The mango in Porto Rico

Front matter

i February 4, 1918.

* 379

D. W. MAY, Agronomist in Charge.

Contents

Page.

Introduction 3

Soil 4

Introduction

The mango industry in Porto Rico has developed practically without attention or interest on the part of the inhabitants, although the fruit is one of the most important of the island, as it is of most tropical countries. The common types, all of which grow without cultivation, are as a rule prolific, the fruit of the best sorts being free from serious insect pests and diseases, but all are of ordinary or poor flavor with an abundance of objectionable fiber in the flesh. With few exceptions the fruits are small, and this, together with their poor keeping qualities, makes them unsatisfactory as a commercial crop.

The production of the superior varieties of mangoes, notably those from India and the East Indies, is a new industry but one worthy of greatly increased interest in Porto Rico, as the climate and soils are suitable and the best markets of the United States may be reached within a very few days. Home markets for this fruit could be quickly developed also, as the liking for the mango is universal among the inhabitants of the island and large quantities of the common types are consumed as soon as they are ripe enough to be edible.

The problems confronting the commercial production of superior mangoes here are in many respects those of a new industry. Methods of asexual propagation are not known among the planters, but chance seedlings happening to spring up in desirable places are protected to furnish the future supply of fruit. The trees have not been cultivated nor the suitability of the soil tested. The present method of marketing is to shake the crop from the tree and to load it loosely into cars or wagons for transportation to local markets or those in other parts of the island. Tests with fruits of superior varieties show that they will keep longer after harvest than common kinds, but that they must be handled carefully in order to reach distant markets in attractive condition. There is a wide difference between varieties in vigor of trees and in size and quality of fruit, and as the general conditions in Porto Rico are suited to the production of this fruit, the proper selection of varieties for planting seems to be the most important consideration. The success of an orchard will depend mainly upon the planting of prolific varieties suited to the locality and with fruit of a size and quality to command a ready market.

As the observations here reported are drawn from the work of several years during which trees of many varieties have been imported, propagated, and in some cases brought into satisfactory production, they should prove of value to those who expect to plant mangoes for sale or for home use. Over 40 varieties which have not yet fruited will be discussed in subsequent reports.

SOU.

Porto Rico has a very wide range of soil types, a given type, however, occurring in only small areas in any section. As the mango tree is found in abundance iri almost all parts of Porto Rico, the quality of soil in which it is planted seems to be an unimportant factor in its growth, provided the depth of the soil is considerable. A shallow soil underlain with stone or hardpan, although sufficiently deep to produce shrubs or other low-growing wild vegetation, will not satisfy the needs of the deep-rooted mango, whose growth in such ground will be slow and its yield poor, at least after the first few years. The application of fertilizers, however, will materially decrease the depth of soil required. While the mango is less affected by the quality of the soil than many other fruit trees, it is sensitive to an overabundance of soil moisture. It is never vigorous or prolific in low, poorly drained lands or on higher planes where the water level is near the surface throughout long periods. Where subdrainage is poor, the vigorous roots which penetrate to some depth during a dry season are always severely injured if not killed by the excess of water during the period of heavy rains lasting for several months each year in almost all parts of Porto Rico. Subdrainage is generally poor through the rolling districts and also in the western part of the island where the mango is most plentiful, though, in the latter district practically all of the mango trees are found growing at the brink of steep hillsides, on short, narrow knolls and ridges, near road cuts or on grades, etc. A ditch only 2 or 3 feet deep will often cause a tree growing at its edge to make a normal-growth and bear good crops. Where the soil is loose, with good filtration of water, large and prolific trees may be found on level land or even in depressions where water remains above the surface a few hours after heavy rains. Mango trees are often found on very light, unfertile sand, which may be a few feet in depth and still produce flourishing growth if the subsoil is suitable. As the mango, like most other fruit trees, thrives best on a deep, loose loam with good drainage and a high percentage of humus, those who intend planting it commercially should secure, if possible, this type of soil. Imported mango trees planted on such land in Porto Rico have reached a height of 26 feet and a spread of 34 feet in 12 years, while others of the same variety, receiving an equal amount of rainfall litit growing in a soil with poor subdrainage, are at the same age 16 feet tall and 21 feet in spread. However, the latter have been more prolific.

CLIMATE.

