Research Report MAHA 1993/94, RARC, Aralaganwila

1. Name of Researcher(s)K.H.S Peiris (RO),

A.S.P Weerasinghe (RO)
W.M.U.B. Wickrama (RA)

2. Title of Experiment  Mango Flowering studies with Paclobutrazol

3. Objective(s)        

To assess the efficacy of Paclobutrazol for flowering enhancement of Mango

4. Crop                 Mango

5. Location             RARC, Aralaganwila

ARC, Girandurukotte and
HRF, Ulpothagama

6. Season               MAHA 1993/94

7. Methodology

A number of trials were conducted at RARDC, Aralaganwila, ARC, Girandurukotte and HRF, Ulpothagama to assess the feasibility of using Paclobutrazol to improve flowering and productivity of several mango varieties. The observations and results are presented separately for each trial.

The product used in this experiment was Cultar, a commercial formulation marketed by ICI, London, having 25% v/v of Paclobutrazol.

8. Results

Trial # 1. RARDC, Aralaganwila.

      Two trees each from varieties Willard and Malwane were treated with Paclobutrazol in June 1993. Six milliliters of Paclobutrazol was applied in 1.0 L of water as a collar drench. Thus each tree received 24 ml of Cultar (25 % v/v Paclobutrazol). Plants were observed closely for flowering, flowering intensity, flowering periods, flower morphology, fruit yield and characteristics of subsequent vegetative flushes.

      The yield data for experimental trees are given in Table 1. Paclobutrazol treated Willard trees had high intensity of flowering while untreated tree had extensive vegetative flushing during fruit development. The highest fruit yield given by untreated tree is due to its large size. Tree number 3 produced few fruits as its flowering was delayed until September. This tree flowers latter in every year Paclobutrazol did not advanced its flowering.

      Few days after Paclobutrazol application to Willard trees, leaves of treated trees had turned to dark green in color compared to the control tree. During flowering Paclobutrazol treated trees produced shorter panicles compared with panicles in untreated trees. The vegetative flush in following year showed more compact appearance than that of flushes in control trees. The dwarfing nature of flushes and leaf wrinkling was more pronounced in smaller tree applied with 6 ml of Paclobutrazol.

These differences in leaf color, panicle size and subsequent flushes are the evidence that Paclobutrazol has been taken up by the tree and moved to apical meristems where it exert its physiological effects. However, this kind of morphological changes were not observed in Malwane trees. Though Malwane trees did not flower in July or September, 1993 as observed in variety Willard, only one tree flowered in early April, 1994 and again in mid June, 1994 for the second time. However, though this tree fully flowered all developing fruits dropped prematurely. Apart from these two treated trees there were 25 more untreated Malwane trees that did not flower at all. Therefore, this observation suggest that even if Paclobutrazol induce flowering in unproductive varieties, trees can not support the growth of fruits possibly may be due to low levels of carbohydrate reserves in storage to support fruit development.

Table 1. Effect of Paclobutrazol on mango productivity.

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Tree  TRT   NF     FW  AFW   SD     CV  FW/m3  FN/m3      FLWR

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1 WLD  6    235   31.4  134  51   16.9  1.9    13.9      July
2 WLD  0    326   49.4  151  64   42.9  1.2     7.6      July
3 WLD  6     62   14.8  240  59   53.5  0.3     1.2      Sept

4 MWN  6    No flowering

5 MWN  6    No flowering

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Tree:  WLD-Willard; MWN-Malwane    

TRT:   Treatment (ml of Paclobutrazol/tree)
NF:    Number of fruits
FW:    Fruit weight (Kg per tree)
AFW:   Average fruit Weight (g/fruit)
SD:    Stem diameter (cm)
CV:    Canopy volume (m3)

FW/m3: Fruit weight/ cubic meter of canopy

FN/m3: Fruit number/ cubic meter of canopy

FLWR : Month of flowering

      What is interesting here to note is that in variety Willard number of fruits as well as fruit number per unit canopy volume is higher in tree treated with Paclobutrazol that flowered in July. Canopy volume was calculated by using canopy width, breadth and height measurements assuming a conical shape of all canopies. The lower yields given by the tree flowering in September is due to bad weather conditions prevailed during flowering time.

Trial # 2: ARC, Girandurukotte

      Two trees each from six exotic mango varieties were treated with 6 ml of Paclobutrazol in June 1993. The varieties used for this experiment were Joe Welch, Sensation, Kensington, Pope summer, Tommy Atkins and Haden. When the treatments were applied, the trees were  approximately 3.5 years old and two varieties, Joe Welch and Sensation had already started to bear few fruits. Observations indicated no signs of Paclobutrazol activity in trees of any variety tested as displayed by variety Willard in response to Paclobutrazol application at Aralaganwila. However, varieties Sensation and Joe Welch produced few fruits, both in treated as well as untreated trees showing that the bearing is not as a result of Paclobutrazol application.

Trial # 3: HRF, Ulpothagama.

Three rates of Paclobutrazol (0, 4 and 6 ml/tree) were tested for three mango varieties, Willard, Karuthakolomban and Velleikolomban. This experiment was conducted in a Randomized Complete Block Design having four replicates with one tree per replicate. Plants were blocked according to tree size. Treatments were applied in June, 1993. Table 2. list the tree number for each variety and replicate treated with different Cultar rates

Flowering intensity and fruit yield records were taken to evaluate the effects of Paclobutrazol on flowering and fruit yield of trees. Visual counts of flowering intensity, ( approximate % of shoots flowered on the canopy) were recorded on September 22, 1993, when peak flowering was observed in mangoes at Ulpothagama. Fruits were harvested from late December through mid January.

Table 2. Tree numbers for each replicate and Cultar treatments for different varieties.

