Recently, some concerns have been raised about the health of the world's banana plants. Many media reports have said that bananas may completely disappear in the coming ten years. Bananas are one of the world's most important food crops. They are also the fourth most valuable export. Bananas do not grow from seeds. Instead, they grow from existing plants. Bananas are threatened by disease because all the plants on a farm are copies of each other. They all share the same genetic weaknesses. For example, the Cavendish banana is most popular in American markets. It is an important export crop. However, some kinds of fungus (真菌) organisms easily infect the Cavendish. Black Sigatoka disease affects the leaves of Cavendish banana plants. The disease is controlled on large farms by putting chemicals on the plant's leaves. Farmers put anti-fungal chemicals on their crops up to once a week. Another fungal disease is more serious. Panama disease attacks the roots of the banana plant. There is no chemical treatment for this disease. Infected plants must be destroyed. Panama disease has affected crops in Southeast Asia, Australia and South Africa. There is concern that it may spread to bananas grown in the Americas. This could threaten an important export product for Central and South America. The International Network for the Improvement of Banana and Plantain, whose headquarter lies in France, supports research on bananas. The group says that more research must be done to develop improved kinds of bananas. The group says that fungal diseases mainly affect only one kind of banana. In fact, there are five-hundred different kinds of bananas. The United Nations Food and Agriculture Organization says the Cavendish banana represents only ten percent of world production. The UN agency says farmers should grow different kinds of bananas. This protects against diseases that affect only one kind. Experts warn that disease may cause the Cavendish banana to disappear. This has already happened to one popular banana because of its genetic weakness against disease. (words: 335) 小题1:What does the passage mainly tell us?
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