The temperature in Porto Rico is well suited to the production of mangoes, for, as in other islands in this region, it is swept by warm trade wind and sea breezes which keep it always warm enough for the best growth of the trees. This is especially true in the low-lying districts, those which lie between the sea and the mountains of the interior having an average daily maximum temperature varying from 84° F. in winter to 89° in summer and a minimum from 66° F. in winter to 73° in summer, an excellent temperature for the mango, which is more tropical than subtropical in its needs. Through the interior of the island the temperature averages from 2° to 3° cooler during the day and from 5° to 6° cooler at night. At the highest elevations, a number of which are over 2,000 feet, the temperature during the coldest months is occasionally in the lower fifties. Here the mango trees grow well but fruit very poorly, the small crops probably resulting directly from the temperature.

While the temperature is even and satisfactory, the rainfall and general humidity vary considerably in different districts. In some places, especially through the interior and along the northern slopes, the rainfall is too great during the mango blossoming season for the best fruit production. Along the western and southern coasts the greater part of the year's rainfall occurs during summer and fall, and during late winter and spring the rainfall is always light and the drought usually severe. Here the crop of mangoes is almost invariably heavy. The trees make a satisfactory growth unless the drought is very long and severe, as they are capable of thriving on rather slight moisture as well as of withstanding a little excess moisture without visible injury.

Where the drainage is good the only time at which the rains have proved detrimental is while the trees are blossoming. Rains are always injurious to mango flowers, as they wash away the pollen, injure the stigma, and cause the pollen to remain damp, thereby improving conditions for the growth of the anthracnose fungus which is so destructive to the blossoms. The mechanical injury is easily effected, for the one pollen-bearing stamen and the prominent pistil are not protected by the small, widely divergent petals. The moistening of the pollen by the intermittent rains and low clouds, which drift for some distance down the slopes of the highest hills of Porto Rico, encourages the growth of the blossom-destroying fungus, and this, together with the mechanical injury due to the heavy rainfall in these sections during the mango blossoming season, is probably responsible for the low yields and frequent fruit failures.

The importance of moisture conditions should not be overlooked in planting mangoes. Fortunately for the prospective orchardist the rainfall in Porto Rico for corresponding months in different years varies little, this constancy permitting the selection of a locality where the mango blossoms during a season of light rainfall. Where irrigation water is obtainable, a dry section would prove most satisfactory as the blossoms would set fruit regularly and the fruiting tendency could be encouraged by the proper application of water.

The effect of wind on mango blossoms is also probably important, although seldom referred to. Its stimulating effect may induce blossoming and its drying effect no doubt enables this fruit to set. For a number of consecutive seasons it has been noted at Mayaguez that trees situated in exposed places always bear more heavily on the branches facing the prevailing winds, often producing a large percentage of their crop on the windward side. The drying action of the wind probably protects the blossoms from fungus attack, since the windward side of the tree is dry much earlier in the morning than the leeward side or than trees in low, wooded, or otherwise protected places, where the heavy tropical dews remain on the leaves until late in the forenoon. As the prevailing winds during February and March, the principal mango blossoming season, are from the northeast, the morning sun may be as necessary as the winds for inducing blossoming, although the section of the tree facing the wind is more prolific than that exposed directly to the morning sun, which is south of east at this season. The stimulating effect of wind on the growth of the branches is probably an important factor in the production of blossoms, as the wood growth and inflorescence are much heavier on the side of the tree facing the wind than on other portions, sometimes causing a very one-sided development (PI. I, fig. 1). This effect is more pronounced on imported varieties than on uncultivated Porto Rican types and more so on some of the imported varieties than on others. Those which afford the most striking examples of this in both growth and fruit production are Bennett, Paheri, Sandersha, and Cambodiana. While newly placed buds and grafts and small trees just transplanted should be protected from strong drying winds, the orchard site should be well exposed to the prevailing winds and morning sun.

BLOSSOMING.

Although in some parts of Porto Rico climatic conditions are not favorable to the setting of a crop of fruit, the mango is well adapted for fruit production, as it blossoms at intervals throughout the spring and thereby improves its chances of meeting suitable weather for pollination. From observations already made, it appears that the imported kinds have a longer blossoming season than the common sorts, as some of them bloom almost continuously for ten or more weeks when conditions do not permit the setting of a crop before the end of that time. To this class belong Sandersha, Totafari, and Amini, a single tree of the first having blossomed as early as December 10 and as late as May 10 the following spring, with the production of two heavy crops and a number of light crops of blossoms during the intervening time. Cambodiana, Bennett, Bulbulchasm, Sufaida, and others are varieties with long blossoming seasons.

In the southern and western portions of the island the mangoripening season is usually much longer than in other sections, as the drought which occurs during the late winter favors the fertilization of early and late blossoms. Under normal conditions only a very small percentage of the early blossoms produce fruit, while good crops have resulted from extremely late blossoms. As few varieties have been cultivated in Porto Rico over a long enough period to determine blossoming habits, close attention should be given the untested kinds and a careful selection made based on these habits before an extensive planting is made.

