Genotypic response of mango yield to persistence of paclobutrazol in soil

Scientia Horticulturae 106 (2005) 53–59 www.elsevier.com/locate/scihorti

Genotypic response of mango yield to persistence of paclobutrazol in soil V.K. Singh *, A.K. Bhattacherjee Central Institute for Subtropical Horticulture, Rehmankhera, Lucknow 227 107, India Received 26 April 2004; received in revised form 12 August 2004; accepted 10 February 2005

Abstract Persistence of paclobutrazol and its subsequent impact on the yield of different commercial cultivars of mango, viz. Chausa, Dashehari and Langra have been studied. Results based on 2-year averages indicate that trees treated with 6 g a.i./tree of paclobutrazol recorded maximum yield in Chausa and Langra, whereas only 4 g a.i./tree was most effective in Dashehari. The application of paclobutrazol, at half the above doses, was effective in inducing flowering as well as fruiting in the third year, but only in cv. Dashehari; still substantially higher yields (47.30 kg/tree) were recorded over control (26.20 kg/tree), but not so in cvs. Chausa and Langra. The trees which were not given paclobutrazol treatment in the third year showed residual effect only in cv. Dashehari, while cvs. Chausa and Langra did not show any residual response. The paclobutrazol residue in the soil collected during the third year from the root zone of trees was in the range of 0.4898–1.0005 mg/g by gas–liquid chromatography. # 2005 Elsevier B.V. All rights reserved. Keywords: Paclobutrazol; Persistence; Soil; Mango; Yield

1. Introduction Mango (Mangifera indica L.) is one of the most important and economic fruit crops of India. Mango plant exhibits alternate bearing and the yield varies considerably in alternate years, the year of optimum or heavy fruiting (on year) is followed by little or no fruiting (off year) in the following year. However, certain plant growth regulators (PGRs) * Corresponding author. Tel.: +91 522 284 1022/24; fax: +91 522 284 1025. E-mail address: [email protected] (V.K. Singh). 0304-4238/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2005.02.012

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can effectively induce flowering in mango during the off years. Among various PGRs, paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1yl) pentan-3-ol] has been found to be particularly effective (Kulkarni, 1988; Burondkar and Gunjate, 1993; Kurian and Iyer, 1993; Shinde et al., 2000). Paclobutrazol is a potent inhibitor of gibberellin biosynthesis (Hedden and Graebe, 1985) and can be applied as an overall spray, as a soil drench or by way of trunk painting; better results have been achieved when used as a soil drench, either in the root zone or the collar region of the tree. It is a broad-spectrum growth retardant and reportedly effective in inducing flowering in apple and pear (Williams and Edgerton, 1983) and reducing stem elongation in apple (Steffens and Wang, 1985; Sterrett, 1985), citrus (Aron et al., 1985) and peach (Erez, 1984). Paclobutrazol was reportedly absorbed through the roots and transported primarily through stem (via xylem) before accumulating in the leaves (Wang et al., 1986). The amount of paclobutrazol residue left in the soil or plant parts would appear to depend on the methods of application, doses and the crop. Xi et al. (1995) reported that the highest paclobutrazol residues (0.107 ppm) were found in the roots of rapeseed from normally applied paclobutrazol solution (150 ppm), followed by the leaves, seed, stem and hull (0.070, 0.039, 0.034 and 0.027 ppm, respectively). They also reported substantial amounts of residue in the soil: 0.015 ppm (0–5 cm) and 0.01 ppm (5–10 cm) depending on the soil depth. However, Li and Pan (1997) did not detect residue in the soil after 230 and 130 days of application in rice and groundnut fields, respectively. It reportedly persisted upto 2–5 years in apple (Ma et al., 1990), 1–3 years in peach (Erez, 1986), 1–2 years in apricot (Jacyna et al., 1989), cranberry (McArthur and Eaton, 1989), citrus (Aron et al., 1985) and blueberry (Spiers, 1988). However, very little amount of paclobutrazol is required to promote flowering and fruiting in fruit crops (Browning et al., 1992). Persistence of paclobutrazol in the soil can be determined by chromatographic methods. The present study was undertaken to analyse the persistence of paclobutrazol in the soil by a simple GLC method and to examine its long-term impact on mango yield in cvs. Chausa, Dashehari and Langra.

2. Materials and methods A statistically laid out field trial in randomized block design (RBD) with three replications was carried out during 1997–2000 mango cropping season at the experimental farm of CISH, Lucknow, located at latitude 26–558N and longitude 85–898E. The average temperature was between 12.5 and 32.5 8C and the annual precipitation was 765 mm with 85–90% relative humidity during mango season. Twenty-year-old mango trees of cvs. Chausa, Langra and Dashehari were used for this trial. Paclobutrazol as an aqueous solution was procured from ICI Agrochemicals Ltd., UK. It was applied as a soil drench at 2, 4, 6 and 8 g a.i./tree in the month of September within the manuring ring at 10 cm depth during the first 2 years (on and off years) of experiment. During the third year the plants were divided into two sets, one set of plants received half the dose of paclobutrazol applied in the previous years, and no treatment was given to the second set of trees in order to study its long-term effect on mango production. Trees without paclobutrazol treatment were used

