 9.36 ± 1.32

9.68 ± 1.37 7.17 ± 0.08

of modifications in the isoprenoid pathway which is partially common in ABA and gibberellins biosyntheses (Murti et al., 2001; Abdel Rahim et al., 2011). ABA increase might also be the result of reduced ABA catabolism to phaesic acid by triazole compounds as reported by Hauser et al. (1990). The high ABA levels are expected to induce bud dormancy, which consequently help in floral bud formation as flowering in mango is found to occur on buds at rest. The positive relationship between ABA and C:N ratio (R2 = 0.783, p ≤ 0.05) depicted possibility of dependence of carbohydrate mobilization by ABA. However, this aspect needs further detailed investigation. The similarity in the pattern of ABA and w is indicative that increased ABA may of help in conserving water possibly by regulating stomatal conductance which could be of relevance to floral bud differentiation. Zeatin riboside (ZR) was prominent cytokinin in the buds of paclobutrazol untreated trees. In such trees, the component cytokinins, zeatin (Z), ZR and dihydrozeatin riboside (DHZR) and total cytokinin contents increased gradually in the buds from 30 days before flowering till bud break (Table 2). Leaf cytokinins were marginally influenced by paclobutrazol application. Both in the paclobutrazol untreated and treated trees, the trends with respect to different stages were similar, with cytokinin contents attaining peak at bud break stage. The increases in cytokinins in buds as buds approached bud break stage and induction in cytokinin contents by paclobutrazol give strong evidence of a role of cytokinins in floral induction in mango. Chen (1991) in lychee and Abdel Rahim et al. (2008) and Chen (1987) in mango reported increase in cytokinin at floral bud formation. The increase in cytokinins by paclobutrazol could be the either due to stimulated synthesis of cytokinins that are transported to shoots or arresting of cytokinin degradation (Grossman, 1992) and is suggested to act positively in floral bud induction by regulating cell division process, as cytokinins are well accepted stimulators of cell division. Further support for cytokinins in floral bud formation is well supported by Chen (1985) through external application of benzyl adenine resulting accelerated floral bud formation in mango. The increase in ZR (R2 = 0.0.824, p ≤ 0.05) and DHZR (R2 = 0.733, p ≤ 0.05) exhibited positive relationship with w revealing their involvement in maintenance of plant water balance.

Among the component gibberellins – GA4 followed by GA3 , GA7 and GA1 were the major gibberellins identified in the buds and leaves of paclobutrazol untreated trees, with buds recording high levels of these gibberellins. Other minor gibberellins identified were GA5 , GA9 , GA13 and GA25 . Both in buds and leaves of paclobutrazol untreated trees, the gibberellin content showed declining trends from 30 days before flowering till bud break, and buds experienced greater decline than the leaves (Table 3). Following paclobutrazol application, different gibberellins declined and the concentration trends witnessed with respect to stages were similar as observed in the untreated trees. The magnitude of decline in major identified gibberellins by paclobutrazol was dependent on stages. While paclobutrazol induced decline in GA1 was more in the buds and leaves at 15 days before bud break, GA3 , GA4 and GA7 registered greater decline at bud break stage. The paclobutrazol induced decline in gibberellins is substantiated by the earlier reports that paclobutrazol inhibits gibberellin biosynthesis (Fletcher and Gilley, 2000). Reduction in gibberellins content favouring floral bud formation has been reported previously by Abdel Rahim et al. (2008) and Chen (1987) in mango, Chen (1990) in lychee and Koshita et al. (1999) in citrus, and it may related to reduction in internodal length or accumulation of carbohydrates favoured by declining gibberellin contents. Kulkarni (1988) and Protacio et al. (2000) reported reduction in internodal length by paclobutrazol as the result of reduction in gibberellins. Decline in the gibberellin is an important contributor to floral bud initiation, and this is well substantiated by the studies of Tomer (1984) and Oosthuyse (1996) that gibberellic acid application reduced markedly the floral bud initiation and also prevented carbohydrate accumulation (Jacobsen and Chandler, 1987). Further, not all gibberellins have similar role to play in the induction of floral buds. While decline in GA1 may be important in preparing the buds for floral induction and those of GA3 , GA4 and GA7 might act in floral bud initiation. It was found that total gibberellins in buds were negatively correlated with w suggesting a role of gibberellins in maintenance of plant water balance. Similar observations in mango have been reported by Pongsomboon et al. (1997). It is worthy to mention that the side chain in the cytokinin molecule is obtained from isoprenoid pathway leading to gibberellin biosynthesis, thus