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Treatment  

Willard           Velleikolomban          Karuthakolomban

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Control

R1 - 405          R1 - 188                R1 - 264

R2 - 406          R2 - 197                R2 - 265

R3 - 390          R3 - 199                R3 - 262

R4 - 392          R4 - 200                R4 - 299

4 ml/tree

R1 - 397          R1 - 216                R1 - 254

R2 - 398          R2 - 208                R2 - 259

R3 - 399          R3 - 209                R3 - 263

R4 - 407          R4 - 218                R4 - 260

6 ml/tree

R1 - 394          R1 - 248                R1 - 250

R2 - 395          R2 - 249                R2 - 246

R3 - 396          R3 - 230                R3 - 247

R4 - 391          R4 - 228                R4 - 251

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Table 3. Flowering intensity (% shoots flowering)

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Treatment                       Variety

(ml,PBZ/Tree)     WLD               KC                VC

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0                 12.5               8.7              40.0

4                 72.5              25.0              90.0

6                 87.5              48.7              96.7

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Paclobutrazol had a clear effect on enhancement of flowering in all three varieties (Table 3). Results demonstrated that at the rates tested in this experiment, Karuthakolomban trees did not attain full flowering like in varieties Willard and Velleikolomban. Application rates more than 6 ml per tree must be further tested for Karuthakolomban.

Fruit yields of varieties Willard and Karuthakolomban are presented in Tables 4 and 5. Even though four trees were used for each treatment some trees had to be removed from each treatment as a result of some mistakes made in recording yield data. Velleikolomban yields are not presented as fruit yield data records were not taken properly in this season for that variety. Number of trees used for calculating mean values are given against each treatment.

Table 4. Fruit yield of variety Willard.

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Treatment         No of       Fruits      Fruit Weight      Fruit 

(ml,PBZ/Tree)     Trees       per tree    per tree (kg)     Size (g)

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0                 4            29          6.1              211

4                 3            32          7.5              232

6                 2           164         32.5              198

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Table 5.    Fruit yield of variety Karuthakolomban.

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Treatment         No of       Fruits      Fruit Weight      Fruit 

(ml,PBZ/Tree)     Trees       per tree    per tree (kg)     Size (g)

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0                 3            17          6.7              394

4                 3            25          9.0              360

6                 2            53         20.3              383

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Results on yield figures for both varieties unquestionably indicate that Paclobutrazol directly improve the fruit yields. However, with increasing fruit number average fruit weight has been slightly diminished.

9. Remarks

The experimental data and observations revealed that Paclobutrazol is a very valuable growth regulator to be used in mango production. Apart from mango, it has many uses in other fruit species such as Citrus, avocado etc. and vegetables as well as in ornamental crops.

In relation to the effects of Paclobutrazol on mango, it seems that Paclobutrazol influences depend on mango variety. Variety Willard seems to be very sensitive to Paclobutrazol as shown by its immediate uptake and its effects on enhancing flowering and fruit yield. Varieties Karuthakolomban and Velleikolomban also showed good response to Paclobutrazol application. Further information is required to assess the exact quantities to be applied because it seems that the optimum responses are given under a narrow concentration range. Experimental applications are necessary to get a clear idea, as quantities to be applied are determined by variety, tree size (rather than tree age) and soil type.

10.   Summary

A number of experiments conducted to find out the efficacy of Cultar (Paclobutrazol) on mango flowering indicated that Cultar enhance the flowering of mango varieties Willard, Velleikolomban and Karuthakolomban. However, this growth regulator did not influence flowering of some exotic varieties. Though Cultar promoted flowering of variety Malwane, fruit set was very poor. Among the responsive varieties, Willard showed a great sensitivity to this growth regulator.

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Mango Flowering Improvement with Paclobutrazol[1]

K. H. Shantha Peiris
Research Officer, RARDC, Aralaganwila

Introduction

Mango yields in a particular fruiting season to a greater extent depend on flowering intensity of trees. Best yields are obtained when most of the shoots flower without any development of growth flushes from flowering to maturity, when trees of an appropriate variety are well managed during the period prior to flower initiation. However, even with the employment of a sound tree management package, it is a common phenomena that under most circumstances vegetative flushes occur during the period from flowering to fruit maturity. Vegetative flushes at this time affect fruit set and fruit size because growing vegetative flushes have the highest competitive demand for tree reserves, and as a result more fruits drop prematurely and remaining fruits become smaller. Therefore, methods to control vegetative flushes at flowering may support increasing yields.

      Paclobutrazol (Cultar) or P333 is a plant growth regulator showing much promise in controlling vegetative growth in fruit trees and thereby enhancing flowering, fruit set and fruit yields. This chemical belonging to the category of growth retardants. Paclobutrazol has been tested on mangoes in other countries and results are very encouraging. Results indicate that while enhancing flowering and fruit yield, it also keeps the trees dwarf. This is a good characteristic for fruit trees as it facilitates better orchard management, with a higher plant density for improving orchard productivity.

      Trials have been conducted since June 1993 to study the effect of Paclobutrazol on mango productivity. Preliminary results of these trials are presented in this report.

Methodology

      A number of trials were conducted at RARDC, Aralaganwila, ARC, Girandurukotte and HRF, Ulpothagama to assess the feasibility of using Paclobutrazol to improve flowering and productivity of several mango varieties. The observations and results are presented separately for each trial.

      Trials conducted in Australia have shown that best results are obtained when 4 - 6 ml of Paclobutrazol is applied to 5-7 year old trees. In trials testing different methods of application, results have shown that application as a collar drench around the base of the tree is far superior to all other application methods such as foliar spray, trunk injection, soil application to root zone as band applications or complete spreading around the root zone etc.( Winston, 1992). Therefore, in all trials going to be presented here experimental dose of Paclobutrazol was applied as a collar drench in one liter of water. The product used in this experiment was Cultar, a commercial formulation marketed by ICI, London, having 25% v/v of Paclobutrazol.

