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VALUE OF DIVERSITY
The fate of all forms of life ... depends on the continuity of variation. At the entrance to CERES, the Controlled Environment Research Laboratory in Canberra (Australia), there is the following inscription: "Cherish the earth, for man will live by it forever." We might have said with equal justification: "Cherish variation, for without it life will perish."-Sir Otto Frankel
Little is "natural" in contemporary agriculture. It is not nature's way to allow large expanses of land to be planted to a single crop, much less to a single variety of that crop. As agriculture took hold and developed in ancient times, however, a certain fragile balance came to exist between plants and pests and diseases.
Primitive varieties-landraces-exhibited a great deal of genetic variation. A cursory look at a Neolithic wheat field would reveal differences from plant to plant. To be sure, pests and diseases struck, but their attacks were muted by the diversity and strength of the defences accumulated by the plants during thousands of years of adaptation under agriculture. On the margin of many a field grew wild relatives of crops, which frequently crossed with those crops, infusing them with greater stamina and resistance. Moreover, fields were not contiguous; there remained ecological barriers to the spread and buildup of diseases. As a rule, diseases only rarely exploded into widespread epidemics. Crops were damaged, but not devastated.
But then the world changed-or at least our perception of it did. The event was the visitation to Ireland of Phytophtora infestans in the 1830s.
A native of the Andes, the potato was unknown in Europe prior to the "discovery" of the New World. Potatoes were introduced into Spain in 1570 and into England and Ireland about 1590 or a few years earlier. For 250 years all potatoes grown in Europe were descendants of these two introductions.
In France, King Louis XVI became an advocate of the potato. In a neglected field near Paris he grew a wonderful crop of potatoes protected during the day by royal guards. Realizing that the peasants would be impressed by any crop so guarded, he cleverly withdrew the guards at night, allowing the peasants to raid the fields, which they did. Soon the king's goal was accomplished-all over France potatoes were growing.
In Ireland the potato became the staple crop of the poor. By the 1840s the average adult was eating nine to fourteen pounds a day. The summer of 1845 was a particularly good one for Irish farmers and reports from a number of counties indicated potato crops of "the most luxuriant character ... promising abundant yield."
Then it happened. On September 11, the Freeman's Journal announced:
We regret to have to state that we have had communications from more than one well-informed correspondent announcing the fact of what is called 'cholera' in potatoes in Ireland, especially in the north. In one instance the party had been digging potatoes-the finest he had ever seen-from a particular field, and a particular ridge of that field up to Monday last; and on digging in the same ridge on Tuesday he found the tubers all blasted, and unfit for the use of man or beast.
The potatoes in the ground as well as those already harvested began to turn black and rot. An awful stench filled the countryside. The weather was blamed. Next year would be better.
But it was not. The failure of the potato crop was a disaster for the Irish poor, who were numerous. Though three-quarters of the land was devoted to cereal crops (which were producing fine harvests), nearly all of this was exported to England or used to pay rents to landlords, many of whom were foreign. At the time, four thousand people owned eighty percent of the land, while the annual earnings of a rural laborer rarely equalled the rent on a single acre of land. John Mitchel, an Irish journalist of the time, charged that "in 1847, during the Great Hunger, Ireland produced agricultural products to the value of £44,958,120, enough to feed Ireland twice over, and continued to do so, but the people starved because with this produce the rent had to be paid." On occasion mobs attempted to prevent the grain from moving to the seaports for export, but such efforts were thwarted by the military.
The peasants could afford neither to keep nor to buy the grain they raised. Instead they lived on potatoes. A third of the Irish population was totally dependent on the potato for nourishment.
The British who ruled Ireland were concerned, but, as one observer noted at the time, "one must remember that the Irish had a terrible tendency to exaggerate." The British did repeal import duties on grain in order to lower the price of bread. But in the best of times, the poor could not afford bread-that was why they existed on potatoes.
The British opposed giving food to the starving lest it encourage the idle poor. Charles Trevelyan, the British bureaucrat in charge of the government's famine policy in Ireland, finally shut down public work programs and ceased all other government relief in 1847, declaring in effect that the famine was over and voicing his concern that "the only way to prevent people from becoming habitually dependent on government is to bring operations to a close.
But the famine was not over. The winter of 1847-48 saw corpses lying in the streets unburied for days. By the spring of 1849, the toll had become staggering. One county with a population of five thousand had over seven hundred people die in a two-week period. Some then-as now-said that the dreadful poverty of the people was caused by overpopulation. But as the population was decimated, the poverty remained. The famine continued for five years altogether. For five years Ireland's potatoes rotted. One to two million people died and as many migrated to North America.
