Mango Flower Induction and Production Strategies

Mango Flowering Induction Strategies In Six Latin American Countries

Pánfilo C. Tabora, Jr., EARTH University José R. Mondoñedo, S. River Condo 503 P. O. Box 4442-1000, San José Costa Rica 930 Astern Way, Annapolis MD 21401-714

Ramón C. Barba, MADECOR Javier Ramos, Urb. Bello Horizonte P. O. Box 152, College, Laguna, Phil 4031 Km. 3 S/N, Zona Industrial, Piura, Perú

Keywords (Mangifera x indica), mango, potassium nitrate, ammonium nitrate, flower induction

Abstract A 16-year experience is reviewed covering 6 countries (Guatemala, Honduras, Nicaragua, Costa Rica, Ecuador and Perú). Potassium nitrate, ammonium nitrate (1%-5%), bark ringing, pruning, irrigation control, timing of application and the use of paclobutrazol, flowerset and flowerkem were all tried. These experiences were supported by the USAID in Latin America. Potassium nitrate had better results in the warmer sites and ammonium nitrate had better results in the colder sites. Combinations of ammonium nitrate, potassium nitrate and flowerkem gave slightly better responses. Smaller, yellower and greener varieties responded better to potassiium nitrate and larger and redder varieties responded better to ammonium nitrate. Increasing concentrations near 5% and double applications gave better responses. Mangos with previous production had lower responses than those without production the previous year. Strategies are proposed and the continued use of these strategies are evaluated and related to experiences in other parts of the world.

INTRODUCTION Mango’s rise as an all-season tropical fruit in the supermarkets of the northern hemisphere just like banana has finally occurred after many trials (Cheema, 1954, Ruehle, 1956 and PCARRD, 1975). Among of the major technologies that have given it regularity is the flowering induction technology coupled with the relayed niche periods for different countries which complement Florida’s July-September niche (Campbell and Malo, 1976).

The flowering induction technology itself has had a transformation from centuries of observations on the draining (to dry) of the soils in India and also the burning of slashed debris (kaingin) in the Philippines which has become the smudging technique (Tabora, 1993). This smudging and drying have ushered theories on growth-regulating hormones in flowering and spawned much research in the 1960s.

Among the results of these researches have been the identification of potassium nitrate as an effective flowering inducer (Barba, 1974) and later the addition of ammonium nitrate and also urea as additives or as substitutes. Mango flower induction has become a regular practice and a necessary strategy in many mango production areas in order to ensure the production and quality of fruits at the time of the export niche. In this paper the objective is

1 to review the developments related to the use of flower induction for production and to discuss strategies to make mango production more efficient.

MATERIALS AND METHODS We focus only on six mentioned countries where work was much more extensive although the work was also done in Mexico, Brazil, Panamá and El Salvador. .

Work was conducted in the Brilliants Station in Guatemala, the Foundation Honduran de Investigation Arcola and the Escuela Agrícola Panamericana (El Zamorano) in Honduras, the Mangosa Farms in Nicaragua, the COONAPROSAL and Mango Tico, S. A. in Costa Rica, the Fundación Hualtaco in Perú and the Durexport farms in Daule, Ecuador.

The normal flowering season was the initial base for planning the application of the flowering inducers. Schedules of application started some 3, 2 and 1 months ahead of the normal flowering season in order to advance the flowering, or simply to make flowering uniform and programmable.

Different equipment were used in different places, but there were a few guiding rules: to have (a) mist application, (b) wetting the leaves up to the point of dripping, (3) wetting the terminal point or the leaves that attach to the terminals. Re-application was done when the rains occurred less than 6 hours after the application.

The experience was started in 1985 in the mango collection of the Pan-American Agricultural College in Honduras, then in 1987 in the Brillantes Experiment Station in Guatemala, the COONAPROSAL and Mango Tico farms in Costa Rica and in the Mangosa farm in 1988. The experience in Perú began in 1992 and that in Ecuador in 1995.

Several varieties were tested in the different collections of Guatemala, Honduras and Perú, but the focus of the study was based on 6 commercial varieties such as Erwin, Haden, Tommy Atkins, Kent and Keitt.

RESULTS AND DISCUSSION Responses of the different varieties to KNO3 The yellowish and smaller-fruited varieties (Carabao, Manila, Filipino, Julie, Fairchild, Haden, Irwin) responded fairly well to the induction in September (1989 and 1990) using KNO3 in the Brillantes Experiment Station in Guatemala (Table 1). Julie responded fast and was harvested early in January 1991 while the others were harvested in March 1991 with sprays of KNO3 in September-October, 1990. The larger varieties Tommy Atkins, Kent, Lancetilla and Keitt responded sporadically and the responses were also much later. These were the same observations as those in Costa Rica.

