Most people in the temperate world are familiar with only one type of banana: the Cavendish bananas that dominate the international trade. But even though these export bananas are grown on large plantations, they account for only about 15 percent of the 100 million tonnes or so of bananas that are produced each year.

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Essential for food security
Cultivated diversity
Threats to banana diversity

Essential for food security
Most bananas are grown on smallholdings, to eat at home or to sell in local markets. The cooking types are especially important for food security. In places, they are to the local people what potatoes are to their counterparts in the Andes and rice to those in the lowlands of Southeast Asia.

Bananas are popular with farmers because they are easy to grow and do not need to be replanted each season. They thrive in a range of environments and produce fruit year-round, thus providing a continual source of food, even during the 'hungry-period' between harvests of annual crops. They are also well suited to intercropping systems and to mixed farming with livestock.

As well as being a good source of energy, bananas are rich in vitamins and minerals, especially potassium. Thus, they provide a good quality staple food, and because they are so easy to digest they are often the first solid food given to babies. With growing urbanization in many developing countries, bananas are increasingly produced in backyards, along roadsides and in unused open spaces in the cities. This production has become an extremely important source of energy, nutrients and income for city dwellers.

Cultivated diversity
Wild bananas belong to the genus Musa, which is native to the tropical and sub-tropical forests of Asia and Oceania. Botanists have identified more than 50 species of bananas. These species produce inedible fruits that are full of seeds. Like humans, they are diploid, that is they have two copies of each gene.

Little is known about the diversity and the status of these species in the wild, not least because some of the areas where they are at their richest are poorly explored by botanists. The best known are Musa acuminata and Musa balbisiana. Barring a group of cultivars, Fe'i bananas, which developed independently in the Pacific region, today's bananas are descended from one or both of these species. Overall, there are believed to be some 1 000 varieties of bananas.

Scientists believe that bananas were among the first plants to be domesticated, some 10,000 years ago, when banana forms that bear edible fruit appeared. Edible diploids are increasingly rare, except in Papua New Guinea, where their diversity is at its greatest. They have been displaced by triploid varieties, which appeared when one of the parents 'accidentally' gave both copies of its genome instead of just one. More vigorous, with large seedless fruit, these varieties found favour with the early farmers, and spread far and wide. Since its beginnings, the international trade has been dominated by triploid varieties of acuminata origin.

Cooking bananas, on the other hand, tend to be triploid hybrids of acuminata and balbisiana bananas. The best known cooking bananas are plantains, which are especially diversified in West and Central Africa. This region, together with the highlands of East Africa, where a distinct group of cooking bananas of acuminata origin is found, are the two most important secondary centres of diversity outside of the Asia Pacific region.

Threats to banana diversity
In traditional banana farming systems diversity is valued because it fulfills various needs, uses and tastes-and contributes to the ecological and economic stability of such systems. But the industrialization of agriculture and the pressure to grow commercial crops is threatening this diversity as farmers give up on the less commercial varieties and the ones that are more susceptible to pests and diseases.

Like any other plant, the banana is attacked by numerous pests and diseases. Banana plants are eaten from within by weevils that tunnel through the underground stem, making the plant physically unstable, and nematodes, microscopic worms that burrow into the root system, reducing yield and, like the weevils, allowing plants to be more readily blown over. In Africa, weevils and nematodes are regarded as a growing problem.

Viruses and bacteria can also cause devastating diseases. In parts of Asia, one of the main threats is the Banana bunchy top virus, which stunts plant growth and has driven many farmers to stop growing bananas. In East Africa, a bacterial disease confined until recently to Ethiopia, is spreading through Uganda and neighbouring countries. The first global epidemic to affect bananas was of Fusarium wilt, popularly known as Panama disease, an essentially untreatable disease that is caused by a soil-borne fungus. The disease was responsible for the demise of Gros Michel, the variety that dominated the international trade until it was replaced by resistant Cavendish bananas in the 1950s. In recent years, a new version of the disease that can attack Cavendish bananas has been spreading widely in Southeast Asia.

Another fungal disease, black leaf streak, takes its popular name, black Sigatoka, from the valley in Fiji where it was first noticed but has subsequently spread rapidly around the globe. The fungus attacks the leaves and by disrupting photosynthesis can reduce yields by up to 50 percent. Keeping the disease in check on the commercial plantations demands one of the most intensive spraying regimes currently in agricultural use. This not only drives up production costs, but threatens the health of workers and their environment. Where fungicides are not an option because of their expense, banana farmers have few means to combat the disease and are, at times, forced to abandon the crop.

Managing pests and diseases in an environmentally friendly way, based on an understanding of agro-ecological processes and principles, and helping smallholder farmers to sustain or increase productivity without damaging the natural resource base is one of the main concerns of Bioversity's banana and plantain research group. Originally created as an independent networking organization in 1985, this group of scientists with regional bases in Africa, Asia and Latin America, continues to address the conservation of the crop's diversity, and other research and development objectives using an approach based on partnerships and networks. Its overarching aim is to improve the well-being of smallholders through an effective use of banana biodiversity - that is the diversity of bananas themselves as well as the diversity of other organisms found in banana production systems.