It was not the weather that struck down Ireland's potatoes in the 1840s; it was Phytophtora infestans, a potato blight. The potatoes grown in Europe-genetically limited, as we have seen-were not resistant to this disease, and their lack of resistance allowed the blight to reach epidemic proportions.
Luckily not all potatoes were vulnerable. Among the thousands of distinct types in the Andes and in Mexico, resistance was located. Without it, potatoes probably would not be a major crop in the developed world today.
But the blight has consistently been blamed for the famine. As devastating as the disease was to potatoes, it was the social system, by allowing few to own and control so much, that caused the famine. How else can we explain the fact that eighty percent of the countryside was still being grazed, not cultivated, and that grain continued to be exported at a time when hundreds of thousands were perishing? Even as people were starving, Ireland produced enough food for everyone. The Irish themselves said: "God sent the blight; the English brought the famine."
Potatoes were the first crop in modern history to be devastated by lack of resistance-and the first crop to be rescued by the wealth of defenses built up over thousands of years in its center of diversity. Thus the Irish potato famine stands both as the most dramatic warning of the dangers of genetic uniformity and the clearest example of the value of preserving genetic diversity.
Differences in the performance of different crop varieties had long been noted. Various Greek and Roman writers recorded their observations on this matter. But little use of this knowledge was made until the advent of modern plant breeding in the 1800s and the rediscovery of Gregor Mendel's laws of heredity at the turn of the century.
With this knowledge, plant breeders were able to use the diverse characteristics of landraces developed over thousands of years to fashion new crop varieties designed for particular situations. By carefully selecting for the desired characteristics, breeders could "weed out" unwanted traits and arrive at a "pure line," a variety that was uniform and reproduced this uniformity.
The diversity and variability of the old landraces used in early breeding programs were thus whittled down to a pure line. And often one pure line was bred with another to create a hybrid. In the field these genetically restricted varieties replaced the wide open diversity, the "harmonious disorder" of the landraces.
"A pure line mentality, convinced that variation was bad, uniformity was good, and off-types in the field somehow immoral, developed. Symptoms of the mental climate could be found in crop judging contests, ribbons awarded at county and state fairs, crop improvement associations, seed certifying agencies, and in some provisions of state and federal seed acts. It did not seem to occur to anyone that a deliberate mixture of cultivars could be a useful alternative to pure line culture. Although grain is frequently mixed in the elevator anyway, a mixture in the field was considered bad husbandry and a slightly less than mortal sin to be kept hidden on the back forty off the road."
Though the new varieties were clearly superior in some respects-yield being the most obvious-they sometimes lacked the breadth of resistance, or a trait like cold tolerance, contained in the landraces. Simply put, the landraces would not have survived as long as they had under harsh conditions without fertilizers or pesticides if they had not been adapting effectively. Contributing to their success was the spatial heterogeneity provided by early farming systems. Mixed cropping made it difficult for pests and diseases to build up excessively.
With the new varieties the flexibility of general adaptation and resistance was traded for something more focused and inflexible. Replacement of landraces with new, pure line varieties planted over thousands of acres opened the way for pests and diseases to attack the uniform, inbred plants. In a field of landraces a pest might gobble up one plant but find the next one different enough to be distasteful. In a field of modern varieties, if the first tasted good, they were all going to taste good.
In the 1870s coffee rust essentially wiped out the coffee industry in Ceylon (now Sri Lanka), India, East Asia, and parts of Africa. As a result, England became a nation of tea drinkers. Epidemics hit cotton in the 1890ís. And in 1904, an epidemic of stem rust struck the U.S. wheat crop. By 1905, what is probably the oldest program designed to develop disease resistance in this crop was begun by the U.S. Department of Agriculture.
The race continued. Other epidemics followed. In 1917, "wheatless" days were declared in the U.S. in response to an epidemic. Twenty-six years later and half a world away, brown spot disease devastated the Indian rice crop, touching off the infamous Bengal famine. In the 1940s, cultivars accounting for eighty percent of the U.S. oat crop were eliminated, and oats experienced more problems in the 1950S. Then in the early 1970S, corn blight struck in the U.S., sparking concern over genetic uniformity in the nation's crops. And a major failure of the Soviet wheat crop, caused in part by the large-scale planting of an inappropriate variety, precipitated the "Russian grain deal" and dramatic (and ultimately costly) shifts in American farm policy.
