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WE DEPEND on the diversity of plants today more than ever before. It has provided us with a menu of fabulous proportions, regardless of whether it is spring or winter or whether we live in the mountains of Bhutan or the hills of Bristol. Diversity within species has ensured us a harvest in spite of constantly changing pests, diseases and climate. As the Earth grows warmer our patterns of agriculture will have to change to suit the new climatic regime. We will look again to the natural variability within plant species, to the genes that give rise to that variability, for the characteristics that our future crops will need for life in a ‘greenhouse world’.

But now there is a new threat: genetic erosion, the extinction of races and species of plants. It is happening so rapidly and is so widespread that 50 years from now natural habitats may have little to offer plant breeders searching for genetic variability. Breeders would better spend their time searching the world’s gene banks in the hope that enough material was saved, and is in a good enough condition, to provide them with the genes they need. Gene banks hold our common future.

The causes of genetic erosion are of our own making. Industrialisation, advances in plant breeding and modern agriculture have done much to narrow the genetic base of our food crops. The UN Population Fund (UNFPA) estimates that the world’s population will reach 8.5 billion in 2025 and may stabilise at 10 billion a century from now. Many scientists believe that we have managed to feed the world only by making agriculture more productive, and that only by continuing to increase its productivity will we have any chance of continuing to feed it a century from now.

Breeders have made crops more productive by crossing breeding lines with valuable characteristics and screening the progeny for individuals that have the desired traits. A consequence of that improvement is to narrow the genetic base of commercial varieties. Variability is anathema to modern growers. They need cultivars (cultivated varieties) whose individuals all look alike, taste the same and behave in exactly the same way in the field, after harvest and in the kitchen. A field of wheat that grows to the same height within the same number of days, that produces good heads of grain all ripe and ready for harvesting at the same time and that is resistant to all the known major pests and diseases is much more valuable than a field of different wheats all responding in different ways.

Uniform varieties make economic sense. They are more profitable for growers. Because farmers justifiably prefer to grow them there follows the second side effect of widespread displacement of old varieties. The ‘green revolution’ in the 1960s required farmers in developing countries to grow new varieties of staple crops that were specially bred to make more efficient use of fertilisers. Although the improved varieties led to self-sufficiency in food, for India and Indonesia for example, they also contributed to genetic erosion on a massive scale. Old varieties of staple crops and local vegetables were quickly dropped in favour of the new improved varieties. It is impossible to say how much variability, how many potentially valuable genes, were inadvertently made victims of the green revolution.

The same process has occurred over a much longer period in Europe. In Italy, for example, the original home of the cauliflower and cabbage, it is still possible to find good variability in the old land races grown by peasant farmers. Dave Astley, director of the Genetic Resources Unit (Vegetable Gene Bank) at Wellesbourne in Warwickshire, says: ‘The problem is that commercialisation of agriculture is leading to displacement of that material by modern varieties. Farmers, after all, must be economically sensible.’ Where Italian peasants once grew cauliflowers for their local markets they are now growing what the supermarkets demand, and what can be profitably shipped to the nearest town. Astley is in charge of running the gene bank at Wellesbourne, which has an international responsibility to conserve the genetic material of Brassica, the genus to which cauliflower, broccoli, cabbage and Brussels sprouts belong. He says: ‘What’s worrying is that the much more commercialised growing of the north (of Italy) is shifting south and, while moving, will displace traditional material.’

Disappearing melons and meadows

Jose Esquinas-Alcazar, of the UN Food and Agriculture Organization (FAO), collected more than 300 primitive cultivars of melon in Spain in 1970. Three years later he attempted to recollect the seeds of 10 of the samples from the same sites but three had already disappeared. He happened on what were probably the last stocks of a fourth cultivar that was about to be destroyed. The farmer was about to move to the city and would have just left the seeds on the farm.

Bruce Tyler, genetic resources officer at the Agricultural and Food Research Council’s Institute for Grassland and Animal Production, at Aberystwyth, says that British farmers are ploughing up old pastures all the time and planting new varieties. ‘By doing so they destroy the very genetic variability that, through plant breeding, we strive so hard to create.’ Working with the Nature Conservancy Council, Tyler has concentrated on collecting species from threatened agricultural habitats such as the Somerset Levels and the sheep-grazing pastures of Romney Marsh in Kent. ‘The water meadows of Dorset and Berkshire, managed traditionally since the Middle Ages, have all but disappeared now. We managed to get in five years before they were gone,’ Tyler said.

Trade regulations, too, have contributed to genetic erosion. A uniform variety of wheat is good not just for the grower but also for the machines that will harvest it, for the buyer and (according to seed companies, at least) for the consumer. A uniform variety can be trusted to perform to certain standards under a given set of environmental conditions and so can be traded with confidence both nationally and internationally.

