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Banana |
The banana is a plant of the tropics and subtropics, requiring hot humid conditions. It originated in the Indo-Malaysian region of Asia, but people transported it to other areas in the wet tropics, firstly to tropical Africa during prehistoric times and then to central and southern America during the sixteenth century. Brazil and India produce large commercial crops of bananas, mainly for local consumption. The largest exporter is Ecuador. Bananas are the fourth largest fruit crop in the world, after grapes, citrus fruits and apples.
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What does a banana plant look like?Often wrongly described as a tree, the banana is, in fact, a giant herbaceous plant with a 'trunk' (or more correctly a pseudostem) made up of a series of tightly wrapped leaf sheaths. Each pseudostem grows from a bud on the true stem, which is an underground rhizome. Leaves emerge through the centre of the pseudostem and expand at the top to form large glossy oval blades, up to 4 m by 1 m in size. The blades are often torn by the wind, and hang in strips from the midrib. The inflorescence (flowering head) also grows up through the pseudostem when the plant has produced a certain number of leaves. It is made up of groups of tubular creamy white flowers. Each group of flowers is surrounded by a large purple-red bract (a leaf-like structure) that is shed as the fruit develop. Female flowers are borne at the base of the inflorescence with a male bud enclosed by persistent bracts at the tip. Fruit developing from the female flowers are parthenocarpic; that is they develop without pollination, and consequently there are no seeds in most cultivated forms of banana. The characteristic bunches or 'hands' of bananas are formed from the double rows of female flowers in each group. Each inflorescence produces 200-300 individual fruits or 'fingers' depending on the cultivar. Under the weight of the fruit, the inflorescence bends down towards the ground. |
The cultivated banana is in the genus Musa. Two wild species, Musa acuminata and M. balbisiana, are the source of the genetic material of most cultivars. Dessert bananas, such as the commercially important 'Gros Michel' and 'Cavendish', contain only genes from M. acuminata, whereas the plantains and other cooking bananas also have genes from M. balbisiana.
Since they do not produce seeds, bananas are vegetatively propagated by means of 'suckers' which develop from buds on the underground rhizome. Each sucker is genetically identical to its parent plant. This means that each banana cultivar consists of a group of genetically identical plants (a clone). Variation between clones results from mutations in the vegetative cells of the plant. In all there are some 300 cultivars of Musa, all differing slightly in various characteristics such as height, disease resistance or colour and type of pulp.
As dessert bananas develop, some of the starch in the pulp is converted to sugars. These bananas are generally allowed to ripen and are eaten uncooked. Since the fruit is high in energy but low in fat and is rich in vitamins B6 and C, it is a useful food for invalids, particularly people with digestive problems. Dessert bananas can also be cooked or processed by canning, freezing or drying, the most important product being banana puree. Some tribes in East Africa produce beer from fermented bananas for local consumption.
Plantains and cooking bananas, on the other hand, are used when still unripe, and need cooking because the pulp is very starchy. These fruits are important staple foods in equatorial Africa. Over half of the total world production of bananas is used for cooking. In some countries, the male bud is considered a great delicacy.
Another species of Musa, M. textilis (also known as abaca or Manila hemp) is not used for food at all; the fibres in its leaves are used to make ropes and paper.
Ornamental bananas are best grown indoors, although M. basjoo is nearly hardy and can be left outside over winter if it is protected from frost. Although this species does bear fruit these are inedible, and it is grown in warmer countries for its fibre. Other ornamental species of banana for the warm conservatory include those with variegated leaves, such as M. vitata and M. zebrina, and those with colourful inflorescences, such as M. coccinea. Ensete ventricosa (sometimes known as Musa ensete) is a closely related plant that can also be grown as an ornamental.
Edible bananas, such as the cultivar 'Dwarf Cavendish', can be grown under glass although they require a large area, at least 7 m in height. High atmospheric humidity is essential and temperatures of at least 18°C during winter nights and 24°C during summer days are required. The plants also need full sun, possibly with some shading in the summer to maintain the requisite high levels of humidity. A fairly well-drained soil with a high organic matter content is ideal, and plenty of water should be provided throughout the growing season.
Banana plants grown under glass in this country will bear fruit, particularly under warm humid conditions. Fruit should be left on the plant until fully developed and then removed for ripening. The pseudostem will then die and, as for the commercial crop, propagation is by means of suckers. Cutting the plant back to soil level after fruiting will encourage suckering.
Bananas can also be grown successfully as foliage pot plants if the temperature and humidity are high enough. They require plenty of water, but the soil must be well drained as they will not tolerate water-logging. The plants should be fed whenever they are watered except in winter. Artificial liquid fertilisers can be used when the plants are growing strongly but may cause damage if plants are in poor condition. Dry air in houses is one of the main causes of leaf deterioration (brown tips and edges); others include poor soil conditions, over-watering or lack of water, sudden changes in growing conditions, or even over-feeding.
At Kew different types of banana are grown in the Palm House, the Princess of Wales Conservatory and the Temperate House.
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