Each time resistance was needed. And each time it was found in the centers of diversity, in landraces that had somehow escaped homogenization, or in those crops' wild relatives.
As use of the pure line and hybrid varieties increased, so did pest and disease problems. The greater pest and disease problems grew, the more farmers turned to chemicals to solve them. In 1945, less than 200 million pounds of pesticides were employed in the U.S. Thirty years later the total had risen to 1,600 million pounds.
But the chemicals did not solve the problems. It could even be argued that as pesticide use increased, so did pest problems. With all the increased "firepower" in the hands of farmers, it might be expected that the pest rebellion would have been put down. But in the last forty years the percentage of the annual crop lost to insects has doubled in the U.S. Losses due to diseases have also increased. There are reasons for this.
Much of agriculture's pest control work is done by "beneficial" insects that feed on or otherwise control "harmful" insects; or by spatial heterogeneity. In a "natural" setting there are more harmful than beneficial predatory insects. If there were not, the beneficial insects would begin dying off from lack of food. A one-to-one ratio between harmful and beneficial insects would mean that the useful insect's first meal would probably be its last.
Most pesticides kill both useful insects and agricultural pests without distinction. One corporation, Rockwell International, advertised in a magazine that its pesticide would "kill every bug you've got" and all the insects pictured were creatures that never harm crops.21 A pest problem may be alleviated temporarily by a pesticide as it kills all insects at hand.
But, as Dr. Carl Huffaker of the University of California says, "When we kill a pest's natural enemies, we inherit their work." When the pesticide dissipates or is washed away by rain, the harmful insects multiply rapidly. The population of beneficial insects-small to begin with and now completely decimated-cannot recover as quickly. Nor, because of their small numbers, do these beneficial insects develop resistance to chemicals as easily. The result: harmful insects return with a vengeance, this time with even less to stop them.
It is becoming common knowledge that insects are developing resistance to the pesticides that once killed them. Resistance to DDT began appearing among crop-eating insects just six years after introduction of that infamous pesticide. Most people realize that today's super pest could enjoy several doses of yesterday's pesticide for dessert, ask for more and live to tell about it. Over four hundred species of pests have now developed resistance to the chemicals that once destroyed them. More than a million chemicals have already been screened for their effectiveness as pesticides and yet "the progress of resistance may outpace the discovery of effective new materials."
Insects can also learn to evade the plant's natural resistance. In an experiment conducted by the International Rice Research Institute (IRRI, pronounced "eerie"), plant pathologists raised the troublesome brown planthopper on a rather poor quality, but brown planthopper-resistant rice variety by the name of Mudgo. The insect, which is now the most serious pest in Asia according to T.T. Chang of IRRI, was unknown to rice workers in the early 1960s.
The Bangladesh Rice Research Institute (BRRI) has developed a 'Super High Yielding Variety (S-HYV)' of rice with a growth potential of 12 to 14 metric tons per hectare, BRRI Director General Dr Nurul Islam Bhuiyan announced yesterday. He said the new variety, developed through hybridisation of a HYV with a foreign variety, would be in the hands of farmers after two to three seasons of field trials. This thick and sturdy Super HYV has no lodging problem and each panicle holds more grains than any HYV (The Daily Star 29.05.01).
In this experiment many brown planthoppers starved to death rather than eat Mudgo. On average the first generation of planthoppers lived only 4.2 days, but that was long enough for them to produce a new generation. The new generation did not find Mudgo quite as distasteful. By the tenth generation, the planthoppers were indicating that Mudgo was all right. They lived an average of sixteen days eating nothing else, which is about as long as they lasted feasting on one of their favorite, susceptible rice varieties.
With insects developing both immunity to pesticides and a taste for resistant varieties so quickly, it is little wonder that the average life span of a new cultivar has, in the memorable words of Lawrence Hills, "been reduced to that of a pop record." Kenyan wheats, to cite but one example, last an average of 4.3 years before they have to be pulled off the market and replaced by a new variety.
Like insects, diseases also adapt both to chemicals and to the genetic defenses of plants. Diseases mutate, developing new races to overcome the resistance of plants and the farmers' chemicals. "Race i" of the standard wheat stem rust was identified in 1917. Fifty years later, three hundred were known. Like insects, plant diseases have coevolved with their host organism. They are not in the business of becoming extinct. By adapting to their changing environment they are able to survive. And survive they do.
