by FAO staff
This survey was prepared for submission to the United Nations International Conference on the Peaceful Uses of Atomic Energy held in Geneva, August 1955. It is reproduced in Unasylva at the request of the Permanent Committee of the International Union of Forest Research Organizations. In the course of their last session at Stockholm in September 1955, the members of this Committee visited the field research station of the Swedish Forest Research Institute at Bogesund, and Professor Ake Gustafsson, of the Department of Genetics, demonstrated the nearby center for experiments into the genetic effects of acute and chronic 60Co gamma irradiation on different plant species. The radiocobalt source used is in the middle of an experiment field about 100 meters square, surrounded by earth walls and high steel fencing to secure protection and prevent uncontrolled entry to the irradiated area. When in use the source is 70 centimeters above ground. It is suspended by a wire in a brass tube and there is an iron extension of the tube to a depth of about two meters below the ground. The lowering of the source into the iron part of the tube is operated from the fence gate, the gate lock being connected with the lowering winch so that entrance into the experimental area is impossible until the source is safely below ground.
THE present world population of about 2.5 thousand million is growing at the rate of nearly 1.5 percent each year. Every day nearly 100,000 additional hungry mouths appear at the breakfast table, and twenty-five years hence it is expected that we shall be 3.5 to 4 thousand million in number. Evidently one of the many major problems facing us, probably basically the most important for the future welfare of mankind, is how we shall be able to provide food, clothing and shelter for the world's peoples at the ever higher standards that they so rightly expect.
The neo-Malthusians believe that we are engaged in a losing battle and that it will not be possible for world resources to meet requirements. FAO believes that technically it is possible to achieve the necessary increases in production of foodstuffs and basic raw materials to meet world needs for the foreseeable future, and has recommended to governments that they aim at increases in production one to two percent greater than their anticipated growth in population. For many countries this will mean production increases of 3 to 4 percent a year. This admittedly will do little more than maintain the status quo but even so the social, political and administrative problems involved will be of immense magnitude. Their solution alone, quite apart from the further urgent need to make a real improvement in the inadequate subsistence levels which at present characterize so many parts of the world, will require determination and fortitude on the part of governments. Although freedom from want must depend essentially upon the efforts made by each country on its own behalf, success in achieving this is of such general concern to all peoples that these national efforts should be supplemented by pooling the knowledge and experience of all countries on an international basis for the common good. In doing so, it is imperative that all possible advantage be taken of the contributions to increased production that might come from scientific and technical advances in other fields. Amongst those advances the development of atomic energy is of great significance for agriculture and the related industries of forestry and fisheries.
From the technical standpoint the solution of the problems of providing more of the primary necessities of life can come in three main ways. The easiest method of increasing supplies is by taking adequate measures to reduce the heavy losses which at present occur in all segments and stages of production, storage and distribution. Secondly, the productivity of land now under cultivation could be much increased and the current utilization of our fisheries and forestry resources intensified through development of improved technical methods. Finally, supplies could be increased by developing new areas and resources, but this is the most difficult course as those areas and resources most easily developed are already being utilized.
The ways in which atomic energy can help in feeding, clothing and housing the world's growing population will be considered in relation to these three main ways of improving production and making better use of our natural resources.
When relatively inexpensive power from nuclear reactors becomes generally available it will undoubtedly make a substantial impact on agriculture, if only by cheapening costs of production and distribution, improving conditions of work and making modern conveniences and comforts more widely available in rural communities. This is particularly true in areas where other sources of power are deficient. These and other at present more speculative developments must, however, await the widespread application of nuclear power in industry, and its possible contributions will be discussed a little more fully later. At present and for the immediate future the radioactive isotopes and radiation that have become available as by-products of nuclear reaction are of greater importance to agriculture.
It was at one time thought that radiation and radioactive isotopes might prove of direct value in the stimulation of plant growth. To date, the only stimulatory effects in the irradiated generation which have been observed in extensive investigations conducted in the United States of America, the United Kingdom and Canada have been those associated with damage to the plant, much as growth is stimulated, in a sense, by the use of the pruning knife, and there has been complete failure to substantiate the earlier hope for useful stimulation of growth.
Neither radiation nor radioisotopes, therefore, can make any direct contribution to increased production in the sense that an application of fertilizer leads to increased crop yields. Their contribution to food and agriculture is indirect, but nevertheless of immense potential. The value of radiations lies partly in their ability to induce inherited changes in the germ plasm and partly in their sterilizing effects on biological tissues. The ability to induce mutations is being used in plant breeding programs and in other ways, whilst the sterilizing effects have promising applications in food preservation and pest control. The value of radioisotopes in agriculture arises from the ease and accuracy with which they can be identified and measured in extremely minute amounts, which makes it possible to use them as highly refined research tools in so-called tracer studies in a wide range of nutritional, metabolic, developmental and pathological investigations in plants, animals and man. In this way they are giving information which at the present time could be obtained in no other way or only at much greater expense in terms of time and money. Thus, by giving a clearer insight into basic biological processes that have hitherto been obscure, the use of radioisotopes in tracer studies is already leading to greater efficiency and economy in the production and utilization of agricultural products. Bearing in mind that it was only unfettered scientific investigation of the nature of the atom - the pursuit of knowledge for its own sake - that made nuclear energy available to mankind, the potential value of the contributions which radioactive tracer studies can make to food and agriculture may similarly be almost unlimited.