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Table 1 Physico-chemical parameters of soil Parameters

Amounta

Type of soil pH Organic carbon Phosphorus (P) Potassium (K) Sodium (Na) Calcium (Ca) Zinc (Zn) Copper (Cu) Manganese (Mn) Iron (Fe)

Loam to fine sandy loam 7.30 0.68% 9.23 ppm 81.25 ppm 63.75 ppm 1400 ppm 1.28 ppm 1.94 ppm 24.76 ppm 32.86 ppm

ppm: parts per million. a Values are on dry weight basis.

as control. The time of flowering in Dashehari and Langra is February and in Chausa is March. The yield observations were made in respect of fruit numbers and fruit weight per tree at the time of harvest. Soil samples from 15 cm depth were collected from the root zone of mango trees for physico-chemical and residue analysis. The soil physico-chemical properties are presented in Table 1. The soil was deficient in phosphorus (<10 ppm), zinc (1.28 ppm) and copper (1.94 ppm) but very rich in calcium (1400 ppm). The extraction and GLC analysis of soil samples were carried out by the method of Bhattacherjee and Singh (2002). The solutions of various concentrations of paclobutrazol were prepared by dilution of 1000 ppm stock solution in methanol. Methanol used in this experiment was distilled and dried before use.

3. Results 3.1. Effect of paclobutrazol on fruiting behaviour of mango Pooled results of the first 2 years of experiment when the plants received full dose of paclobutrazol, and that of the third year when the dose was reduced by half, for each cultivar, are summarized in Table 2. When paclobutrazol was applied at 2, 4, 6 and 8 g a.i./ tree in cvs. Chausa, Langra and Dashehari, mango yield in all three cultivars was found to increase in terms of the number of fruits per tree over control. Pooled mean of first 2 years indicated that trees treated with 6 g a.i. of paclobutrazol recorded maximum number of fruits in cvs. Chausa (247) and Langra (257) as compared to control (92 and 51.50 for Chausa and Langra, respectively). On the other hand, treatment at 4 g a.i./tree produced maximum number of fruits in cv. Dashehari (379) over control (151.50). During the third year when the dose was reduced to half of the optimum concentration of paclobutrazol (6 g a.i.), there was little effect on fruit numbers in cvs. Chausa and Langra (Table 2). In contrast, reduced dose of paclobutrazol was effective in cv. Dashehari and the number of

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Table 2 Long-term effect of paclobutrazol on yield of mango cvs. Chausa, Langra and Dashehari Paclobutrazol Number of fruits per tree Yield (kg/tree) (g a.i./tree) I II Pooled mean III IV I II Pooled mean III IV (1997–1998) (1998–1999) of I and II (1999–2000) (2000) (1997–1998) (1998–1999) of I and II (1999–2000) (2000)

Chausaa

0 2 4 6 8 CD at 1%

92 238 207 190 163 23.4

0 177 215 304 198 16.2

46.0 207.5 211.0 247.0 180.5 25.5

190 0 9 21 217 51.0

– 0 0 0 68 –

18.4 47.6 41.4 38.0 32.6 9.1

0 36.88 44.79 63.34 41.25 15.20

9.20 42.24 43.10 50.67 36.93 10.50

38.40 0 1.87 4.40 43.40 16.50

– 0 0 0 13.6 –

Langrab

0 2 4 6 8 CD at 1%

98 140 150 200 130 21.6

5 79 175 314 169 34.2

51.5 109.5 162.5 257.0 149.0 13.6

101.0 3.0 8.5 82.0 162.6 29.2

– 0 0 10 55 –

19.3 23.4 30.0 41.5 30.43 5.9

0.85 20.0 35.6 41.3 33.8 10.5

10.08 21.7 32.8 41.4 32.21 3.89

20.2 0.6 1.7 16.4 33.12 11.76

– 0 0 1.9 12.8 –

198.0 299.7 478.0 309.56 291.6 33.6

105.0 199.7 280.0 103.22 111.5 32.3

151.5 249.7 379.0 206.28 201.6 25.6

131.00 167.75 260.15 166.1 160.6 16.3

50.5 73.0 165.8 170.0 150.0 21.2

36.0 54.49 86.91 56.28 53.01 21.2

19.09 36.31 50.90 18.77 20.27 21.56

27.55 45.40 68.90 37.52 36.65 9.35

23.82 30.50 38.40 30.20 29.20 6.35

9.19 13.28 30.15 30.90 27.27 5.35

Dasheharic 0 2 4 6 8 CD at 1%

Treatments: I = full dose (on year; first year), II = full dose (off year; second year), III = half dose in third year, IV = no treatment in third year, three trees per treatment. a ANOVA (F-test) value at 5% level of significance. Cultivar = 4.16; treatment = 0.58. b ANOVA (F-test) value at 5% level of significance. Cultivar = 7.82; treatment = 3.25. c ANOVA (F-test) value at 5% level of significance. Cultivar = 15.46; treatment = 10.09.

