From the Manual Of Tropical And Subtropical Fruits
by Wilson Popenoe
The Mango
The Mango Flower And Its Pollination
The scanty productiveness of many Indian mangos has been attributed
by several writers to defective pollination. A. C. Hartless,
superintendent of the Government Botanical Gardens at Saharanpur,
India, discussed the matter at some length in the Agricultural Journal
of India, April, 1914. The writer has personally investigated the
subject in Florida, and the results have been published in Bulletin 542
of the United States Department of Agriculture. Burns and Prayag have
written on the structure and development of the mango flower in the
Agricultural College Magazine, Poona, India, March, 1911. The mango is
polygamous and produces its flowers on terminal panicles varying in
length from a few inches up to two feet. Each panicle carries from 200
or 300 up to more than 4000 flowers, of which only 2 or 3 percent are
perfect in some varieties, or as many as 60 to 75 percent in others.
The character of the panicle and the number of flowers produced upon it
differs according to the variety.
The individual flower (Fig.
13) is subsessile, 6 to 8 millimeters in diameter when the corolla is
outspread; the calyx composed of five ovate-lanceolate, finely
pubescent, concave sepals; and corolla of five elliptic-lanceolate to
obovate-lance-olate petals, 3 to 4 millimeters long, whitish, with
three or four fleshy orange ridges toward the base, and inserted at the
base of a fleshy, almost hemispherical disk, obscurely 5-lobed and
usually about 2 millimeters in diameter. In the perfect flower the disk
is surmounted by a globose-oblique ovary 1 millimeter broad, with a
slender lateral style about 2 millimeters high. To one side and
inserted upon the disk is the single fertile stamen, composed of a
slender subulate filament about 1.5 millimeters long, surmounted by an
oval purplish red anther 0.5 millimeter long, which dehisces
longitudinally. Occasionally two such stamens are produced. The whorl
is completed by staminodes of varying prominence, short and subulate in
some varieties, larger and capitate in. others, some even becoming
fertile and producing a few pollen-grains. In the staminate flower the
ovary is wanting.
Fig. 13. A bisexual mango flower. (X 4)
Several
writers have affirmed that the mango is largely if not solely
wind-pollinated. It seems evident, however, that it has none of the
characteristics of an anemophilous plant, but, on the other hand,
presents well-developed adaptations to insect pollination. In
anemophilous or wind-pollinated flowers, the pollen is usually abundant
in order to compensate for the enormous loss in transport; the
pollen-grains are dry and incoherent, so that they may easily be
carried by the wind; and the stigmas are commonly bushy and freely
exposed, so as to have every chance of catching the floating grains.
The mango shows none of these adaptations. It produces comparatively
few pollen-grains, often not more than 200 or 300 to an anther. These
grains show a decided tendency to cling together, especially in damp
weather; and even in dry sunny weather it is difficult to dislodge them
with a strong draft of air. The stigma is small and not provided with
projections of any sort to assist in catching pollen.
The
production of nectar for the attraction of insects also indicates that
the mango is entomophilous. Observations have shown that the flowers
are visited by numerous insects of the orders Diptera, Hymenoptera,
Lepidoptera, and Coleoptera, ranking in the order given as to the
number of visits. Pollen-grains have been observed adhering to the
bodies of many species belonging to these orders.
In spite of
numerous insect visits, however, a large number of the stigmas are
never pollinated, and it seems probable that very little pollen is
transferred from one flower to another. Most of the stigmas receive
their pollen from the anther (rarely is more than one fertile) of the
same flower. Cross-pollination is in all probability uncommon. In damp
cloudy weather the pollen-grains swell and are much more difficult to
dislodge than when the weather is dry and sunny. After a heavy dew they
will be found in this swollen condition, but when the sun comes out
they return to their normal dry form. Protection of the flowers from
dew and rain by means of a canvas shelter did not increase the
production of fruit in the case of an experiment carried out in Florida.
Sometimes
there is considerable differentiation in the size of the pollen-grains.
In most varieties the larger number, however, are uniform in shape and
size, plump and apparently perfect. They can be germinated in sugar
solution of the proper density, and there is nothing to suggest that
impotency is common.
From the fact that pollination ordinarily
is scanty, it might be assumed that productiveness could be increased
by making it more abundant. This has not, however, been found to be the
case, except when the pollen was obtained from a tree of a different
variety (cross-pollination); under these conditions there was a
somewhat better yield. The total number of flowers produced is so
enormous that it is of little importance whether all are pollinated or
not. Seedling mangos, which are not pollinated more abundantly than
budded varieties, nor furnished with a greater number of anthers, nor,
so far as can be ascertained, with pollen of greater potency, often set
many more fruits than they can carry to maturity. This has been noted
also with several grafted kinds, such as Bennett and Cambodiana.
Sometimes
the entire tree comes into bloom at one time, covering itself with
flowers; again, one side of the tree may flower, while the other shows
no buds; or the flowering may be confined to a small section of the
tree, probably the branchlets arising from one large limb. This
behavior of the mango corresponds to the growth habit of the tree which
is mentioned but not explained by A. F. W. Schimper.1 When
one side of the tree flowers independently, it might be expected that
the remainder would flower at another time, but this is not always the
case.
Some varieties develop all their flowers within ten days
after the first buds open; others, such as Sandersha and Julie, push
out flower-panicles during a period of several weeks, or even months;
thus, in 1915 there was not a single day between the middle of January
and the latter part of May on which flowers could not be found on the
old Sandersha tree in the Plant Introduction Garden at Miami, Florida.
This feature is of importance in that it gives the tree a greater
opportunity to set fruit. Often the attacks of the anthracnose fungus
are severe when the tree is in bloom, and the entire crop of flowers is
destroyed. In some varieties this means a crop failure, since the tree
will not produce any more flowers that season; but in the Sandersha (if
early in the season) it need mean only the loss of the flowers which
were present at that particular time. Those developed later might enjoy
more favorable weather, with consequent freedom from the anthracnose
peril, and a crop of fruit would result. Anthracnose, one of the
greatest enemies of the mango, is discussed under the heading pests and
diseases.
Some varieties which fruit heavily are characterized
by a high percentage of perfect flowers. Others which are known to be
unusually regular in fruiting, although they may not produce such heavy
crops, have relatively few perfect flowers. The Philippine race of
seedlings, which sometimes bears heavily, commonly has more perfect
than staminate flowers. Most of the Indian varieties have fewer perfect
flowers than the seedling races.
1 Plant Geography.
The
experiments conducted in Florida indicate that the scanty fruiting of
many varieties is not due to any morphological defect in the pollen or
to defects in the mechanism of pollination. While such factors as lack
of pollinating insects and loss of pollen through rains or moist
weather probably lessen the production of fruit in some seasons, from a
practical standpoint the question of pollination seems relatively
unimportant. The problem is more probably a physiological one,
connected with nutritional conditions as influenced by changes in
soil-moisture and food-supply, principally the former. Suggestions are
given under the heading culture for encouraging the formation of
fruit-buds on soils or under climatic conditions which normally tend to
produce vegetative growth to the detriment of reproduction.
The Mango
Botanical
Description
History and
Distribution
Composition
And Uses Of The Fruit
Climate And Soil
Cultivation
Propagation
The Mango Flower
And Its Pollination
The
Crop
Pests And
Diseases
Races and
Varieties
Back to
The Mango Page
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