Food preservation and storage
Potential food supplies and other agricultural products are subject to heavy losses in all phases of production, distribution and storage through fungal and bacterial infection and the ravages of insect pests, and it is by combatting these that the most immediate and spectacular improvements in supplies can be achieved. No valid estimate of total world losses is possible, but they are undoubtedly of immense magnitude. A very conservative estimate that has been brought forward for losses in stored grain, largely from the depredation of weevils and other insect pests, is 10 percent, but the losses are undoubtedly much greater in the hot and humid areas of the world, where the figure of 25 to 50 percent loss of harvested cereals and pulses which has been estimated for Central America is probably generally applicable in most of the less advanced countries. In addition, perishable foodstuffs such as fruits, vegetables, meat and fish are particularly subject to spoilage in distribution and storage. Similarly the deterioration resulting from fungal infection and the attacks of various insect pests is of major concern in timber utilization.
Evidently there is great scope for the adoption of control measures, and these can be applied relatively easily at a cost which is usually but a small fraction of the value of the returns. Already radiations and radioactive isotopes show promise of making important contributions to the development of improved control measures which would markedly improve the supply situation. Thus the destructive power of radiation has been used to eliminate insect infestations in grain and cereal products at costs which compare favorably with those of the more conventional procedures such as fumigation. The sprouting of potatoes has been successfully inhibited as a result of the effects of radiation on the enzyme system, thus permitting transportation under less stringent conditions than are usually required and extending storage life by many months. Much attention is also being given to the possibility of food preservation through cold sterilization by irradiation at normal temperatures. Whilst full success has not yet been attained, significant improvements in the keeping quality of meat and meat products have been achieved without off-flavors or color changes arising from detrimental side reactions. In some countries, trichinosis is an important health problem and it has been shown that the irradiation of pork can kill or sterilize the trichinae, thus rendering infected meat safe for human consumption.
Evidently radiation may have a very useful field of application in food processing and preservation, although much more exploratory work must be done to evaluate its full potentialities. One of the most attractive features of this application is the wide scope it offers for the useful employment of the radioactive residues arising as a by-product of the operation of nuclear reactors.
Reducing losses in growing crops
Every year a large part of the potential harvest is destroyed by diseases and pests which attack the growing crop. It has been said that, even in such relatively developed countries as the United Kingdom, the work of over 51,000 skilled farm workers is lost each year, and that in the United States of America losses caused by insects, weeds and plant diseases account for losses in farm output equivalent to 13,000 million dollars per year. Most of these losses could be avoided by the timely application of control measures, and radioisotopes are proving to be exceptional tools in studies which are leading to the development of improved materials and methods for safeguarding our harvests. Adequate control of a destructive insect, for instance, generally requires a thorough knowledge of its life cycle and habits, and tagging insects with radioisotopes provides a much more efficient means of determining their flight range, migrating routes and overwintering habits than methods such as painting which were previously used. In Canada, cobalt-60 has been used to label wireworms, making it possible to follow their underground meanderings while, in both the United States of America and Canada, the flight and overwintering habits of a num her forest insects are under investigation, using similar techniques. These studies will undoubted!: be important factors in better control.
Extremely effective insecticides have become avail able in recent years but one of the problems associated with their continued use is that insects frequently, build up resistance to these poisons. Studies with insecticides labelled with a radioisotope permit comparison of uptake and metabolism by normal insects and by those that have developed resistance. This work may be a step in determining the nature of resistance to the poisons, concerning which so far little is known except that resistant insects take up the poisons just as susceptible ones but do not react to them in the same way.
Similarly radioactive tags are playing an important part in the development of fungicides, insecticide, and weed killers, for use either as direct application or as systemic poisons. These latter are substances which are applied, usually through the soil, and taken up by the plant without harm to it but are toxic to pests feeding on the plant. It is important to know that such substances are not altered in use to products harmful to man or animals. For instance, the weed killer 2-4-D when used to kill weeds in the bean field is readily absorbed by the bean plant also and has been found by the use of labelled material to be distributed throughout the plant together with at least two additional products derived from 2-4-D. It is obviously important in the case of edible plants to be able to trace such compounds and their metabolic products because of their possible effects on the consumer, animal or man, and the use of radioactive labels is playing an important part in the development of safe materials and methods.