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Cultivars

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fruits was twice that of control. In the second set of trees, which were kept free from paclobutrazol treatment in the third year, residual effect in respect of higher number of fruits was seen only in cv. Dashehari, while cvs. Chausa and Langra did not show any response, barring some stray fruits at higher dose (8 g a.i.) of initial application (Table 2). 3.2. Effect of paclobutrazol on mango yield The data pertaining to yield (Table 2) indicated that paclobutrazol significantly increased fruit yield; the maximum values recorded were 50.67 and 41.40 kg/tree in cvs. Chausa and Langra, respectively, at 6 g a.i./tree over untreated control wherein the yield recorded over a period of 2 years were only 9.20 and 5.04 kg/tree, respectively. During the third year when paclobutrazol dose was reduced to half, only half dose of the highest concentration (8 g a.i./tree) was found to cause yield enhancement in cvs. Chausa and Langra. Trees which received half the dose of 2, 4 and 6 g a.i./tree of paclobutrazol recorded low yield, i.e., 0, 1.87 and 4.40 kg in Chausa and 0.60, 1.70 and 16.40 kg in Langra, respectively. In contrast to these two cultivars, the half dose of paclobutrazol was found to be significantly effective in increasing the fruit yield in cv. Dashehari; maximum (38.40 kg/tree) yield was in trees which received half dose (2 g a.i.) of optimum concentration of paclobutrazol as compared to control (23.82 kg/tree). The ANOVA F-test values at 5% level of significance also indicated that cv. Dashehari responded better to treatment with paclobutrazol than cvs. Chausa and Langra. Residual effect of paclobutrazol was also observed only in cv. Dashehari when its application was not done during the third year (Table 2) recording higher yield (30.90 kg) in comparison to control (9.19 kg/tree). On the other hand, cvs. Chausa and Langra did not show any response in this condition (Table 2). 3.3. Residue analysis Residue analysis was done in soils from all the three cultivars of mango, but the results have been presented in respect of Chausa field only (Table 3); similar results were obtained for soils of other two cultivars. Results clearly show that maximum residue persisted in soil (1.0005 ppm), which had received paclobutrazol at 8 g a.i./tree, followed by 6 g a.i. (0.7211 ppm), 4 g a.i. (0.6734 ppm) and 2 g a.i. (0.4898 ppm). No residue was detected in controls. Table 3 Paclobutrazol residue in the soil Paclobutrazol treatment (g a.i./ha)

Residues (mg/g or ppm) R1

R2

R3

Mean

0g 2g 4g 6g 8g

0.00 0.4769 0.7042 0.6881 0.9985

0.00 0.4995 0.6672 0.7401 0.9608

0.00 0.4930 0.6489 0.7350 1.0423

0.00 0.4898 0.6734 0.7211 1.0005

R1–R3 = Replications.

Coefficient of variation (%)

0.00 1.94 3.41 3.24 3.33

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4. Discussion The efficacy of paclobutrazol on growth, flowering, fruiting and fruit quality have been reported earlier (Singh and Saini, 2001). The results of long-term effect of paclobutrazol on fruit yield clearly show that cvs. Chausa and Langra are much more prone to alternate bearing in comparison to Dashehari. Excessive vegetative growth and high levels of gibberellins production are main factors for erratic flowering in mango (Chacko, 1991). Several reports indicate that paclobutrazol, a broad-spectrum growth retardant, exerts its antagonistic effect due to lowering of endogenous gibberellin levels which in turn causes reduced vegetative growth but profuse flowering in mango (Williams, 1984; Voon et al., 1991). Thus increased fruiting during the ‘off’ year in mango trees could be due to reduction in gibberellin levels, which may alter the pattern of assimilate partitioning in trees during the flowering. Thus, this study provides evidence that fruiting in mango cv. Dashehari could be regulated by the application of 4 g a.i. paclobutrazol per tree in the first year and repeated with half dose in the second year. However, in cvs. Chausa and Langra it could be regulated by the regular application of paclobutrazol. Higher amount of paclobutrazol residue in the soil during third year indicates long persistence of paclobutrazol in mango orchard. Electron capture detector (ECD) was used for the residue analysis by gas–liquid chromatography because of its high sensitivity. Early and Martin (1988) studied the translocation of paclobutrazol in peach seedlings by highperformance liquid chromatography (HPLC) and the same was studied by Wang et al. (1986) using gas–liquid chromatography (GLC) with flame ionization detector (FID) in apple seedlings. Bolygo and Atreya (1991) developed a multi-residue analytical method for the analysis of paclobutrazol in groundwater by GLC using nitrogen–phosphorus detector (NPD).

Acknowledgements Authors are thankful to Prof. R.K. Pathak, Director, Central Institute for Subtropical Horticulture, Lucknow for constant encouragement and providing necessary facilities. Authors are also thankful to Dr. (Ms.) P. Dureja, Principal Scientist, Division of Agricultural Chemicals, I.A.R.I., New Delhi for her generous help during GLC analysis.

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