Where mango trees grow vigorously, as in nearly all parts of Porto Rico, they are inclined to bear no crop or very small ones for a season or more after they are of sufficient size and age to produce heavily. Varieties or individual trees which do not bear when sufficiently mature may be induced to blossom by any of a number of methods. Girdling, branch pruning, and root pruning are common practices, but they should be used with caution and moderation, as a tree may easily be so severely injured as to prevent its bearing for one or more seasons. Pruning back the ends of the branches to induce blossoming has been practiced with good results at the station. In the operation, from a few inches to a foot of the end of the branch was removed, depending upon the stage of maturity of the wood, leaving a few nodes from which the leaves had not fallen. From these nodes blossoms developed profusely, no blossoms appearing on untreated branches. To secure best results, the pruning should be done in the late summer or fall, several months before the blossoming time. This method should be employed on branches which are too low or too crowded or on those which would have to be removed later to improve the shape of the tree, as after a branch is pruned, it makes little growth for several weeks or months or even for a year or more after the fruit ripens, and by this time it may be well overgrown by surrounding branches.

As good results have been obtained from- girdling as from other methods. A branch 1 to 3 inches in diameter was selected on each of a number of trees and a band of bark removed in September. These branches produced good crops in the following spring, even when no fruits at all were borne on the remainder of the tree. Such favorable results, however, were obtained on varieties which are inclined to bear well and where the band of bark removed was wide enough to prevent the new bark from growing over the area too rapidly. Bands one-eighth and even one-quarter of an inch in diameter were overgrown so quickly that no effect was seen on the branch. Bands from one-half to three-quarters of an inch produce the best results, as they do not heal over until after the blossoming season, the callus growing downward over the wound at the rate of 1 inch a year. The photograph in Plate II, figure 1, was taken in April and shows a branch of Paheri, from which a band of bark 1£ inches in width was taken in September. This branch bore 39 fruits of extra large size and was the only branch of the tree to bear. The effect on Cambodiana, Bennett, and Amini was equally striking. Girdling the branches of 10-year-old trees of Davy's and Madras, varieties which have so far been very unproductive, some of the trees having never borne, did not induce fruiting. As removing enough bark to induce fruiting is very injurious to the branch, this practice is most profitably employed on undesirable branches which are to be removed later.

Root pruning has been recommended, although no definite results have been noted from experiments with it. It is best accomplished by cutting into the soil with a sharp spade about 2 feet inside the tips of the branches. In extreme cases the cutting may encircle the tree to a depth of 8 to 10 inches in heavy soil and even deeper in light soil where the root system is considerably below the surface. Cutting at such intervals as to sever the roots for one-half to two-thirds of the distance around the tree will induce blossoming under normal conditions without seriously checking the growth or thrift of the tree.

Plate I.

I o

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II Plate II

PROPAGATION.

Where it is desired to reproduce the qualities of the parent tree, simple and satisfactory methods for general use in mango propagation are inarching, or approach grafting, and bark grafting. Seedling trees of Cambodiana and a few other types will, it is claimed, produce fruit very similar to that of the parent and sufficiently uniform for orchard use, but seedlings should not be used for general planting until more information regarding the habits of the different types has been secured.

When any of the asexual methods of propagation are used, success in the work and development of the tree will depend mainly upon the seedling stock. To secure good stocks seed just taken from the fruit or those which have been removed only a few days should be used, as the seed lose their viability quickly and are very liable to decay after being removed from the fruits. To insure prompt germination and normal plants the seed should be husked before planting, care being taken not to injure them in any way. This may be quickly done by peeling off with a sharp knife a narrow strip of the husk which may then be readily opened. The husks of many of the East Indian varieties are very thin and easily removed, but those of the uncultivated Porto Rican types are very thick and tough and their removal difficult. Delay in growth and injury to plants are proportionately greater where the seed coat is not taken off.

To test the effect of taking off the husk three lots of 100 seeds each were planted, one with the husks removed, one with the husks cut on one side, and one with the husks entire. The seeds, all very uniform as to size and shape, had been taken from uniform fruits of the native variety Blanco, which has a very thick seed coat, and planted immediately after removal from the fruit. The following table gives the detailed record of the germination :

Effect of different seed treatments on germination.

Number of days after planting.

Percentage of seeds germinated.

Husked.

Opened on one side.

Unhusfced.