Trial # 1. RARDC, Aralaganwila

      Two trees each from varieties Willard and Malwane were treated with Paclobutrazol in June 1993. Six ml of Paclobutrazol was applied in 1.0 L of water as a collar drench. Thus each tree received 24 ml of Cultar (25 % v/v Paclobutrazol). Plants were observed closely for flowering, flowering intensity, flowering periods, flower morphology, fruit yield and characteristics of subsequent vegetative flushes.

      The yield data for experimental trees are given in Table 1. Paclobutrazol treated Willard trees had high intensity of flowering while untreated tree had extensive vegetative flushing during fruit development. The highest fruit yield given by untreated tree is due to its large size. Tree number 3 produced few fruits as its flowering was delayed until September. This tree flowers latter in every year Paclobutrazol did not advanced its flowering.

      Few days after Paclobutrazol application to Willard trees, leaves of treated trees had turned to dark green in color compared to the control tree. During flowering Paclobutrazol treated trees produced shorter panicles compared with panicles in untreated trees. The vegetative flush in following year showed more compact appearance than that of flushes in control trees. The dwarfing nature of flushes and leaf wrinkling was more pronounced in smaller tree applied with 6 ml of Paclobutrazol.

      These differences in leaf color, panicle size and subsequent flushes are the evidence that Paclobutrazol has been taken up by the tree and moved to apical meristems where it exert its physiological effects. However, this kind of morphological changes were not observed in Malwane trees. Though Malwane trees did not flower in July or September, 1993 as observed in variety Willard, only one tree flowered in early April, 1994 and again in mid June, 1994 for the second time. However, though this tree fully flowered all developing fruits dropped prematurely. Apart from these two treated trees there were 25 more untreated Malwane trees that did not flower at all. Therefore, this observation suggest that even if Paclobutrazol induce flowering in unproductive varieties, trees can not support the growth of fruits possibly may be due to low levels of carbohydrate reserves in storage to support fruit development.

Table 1. Effect of Paclobutrazol on mango productivity

Tree:  WLD-Willard; MWN-Malwane    

TRT:   Treatment (ml of Paclobutrazol/tree)
NF:    Number of fruits
FW:    Fruit weight (Kg per tree)
AFW:   Average fruit Weight (g/fruit)
SD:    Stem diameter (cm)
CV:    Canopy volume (m3)

FW/m3: Fruit weight/ cubic meter of canopy

FN/m3: Fruit number/ cubic meter of canopy

FLWR : Month of flowering

      What is interesting here to note is that in variety Willard number of fruits as well as fruit number per unit canopy volume is higher in tree treated with Paclobutrazol that flowered in July. Canopy volume was calculated by using canopy width, breadth and height measurements assuming a conical shape of all canopies. The lower yields given by the tree flowering in September is due to bad weather conditions prevailed during flowering time.

Trial # 2: ARC, Girandurukotte

      Two trees each from six exotic mango varieties were treated with 6 ml of Paclobutrazol in June 1993. The varieties used for this experiment were Joe Welch, Sensation, Kensington, Pope summer, Tommy Atkins and Haden. When the treatments were applied, the trees were  approximately 3.5 years old and two varieties, Joe Welch and Sensation had already started to bear few fruits. Observations indicated no signs of Paclobutrazol activity in trees of any variety tested as displayed by variety Willard in response to Paclobutrazol application at Aralaganwila. However, varieties Sensation and Joe Welch produced few fruits, both in treated as well as untreated trees showing that the bearing is not as a result of Paclobutrazol application.

Trial # 3: HRF, Ulpothagama

      Three rates of Paclobutrazol (0, 4 and 6 ml/tree) were tested for three mango varieties, Willard, Karuthakolomban and Velleikolomban. This experiment was conducted in a Randomized Complete Block Design having four replicates with one tree per replicate. Plants were blocked according to tree size. Treatments were applied in June, 1993.

      Flowering intensity and fruit yield records were taken to evaluate the effects of Paclobutrazol on flowering and fruit yield of trees. Visual counts of flowering intensity,( approximate % of shoots flowered on the canopy) were recorded on September 22, 1993, when peak flowering was observed in mangoes at Ulpothagama. Fruits were harvested from late December through mid January.

Table 2. Flowering intensity (% shoots flowering)

      Paclobutrazol had a clear effect on enhancement of flowering in all three varieties (Table 2). Results demonstrated that at the rates tested in this experiment, Karuthakolomban trees did not attain full flowering like in varieties Willard and Velleikolomban. Application rates more than 6 ml per tree must be further tested for Karuthakolomban.

      Fruit yields of varieties Willard and Karuthakolomban are presented in Tables 3 and 4. Even though four trees were used for each treatment some trees had to be removed from each treatment as a result of some mistakes made in recording yield data. Velleikolomban yields are not presented as fruit yield data records were not taken properly in this season for that variety. Number of trees used for calculating mean values are given against each treatment.

Table 3. Fruit yield of variety Willard

Table 4. Fruit yield of variety Karuthakolomban

      Results on yield figures for both varieties unquestionably indicate that Paclobutrazol directly improve the fruit yields. However, with increasing fruit number average fruit weight has been slightly diminished.

Discussion

      The experimental data and observations revealed that Paclobutrazol is a very valuable growth regulator to be used in mango production. Apart from mango, it has many uses in other fruit species such as Citrus, avocado etc. and vegetables as well as in ornamental crops.

      In relation to the effects of Paclobutrazol on mango, it seems that Paclobutrazol influences depend on mango variety. Variety Willard seems to be very sensitive to Paclobutrazol as shown by its immediate uptake and its effects on enhancing flowering and fruit yield. Varieties Karuthakolomban and Velleikolomban also showed good response to Paclobutrazol application. Further information are required to assess the exact quantities to be applied because it seems that the optimum responses are given under a narrow concentration range. Experimental applications are necessary to get a clear idea, as quantities to be applied are determined by variety, tree size (rather than tree age) and soil type.