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paclobutrazol while blocking gibberellin biosynthesis would channelize the metabolic intermediates to cytokinins production as stated above. The similarity in the trends of C:N, ABA, cytokinins and gibberellins in the buds of paclobutrazol untreated and treated trees with respect to stages studied revealed a role of these parameters in the formation of floral buds in mango. It is also found that increase in C:N ratio, w , ABA and cytokinins concomitant with decline in gibberellins in buds as a result of paclobutrazol are important attributes contributing to floral bud production in mango. 4. Conclusion The results presented showed that application of paclobutrazol as soil drench @ 3.0 ml/m canopy diameter during the 3rd week of August induced early flowering and advanced fruit harvest period in mango cv. Totapuri, with no distinct changes in fruit quality parameters. The induction in early flowering was found as the result of increases in shoot C:N ratio and leaf water potential due to increase in ABA and cytokinins and decline in gibberellins, GA4 , GA3 , GA7 and GA1 in buds. Acknowledgements The authors are thankful to the Director of the institute for encouragement during the study. We gratefully acknowledge the financial support from NAIP, ICAR, New Delhi. References Abdel Rahim, A.O.S., Elamin, O.M., Bangerth, F.K., 2008. Effects of paclobutrazol on floral induction and correlated phyto-hormonal changes in grafted seedlings of different mango (Mangifera indica L.) cultivars, Sudan. J. Agric. Res. 11, 111–120. Abdel Rahim, A.O.S., Elamin, O.M., Bangerth, F.K., 2011. Effects of paclobutrazol (PBZ) on floral induction and associated hormonal and metabolic changes of biennially bearing mango (Mangifera indica L.) cultivars during off year. ARPN J. Agric. Biol. Sci. 6, 55–67. Abdul Jaleel, C.A., Manivannan, P., Sankar, B., Kishore Kumar, A., Sankari, A., Panneerselvam, R., 2007. Paclobutrazol enhances photosynthesis and ajmalicine production in Catharanthus roseus. Process Biochem. 42, 1566–1570. Barthe, G.A., Stewart, I., 1985. Enzyme immunoassay (EIA) of endogenous cytokinins in citrus. J. Agric. Food Chem. 33, 293–297. Blaikie, S.J., Kulkarni, V.J., Muller, W.J., 2004. Effects of morphactin and paclobutrazol flowering treatments on shoot and root phenology in mango cv. Kensington Pride. Sci. Hortic. 101, 51–68. Burondkar, M.M., Gunjate, R.T., Magdum, M.B., Govekar, M.A., 2000. Rejuvenation of old and overcrowded ‘Alphonso’ mango with pruning and use of paclobutrazol. Acta Hortic. 509, 681–686. Chacko, E.K., 1986. Physiology of vegetative and reproductive growth in mango (Mangifera indica L.) trees. In: Proceedings First Australian Mango Research Workshop, CSIRO, Australia, Melbourne, pp. 54–70. Chen, W.S., 1985. Flower induction in mango (Mangifera indica L.) with plant growth substances. Proc. Natl. Sci. Counc. Repub. China B 9, 9–12. Chen, W.S., 1987. Endogenous growth substances in relations to shoot growth and flower bud development of mango. J. Am. Soc. Hortic. Sci. 112, 360–363. Chen, W.S., 1990. Endogenous growth substances in the xylem and shoot tip diffusate of lychee in relation to flowering. HortScience 25, 314–315. Chen, W.S., 1991. Changes in cytokinins before and during early flower bud differentiation in lychee (Litchi chinensis Sonn.). Plant Physiol. 96, 1203–1206. Corbesier, L., Bernier, G., Perilleux, C., 2002. C:N ratio increases in the phloem sap during floral transition of the long-day plants, Sinapis alba and Arabidopsis thaliana. Plant Cell Physiol. 43, 684–688. Davenport, T.L., 2000. Processes influencing floral initiation and bloom: the role of phytohormones in a conceptual flowering model. Hortic. Technol. 10, 733–739.

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