Crop diversity embraces the great variety within and between crops and their wild relatives. Not only are there hundreds of species of crops - from wheat to carrots to mangoes - but each species may also have hundreds or thousands of varieties containing subtle yet important genetic differences.
These varieties evolved over thousands of years in a dynamic interaction between nature and farmers' careful selection and breeding. The uses of crop diversity go beyond the production of food. In many cases crop diversity is at the root of sustainable agriculture and provides environmental benefits.
Humanity has historically used the wide variety of wild and cultivated crop plants to meet needs for cloth fibres, housing materials and livestock feed. Crops also underpin many cultural traditions, aesthetic aspirations and medical needs. Even today 80 percent of the world's people rely on herbal cures rather than on pharmacies when they are sick.
Generations of farmers have enhanced the world's crop diversity. Varieties that have arisen through selection by farmers - sometimes called landraces - suit their immediate environments and other preferences. In the last hundred years, scientific research institutions have contributed enormously to the breeding of new crop varieties for improved production and for adaptation to a broad range of farming environments.
Each crop variety may be adapted to a particular type of soil, climate and growing season. Its genes may endow it with traits needed by farmers: disease resistance, cold or heat tolerance, special taste or nutritional qualities. These qualities provide farmers and plant breeders with raw materials to improve their crops and adapt them to changing environmental conditions.
For example, farmers have adapted varieties of maize that flourish in the Brazilian prairies and the northern Mexican deserts, in the mountainous highlands of the Andes and the islands of the Philippines. Different varieties of maize may be particularly high in protein or good for making tortillas, grits or flour.
DIVERSITY OF MAJOR AND MINOR CROPS:
In 10,000 years of settled agriculture, men and women have discovered some 50,000 varieties of edible plants. Today, human beings cultivate 7,000 plants for food, and many more for fibres, medicines and other purposes. Yet just three crops - wheat, rice and maize (corn) - together provide more than half of humanity's global food supply and are staple foods for four billion people.
Although these three crops dominate agriculture, region-by-region a more complex picture emerges. Bananas and plantains are the developing world's fourth most important food.
Sorghum, millet, potatoes, sugar cane and sugar beet, soybean, sweet potatoes, beans and cassava all provide much needed calories for millions of the world's poor. For example, cassava supplies over half of the plant-derived energy for Central Africa. In developing countries, groundnut, pigeon pea, lentils, chickpea and cowpea (black-eyed peas) are important high-protein sources of food.
In the Andes Mountains of Peru and Ecuador, native people have grown dozens of roots and tubers found nowhere else in the world. In sub-Saharan Africa about 1,000 plant species can be eaten as green leafy vegetables. Nobody knows how many of these are cultivated, but farmers grow diverse species in small forest and farm plots. These traditional vegetables have very high nutritional value and may often be used for their medicinal as well as food benefits. It is essential to conserve the diversity of carefully tended minor crops.
A WORLD FOOD WEB:
Each crop species has at least one centre of diversity - the place where the crop's wild relatives first proliferated and humans domesticated the crop. It is particularly in their historic homes that a crop and its wild relatives continue to co-evolve, creating still more novel genetic combinations.
However, regardless of their places of origin, today's major crops are bred, grown and marketed all over the world. For example, farmers in many African countries grow cassava, which originated in Latin America. Meanwhile, farmers in South Asia and Latin America grow pearl millet, which originated in Africa. Citrus, which originated in Southeast Asia, flourishes in tropical and subtropical regions across the glob. Soybeans, one of the principal crops grown in the United States, originated in China.
In today's world then, counties strongly depend on crops with foreign origins for their agriculture. This complex web points to a simple truth: all countries are interdependent with regard to crop diversity. Ultimately farmers around the world are likely to depend upon diversity from elsewhere as a source of new genes to maintain the heath and productivity of their harvests. But as diversity is lost from farms and from the wild, as land is ploughed or paved, crop genebanks may be the only way to preserve a genetic legacy evolved over millennia.
LOSS OF CROP WILD RELATIVES:
The world contains an estimated 250,000 species of flowering plants, but one in 12 of them (8 percent) now seem likely to disappear before 2025. Of the many factors that contribute to this extinction crisis, chief among them is modern agriculture. Clearing forests to create farmland is the cause of most extinction's today. More than 15 million hectares of tropical forest are lost each year to agriculture and development. Among the losses are the wild relatives of domesticated plants and species with as yet untapped potential. Such losses are occurring on every continent and in every region.