In Honduras, the responses to KNO3 were more than 80% flowering in such varieties as Sensation, Irwin, Haden, Julie, Cambodiana, Carabao and Arumanis at the Pan American College of Agriculture (Zamorano). Again, the larger varieties (Tommy Atkins, Kent, Keitt and Lancetilla) responded later and were more sporadic just as in Guatemala.

2 In Perú, Edward, Haden, Tolbert and Cambodiana responded to KNO3 at 80% or more of flowering at the Hualtaco Experiment Station in Piura with spraying in May and June. Kent responded erratically as did Keitt, Tommy Atkins, Rosado and Chato. Piura´s climate is such that the cold weather in July and early August triggers the response of flowering in late August and September. For a harvest beginning in November and going up to January spraying has to be done earlier in May and June, just when the leaf flushes that come out in March are just about maturing. This is in the case of the late- maturing varieties such as Tommy Atkins, Keitt and Kent (Table 1).

Table 1. Responses of different varieties to KNO3 at 2% spray trials in Guatemala, Honduras and Perú from 1987 to 1993.

80%= High Response Locations (countries where trial were made) and the rate of 30% =Low Response Response of the different varieties Costa Rica (Mango Tico, S. A., COONAPROSAL) High Yellow Haden, Irwin Medium Red Haden, Tommy Atkins Low Keitt, Kent Guatemala (Brillantes Experiment Station, Min. of Agriculture) High Carabao, Manila, Filipino Medium Haden, Julie, Fairchild, Irwin, Jaayake, Mora, Pope Low Tommy Atkins, Kent, Keitt, Lancetilla Honduras (Escuela de Agricultura Panamericana, El Zamorano) High Sensation, Irwin, Haden, Julie, Cambodiana, Carabao, Fairchild, Arumanis Medium Ruby, Springfels, Palmer Low Tommy Atkins, Keitt, Kent, Lancetilla Perú (Fundación Hualtaco Experiment Station) High Edward, Haden, Tolbert, Cambodiana Medium Criollo, Chato, Tommy Atkins, Keitt, Low Kent, Rosado

Responses to type and concentration of the growth regulators. Five different types of growth regulators were tested: KNO3, NH4NO3, Flowerkem, Flowerset and Paclobutrazol. Flowerkem and Flowerset are commercially available in the Philippines as a combination of different flower-inducing hormones. Paclobutrazol is available in Australia as a growth retardant and also in the U.S. A. under the trade name Bonzai, normally used to dwarf ornamentals. A variant of Paclobutrazol is Uniconazol (Mondoñedo, 1994).

The results show that KNO3 is increasingly more effective from Honduras towards the south to Perú and NH4NO3 is increasingly more effective towards the north to Mexico for the more recalcitrant varieties such as Tommy Atkins and Kent. Concentrations as high as 8% of KNO3 was not effective in Guatemala near the border of Mexico, and this was so in Mexico itself. Ammonium nitrate, however, was highly effective in Mexico and Guatemala and the higher elevations of Costa Rica (Mondoñedo, 1994). On the reverse,

3 trials in Piura, Perú showed that ammonium nitrate was less successful than potassium nitrate especially in the lower areas.

Flowerkem and Flowerset, however, induced flowering in Guatemala at concentrations of 4% to 8% in Tommy Atkins. Increasing concentrations however, have a burning effect on the tips and margins of the leaves. Due to this, double applications have been made with increasing success, but using lower concentrations to avoid the burning effect. Another strategy is to combine Flowerkem with KNO3 and NH4NO3 to improved the performance of the two chemicals (Tables 2 a, b).

Table 2a. Responses to combinations of flowering inductors in different varieties of mango in the Hualtaco Experiment Station, Piura, Perú (1993-1994).

Variety Flower inducers % of Induction Kent 45.0 Chato 2% KNO3 only 47.5 Criollo 96.5 Haden 57.5 Kent 2% KNO3 (90 parts) 60.0 Chato + 45.0 Criollo 1% Flowerkem (10parts) 90.0 Haden 32.5 Kent 22.5 Chato 2% NH4NO3 only 45.0 Criollo 60.0 Haden 60.0 Kent 2% NH4NO3 (90 parts) + 2.5 Chato 1% Flowerkem (10 parts) 0.5 Criollo 99.0 Haden 62.5

We also made similar trials for Chato, Criollo and Haden in farmers´ fields using the combination 2%KNO3 at 90 parts volume combined with 1%Flowerkem at 10 parts volume in Chato, Criollo and Haden (Table 2b).

Table 2b. Responses to combination of inductors in different varieties of mango in two trials in farmers´ fields in Piura, Perú (1993-1994).