Breeding improved, crop varieties
Although control of crop pests and diseases by chemicals can be extremely effective, their use involves additional expenditure and usually requires considerable care. Undoubtedly the most satisfactory safeguard, and one that is particularly applicable in the underdeveloped areas, is the growing of crop varieties resistant to the prevalent pests and diseases. The plant breeder has long been engaged in developing such varieties by well-known conventional methods involving selection and hybridization, and has achieved marked success, but this is a never-ending task, for existing varieties do not satisfy all needs and new pests and diseases or new forms of old ones are constantly appearing. In his task of developing disease- and pest-resistant varieties, as well as other improved types with better agronomic characteristics and higher productivity, the plant breeder is already being greatly assisted by the new potent sources of radiation which have recently become available, and their use in this connection may well ultimately prove to be one of the most significant contributions of atomic energy to agriculture. It has long been known that radiations cause heritable mutations in plants and animals. With the advent of atomic energy further kinds of radiations and more potent sources have become freely available for experimental use, and in many countries extensive programs have recently been initiated for crop improvement through irradiation, with a view to accelerating the normal rate of mutation and so increasing the variability available to the plant breeder for selection.
Radiations are applied either in the early flowering stages in order to affect the developing gametes or to seeds in which somatic mutations are first induced, and such affected cells may subsequently give rise to germinal tissue, in which case the mutations are transmitted to later generations. Although, as in the case of spontaneously appearing mutations, the vast majority are deleterious, desirable types occur in low proportion and have been selected in a wide variety of crops. Improved types that have been obtained include higher-yielding or disease-resistant strains of cereals and other crops such as peanuts, stiff-strawed types of cereals resistant to lodging, types better adapted to mechanical harvesting on account of particular size or shape characteristics, types with extended or reduced maturity period, and types with changed ecological requirements, for instance in relation to higher or lower rainfall or soil fertility. An example of a particularly significant outcome of work of this type may be cited from Canada where, amongst some 20 barley mutants produced by irradiation and now under field trial, are Home maturing sufficiently early to extend the area in which barley might be grown in that country.
Plants such as some orchard crops which are nor many propagated vegetatively are also receiving 3 radiation treatment for the induction of bud Mutants have similarly been induced in algae and in this way types have been obtained which are adapted to high temperatures and thus more suitable for growth in mass culture. Such types may one day become an important source of food and industrial raw materials. In forestry, increasing emphasis is being given to the breeding of fast-growing types and varieties resistant to pests and diseases, and radiation may play an important role in the production of such improved strains of trees.
In the case of disease control, the ability of radiations to induce mutations in the disease-producing organism itself may also prove to be a tool of exceptional value.
Such pathogens as the rusts that affect wheat and; oats or the smut attacking maize undergo spontaneous mutations in nature at a rate rapid enough to cause constant trouble for the crop breeder. If he develops, for example, a wheat resistant to black stem rust, he may find that within a comparatively short time a new mutated form of the rust organism appears to which his variety is no longer resistant as it was to the original form. Current work has shown that radiation will produce new races of such disease organisms with increased virulence. By developing these new races artificially and under controlled conditions, the breeder may be able to anticipate the resistance requirements of his crop and to breed adequate resistance prior to the appearance of new strains of the pathogens in the field.
Increasing productivity through improved practices
In addition to the adoption of adequate measures for the control of plant and animal diseases and pests and the use of higher yielding crop varieties developed by the plant breeder, the productivity of land now under cultivation can be increased by the adoption
Of a wide range of improved methods of crop and animal husbandry. Here again, through tracer studies using radioisotopes, atomic energy is making notable contributions to the development of improved techniques through the advancement of fundamental knowledge in animal and plant nutrition and physiology and a better understanding of the complex relationship between animal, plant, soil, water and sunlight on which man is dependent for his existence. The study of such a dynamic biological systems is normally particularly difficult and the tracer technique has immeasurably facilitated such investigations. In many cases it provides the only practical approach to the solution of a problem and without it further progress in certain directions would at this time have been impossible.
Soil fertility
The major limiting factors in the productivity of land now in cultivation are the inherent yielding potential of the crops and livestock on them and the amount of nutrients available to enable those plants and animals to produce to their capacity. Contrary to general belief, some of the most productive soils in the world were originally of rather poor fertility and have been brought to their present capabilities by man's careful tending of the soil and the development of various principles of good husbandry, which through the ages have built up the fertility of the soil. The potentialities for increasing production through adoption of those principles on a wider scale are very great. As just one example, the yield of rice in Japan is about four times that of India's one ton per hectare. Much, though admittedly not all, of this increased productivity is due to the much greater use of inorganic fertilizers in Japan, and evidence from experiments indicates that through the use of only a moderate dressing of 30 kilograms of nitrogen per hectare, with other plant nutrients where necessary, India's annual rice production of about 35 million tons could be raised by more than 10 million tone - which would mean much to the welfare of the population and to the economy of the country. However, the present limited use of fertilizers in such countries is almost entirely a question of economics, so that it is essential that the best use is made of the natural fertility of the soil, and that added fertilizers are employed in such a way as to ensure the fullest possible return from them. Here tracer studies with isotopes in many countries are providing a wealth of fundamental information and practical hints. Radioisotopes of most of the important plant nutrients are now available and they have opened up new avenues of attack on important problems of soil fertility.