The loss of crop wild relatives has profound implications for agriculture. Plant breeders and farmers depend on the wild relatives of crops as an essential source of genes. For example, wild wheat's have recently provided domesticated wheat with genes to resist fungal diseases, drought, cold, and heat. A single sample of wild rice from Central India provided resistance to two of Asia's main rice diseases.
It is difficult to know exactly when a crop's wild relative has completely disappeared. Wild crop species grow as distinct populations and each typically has its own distinct genetic identity and so contributes to the total genetic diversity of the species. The loss of individual populations is a form of genetic erosion - a process that can lead to extinction.
WILD CROP RELATIVES NEARING EXTINCTION:
The negative impacts resulting form the loss of wild species are hard to measure, since in most cases lost species were not previously well studied. Nonetheless, like the growing tide of animal extinction's, the loss of wild crop relatives changes not only the ecosystems in which they once flourished but also limits human opportunities for the future.
FOLLOWING ARE A FEW EXAMPLES OF WILD CROP RELATIVES ON THE WAY TO EXTINCTION:
Soybean: Wild soybeans could once be found growing over almost all of China's Yellow River Delta and Sanjiang Plain, but now they are scattered in just a few sites.
Tomato: Across the South American centre of diversity, populations of wild tomato are being severely reduced. Many are endangered by goat herding in the highlands and by habitat loss. One species in Chile is now restricted to about half a dozen populations and open pit copper mines pose a potential threat to another desert species. Sprawling shantytowns around Lima, Peru, have eliminated others. The loss of just one extremely diverse population can have disproportionate effects.
Coffee: A wild species of coffee that once grew in Cote d'Lvoire in West Africa is known to be extinct. Ten others are either endangered or vulnerable in the wild.
Hard wheat: Triticum monococcum is a species that was widely grown for bread in the ancient Roman Empire. Today it is almost lost, with relic populations existing only in Turkey, and possibly in Yemen. Because of its high fibre content, T. monococcum is again in demand, and a special project has begun to bring back this crop.
Grape: The world's grape species are threatened in all areas of their range. In North America, the grape species Vitis rupestris has been grazed to the point of near extinction. It was once found in gravelly and sandy creek beds from Tennessee to Texas. Seven other North American grape species are also threatened. Scientists believe these may contain a range of valuable genes, including for drought tolerance and resistance to the pest root-knot nematode.
LOSS OF CROP DIVERSITYL:
The United Nations Food an Agriculture Organisation (FAO) estimates that about three-quarters of the original varieties of agricultural crops have been lost from farm fields since 1900. And this trend has accelerated in the last half century.
The intensification of agriculture often means less, not more, crop diversity. Although modern plant breeders have made considerable use of the genetic diversity present in landraces to create high-yielding modern varieties, the widespread use of these new varieties has replaced many of the older ones.
Since the Green Revolution was launched in the 1960s, farmers have increasingly abandoned their traditional landraces of wheat, rice and other crops in favour of high-yielding new seeds. By the 1990s, adoption of modern varieties of wheat, rice and maize in-developing countries had reached 90, 70 and 60 percent respectively. In China farmers grew nearly 10,000 wheat varieties in 1949. By the 1970s only about 1000 varieties remained in use. Today, wheat landraces are extensively cultivated only in isolated patches of the drier production zones of West Asia-North Africa and in the highlands of Ethiopia.
A wide range of crops - from broccoli to sugarcane - is following a similar trend. In the United States less then five hybrid broccoli plants account for 80 to 90 percent of the broccoli crop, and one hybrid, 'Marathon,' accounts for more than 50 percent of acreage. Most sugarcane cultivars in the world today were derived from crosses made with only a few clones selected in the late 1800s and early 1900s in India and Java. This narrow genetic base puts sugarcane cultivation at risk from several diseases, including rust, smut, and eyespot and has resulted in a yield plateau.
The world's crop landraces and their wild relatives, with their huge genetic variation, are dwindling fast. Like wild plants and animals, agricultural diversity is in decline.
WHY CROP DIVERSITY MATTERS:
Diversity occurs in two main forms: diversity among crops and diversity within a crop. Both are essential. Although just fifteen food crops now provide 90 percent of the world's food energy intake, a much wider diversity is needed to meet human nutritional needs. Scientists have focused their crop-improvement efforts on a handful of key species in an effort to produce enough food for the rapidly growing human population.