In 1981, the EEC imposed a regulation preventing the sale of any plant variety not listed in the ‘common catalogue’. Prior to Europe’s common catalogue almost any seed could be sold as a new or improved variety. The regulation sought to rationalise national lists, to rid them of synonyms so that everyone could know which variety they were talking about. But the legislation had much more far-reaching effects. Alan Gear, director of the Henry Doubleday Research Institute in Warwickshire, says: ‘Two thousand named varieties were lost. Undoubtedly some were synonyms. But the government selected the best-known name and called everything else a synonym. In the early days (of the legislation) hundreds of varieties were being struck off the list every quarter.’ Many were local varieties, never properly evaluated, characterised or counted so no one knows the exact number that were eventually lost through the EEC’s programme of ‘rationalisation’. According to Gear, the characterisation was done ‘by eye’; qualities such as flavour, nutritional content, and resistance to pests and diseases were ignored.

Agriculture always was a risky business. Genetic uniformity makes it increasingly so, and history is littered with examples of the disastrous consequences. The Irish potato famine in the 19th century is probably the most well known. Explorers had brought back to Europe some clones of potato from the Andes of South America. A few of those clones were later taken to Ireland where, isolated from their natural pests and diseases, they flourished. That is, until a new fungal disease, called late blight, appeared. The narrow genetic base of the 19th-century Irish potato had no resistance to the pest which, in a short time, wiped out the crop. Two million Irish people died and as many again emigrated within the space of a decade. Even then, potato breeders knew that something was amiss and complained that the potato was ‘degenerating’ and needed ‘new blood’.

In 1970, the US lost half of its maize crop to another fungal disease called southern corn leaf blight. Again, this devastation was due to the fact that most varieties of corn then grown in the US had a single gene that made them susceptible to the disease. Genes from other varieties of corn were hunted out and used to rescue the American varieties.

A more recent example is that of a famous variety of wheat called Bezostaja. The variety was so popular that, by 1972, the Soviet Union was growing it on 15 million hectares. It was even pushed into the Ukraine, far outside of its normal area of cultivation, during a period of mild winters. The winter of 1972 proved too severe for Bezostaja and the country lost millions of tonnes of winter wheat.

Our activities in the past century have done more to kill diversity than anything we have done in the 10 000 years since we began to domesticate food plants. Development projects that involved the commandeering of ‘waste’ lands or forests may destroy important refuges for threatened species of plants. Even gene banks themselves are not safe from human destruction, as events last November at the International Potato Centre (CIP) in Peru made tragically clear. A group of Maoist guerrillas murdered the man whose job it was to protect the world collection of potatoes.

The Sendero Luminoso, or ‘Shining Path’, had gone to ‘liberate’ the town of Huancayo, in the Peruvian Andes. They set out to kill the Peruvian scientists who run the agricultural research station at Huancayo, one of CIP’s four sites in the country. But the scientists were all at CIP headquarters in Lima at the time, so the terrorists killed the head of security instead.

Nontechnical staff are currently maintaining the field gene banks in which 4100 different clones of potatoes are conserved. Fortunately for Peru and the rest of the world, the potato collection, and the fantastic variety of genes that make it up, is duplicated.

Much less certain is the future of Afghan staple food crops. ¿ìè¶ÌÊÓƵs fear that valuable land races of upland wheats, adapted to Afghanistan’s unique topography, may have been destroyed in the war. Farming families cut off from food supplies could be forced through starvation to eat their seed stocks and, in doing so, may well swallow the last remaining genes.

The speed with which genetic erosion is taking place has prompted an international effort to conserve the plant genetic resources of food crops and other commercially important crops. ¿ìè¶ÌÊÓƵs now have the unenviable task of deciding which plants are on the verge of extinction, which need to be conserved and how best to conserve them.

Their starting point is to survey the so-called centres of diversity for food plants and the wild relatives that grow in association with them. The Russian geneticist Nicolai Vavilov identified eight such centres of diversity in the early part of this century. These, he assumed, were where our food plants originated. Wheat, for example, came from Asia Minor, maize from Central America, rice from West Africa, Indo-Burma and Southeast Asia. A centre of diversity, as the name implies, harbours the greatest variability for that plant.

There is now a global effort to conserve the genetic material, or germ plasm, of important crops. In 1972, the Consultative Group on International Agricultural Research (CGIAR) set up an organisation to aid the collection, conservation and utilisation of plant germ plasm worldwide. Two years later that organisation, the International Board for Plant Genetic Resources (IBPGR), began its work at the FAO’s headquarters in Rome.

Since that time the IBPGR has coordinated efforts at collecting the germ plasm of important crops. Seven of the CGIAR’s nine international agricultural research stations have germ plasm collections of food plants and are based in centres of diversity. The world’s most important food crops are well represented in these international gene banks. The IBPGR is now concentrating on collecting wild relatives of the commercially important crops. National gene banks and botanical gardens already exist in industrialised countries and have been set up in many developing countries.