      Observations also indicate that Paclobutrazol can do very little to increase fruit yields of un-adaptable varieties of mango. Though, in some instances Paclobutrazol induces the trees to flower, poor fruit set and severe premature fruit drop limit the fruit yields of such varieties. This may be as a result of insufficient tree reserves to support growth and development of fruits under such conditions.

      In previous trials conducted by Dissanayake (1992) off-season flowering of mango variety Karuthakolomban has been successful in wet zone yielding 11.8 - 23.5 kg of fruits per tree in November at Walpita. However, our observations at Aralaganwila and Ulpothagama indicate that effects are more pronounced in enhancement of flowering and fruit set rather than on off-season flower induction to get fruits at any time of the year. Observations have confirmed that during the normal season Paclobutrazol treated trees flower profusely and produce higher yields compared to control trees. Little off-season flowering was also observed, but fruit set was very poor as most of the flowers dried out as a result of inclement weather conditions during the time of flowering. This is however good to happen in such a way as it will not affect over exploitation of trees which is an inherent problem with flower induction technology as observed in the Philippines now. Philippines mango growers has now felt this problem and expressed their concerns about the declining tree productivity with the use of potassium nitrate technology for off-season flowering.

      Another concern in using new agricultural chemicals is issues in relation to their toxicology, environmental and residual effects. Paclobutrazol is of low acute toxicity, the oral LD50 to rat being 1300 - 2000 mg/kg. This chemical is rapidly excreted by mammals and does not accumulate in the tissues. It is not mutagenic. Paclobutrazol is also of low toxicity to fish, birds, bees, earthworms and soil microorganisms.

      Residues have not been detected in fruits after soil applications, even where large reductions of vegetative growth have been observed. When foliar applications were made 2 weeks before harvesting on apples at 1 kg/ha, residues at harvest have been found to be below 0.5 ppm. The half-life of Paclobutrazol varies with soil type and climatic conditions, but is generally between 6 and 12 months. Paclobutrazol has a low mobility in soils (Helling Class 2) so residues should not constitute a leaching risk.

In the final analysis, it is evident that Paclobutrazol can be integrated into mango tree management systems provided that other cultural practices are well adopted to sustain the yield increases with out affecting the long term tree productivity. Introduction of Paclobutrazol to growers requires good extension effort and technical support to successfully transfer this useful technology (Voon et al, 1992). If this technology is properly employed, orchard productivity and profitability could be significantly improved.

References

Dissanayake, L.D. (1992). Soil applied Paclobutrazol can induce flowering in mango. Krushi 16-23.

Voon, C.H., A. J. Rowley, N. Hongsbhanich and C. Pitakpaivan (1992) Cultar development in tropical fruits - An overview. Acta. Hort. 321:270-281.

Winston, E.C. (1992). Evaluation of Paclobutrazol on growth, flowering and yield of mango cv. Kensington Pride. Australian J. Exp. Agric. 32;97-104.

Discussion

Q.   

Mr. Bruce Spake: How safe is mango treated with Paclobutrazol for human consumption?

A.

I have not come across any reports indicating that Paclobutrazol is harmful to humans. Paclobutrazol is being used commercially in other countries as well on a variety of fruit crops including apple, pear and avocado etc., in addition to mango. Uses are many more in ornamental horticulture.

      Paclobutrazol is a plant growth regulator affecting the bio-synthesis of Gibberellins, a class of natural hormones synthesized by plants to promote vegetative growth. Paclobutrazol molecules irreversibly and very competitively couples with two enzymes involved in Gibberellins synthesis. This reaction is very specific only to those two enzymes found in plant systems. Being a plant growth regulator, Paclobutrazol is active only in plant systems, but not in animal systems like in the case if insecticides. We must not be too alarmed toward the use of agricultural chemicals as far as those are judiciously used to harness their potential applications. When Paclobutrazol is commercially used it shows us that it has passed all rigorous FDA tests in USA in order to utilize it for agricultural purposes. 

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Research Report 2000, FCRDI, Maha Illuppallama

Flower induction studies for off-season fruit production in mango

K.H.S. Peiris, RO, and A.G. Premachandra, RSA.

Introduction   

            Mangoes in Sri Lanka flower twice a year. Generally, majority of the trees in Wet and Intermediate Zones flower in February - March for the Yala crop harvested in June- July which is considered as the main crop for the above mentioned agro-climatic zones. Trees in the Dry Zone flower July through September for the main Maha crop harvested in November-January. Since mangoes are mostly cultivated as a rain fed crop, timing of the seasons varies however, depending on rainfall distribution patterns.

            Production drops in between the two seasons. Prices of fruit go up. Also production gluts during the main season cause heavy losses and price of fruit fall. Many small scale growers can not sell their produce during the peak season. To overcome these marketing problems, a package of technology to produce fruit in the off-season is a must.

            A package of technology  for off season mango production needs 1. A technique to get the leaf flush that emerge after harvesting mature without additional flushes and 2. a technique to induct flowering in mature shoots. Apart from the above growers must have irrigation facilities to facilitate growth and development of fruit after flowering. A good pest and disease management program is another important requirement to get a good crop because pest and disease pressure is heavy in off-season.

            Experiments were conducted to identify mango varieties that responds to the application of Thiourea, To determine the effect of Paclobutrazol on mango flowering with the objectives of identifying varieties and suitable rates of application.

Materials and methods

            An observation study was conducted at FCRDI, Maha Illuppallama, with 14 mango varieties to ascertain the efficacy of Thiourea as a flower inducer. A solution of 0.75 % Thiourea was sprayed to half of the tree canopy in July 1999. All selected trees (one tree per variety) had mature shoots suitable for flower induction. Flowering was observed three weeks after application of Thiourea.

