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  3. Widespread losses of plant species and varieties are eroding the foundations of agricultural productivity and threatening other

Widespread losses of plant species and varieties are eroding the foundations of agricultural productivity and threatening other

admin2009-06-24  43
问题     Widespread losses of plant species and varieties are eroding the foundations of agricultural productivity and threatening other plant-based products used by billions of people worldwide. Plants provide us with irreplaceable resources. The genetic diversity of cultivated plants is essential lo breeding more productive and disease-resistant crop varieties. But with changes in agriculture that diversity is slipping away.
    Biotechnology is no solution to this loss of genetic diversity. We are increasingly skillful at moving genes around, but only nature can create them. If a plant with a unique genetic trait disappears, there is no way to get it back.
    The effects of plant loss extend far beyond agriculture. One in every four medicines prescribed in the U.S. is based on a chemical compound originally found in a plant. Worldwide, some 3.5 billion people in developing countries rely on plant-based medicine for their primary health care.
    Loss of habitat from forest clearance for logging and agriculture, pressure from nonnative species and overharvesting have put one out of every eight plant species at risk of extinction. It is not just obscure or seemingly unimportant plants that are in trouble. Those that we rely upon most heavily are also declining. About two-thirds of all rare and endangered plants in the U.S. are close relatives of cultivated species. Crop breeders often turn to wild relatives of crops for key traits, like disease resistance, when they cannot find those traits in cultivated varieties.
    Many medicinal plants are in trouble from overharvesting and destruction of habitat. The bark of the African cherry tree is widely used in Europe for treating prostate disorders, but the medicinal trade has led to severe depletion of the tree where it grows in the highlands of Cameroon and other Central African countries.
    Since fewer than 1% of all plant species have been screened for bioactive compounds, every loss of a unique habitat and its species is potentially a loss of future drugs and medicines. Until recently, gene banks, botanical gardens and protected areas have been the first line of defense in maintaining the diversity of plant life. The world’s 1,600 botanical gardens collectively tend tens of thousands of plant species. But these conventional approaches need significantly higher levels of support. Many conservation facilities must scrape by on increasingly scarce funding, particularly those nm by national government.
    Additional steps must be taken to reform policies and practices that work against plant diversity. Those who garner the benefits of plant diversity, such as agribusiness and pharmaceutical consumers, should acknowledge and support those who maintain it, including indigenous cultures and national gene banks.
    Through benefit-sharing agreements, international conservation endowments and grass-root development projects attuned to the links between cultural and biological diversity, many options exist for supporting plant diversity rather than diminishing it.
选项 A、to supply more funding to gene banks, botanical gardens and protected areas.
B、to stop overharvesting and smuggling.
C、to save those seemingly unimportant plants.
D、to take further steps to revise policies and practices that hinder the keeping of plant diversity.
答案D
解析
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