98 98 98 98

18 68 74 88 90

None.

This shows not only that the total number of husked seed germinated was somewhat greater than of unhusked seed but that the time required for germination was much shorter. Where the husks were 13137°— 18 2 not removed, the development of the plants was, in the majority of the cases, hindered, often so severely that they were discarded as valueless. Plate III shows plants of the same age from plantings of husked and unhusked seed, one an extreme specimen from an unhusked seed which is typical of about 30 per cent of the plants from seed planted in this manner (fig. 1, center).

Kernels which produce a single plant are preferable to those sending up a number of plants, as the seedlings are more thrifty and vigorous and are ready for use as stocks in a short time, while where a number of seedlings are produced they are very slender and slow growing and in many cases never become satisfactory for working. Among the wild Porto Kican types grown, Rosa and Redondo seldom produced more than one seedling, while all of the other more common ones produced two or more. The seedlings of East Indian varieties produce large thrifty plants which are preferable as stocks, as they grow faster than the Porto Rican kinds, and during the few years they have been under observation no undesirable qualities have been noted. Among the varieties tested Sandersha, Totafari, Alphonse, and Amini produce only one plant per seed and are most satisfactory as stocks. Cambodiana seedlings are vigorous, but, as from two to seven plants grow from a single seed, care must be taken to remove all but one of the seedlings soon after they appear, if a good stock plant is desired.

Whether the seeds are planted in pots or in the nursery the soil should be a rich loam with plenty of sand to insure good drainage, for if the growth of the seedling is checked by lack of food or excess of soil moisture it will be permanently injured and often will not recover its vigor sufficiently to be of value as a stock. The seeds require shallow planting to prevent suffocation.

GRAFTING.

When seedlings are somewhat thicker than a lead pencil (about f inch in diameter) and the bark has assumed a grayish color (about seven months after planting the seed) they are of a convenient size for grafting. Then as soon as they make a flush — that is, as soon as they are in a growing condition and the new red leaves are just appearing — they are ready for use. If the plants are thrifty they will remain in good condition for several days and often two weeks.

Branches must be selected for scions which have not made a recent flush, but are just on the point of starting a new growth. Such tips have rather mature wood and the buds nearest the end are swollen but not quite ready to open into growth. They should be cut below the third or fourth node. If any of the buds just below this point, on wood of the same age, are swollen preparatory to opening, the section bearing them will also be satisfactory and sometimes more desirable than the tip section for grafting, as this wood is often better developed. If at the time the stocks are just starting a new growth there are no branch tips suitable for scions, the upper axillary buds can often be forced into condition in a week or more by cutting off the tips of the branches.

To make the graft the seedling should be cut off by a smooth transverse stroke a few inches above the crown, a perpendicular slit about an inch in length being cut barely through the bark on one side of the upper end of the remaining stump (PL II, fig. 2). The scion, which is prepared by cutting the lower end with a smooth slanting surface about an inch in length having a sharp, wedge-shaped point, is then forced gently down under the lips of the slit in the bark of the stock. The scion should be fitted firmly into place in order to have the cambium of the stock and scion in close contact over as long a surface as possible. To hold the scion in place a cotton string is wound firmly around the graft, commencing at the top of the stock to prevent forcing the scion out of place. A waterproof paper should then be wrapped around the scion and the upper end of the stock and folded over the top of the scion to secure fairly uniform humidity and to prevent an excess of moisture from entering and causing decay. It is important to perform the operation rapidly enough to prevent any drying of the cut surfaces.

In about three weeks the scions should have started growth. The paper should then be removed, as it is injurious to the new growth, and the cotton string used for binding the scion should be cut as soon as the union is well formed.

INARCHING.

When it is planned to propagate by inarching, the seedling to be used as a stock should be in a large pot (PI. Ill, fig. 2) or box. To secure a good stock it is best to plant the seed in the receptacle to be used rather than to attempt to transplant young seedlings. Although the success of the operation does not depend so entirely as in grafting upon the condition of the stock and scion, these should be as nearly as possible in the same stages of growth as for grafting and the seedlings should be about the same size and age as those for grafting if outdoor work is practiced. For indoor work, where moisture can be controlled, or in the orchard if climatic conditions are favorable, both seedling and scion need be only a few weeks old. A very dry atmosphere and excessive wind, which are common in practically all sections of Porto Kico during parts of the year, make it impossible to use such young plants.