¿ìè¶ÌÊÓƵs have made a cursory examination of perhaps 10 per cent of the Earth’s 250 000 species of higher plants and have studied in detail some 5000 species. Of those, just 30 plants account for 95 per cent of human nutrition. Leaving aside those 30 plants, which are already adequately conserved, where does one begin to decide what to save? The Royal Botanic Gardens at Kew has the most extensive collection of wild plant species in the world. Roger Smith, who is head of physiology at the Jodrell Laboratory at Kew, says: ‘We’re interested in conserving plants of potential value not 10 years hence but possibly 50 years hence.’ The main collection is of wild legumes and grasses belonging to the family Graminae.

Smith and his colleagues narrowed down the choice by listing threatened habitats, putting them in order of how urgently material should be collected. They began by collecting grasses and legumes in the Mediterranean. Many of the species may prove useful to agriculture in the future. The Mediterranean exercise taught them much about the task they had set themselves. They then began collecting in the semiarid tropics, in countries such as Mali, Somalia, Botswana, Rwanda, Brazil and Burundi. Burgeoning populations in those countries, coupled with very varied climates, put vegetation under extreme pressure.

Although the IBPGR is satisfied that the germ plasm of the major food crops is well represented in the world’s gene banks, there is still more work needed on crops of local or national importance. According to Melaku Worede, director of Ethiopia’s national gene bank: ‘There are a lot of gaps in the type of crops collected for conservation. Crops of particular socioeconomic importance to developing countries are not adequately studied, surveyed or handled to the same extent that the commercially important crops have been.’

What Worede says is undoubtedly true for indigenous Andean crops such as Chenopodium quinoa, Chenopodium pallidicaule and tuber and root crops such as Canna edulis and Arracacia esculenta, which would have vanished were it not for a last-ditch rescue by the Peruvian government. Indigenous crops of Asia and Africa suffer the same neglect.

About 20 different types of oil seed crops, almost unknown to the rest of the world, are to be found in East Africa. In the Sahel are some 30 species of forage trees and shrubs, another 30 species of grasses and at least 12 species of forage legumes that have been identified and whose continued existence is threatened by increasingly severe and long periods of drought. No one knows how many more species remain to be identified and used yet are on the verge of extinction.

Jane Toll, the IBPGR’s coordinator for West Africa, says the board has since 1984 given special attention to the Sahel because it is not only the centre of diversity for food crops such as millet, cowpea and sorghum, but also for many species of forage. Although the main cultivated varieties are already conserved, it is important to collect wild species and forage resources. Last year the northern Sahel had exceptionally good rainfall. Emergency collecting missions for priority species of forage crops found one grass that the local Tuareg people claimed not to have seen for 20 years. If scientists are correct in their predictions about the consequences of the greenhouse effect, the deserts of Africa are set to expand, making collecting in the Sahel of vital importance.

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How to select the survivors

BEFORE setting off on their trips collectors may be able to find out a lot about their plants of interest from existing gene banks or from herbaria. They would probably find sufficiently precise information about where the locations were made and where the areas of greatest variability are. In some cases, enough material has been conserved to run biochemical tests of diversity.

Restriction fragment length polymorphisms (RFLPs) are small segments of DNA cut out from chromosomes by restric tion enzymes. The fragments separate from each other under gel electrophoresis to produce a pattern of bands visible to the naked eye. Genetically similar samples produce a similar pattern of fragments.

According to Alison McCusker, head of research at the International Board for Plant Genetic Resources, the RFLP techniques could prove useful in narrowing down the search for areas where particular crops show rich diversity and to help in trimming the increasingly cumbersome collections. The board commissioned a study from Cornell University, New York, on the variability of collections of Pisum or garden pea. The researchers found that cultivated Pisum collections were uniform throughout most of Europe. The only different material came from West Turkey. ‘That finding in itself points us to doing further collecting in Turkey and adjacent parts of the USSR,’ says McCusker.

Existing collections are becoming bulkier as more is added to them. ‘I suspect that quite a lot of what is collected may turn out to be very similar,’ McCusker says.

World centres of diversity

Chinese Soya bean, aduki bean, small bamboos, apricot, peach, orange, China tea

Indian Rice, finger millet, chickpea, asparagus bean, aubergine, taro yam, cucumber, tree cotton, jute, pepper

Indo-Malayan Yam, banana, coconut

Central Asiatic Bread wheat, pea, chickpea, lentil, sesame, flax, safflower, carrot, apple, pear, walnut

Near Eastern Durum wheat, einkorn wheat, poulard wheat, bread wheat, barley, rye, red oat, pea, lentil, blue alfalfa, sesame, flax, melon, almond, apricot, pomegranate, fig, pistachio, grape

Mediterranean Hulled oats, durum wheat, broad bean, cabbage, olive

Abyssinian Durum wheat, poulard wheat, emmer wheat, barley, chickpea, lentil, tef, finger millet, pea, flax, sesame, coffee

South Mexican-Central American Corn, common bean, sweet pepper, upland cotton, sisal, squashes and gourds

South American Sweet potato, potato, tomato, papaya, tobacco

Chiloe Potato

Brazilian-Paraguayan Cassava, peanut, cocoa, rubber, pineapple