            Another experiment was conducted at the nursery of the Government Seed Farm, Maha Illuppallama to study the effect of Paclobutrazol and Thiourea on flowering of Mango cv. Willard. Three rates of Paclobutrazol ( 0.00, 0.75 and 1.00 g/m of canopy diameter) and three rates of Thiourea (0.00, 0.50 and 1.00%) were tested in a two factor factorial in RCBD with four replicates. Trees were blocked according to tree size as measured by stem girth at 30 cm above the ground. Trees in the experimental block had a major flush in October 1999. Trees selected for this experiment had more than 80% of the shoots as new flush. After the leaf flush fully expanded, Paclobutrazol was applied as a collar drench around the base of the tree, in December 08, 1999. It was planned to apply Thiourea to induce flowering 3 months after Paclobutrazol application. However, trees started to flower naturally in third week of January, 2000. Almost all flowers were destroyed due to severe anthracnose infestation. Then trees were sprayed with Thiourea solution in March 22, 2000. Flowering was observed again in April, 2000. Flowering intensity was visually assessed as % of the flowering shoots in canopy.

Results and Discussion

Observation study conducted to ascertain the efficacy of Thiourea as a mango flower inducer showed that out of 14 varieties, only four varieties, Carabao, Kohu amba, Nam Doc Mai and Willard responded positively (Table 1). Kohu amba tree used in this experiment was a seedling tree and a second application of Thiourea to the responsive varieties in the following year further confirmed that Thiourea can be effectively used to induce flowering of mature shoots of these varieties.

Trees used in the replicated experiment flowered naturally in 3rd week of January, 2000, nearly 6 weeks after Cultar application. Trees treated with Cultar showed a high flowering intensity as measured by % shoots flowered on canopy. Due to the prevailing rainy weather at that time, almost all flowers were dropped due to severe anthracnose infection. These trees were treated with Thiourea in March 22, 2000. Flowering was again observed in second week of April. Again, trees treated with Cultar had higher flowering intensity. Due to the prevailing humid rainy weather conditions, most of the flowers were dropped due to anthracnose resulting a very low fruit set.

It is apparent that application of Cultar at the end of leaf expansion improve flowering of mango cv Willard (Table 2). Effect of Thiourea was not discernible due to complicated early flowering observed in this season. It was clearly noted, however, that length of panicles become very short in trees treated with 1.00g/m of Cultar. There was no significant difference in flowering intensity between the two rates tested indicating that 0.75 g/m of Cultar is sufficient for mango cv. Willard.

It is a common phenomenon that with flowering some of the shoots of mango canopy flush. It was noted that trees treated with Cultar have shown a lower flushing intensity (Table 3.).

Table 1. Effect of foliar spray of 0.50 % Thiourea solution on flowering of mango cultivars

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Cultivar                                    Response

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Kensington                               No flowering

Tommy Atkins                           No flowering

Sensation                                  No flowering

Carabao                                   Flowering

Haden                                      No flowering

Joe Welch                                  No flowering

Momi-K                                   No flowering

Carrie                                       No flowering

Fascell                                      No flowering

Nam doc Mai                           Flowering

Karuthakolomban                     No flowering

Velleikolomban                         No flowering

Kohu amba                              Flowering

Willard                                     Flowering

------------------------------------------------------- 

Table 2.  Effect of Cultar and Thiourea applications on flowering of
mango cv ‘Willard’.

Table 3. Effect of Cultar on formation of vegetative flush at flowering.

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         Treatment                                           % Flush

       Cultar (g/m)                       First flowering          Second flowering

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0.00                               10.8                                       6.7

0.75                                 6.3                                       3.3

1.00                                 2.5                                       1.7

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Research Report 2001, FCRDI, Maha Illuppallama

Flower induction studies for off-season fruit production in mango

K.H.S. Peiris, RO, and S. A. Senevirathna, RA

Introduction

Mango production in Sri Lanka is seasonal. Majority of trees in the Wet and Intermediate Zones flowers in January through March for the Yala crop harvested in May - July that is considered as the main crop for above-mentioned agro-climatic zones. Trees in the Dry Zone flower July through September for the main Maha crop harvested in November-January. Mangoes are mainly cultivated as a rain-fed crop, thus the time of flowering and harvesting may shift considerably depending on rainfall distribution patterns. Abundant production of in-season mangos within short period of time leads to low prices. Production drops in between the two seasons resulting in higher prices. Therefore, an off-season mango production technique is very important for production management of mango.

Reliable flowering is necessary to obtain consistent production of mango under tropical climatic conditions. Flowering from one season to the other is unreliable because of the environmental signals for flower initiation is often inconsistent, subtle or poorly defined. Understanding of the factors controlling flower bud initiation in mango trees has been very limited. An alternative to dependence upon environmental signals for flower initiation is the development of management strategies that can substitute these signals.

Though growth regulators have been tested for promoting/inhibiting flower production in mango in different countries, their effects have been limited to certain cultivars and geographical locations. Therefore, growth regulator chemicals and application rates that can promote or induce flowering must be tested under local conditions for the locally available mango varieties. The objectives of these studies were to study the influence of application rate of Paclobutrazol on enhancement of flowering and fruit production in mango.

Materials and Methods

A field experiment was conducted at Government Seed Production Farm, Maha Illuppallama, to study the effect of rate of application of Paclobutrazol on flowering of mango cultivars Velleikolomban and Willard. Three rates of Paclobutrazol (0.00, 0.50 and 0.75 g a.i. /m of canopy diameter for cv Willard and 0.00, 0.75 and 1.25 g a.i. /m for cv Velleikolomban ) were tested. The formulation used was a wettable powder with 10% Paclobutrazol. The amount to be applied to each tree was dissolved in 1.5 l of water and applied as a collar drench around the base of tree at about one month after leaf bud break when the leaf flush was fully expanded.

Experiment was conducted in a RCBD with six single-tree replicates. Trees were 8 years old. Experiment was blocked according to tree size as measured by stem girth at 30 cm above the ground. Mango trees selected for this experiment had more than 80% of the shoots in the canopy as new flush. 