Variety, Trial 1 Flower Inducers % Induction Chato 2%KNO3 at 90 parts and 7.0 Criolo 1%Flowerkem at 10 parts 65.0 Haden, Farm A “ 71.3

Variety, Trial 2 Flower Inductor % Induction Haden, Farm B 1% NH4NO3 92.5 Haden, Farm B 2% NH4NO3 45.0

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Haden variety remained erratic in response to both potassium and ammonium nitrate even with changes in concentrations. Although with uneven success, it is notable that the addition of Flowerkem to KNO3 increased the flowering significantly. This was not so apparent in the combination with NH4NO3. Criollo did quite well in several trials.

Because Chato was recalcitrant to KNO3, Flowerkem and to NH4NO3 at the Hualtaco trials, we tried Flush, another cocktail combination designed for vegetative shoot development. This, in fact gave us an average flowering of 75%. Some components of Flush (ANAA and GA) may be involved in the induction of flowering.

As Haden was also somewhat recalcitrant to 2% KNO3 applications, we tried increased dosages of KNO3 for Haden at low elevation and another at a higher elevation. The results indicate better results in lower elevation (Table 3) area. The results here are the same as those in Honduras and Costa Rica.

Table 3. Flowering responses of Haden variety at increased dosages of KNO3, at high and low elevations, Piura Perú (1993-1994)

Dosages of KNO3, % % Flowering, % Flowering, Low Areas High Areas 1 95.0 10.0 2 90.0 22.5 3 85.0 35.0 4 94.0 45.0

Suspecting that the results would be erratic, we also had a trial where we coupled the increase in concentration of KNO3 with a combination with Flowerkem. To 80 parts of 1% and 2% KNO3 concentrations we added 20 parts of 1% Flowerkem. At higher concentrations of 3% and 4 % of KNO3, we lowered the amount of Flowerkem to 10 parts. Flowerkem greatly improved flowering induction (Table 4).

Table 4. Flowering responses of Haden variety at increased dosages of KNO3 combined with Flowerkem (F), at high and low elevations, Piura, Perú (1993-1994).

% KNO3 and Proportion % Flowering, % Flowering, to Flowerkem (F) of 1% Low Areas High Areas 80% of 1% KNO3-20%F 96.5 22.5 80% of 2% KNO3-20%F 96.0 45.0 90% of 3% KNO3-10%F 95.0 67.5 90% of 4% KNO3-10%F 99.0 77.5

Flower induction was improved by Flowerkem at both high and low elevations and progressive concentrations with a slight dose of flowerkem enhanced flower induction. This means that there are other substances in flowerkem acting to improve flowering. We

5 also tried to check again the response of the Haden variety to NH4NO3 at a farmers´ fields and got an uneven result.

Response of trees with production in the previous year and those without production in the previous year. Kent and Haden varieties that produced the year before were tested for responses to KNO3 and NH4NO3 applications to determine their difference with those trees with no production the year before. The results (Table 5) indicate that plants with production the previous year still responded, but much less than those which did not produce the previous year. The Davenport (1988) model for flowering in mangos predicted this.

Table 5. Comparison of rate of flowering of Haden and Kent varieties in those trees with previous production and without, Piura, Perú (1995).

Inductors: Induction: Trees Induction: Trees Variety/Farm KNO3 and Produced Fruits Did not Produce Flowerkem (FK) Previous Year Previous Year Kent, Farm 1 2%KNO3, 90 parts 12.75 21.25 + 1% FK, 10 parts Haden, Farm 1 “ 26.25 47.50 Haden, Farm 2 “ 69.00 85.00 Haden, Farm 2 2%NH4NO3, 90 parts 83.20 96.80 + 1% FK, 10 parts

Preparation of the plants and the plantations While flower induction may be initiated solely with chemical sprays, there are also other practices that can enhance the success of the induction applications. In a farm near Lake Managua, Nicaragua, with a high water table, mangos would not flower with the spray applications and instead, vegetative flushes would be observed on almost all varieties. Bark ringing has been practiced and has proven to be a valuable complementary strategy under that particular condition. Bark ringing, just as bark slashing has been old practices and have been replaced by the chemical sprays in the Philippines (Tabora, 1993). In bark ringing in Nicaragua the bark is looped with a metal wire and tightened to affect a cut on the bark. There is no removal of the bark.

Another practice, which is done in Piura, is a scheduled pruning and then an application of foliar fertilizers (Potassium Nitrate) on the flushes that has an effect of “maturing” the vegetative shoots and preparing them for the second application, which successfully induces the flowering. A combination of pruning, bark ringing and the application of paclobutrazol have also shown excellent results. These are strategies that can be alternated depending on the status of the farm and the plants.

Strategies for effective flowering. In Costa Rica, the periods of October and November have not been totally dry and there have been failures in the flowering of the trees such that the window of February 15 to April 15 is not adequately filled. Sometimes during the whole of February and a part of

6 March there are no exportable fruits in sufficient quantities. This may need mangos under protected plastic canopies and with drainage in order to ensure that the applications are not washed out and that the soils are not too wet to encourage the plant to produce vegetative flushes. Mangos under canopies in Okinawa, Japan have been successfully produced.