The fact that phosphorus is to so large a degree retained by soils in forms that are not readily available for use by plants is one of the major concerns of soil science. Advances in the study of this problem are being made through such work as that in the United States of America with phosphorus-32 and calcium-45 on the factors influencing the fixation of phosphorus in calcareous soils. Canadian who were among the first to point out the advantages of the tracer technique in soil fertility and plant nutrition problems, have shown that the usual procedure for evaluating the contribution of a phosphorus fertilizer by comparing the total phosphorus absorbed by the plant from fertilized and unfertilized plots could be misleading. Before the use of tagged material it was thought that the increased uptake from the fertilized plot all came from the fertilizer. Through the use of radioactive phosphorus it has been found that, when the fertilizer is applied, the plant takes up additional phosphorus from the soil itself as well as from the added nutrient.
Rice, the basic food of nearly one-half of the world's population, is typically grown under irrigation, in submerged soil. In Japan, the radioisotopes of phosphorus, sulphur and iron are being employed in preliminary investigations of the chemistry of such submerged soils, which is quite different from that of ordinary soils, and valuable information is to be expected on the factors affecting the uptake and translocation of these nutrients by rice. Similar work on the determination of the phosphorus fertility status of tropical and submerged soils is under way in India. Other investigations are giving information on the most economic source of specific nutrients and the best placement and time of application of added fertilizers, particularly in relation to the growth period when the plant can best use them and their placing in relation to the main feeding zones of the roots. In this connection a good deal of attention is being given to investigation of the characteristic rooting habits of different plants through use of labelled nutrients, and this ability to define the zones from which particular crops obtain the major portion of their nutrients and moisture requirements should make a valuable contribution to better agricultural practices.
Soil moisture, drainage and irrigation problems
Many other soil problems are amenable to attack by this new tool. It makes possible, for instance, rapid determination of the moisture content and the density of soils, a matter of interest alike to the agronomist, the soil conservationist, and the engineer. Moisture content of the soil may be estimated by a method dependent on the degree of neutron scattering by hydrogen atoms contained in the soil water. A similar method involving gamma rays instead of neutrons is used in measuring the density or degree of compaction of the soil. One application of these methods in the United States of America is the study of the effects of tillage and harvesting machinery in compacting the soil.
A different application to soil problems, is the addition of phosphorus-32 or rubidium-86 to surface waters, such as streams or ponds, to determine the rate and direction of drainage into the soil, and to irrigation waters to find out whether they reach the farthest points of the field as well as the nearest points - that is, to evaluate the efficiency of distribution of the water in the soil. Radioisotopes are also being used, for instance in Japan, to detect leakage in irrigation dams and to survey supplies of underground water, and tritium might have a particularly valuable application in large scale research in hydrology, for example over entire watersheds.
Plant nutrition and metabolism
In plant nutrition, the basic mechanisms involved are the uptake of nutrient elements, their transport through cell membranes, and their subsequent translocation or movement throughout the plant. Such mechanisms are of course basic also in the case of animals. Investigation of these fundamental mechanisms through the use of a considerable variety of radioactive elements is under way in many countries. Fuller knowledge of the phenomena involved is essential to the understanding of plant nutrition and growth, and discoveries that were hitherto impossible in this field are now being made. Amongst other practical aspects the mechanism of transport plays an important part in the utilization of growth-affecting or growth-regulating factors - the so-called plant hormones which are used to regulate development in crops, particularly in horticulture - and in the utilization of such compounds as the previously mentioned 2-4-D which are used as weed killers, and the systemic insecticides which are administered to the pest by way of the host plant. An interesting example of the place of such translocation studies in relation to practical problems is the work on mistletoe in Australia, where this parasite is a serious menace of eucalyptus. In work directed towards its control, the isotopes of cobalt, iron and zinc are being used to obtain information on the efficiency of movement of toxic compounds from the host tree to the parasite.
Many of the plant hormones and weed killers are used as leaf applications, and essential nutrients may also be applied to aerial parts of the plant as well as by way of the soil. Thus under certain conditions, especially with trees, temporary deficiencies of such vital elements as iron and zinc may occur, and these can often most readily be corrected by spray applications either in the dormant stage or when in leaf. Radioisotopes have been particularly helpful in demonstrating that some plants can absorb such nutrients efficiently through the foliage and that nutrients so absorbed are rapidly translocated throughout the plant. This principle is already being applied rather widely in practice, urea for instance being used fairly extensively as a leaf spray by fruit and vegetable growers in the United States of America. Additional information on the absorption and translocation of such substances is needed and through the use of urea labelled with carbon-14 it has already been found that crops differ markedly in their ability to utilize this compound as a source of nitrogen, cucumbers using it more than four times as fast, for instance, as do cherries and potatoes. In the case of strawberries, calcium is readily absorbed, but it has been found that it is not translocated into daughter plants and hence foliar feeding as a major source of calcium is not adequate in this plant.