Flowering was assessed as the % of the shoots flowering using randomly selected 20 tagged shoots. Panicle length was measured after full bloom using three panicles taken at random. Data collected were analyzed by analysis of variance in RCBD. For treatment mean comparison LSD values were calculated (P=0.05).

An observation study was conducted in farmers’ fields at Upuldeniya, Anuradhapura to assess the effect of Paclobutrazol on mango productivity. Paclobutrazol was applied as a soil drench when the major leaf flush fully expanded at the rate of 1.00 g a.i/m for mango cultivars Karuthakolomban and Velleikolomban and 0.75 g a.i/m for cv Willard. Five trees of Karuthakolomban and three trees each of Velleikolomban and Willard were treated with Paclobutrazol. An equal number of trees were used as controls. Trees used for this experiment was 12 years old. After flowering, Imidacloprid (10 ml/10 l water) was sprayed to flower buds before full bloom to control Mango Hopper damage to flowers. Total number of fruits harvested in the following season was recorded and mean number of fruits per tree and standard deviation calculated for each treatment in each variety.

Results and Discussion

Mango trees treated with Paclobutrazol showed early bud break about two- weeks before the control trees. Flowering intensity in terms of the percentage of shoots flowered and lengths of flower panicles are shown in Table 1. Paclobutrazol enhanced the flowering intensity of both mango cultivars. There was no difference in the level of flowering between the two application rates used for both varieties. It is a common phenomenon that with flowering, some of the shoots of mango canopy produce leaf flush. It was noted that trees treated with Paclobutrazol had only a few shoots with new flush.

Paclobutrazol shortened panicle length significantly (Table 1) and the compacted flowers were visibly noted in treated trees. However, the rates used did not compact the flowers too much. Shorter flower panicles give an indication of the fact that Paclobutrazol has been taken up by the trees.

Number of fruits produced in mango cultivars Karuthakolomban, Velleikolomban and Willard were higher when trees were treated with Paclobutrazol (Table 2). Variation in number of fruits produced per tree was also lower with Paclobutrazol application. In all three varieties, flower bud break commenced one to two weeks before the flower bud break in control trees that were in close proximity to treated trees. This shows that Paclobutrazol promote early flowering as well.

Conclusions

Paclobutrazol applied as a color drench to mango cultivars Karuthakolomban, Velleikolomban and Willard after the major leaf is flush fully expanded increased flowering intensity and number of fruits per tree.

Table 1. Influence of rate of Paclobutrazol (g a.i./ m of canopy diameter) on percentage of mature shoots flowering and panicle length of mango cultivars
Willard and Velleikolomban

Table 2:  Average number of fruit per tree and standard deviation (STD) of mango varieties Karuthakolomban (KC), Velleikolomban (VC) and Willard (WLD) with and without Paclobutrazol (PBZ)

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Off-season mango production with
Paclobutrazol and Thiourea

K. H. S. Peiris

Fruit Crops Research and Development Center

Kananwila, Horana

ABSTRACT

Experiments were conducted to evaluate Paclobutrazol {(+/-)-(R*,R*)-B-[(4-chlorophenyl)methyl]-alpha-  (1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol} and  Thiourea for off-season flowering in mango. Paclobutrazol applied at 0.50 - 1.25 g a.i./m of canopy diameter as a soil drench promoted early and uniform flowering in mango cultivars Willard and Velleikolomban. Application of Paclobutrazol also reduced the leaf flush emerged at flowering. On-farm observation trials with mango cultivars Karuthakolomban, Willard and Velleikolomban showed that Paclobutrazol increased fruit yield while yield variation among trees were lower in the treated trees than in the control trees. Thiourea applied as a foliar spray of 0.50 % aqueous solution to mature shoots induced flowering in mango varieties Carabao, Kohu-amba, Nam Doc Mai and Willard 11-21 days after Thiourea application. These observations suggest that Paclobutrazol and Thiourea can be successfully used to develop an off-season fruit production technology for some mango varieties.

Keywords: Mango flowering; Off-season flowering; Growth regulators

INTRODUCTION

            Mango production in Sri Lanka is seasonal. Majority of trees in the Wet and Intermediate Zones flowers in January through March for the Yala crop harvested in May - July that is considered as the main crop for above-mentioned agro-climatic zones. Trees in the Dry Zone flower July through September for the main Maha crop harvested in November-January. Mangoes are mainly cultivated as a rain-fed crop, thus the time of flowering and harvesting may shift considerably depending on rainfall distribution patterns. Abundant production of in-season mangos within short period of time leads to low prices. Production drops in between the two seasons resulting in higher prices. Therefore, an off-season mango production technique is very important for production management of mango.

            Reliable flowering is necessary to obtain consistent production of mango under tropical climatic conditions. Flowering from one season to the other is unreliable because of the environmental signals for flower initiation is often inconsistent, subtle or poorly defined. Understanding of the factors controlling flower bud initiation in mango trees has been very limited. An alternative to dependence upon environmental signals for flower initiation is the development of management strategies that can substitute these signals.

A number of diverse chemicals that have growth regulating properties in plants have been tested for promoting/inhibiting flower production in mango in different countries (Chacko, 1991). Paclobutrazol, a strong gibberellin biosynthesis inhibitor, has been reported to be effective in promotion of flowering in many fruit crop species including mango (Burondkar and Gunjate, 1991; Charnvichit  et al., 1991; Dissanayake, 1989; Hiller and Rudge, 1991; Jose and Roboucas, 2000; Kulkarni, 1988; Peiris, 2001; Tongumpai et al., 1989; Tongumpai et al., 1991; Tongumpai et al., 1997; Winston, 1992). Paclobutrazol as soil drench and foliar spray were effective for promotion of flowering in mango, however, soil drench was more significant, convenient and cost effective (Burondkar and Gunjate, 1991; Winston, 1992). Application of 0.75 and 1.00 g a.i./m of canopy diameter of Paclobutrazol to mango cv Willard increased flowering intensity significantly. However, flowering intensity was not different between the two concentrations tested showing that even lower rates of application would be able to promote profuse flowering in cv Willard (Peiris, 2000).