As the pests chalk up victories on the battlefield, chemical company bravado rises in pitch. Government regulations slowing down their ability to add to the chemical load already in use, claim the pesticide manufacturers, have prevented them from winning the war. In one startling editorial in a Dow Chemical Company newsletter, Dr. C.A. Goring, director of agricultural products research for Dow said: "Given the opportunity, the web of man-made chemical technology could continue to grow in beauty and diversity creating many new and beautiful species, eliminating some old species and relegating others to more specific ecological niches."
Did you catch that? "Given the opportunity," Dow's chemicals will create a few new species, eliminate some species (might we ask which?) and assign others to "more specific ecological niches." Anyone opposing this plan, according to Goring, is an "anti-technologist." After all, he continues, "the chemicals we make are no different from the ones God makes."
As agriculture developed in ancient times, the balance between plants and pests and diseases rarely got too far out of line. A disease too successful would ultimately eliminate itself! Plants survived. Pests and diseases survived. With the creation of pure line varieties, however, much resistance was lost as the diversity of the landraces was reduced to create uniform varieties. Plant species that had had to rely on their own natural defenses and on mixed cropping systems for thousands of years were suddenly forced to depend on man to help them resist new or stronger pests. Thus breeding programs were established to re-insert resistance into crop varieties that were now under constant attack.
When plant breeders settle down to the long and expensive job of developing a disease resistant variety, their first line of attack is to look for that resistance in other modern varieties; then they try landraces. Modern varieties and their breeding stocks give the breeder the least trouble, because they are usually similar in other respects to the variety desired. It takes less effort to eliminate the undesirable characteristics while obtaining the needed resistance. Landraces, because they have survived so long among pests and diseases in the centers of diversity, offer a wealth of potential resistance. But they are not as similar to the end product desired and some pains must be taken to eliminate unwanted characteristics as the resistance is obtained.
Canada's famous wheats were produced by breeding varieties and landraces from Australia, England, Kenya, Egypt, India, Poland, Portugal and the Middle East. And in the U.S., a Chinese spinach variety "rescued Virginia's spinach industry from ruin." A thorough listing of such examples would take many books. Suffice if to say that the "primitive" varieties developed by our ancestors continue to play an integral role in the maintenance of modern crop varieties.
When all else fails and resistance or some other desired characteristic cannot be found in cultivated types, the plant breeder will turn to closely related wild or weedy plants for the needed genes. Breeders call these plants "wild relatives." There is no trace of a smile on their faces when they use the term, because working with wild relatives is often so difficult. For every desirable characteristic obtained, a number of completely unacceptable ones must be bred out. Ridding the new variety of wild and weedy characteristics can mean years of extra work for the breeder, hence the use of wild relatives in breeding programs is usually a sign of either desperation or courage on the breeder's part. Many plant breeders do not even know, could not even recognize, the wild relatives of the crops they specialize in breeding. And few are eager to find out.
The diversity of wild relatives has enabled them to survive longer than the oldest cultivated variety-and to survive without human assistance. If their genetic resistance had failed them, they would have become extinct long ago. Thus, as sources of resistance, wild relatives are a treasure.
Wild relatives have now been used in the breeding programs of virtually every cultivated crop. Sugarcane is "an example of a commercial crop that has been completely salvaged" by the use of wild relatives. The same could probably be said of strawberries and sunflowers using genes found in North America.
Wild species from Central and South America offer the only known source of resistance to the most serious disease that strikes black pepper. And in peanuts, wild species are now "the main source of resistance to pests and diseases." Likewise, potato breeders are becoming more and more dependent on wild relatives. In the Federal Republic of Germany, nine out of ten potato seedlings have wild species or primitive landraces in their backgrounds.
Tomatoes and tobacco simply "could not be grown commercially at all in the U.S.," according to Jack Harlan, without the resistance they have developed from wild species. For at least nineteen disorders of tomatoes, wild tomato species are the principal source of resistance. They have supplied resistance to leaf mold, tobacco mosaic virus, nematodes, curly top, Septoria leaf spot, wilt, and other diseases. And they have helped extend the growing range of this crop. Finally, wild species of tomato offer some interesting possibilities for future breeding work. One of the world's leading experts on tomatoes. Dr. Charles Rick of the University of California, found a number of wild tomatoes growing along the beach on one of the Galapagos Islands. Barely five meters (16.5 feet) from the high tide line, these plants were exposed to Pacific salt spray and very salty soil. Back at the University of California at Davis, Rick's colleagues found that these tomatoes could be grown hydroponically in a culture "gradually adjusted to full-strength sea water."