As a strategy, however, the idea is to make the trees easy to spray at any time, and both canopies as well as dry soils are good conditions for effective flower induction. This may in fact be a tool for both advancing flowering and also for delaying the flowering when the mangos are now under full control of the farmer. Timing of flowering becomes then a matter of programming the practices and ensuring the appropriate physiological state of the trees and the right environmental conditions for flowering.

Canopies can also be used to modify the cold climate, which occurs in the Ecuadorian Daule area, which also receives a high amount of rainfall. Japan has successfully used this strategy to modify the climate for mangos. This is not necessary for Piura, which dry.

Suggestions for the future. As we have neared mastery of flowering induction in mangos what remains is ensuring that the trees are adequately healthy in order to receive the signals for flowering induction and also ensure that we have good production. There may now be a need to couple flowering induction with strategies to ensure that flowering encourages quality of the fruits and this may be related to the quality of the flowers and their distribution in a raceme.

Close monitoring of the practices should also give us clear warning signals of failures and problems due to the possible stress that can be accumulated by the trees due to the chemicals specially paclobutrazol and uniconazol.

Our experience in KNO3 and in NH4N03 is now more than 35 years, enough time to tell us that the plantations would have been damaged due to their applications. There are now plantations and trees (in the Philippines) that have received these inductors for 30 years that continue to be healthy although at some points there were indications of stress on some trees. There are now also many agronomic practices that can also be used to relieve stress such as pruning, rejuvenation, and even a few years of rest for the trees.

For organic mango production, the only present avenue without the chemicals will be to use the very old strategy, which is to use smoke. This may find objections, due to the release of CO2 into the atmosphere and therefore another strategy might have to be developed. The use of high nitrogen organic materials such as extracts of fishmeal or meat meal might be able to give us some useful strategies.

CONCLUSIONS Flower induction in mangos using potassium nitrate and ammonium nitrate has finally become a regular practice in many countries. However, as we begin to understand its

7 requirements, we still see room for improvement. This efficiency may still be improved with the complementary practices such as the preparation of plants, reduction in sizes of the trees, regular pruning to synchronize vegetative and reproductive stages, maturation of the flushes, and modification of the microclimate. These alternatives can still make mango production much more lucrative and much more programmable.

ACKNOWLEDGEMENTS We acknowledge the support of many colleagues, businessmen, farmers and researchers who have given us many insights into this work: Dr. Thomas Davenport, Ing. Emilio and Reynaldo Hilbck, Ing. Pedro Echeverria, Ing. Teofilo Ramirez, Ing Luis Castillo, Dr. Romeo Martinez, Dr. Mario Contreras, Dr. Manuel Zantua, Ing. Francisco Miranda, Ing Gino Pinargote, Ing. Pedro and Guillermo Yglesias, and Ing. Victor Zapata Solis among others. We also acknowledge the support of the U. S. Agency for International Development in Perú, Guatemala, Honduras, Costa Rica, Nicaragua and Ecuador, U. S. D. A., Dole Co., Int´l and Chiquita Brands. Likewise the FHIA in Honduras, CINDE and Mango Tico, S.A. in Costa Rica, Durexport in Ecuador, The Gremial and PROEXAG in Guatemala, ADEX in Perú, MANGOSA, APEN in Nicaragua and ACDI in Washington, D. C.

Literature Cited Barba, R. C. 1974. Induction of flowering of the mango by chemical sprays. Proc. of the Crop Science Society of the Philippines. Los Baños, Laguna, Phil. Campbell, C. W. and S. Malo. 1976. Mango cultivars in Florida. Proc. Trop Region Amer Soc. of Hort. Sci. 20:143-150. Cheema, G., S. Bho and C. Nark. 1954. Commercial fruits of India. MacMillan Co., NYNY. Davenport, T. 1988. Hypothetical model regulating vegetative and reproductive growth phases in mango and citrus. Univ. Of Florida. Mimeographed. 12 pages. Mondoñedo, J. 1994. Procedimientos recomendados para la inducción floral. Guía sobre producción de mango. FHIA, La Lima, Honduras. p 49-58. PCARRD. 1975. The Philippines Recommends for Mango. Phil Council for Agriculture and Resources Research and Development, Los Baños Laguna Phil. p 11-13. Ruehle, G. D. And R. B. Ledin. 1956. Mango growing in Florida. University of Florida Bull. 574. 90 pp. Tabora, P. 1993. Métodos para extender la temporada de producción de mango. Proc. Conference: El Mango: Fruta de esta Década. 7-9 Sept. Piura, Perú. 6 pages.

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