It has been demonstrated that foliar spray of aqueous solutions of potassium nitrate (Bondad and Linsangan, 1979; Sergent et al., 1997; Sergent et al., 2000), ammonium nitrate (Medina and Nunez, 1997) and Thiourea (Tongumpai et al., 1997; Nartvaranant et al., 2000) can induce flowering in certain varieties of mango. A single application of above chemicals induced floral bud break in mature shoots two to three weeks after application.

            Though growth regulators have been tested for promoting/inhibiting flower production in mango in different countries, their effects have been limited to certain cultivars and geographical locations (Chacko, 1991). Therefore, growth regulator chemicals and application rates that can promote or induce flowering must be tested under local conditions for the locally available mango varieties. The objectives of these studies were to study the influence of application rate of Paclobutrazol on enhancement of flowering and fruit production in mango and to study the efficacy of Thiourea as a dormancy breaking chemical to induce floral bud break in mature shoots of selected mango cultivars.

MATERIALS AND METHODS

Experiment I

            A field experiment was conducted at Government Seed Production Farm, Maha Illuppallama, to study the effect of rate of application of Paclobutrazol on flowering of mango cultivars Velleikolomban and Willard. Three rates of Paclobutrazol (0.00, 0.50 and 0.75 g a.i. /m of canopy diameter for cv Willard and 0.00, 0.75 and 1.25 g a.i. /m for cv Velleikolomban) were tested. The formulation used was a wettable powder with 10% Paclobutrazol. The amount to be applied to each tree was dissolved in 1.5 l of water and applied as a collar drench around the base of tree at about one month after leaf bud break when the leaf flush was fully expanded.

Experiment was conducted in a RCBD with six single-tree replicates. Trees were 8 years old. Experiment was blocked according to tree size as measured by stem girth at 30 cm above the ground. Mango trees selected for this experiment had more than 80% of the shoots in the canopy as new flush. 

Flowering was assessed as the % of the shoots flowering using randomly selected 20 tagged shoots. Panicle length was measured after full bloom using three panicles taken at random. Data collected were analyzed by analysis of variance in RCBD. For treatment mean comparison LSD values were calculated (P=0.05).

Experiment II

            An observation study was conducted in farmers’ fields at Anuradhapura to assess the effect of Paclobutrazol on mango productivity. Paclobutrazol was applied as a soil drench when the major leaf flush fully expanded at the rate of 1.00 g a.i/m for mango cultivars Karuthakolomban and Velleikolomban and 0.75 g a.i/m for cv Willard. Five trees of Karuthakolomban and three trees each of Velleikolomban and Willard were treated with Paclobutrazol. An equal number of trees were used as controls. Trees used for this experiment was 12 years old. After flowering, Imidacloprid (10 ml/10 l water) was sprayed to flower buds before full bloom to control Mango Hopper damage to flowers. Total number of fruits harvested in the following season was recorded and mean number of fruits per tree and standard deviation calculated for each treatment in each variety.

Experiment III

            To study the effect of Thiourea on floral bud break of mango, an observation study was conducted at FCRDI, Maha Illuppallama, using 14 mango varieties. An aqueous solution of 0.75% Thiourea was sprayed to half of the canopy of selected trees using a modified knapsack sprayer. Trees selected for this experiment had mature shoots suitable for flower induction. Flowering response was recorded up to four weeks after application of Thiourea.

RESULTS AND DISCUSSION

            Mango trees treated with Paclobutrazol showed early bud break about two- weeks before the control trees. Flowering intensity in terms of the percentage of shoots flowered and lengths of flower panicles are shown in Table 1. Paclobutrazol enhanced the flowering intensity of both mango cultivars. There was no difference in the level of flowering between the two rates of application used in both varieties. It is a common phenomenon that with flowering, some of the shoots of mango canopy produce leaf flush. It was noted that trees treated with Paclobutrazol had only a few shoots with new flush.

Paclobutrazol shortened panicle length significantly (Table 1) and the compacted flowers were visibly noted in treated trees. However, the rates used did not compact the flowers too much. Shorter flower panicles give an indication of the fact that Paclobutrazol has been taken up by the trees. Winston (1992) showed that panicle size reduction is due to effect of Paclobutrazol, but not caused by an increase in number of panicles. Excessively compacted panicles may fail to set or hold fruit. Moreover, such excessively compacted panicles are more susceptible to insect and pest attacks.

            Number of fruits produced in mango cultivars Karuthakolomban, Velleikolomban and Willard were higher when trees were treated with Paclobutrazol (Table 2). Variation in number of fruits produced per tree was also lower with Paclobutrazol application. In all three varieties, flower bud break commenced one to two weeks before the flower bud break in control trees that were in close proximity to treated trees. This shows that Paclobutrazol promote early flowering as well. These results agree with numerous studies where promotion of early and profuse flowering and higher yields in mango with Paclobutrazol has been reported (Burondkar and Gunjate, 1991; Dissanayake, 1989; Kulkarni, 1988; Peiris, 2000; Tongumpai et al., 1991; Winston, 1992).

Observation study conducted to ascertain the efficacy of Thiourea as a mango flower inducer showed that out of 14 varieties tested, four varieties i.e. Carabao, Kohu-amba, Nam Doc Mai and Willard responded positively with flowering (Table 3). Carabao shoots showed the earliest bud break 11 days after Thiourea application while Kohu-amba flowered 22 days after treatment. Repeating the experiment with those responsive varieties for three years confirmed that Thiourea could be effectively used to induce floral bud break in mature shoots of these mango varieties.