After a four-year program which tested seventeen thousand rice accessions and over one hundred wild taxa, resistance to grassy stunt virus was found in just one population of Oryza nivara from India. When a new strain of the virus appeared in 1982 more screening was forced. After arduous testing, resistance was again found, again in wild species. And wild species have helped give potatoes resistance to Phytophtora infestans, of Irish potato famine fame. In 1951, an epidemic of barley yellow dwarf virus broke out in California. The search for resistance took breeders to one gene in an Ethiopian barley.
Chocolate and chocolate-lovers were delivered from twin curses of witches' broom and swollen shoot, two diseases that strike cacao, from which chocolate is made. Again, wild and semi-wild species furnished resistance. Wild cottons are being used in breeding programs aimed at producing varieties resistant to the dreaded bollworm and boll weevil. Other wild cottons offer greater fiber strength and some show promise in reducing the cause of brown lung disease which afflicts textile workers. Breeders of rubber, pineapple, cassava, and maize are seeking to introduce greater vigor into their crops by using wild species. The range of soy-beans, grapes, and wheat, in addition to the previously mentioned tomatoes, has been extended by employing genes from wild relatives.
Wild species even show promise of helping improve the nutritional qualities of wheat, rice, rye, oats, soybeans and a number of vegetable crops. And others, like some of the bramble fruits, are being dethorned through breeding programs using wild plants.
Robert and Christine Prescott-Allen estimate that between 1976 and 1980, genetic material from wild relatives contributed $340 million per year in yield and disease resistance to U.S. farmers. According to the Prescott-Allens, wild germplasm has contributed $66 billion to the American economy-an amount greater than the total international debt of Mexico and the Philippines combined; and the comparison is not unrelated. As we shall see in following chapters, this valuable germplasm is routinely donated by Third World countries to the U.S. without any compensation or corresponding reduction of official Third World debt to the U.S.
Using wild species in breeding programs is a difficult, trying, time-consuming, and costly venture. Most breeders work under the pressure of getting new varieties out into the market-and getting them out in a hurry. Since breeders understandably shy away from using the wild relatives, it is doubly impressive that they have recently had to turn to these plants so often for such important traits in so many crops. In many instances cited above, even the primitive landraces were passed by as resources for breeding programs-rejected either because resistance could no longer be found in their ranks, or because the resistance they held was no longer effective.
Plant breeders have the unenviable job of trying to help modern agricultural crops stay one step ahead of thousands of pests and diseases. In any given year they are mostly successful. But resistance is a moving target. This year's resistant variety is next year's main course. Plant breeders have not always been able to prevent this.
In the early days of this century the old landraces provided the raw material with which plant breeders began to work. Highly variable, these primitive varieties have continued to offer much in the way of resistance and adaptability. But today the weedy and wild relatives of these crops have assumed a degree of importance that would have shocked, if not discouraged, yesterday's breeder. In truth, they have become so essential that Jack Harlan-arguably the scientist with the broadest knowledge of their role in agriculture-was moved to say that the "wild relatives stand between man and starvation..."
Years ago, Vavilov described plant breeding as "evolution at the will of man." Like any kind of evolution, plant breeding requires variation.
Artists create paintings using palettes covered with colors. Plant breeders fashion new varieties using the genetic variation within a crop. Robbing the breeder of this variation is like taking colors from the artist. It diminishes what is possible. If too much variation is lost, little or no evolution is possible. Eventually, the crop succumbs and becomes extinct.
Without the landraces and wild relatives, our modern crop varieties would be incapable of changing, of evolving, of adapting to new conditions, or stronger pests. Like so many things in this world, the new depends on the old. Without the old varieties, the new varieties could not continue. They simply could not survive. And herein lies the irony. In the long run, the future of agriculture and the very survival of crops depend not so much on the fancy hybrids we see in the fields, but on the wild species growing along the fence rows, and the primitive types tended by the world's peasant farmers in the centers of diversity. Without these wild species and old landraces, there would be no agriculture. So we turn now to what may be the most important question facing our own species: What is the state and well-being of these little known resources that stand between us and starvation?
Shattering: Food, Politics, and the Loss of Genetic Diversity by Cary Fowler and Pat Mooney, 1990
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