In Puerto Rico, studies of the formation of Hevea rubber are being made in tissue cultures, using possible chemical precursors of rubber tagged with carbon-14. Such investigations should lead to increased knowledge of the basic reactions and mechanisms involved in the secretion of gums and resins and will contribute in the long run to more efficient production of these economically important materials.
Radioisotopes offer a means of determining the rate of movement of water in plants and rather direct evidence of the structural pathways involved. Canadian forests are suffering from a die-back in birch, and radioactive phosphorus and rubidium have been used in the current investigation of the disease. These isotopes have shown that the normal narrow-band upward-spiral path of solution movement is broken in the affected tree and replaced near the dying region by a confused irregular pattern. Although no answer to the die-back problem is as yet forthcoming, it may be anticipated that the new techniques will play their part in the ultimate solution.
Well in the forefront amongst the contributions of radioisotopes to the advancement of fundamental knowledge of plant nutrition and metabolism has been the remarkable progress made through their use in the elucidation of the highly complex mechanism of photosynthesis, the process by which green plants use the sun's energy in the formation, from air and water, of compounds essential to life. Using radioactive carbon, the early principal pathways of this element have been established, and subsidiary pathways and the specific biochemical reactions involved in the synthesis of carbohydrates are being investigated.
The efficiency of energy conversion by photosynthesis is low; probably not more than 1 percent of the total available energy in the sunlight falling on a green leaf is effectively used. This low value arises at least in part from the fact that the process, is limited somehow by the plant itself. Investigations are now under way with the aim of identifying the compound or compounds that limit the photochemical reaction. Inefficient though this process is, so far in earth's history it has been the primary source of all food used by men and animals to sustain life, and the source of all our fuels including wood and the fossil fuels, coal and oil - those to which we now refer as conventional fuels in contradistinction to the nuclear fuels of the atomic age.
The remarkable advances that are being made in the understanding of photosynthesis may well lead to important methods of increasing the efficiency of this conversion of energy from the sun into chemical compounds. How much this might contribute to the enlarging of the world's food supply is at this stage a matter of speculation, but the work so far seems to hold much promise.
Another field of investigation of major importance concerns the part played by enzymes in life processes. More detailed knowledge about them is necessary if we are to have a true understanding of the metabolism and the synthesis- of organic products. In this field, earlier British work on cell metabolism is being paralleled by Canadian studies on the role of enzymes in the synthesis of sugars and amino-acids in the living organism, while in the United States of America fundamental investigations are under way in the basic mechanisms and the factors influencing reaction rates and the dynamic equilibria characteristic of living cells.
Animal husbandry
Tracer studies are also giving much impetus to investigations on basic problems involved in animal production. As in the case of plants, understanding of enzyme action and other metabolic processes is of prime importance in animal nutrition. Some of the more fundamental investigations concern the amino-acids, which are combined in complex ways to make the proteins of the body. Among the amino-acids essential in the animal diet are two that contain sulphur, methionine and cystine. It is known that cystine can partly replace methionine in animal metabolism. Cows, sheep, goats and other ruminants have the power of synthesizing these amino-acids from inorganic sulphur through the action of microorganisms in the rumen, or first stomach. It had been thought that non-ruminants, which do not have multiple stomachs, could not carry out this process within their own bodies. But recent work with inorganic radioactive sulphate in the diet of poultry has shown, through the recovery of radioactive cystine, that non-ruminants can also synthesize at least part of the cystine they require, which in turn can partly replace methionine; and hence that inorganic sulphate should be considered an important mineral nutrient for poultry, and for swine also, as well as for cattle and sheep.
Studies on the biochemistry of lactation provide another example of the effective use of tracer techniques in metabolic studies. In such work in the United Kingdom, radioactive carbon and tritium, an isotope of hydrogen, have been used to label dietary components. Isolation of the milk constituents and determination of radioactivity indicates directly which milk components are derived from the labelled source and permits some well-founded speculation as to the metabolic route involved. In a typical experiment, sodium acetate labelled with radiocarbon was administered intravenously to a lactating goat. Analysis of the fatty acids in the milk clearly indicated that the synthesis of acids from the acetate took place in the udder itself, not earlier. Such studies, evaluating dietary components and elucidating the steps by which they pass into the sugars, fats (lipids), proteins, and other milk constituents, should lead to more efficient feeding and management for production.
Radioisotopes are especially effective in studying the efficiency of food utilization because it is possible with this technique to arrive at more accurate values than are obtainable by the usual methods employed in food balance studies, which permit only the determination of the total intake and loss of nutrients from the body. In materials found in the waste it has not hitherto been possible to differentiate those that passed through the intestinal tract without being absorbed from those absorbed and subsequently excreted.
The use of tagged nutrients permits ready identification of the source of the excreted materials and in such investigations in animals it has been possible, for instance, to distinguish endogenous (body) and exogenous (feed) calcium and phosphorus.