            Unpredictable flowering, yield and production are due primarily to unnecessary growth flushes that emerge as a result of various environmental stimuli at various times during flush maturity. Such additional leaf flushes result in immature shoots on the tree during the period of natural flowering. It is noted that when Paclobutrazol is applied after the leaf flush is fully expanded, it can effectively control emergence of unwanted leaf flushes until the shoots are fully mature and ready to flower.

When the shoots are fully mature, it is necessary to break dormancy of shoots to stimulate floral bud break, as and when the grower desires to get flowers. As shown in this study, Thiourea can be used for this purpose in some mango varieties. Further studies are required to determine if other varieties respond with higher concentrations of Thiourea or with modified application methods. If the inactivity is due to a failure in chemical uptake, an additive to increase Thiourea uptake might be advantageous.

Chemicals such as aqueous solutions of potassium nitrate, ammonium nitrate and calcium nitrate may also be used to stimulate bud break and needs to be tested with varieties that do not respond to Thiourea. However, these chemicals are explosives and therefore should be handled with care. Moreover, as shown in the literature, higher concentrations are required for the above chemicals. Therefore, safety and cost considerations must also be taken into account when using such chemicals.

A package of technology for off-season mango production needs 1. A technique to get the leaf flush mature for about 4-5 months without additional flushes and 2. A technique to induce floral bud break in mature shoots. Paclobutrazol can be effectively used as a valuable tool to suppress the growth of additional flushes in order to promote profuse flowering in mango trees. Thiourea works with some mango cultivars as an efficient dormancy breaker and cause floral bud break in mature mango shoots and therefore it can be used to get flowering on trees as and when the grower desires.

CONCLUSIONS

Paclobutrazol applied as a color drench to mango cultivars Karuthakolomban, Velleikolomban and Willard after the major leaf is flush fully expanded increased flowering intensity and number of fruits per tree. Thiourea can be used as a 0.5% aqueous foliar spray to induce flower bud break in mature mango shoots in some mango cultivars. These preliminary results suggest that these two growth regulators can be used to control growth, maturity and flowering of mango shoots that is an important prerequisite for off-season production of mangoes. Further research is required to fine tune this technology and to apply the same for other mango cultivars grown in Sri Lanka.

REFERENCES

Bondad, N. D. and E. Linsangan.1979. Flowering in mango induced with potassium nitrate. HortScience 14:527-528.

Burondkar, M. M. and R.T. Gunjate.1991. Regulation of shoot growth and flowering in Alphonso mango with Paclobutrazol. Acta Hort 291: 79-84.

Chacko E. K.1991. Mango flowering - still an enigma! Acta Hort 291: 12-21.

Charnvichit, S., P. Tongumpai, C. Saguansupyakorn, L. Phavaphutanon and S. Subhardrabandhu.1991. Effect of Paclobutrazol on canopy size control and flowering of   mango cv. Nam Dok Mai Twai no. 4, after hard pruning Acta Hort 291: 60-66.

Dissanayake, L. D. 1989. Soil applied Paclobutrazol can induce flowering in mango. Krushi 12: 16-23.

Hillier, G.R. and T.G. Rudge. 1991.  Promotion of regular fruit cropping in mango with Cultar. Acta Hort 291:51-59

Jose, A. and T.N.H. Reboucas. 2000. Use of Paclobutrazol in mango orchards in southwest region, Bahia State, Brazil. Acta Hort 509: 713-718.

Kulkarni, V. J. 1988. Chemical control of tree vigor and the promotion of flowering and fruiting in mango using Paclobutrazol.  J. Hort. Sci. 63:557-566.

Medina-Urrutia, V. M. and R. Nuñez-Elisea.1997. Summer promotion of vegetative shoots to increase early flowering response of mango trees to ammonium nitrate sprays. Acta Hort 455:188-201.

Nartvaranant, P, S. Subhadrabandhu and P. Tongumpai. 2000. Practical aspect in producing off-season mango in Thailand.  Acta Hort 509:661-668.

Peiris, K.H.S. 2000. Flower induction studies for off-season fruit production in mango. Annual Research Report. Field Crops Research and Development Institute, Maha Illuppallama, Sri Lanka.

Sergent, E., D. Ferrari and F. Leal. 1997. Effects of potassium nitrate and Paclobutrazol on flowering induction and yield of mango (Mangifera indica L.) Cv. Haden. Acta Hort 455: 80-187.

Sergent, E., F. Leal and M. Anez. 2000. Potassium thiosulphate, urea and potassium nitrate applications on vegetative and floral growth in mango ‘Haden’ Acta Hort 509: 653-660.

Tongumpai, P., N. Hongsbhanich and C.H. Voon.1989. ‘Cultar' - for flowering regulation of mango in Thailand. Acta Hort 239:375-378.

Tongumpai, P., K. Jutamanee and S. Subhadrabandhu. 1991. Effect of Paclobutrazol on flowering of mango cv. Khiew sawoey.  Acta Hort 291: 67-70.

Tongumpai, P., S. Charnwichit, S. Srisuchon and S. Subhadrabandhu. 1997. Effect of Thiourea on terminal bud break of mango. Acta Hort 455:71-75.

Tongumpai, P., K. Chantakulchan, S. Subhadrabandhu and R.  Ogata. 1997. Foliar application of Paclobutrazol on flowering of mango. Acta Hort 455:175-179.

Winston, E.C. 1992. Evaluation of Paclobutrazol on growth, flowering and yield of mango cv. Kensington Pride. Aust. J. Exp. Agric. 32:97-104.

Table 1. Influence of rate of Paclobutrazol (g a.i./ m of canopy diameter) on percentage of mature shoots flowering and panicle length of mango cultivars Willard and Velleikolomban.

Table 2:  Average number of fruit per tree and standard deviation (STD) of mango varieties
Karuthakolomban (KC), Velleikolomban (VC) and Willard (WLD) with and without
Paclobutrazol (PBZ).

Table 3. Effect of foliar spray of 0.75 % Thiourea solution on flowering response of some
mango varieties.

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