But this focus has come at the cost of many more so-called "minor" crops, which are often better adapted to harsh environments - such as poor, salty soils and arid climate - and to the needs of their cultivators. Therefore, minor crops both meet nutritional needs and generate income for local communities. These crops are often closely tied to the history and cultural identity of the communities that have grown them for centuries.
Diversity within a crop comes from its many varieties, each with its own unique complement of genes. Dependence on too few varieties is dangerous because disease or pests can spread rapidly through a genetically uniform crop. In the 1840s, Irish farming was primed for disaster: it relied on one crop - potato - with a narrow genetic base and a susceptibility to late blight. When a virulent pathogen strain entered Irish potato fields, it spread like wildfire. The famine that followed claimed one million lives and forced the emigration of another million of the country's population.
Finally, in today's world, crop diversity is an essential insurance policy against unforeseen changes, from the natural disasters caused by unpredictable climates to the devastation of war.
Gone From Farmers' Fields:
IN THE COURSE OF THE 20TH CENTURY, farmers grew a shrinking array of crop varieties. Here are a few examples:
COLLARD PISTACHIO:
This crop-a regionally important leafy green vegetable- Farmers throughout Central and West Asia and North originated in the south-eastern United States and scientists Africa cultivate pistachio nuts.Hardy wild relatives of the project that its still surviving landraces will be lost domesticated trees help conserve ecosystems prone to in another generation due to development and the drought and provide a source of pest and disease resist-migration of farmers and rural populations to larger ance for cultivated varieties. However, pistachio's broad cities.20 genetic base is being lost as a few high-yielding commercial types replace ancient varieties, and human activity.
MAIZE destroys wild species.23:
In Mexico, between the 1930s and today, farmers have lost about 80 percent of their traditional maize vari - RICE eties.21 Between 1910 and 1920 in Taiwan, the number of lan-draces of rice dropped from 1200 to approximately 400 as
PECAN a result of a campaign against rice diversity. Since then There are over a thousand documented pecan nut culti-numbers have fallen even more dramatically.24In vated varieties, but over half of the acreage sown to Bangladesh, the promotion of high yield rice has led to pecans world-wide is composed of only four varieties. losses of 7000 traditional rice varieties.25Given this narrow genetic base and a steadily shrinking native acreage,scientists say the diversity of this crop is at SOYBEAN risk.22 In the United States, about one quarter of the genetic diversity base of the soybean crop was lost between 1947 and 1988.26.
CROP DIVERSITY:
Farmers have bred tens of thousands of varieties of rice, and Future Harvest scientists and their partners have collected more than 1 100 wild rice species.
2 There are about 200 wild species of potatoes and thousands of named varieties cultivated by farmers.3In the Andes, farming communities use about 3 000 different varieties of potatoes.
More than 1 000 species of native fruits grow in the Americas.
In Java, Indonesia, farmers may plant more than 600 crop species in a single home garden.
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NORTH AMERICA SOUTHERN SOUTHERN AFRICA WEST ASIA
Sunflower MEDITERRANEAN Finger Millet Pistachio
Cranberry Oats Pearl Millet Wheat
Jerusalem Artichoke Beetroot Sorghum Barley
CARIBBEAN Artichoke Melon Lentil
Arrowroot Olive INDIAN OCEAN Pea
CENTRAL AMERICA Grape Mascarene Coffee Fig
Maize Date-palm Banana SOUTH ASIA
Cassava EAST AFRICA EAST ASIA Rice
Beans Sorghum Proso Millet Kodo Millet
SweetPepper Pearl Millet Fox Tail Millet Aubergine
SOUTH AMERICA Finger Millet Soybean Mango
Sweet potato Tef Orange Black Pepper
Potato Pigeon pea Apricot SOUTHEAST ASIA
Cassava Coffee Peach Rice
Beans WEST AFRICA CENTRAL ASIA Winged Bean
Pumpkin Sorghum Wheat (bread,club) Taro
Tomato Yam Onion Yam
Cocoa Cowpea Carrot Breadfruit
EUROPE OilPalm Faba Bean Banana
Brassica spp CENTRAL AFRICA Citrus
Forage species Yam PACIFIC
Apple Kenaf Sugar Cane
Peach Coffee (robusta) Coconut
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