As an example, the value of alfalfa as a source of phosphorus for lambs had long been considered, on the basis of the usual evaluation procedures, to be of the order of 20 percent; is, only one fifth of the phosphorus in the alfalfa was utilized by the body. The tracer technique has shown that the phosphorus from alfalfa is actually far more effectively absorbed, about 90 percent being utilized. The low value previously estimated was due to the fact that phosphorus was being rapidly involved in the body chemistry, and the large amount excreted was not phosphorus from the feed but phosphorus that had been absorbed earlier, used, and returned to the intestinal tract. Studies of this nature on food utilization have been extended to the egg, the fetus and the milk, permitting evaluation of the relative contribution of the diet to each.
All of this newer knowledge contributed by radioisotopes work on the metabolism and nutrition of animals is of major concern for the world food problem since with rising standards of living there is a demand for a higher proportion of animal proteins in the diet.
Just as in the case of crop production, advances in the control of animal pests and diseases and the development of improved breeds also constitute important methods of increasing animal production. In the case of animals, however, experimentation is usually more costly and time-consuming than with plants with the result that, with some important exceptions, the utilization of radioisotopes and radiation has not progressed Ho rapidly. Thus, whilst irradiation for inducing mutations in plants is being quite widely used for crop improvement, this technique has not as yet been employed to the same extent with livestock nor has it yielded comparable results. Irradiation has also been shown to induce mutations in fungi causing crop diseases, and these mutants are being used in experiments to develop greater resistance to those diseases. It may-be expected that this kind of work with animal-disease-causing organisms will have comparable important practical applications. Thus variants of reduced virulence developed by radiation may prove to be of value for use as vaccines in the production of immunity to commonly occurring, more virulent, forms of the pathogen, and irradiation may also be of help in developing polyvalent vaccines. These are possibilities which, though so far untested, may have great significance, since vaccines constitute the most effective way of combating the many widespread animal diseases which cause losses of millions of animals throughout the world.
A somewhat different use of radiation has been made within a limited area in the case of at least one insect pest of livestock, the screw-worm fly (Callitroga americana C. and P.), which is responsible for damage to the cattle industry in the United States of America to the extent of some twenty million dollars annually in killed or crippled animals and damaged hides. An ingenious method of control has been successfully demonstrated by the United States Department of Agriculture in co-operation with the Dutch authorities on the island of Curaçao in the West Indies. Large numbers of male flies were bred in the laboratory sterilized by radiation from radioactive cobalt, and released in numbers far in excess of the normal population of males in the area' so that females were much more likely to encounter a sterilized male than a fertile one. The female fly mates only once in her lifetime and hence there was no possibility that she would subsequently produce fertile eggs. This unique undertaking was carried out after a close study of the life cycle of the insect, the determination of the susceptible developmental stage and dosage requirements, and careful estimation of the screwworm population of the area. The possibility of eradicating other insects by radiation undoubtedly merits further attention following such fruitful results with the screwworm fly.
The world's fisheries at present contribute over 26 million tons of high-quality food. Although this represents but a small proportion of the animal protein consumed by man, fish is an important element of the diet of many peoples, especially in certain countries in the tropics where proteins of animal origin may otherwise be almost absent from the diet. Up to the present, however, the potentialities of the ocean and inland waters as sources of food have been utilized to only a relatively limited extent but, with the application of modern scientific and technological advances, revolutionary developments in man's exploitation of the world's 'aquatic resources may be anticipated.
As in agriculture and forestry, radioactive isotopes have many uses in fisheries research, and their employment will accelerate the conclusion of certain investigations which are essential for the evaluation of fishery resources and the understanding of those resources that will permit efficient exploitation. Probably the most important application has been the use of carbon-14 in estimating the productivity of ocean waters. Carbon-labelled sodium acetate has been added to water samples taken at various depths and the samples incubated under controlled conditions. The growth of the phytoplankton or plant life under these measured conditions gives an estimate of the basic productivity of the water from which the samples were taken. The use of this method is rapidly being extended and will contribute significantly to the achievement of a realistic estimate of the basic productivity throughout the seas. The importance of this contribution will be clear since the production from the plant life in the oceans determines the quantity of organic material in subsequent links of the food chains and more particularly in those links that furnish material of economic value to man:
Applications similar to this have been made in fresh-water studies. Radioactive phosphorus has been used in several investigations in fresh-water lakes to study the efficacy of mixing, or the distribution of the phosphorus throughout the water and to the flora and fauna. Recent experiments in Canada have indicated that the turnover of phosphorus in lake waters is much more rapid than had previously been estimated, and further that the rapid turnover under natural conditions appears to be caused primarily-by bacteria. This clearly indicates the need for further work, since it had not hitherto been thought that planktonic bacteria play an active part in the phosphorus cycle. On the contrary, the primary organisms involved were considered to be algae, which are highly important in the food cycle of fishes. What contribution, if any, the bacteria make to productivity in these waters is therefore unknown, and it is possible that their high consumption of phosphorus may adversely affect the growth of algae. The importance of radioisotopes in this connection is that they will accelerate the analysis of the ecological systems in inland waters and add precision to the available methods. It may be emphasized that this is especially important in inland waters where the opportunities for human intervention to modify ecological systems are much greater than in marine systems.