Before the operation is performed the seedling should be placed near the branch to be inarched, either on the ground or on a scaffold, and the pot so fastened as to prevent disturbance by the winds. Then a thin strip of bark and wood from 3 to 5 inches in length should be removed with a sharp knife from the trunk of the seedling and one of similar shape from the scion, leaving a few inches of the end of the scion above the cut section. The cut surfaces are then placed together, so that the bark and cambium meet over as long an area as possible, and are tied firmly with cord or raffia. It is not necessary to apply grafting cloth, wax, or similar materials in inarching. At the time of inarching, the tip should be removed from the stock, and in three or four weeks the seedling should be cut back within one or two nodes of the union. When the union is well 'formed, the seedling should be cut off just above, and the inarched branch just below, the union. When the plant is cut from the parent tree it should be sheltered from the sun for a few days, then placed in partial shade a week or more and watered frequently. If weather conditions are favorable, it will be ready for planting in a permanent place in a few weeks.

TOP-WORKING OLD TREES.

There are thousands of large, thrifty, uncultivated mango trees growing in Porto Rico, some bearing almost worthless fruit and as many others producing fruit of poor quality, all of which could be grafted and made to bear superior fruit within a few years. (PI. IV, fig. 1. ) To accomplish this the branches should be cut back nearly to the trunk (PI. IV, fig. 2), and when the new branches which spring from adventitious buds are sufficiently mature — that is, in 6 to 8 months — they may be grafted in the manner described above. Although a great number of new branches start from near the point where the old branches were removed, only the best of these should be selected for grafting, all the others being removed except a few near the grafts to protect these from wind and sun. While it is sometimes recommended to leave a few of the large branches when cutting back the old trees, this has been found unnecessary in Porto Rico, as better results have been obtained where all the branches were removed. Where large branches are allowed to remain, the new growth sent out from the stumps of the removed branches is always less vigorous and is not ready for grafting in very dry weather for several months after that on trees with all of the old branches removed.

A field nursery is seldom planted in the mango-growing countries, especially in the West Indies, but experiments with field nursery stock have proved the practicability of shipping the small trees short distances and have shown especially the value of a field nursery to growers who are planting a mango grove on their own fruit plantation. If the land is well prepared, the seedlings will make nearly if not fully as good a growth in the field nursery as in pots. The

Plate III.

Fig. 1.— Mango Seedlings; Plant on Left Grown from Seed with Husk Removed, Others from Seed in Husk.

Fig. 2.— Mango Seedlings in 6-Inch Concrete Tiles; Plants on Left Grown from Seed in Husk, on Right from Seed with Husk Removed.

Plate IV.

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_ rows should be made 4 feet apart, with the plants 1£ feet apart in the row, to allow room for grafting and for the removal of a ball of earth with the roots in transplanting. Where the soil is not perfectly drained, as at the station, ridges sufficiently high to insure good drainage should be made. Only the largest and best seed should be planted. If the soil is fertile, an occasional cultivation will be the only care needed until grafting time — that is, in 7 to 9 months. Where all conditions are favorable, the grafted plants may be transplanted within a few weeks or, if desired, they may remain in the nursery for many months.

Mango trees may be successfully transplanted if rainfall is abundant or irrigation water is at hand and the branches are all well hardened. A large percentage of loss has resulted from transplanting when the trees were in a growing condition or the new growth was not well matured, although all branches were well cut back. In transplanting, a ball of earth should be removed with the tree and the top cut back severely. Where this practice was followed, not only nursery stock, but grafted trees of East Indian varieties with trunks from 4 to 6 inches in diameter which had borne two crops of fruit, were moved without loss. As newly transplanted trees are very susceptible to excessive moisture, they should, unless the subsoil is very well drained, be planted as high as they grew in the nursery, or higher. They must, however, be watered artificially if a drought occurs soon after transplanting.

IMPORTANCE OF CLASSIFICATION.

The present -confusion in classification as to groups and varieties of mangoes is so great that, although considerable interest is being shown in the work, a long period will be required before a satisfactory adjustment is reached. As comparatively few imported varieties have so far fruited in Porto Rico no attempt at classification is made in this bulletin, only a detailed description of the fruit being given under the names received with trees from the United States Department of Agriculture and from other reliable sources. As the East Indian mango is almost unknown in Porto Pico except by name, and as there are few individuals who are familiar with any of the varieties the descriptions given below should be of value, since the cultivation of the mango will, doubtless, become important in a few years. The distinguishing characters of the several varieties are so pronounced that a knowledge of the differences is very important to merchants and planters who wish to satisfy the needs and fancies of domestic and foreign markets. Fortunately, most imported varieties are easily identified, there being a wide range of thrift and productiveness among them and still greater differences in the qualities of the fruits and the uses to which they can be put.