Radioactive tags have also been used in fisheries work for tracing and measuring more massive movements of material. For example, they have been employed in studies of the movement and population density of fish, where they have some advantages over the usual marking methods. There is also the possibility that radioactive tags might be used for following the movements of oceanic currents and for measuring water transport in marine systems. Evidently radioisotopes can play at least as great a part in increasing the productivity of our fisheries resources as they can in agriculture and forestry.
Reference has already been made to the particular value of radioisotopes in analysing the movements of specific nutrients in a dynamic biological system and the important part that such tracer studies can play in elucidating problems of animal nutrition and metabolism. Much of the knowledge concerning human nutrition and metabolism is gained from animal studies and therefore much of what has been discussed earlier with reference to animal nutrition applies equally in the field of human nutrition. Thus work in progress on the metabolism of amino-acids and proteins in mammals is especially significant in connection with certain deficiency diseases such as kwashiorkor in man. Current studies also include work on the absorption and excretion of fat and cholesterol, which are considered important factors, in atherosclerosis, a type of hardening of the arteries.
Use of the tracer technique with human beings is rather limited because of understandable reluctance to submit them to chronic internal exposure to radiation; but such studies are being made in the United Kingdom, the United States of America and France on fat and cholesterol metabolism under normal and abnormal conditions. A limited amount of work has also been done with human beings in the field of amino-acid and protein metabolism, using carbon-14 and radioisotopes of sulphur and iodine. In connection with mineral nutrition, work has been carried out in the United States of America on the metabolism of calcium in young male children.
An excellent example of international co-operation in the study of an important health problem was one involving the use of the tracer technique in an investigation of iodine metabolism in areas of endemic goiter in Argentina where, with the help of radioactive iodine, Argentinian and American doctors made a complete study of uptake and metabolism under conditions of minimum iodine supply. Although the work did not result in any startling new discoveries, it was possible to observe the patterns of iodine metabolism, the changes imposed by deficiency, and the adaptation of the body to deficiency. In addition, this investigation contributed new knowledge of the dynamics of iodine transfer within the body.
It is evident that tracer studies can make valuable contributions to a better understanding of the physiology of human nutrition. This in turn will affect the pattern of utilization of available food supplies and help in the development of adequate balanced diets which are so important for the maintenance of health and efficiency.
Research
It is obvious from the foregoing discussion of past and present work that radiations and radioisotopes will play an increasingly important part in research and development in agriculture and related fields. In fact, the vast field of potentialities of the peaceful uses of atomic energy has hardly been touched, and it may be said that the applications of radioisotopes and radiation to problems of concern to agriculture are limited only by the imagination and ingenuity of the investigators.
The adaptability of radioisotopes to such a wide range of research arises from the fact that they may be quantitatively determined in such minute amounts. As we have noted, this makes it possible to introduce an identifiable component into a complex system such as the soil, a plant or an animal, and follow its path to determine its fate in the dynamic system. The techniques involved, however, require carefully trained personnel and a considerable investment in laboratory facilities and instrumentation. Because of these limitations it would be well, for the immediate future at least, to confine the use of this tool in general to those problems in which it is the only applicable method, or to cases in which the desired information may be obtained by the use of isotope techniques with a marked saving in time and effort.
The supply of the more important radioisotopes is now generally adequate for present needs and the rate of progress in research in the immediate future will be determined largely by the number of investigators with the necessary training and experimental facilities. Hence, it will be necessary to make arrangements as rapidly as possible for the training of investigators in the handling of radioactive materials and the research techniques involved. The governments of those countries with experience in atomic energy are already generously making their training facilities available to the nationals of other countries; and the Food and Agriculture Organization of the United Nations, like other international agencies, is prepared to assist in facilitating arrangements on request, and hopes from time to time to be able to award Fellowships for training and research in the applications of radioisotopes to problems in agriculture and related fields. To make the best use of the available knowledge, skill and facilities, it may be desirable to develop co-operative programs of research on the more important problems of general interest. Many of the fundamental investigations using radioactive isotopes can be pursued at any centers with adequate facilities, irrespective of location, but studies of the applicability of the results in specific regions must often be undertaken locally, and here again it is likely that progress will be accelerated through co-operation between neighboring countries.
The encouragement of promising long-term investigations might well be a suitable function of the projected atomic energy agency in consultation with the appropriate Specialized Agencies of the United Nations, which have much experience in stimulating international co-operative investigations where such procedures can lead to more effective use of relatively restricted resources in trained manpower and facilities.
Power aspects
Little reference has so far been made to the potential benefits to agriculture and related industries that may be expected from the more abundant supplies of cheaper electric power that will eventually become available from atomic energy developments, other than to indicate in a broad way the general lowering of costs of production and distribution, and the improvement in the conditions of work and in domestic amenities for rural populations that would result. With the reservation that such benefits must undoubtedly await the widespread application of nuclear power in industry, mention may appropriately be made of some of the further though admittedly still speculative developments that might be possible in agriculture, forestry and fisheries. Although at this stage any discussion of these possibilities may seem to be purely visionary, some reasonable speculation appears to be fully justifiable in view of the spectacular technological advances in the past few decades that have revolutionized the human way of life in less than the span of a generation. Already an atomic-powered submarine is in existence and in some quarters atomic-powered locomotives and aircraft are said to be only a few years away. Much, therefore, of what appears to be fantastic today may be a commonplace tomorrow.
It has already been pointed out that, whilst the reduction of losses due to diseases, pests and spoilage, and the adoption of various improved techniques which lead to more efficient exploitation of areas already cultivated are the most immediately promising ways of increasing production, attention should also be given to the benefits that might arise through bringing new areas into cultivation, although this is a more difficult and expensive undertaking. Probably the greatest contribution in this direction would be through the provision of irrigation facilities, particularly in the desert and semi-arid areas of the world. Many areas suitable for such development exist in North and South America, Africa, Central Asia and North China, to name but a few. There are also areas where drainage and reclamation of marshlands and deltas, especially in the tropics, could render land fit for cultivation, though there are fewer opportunities for this type of action than in the case of irrigation. The availability of more abundant and cheaper power from atomic reactors might well make possible the development of such irrigation and drainage projects. In addition, work is now under way on the partial desalting of water, and abundant and cheaper power would make it possible to do this on a scale adequate for irrigation. Such applications would be of particular significance to the underdeveloped countries, especially where conventional power sources are deficient.
As in the case of agriculture, in forestry more abundant and cheaper power would have far-reaching implications. It would affect not only the primary, often small, rural forest industries as well as the larger ones, such as the manufacture of pulp and paper, but also forest policy and management in general. For instance, at the present time about one-half of the world's harvest of wood is used for fuel, which forms a particularly important source of energy in rural areas. Past experience has shown that where a more convenient, and sometimes more efficient, source of power is available, the use of wood as fuel drops very rapidly. This may be of advantage or disadvantage to good forest management, according to the circumstances. In areas where wood is scarce and the forests badly abused by destructive harvesting to meet the needs of the population, as in some Mediterranean and Asian countries, the replacement of wood by an alternative source of power would greatly facilitate the much-needed reconstruction of an adequate forest cover. On the other hand, in some regions the use of wood as fuel is often an important factor in good silviculture, offering the sole or one of the few markets for small and rough assortments that would otherwise be unmarketable. This shows the complexity of the problems involved and particularly, in view of the length of time needed to plan and execute changes in forest management practices and policies, explains the unusually keen interest of forestry in the long-time changes in power sources and costs that may be affected by atomic energy developments.
The availability of cheaper power would also make possible the more efficient exploitation of large forest areas and would have a particularly marked effect on the practicability of establishing economically sound and integrated wood industries in the remote and lesser-developed parts of the world. Looking even further afield, it might play a most important part in opening up some of the world's last untapped forestry resources in the tropical areas, particularly in South America and Africa.
Similarly, atomic power could be of considerable significance to the fishing industry, where the development of nuclear power units of a size suitable for installation in ships would be of particular interest for possible use in mother and factory vessels of fishing and whaling fleets operating over long periods at great distances from their bases, especially in the Antarctic, since they might in various ways lead to substantial reductions in operating costs.
This discussion of the possible implications of cheaper and more abundant power for agriculture, forestry and fisheries is by no means intended to be exhaustive but rather to give in broad outline an indication of what atomic energy developments could mean to these industries.
Agriculture is perhaps the most conservative of our arts, but when modern methods of farming and the multitude of highly technical services provided by an up-to-date department of agriculture are compared with primitive nomadic and pastoral systems of food production, it is obvious that the farmer is ever ready to adopt improved methods which increase the efficiency of his usage of land, water, capital and labor. It is therefore reassuring to know that this newest of our scientific advances, atomic energy, can contribute in so many ways to man's oldest industry and thus open up the way to improved methods of feeding, clothing and housing the world's ever-growing population.
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THE Conference of FAO, at its Eighth Session in November 1955, requested the Director-General to arrange for all FAO periodicals and other documentation of a topical nature to be distributed simultaneously in the three working languages: English, French and Spanish. The Conference further urged the Director-General to make arrangements whereby this request should be complied with as soon as possible. To permit this in the case of Unasylva, it as been decided to make Vol. 10, No. 1, a special issue devoted to a single topic. As from Vol. 10 No. 2, Unasylva will revert to its normal features; and as from that issue the three language versions will be distributed simultaneously. |
