Zambezia (1980), VIII (i).OUR DAILY BREAD*M. A. SCHWEPPENHAUSERDepartment of Crop Science, University of ZimbabweTHE STORY OF our daily bread, in the literal sense, is older than civilizationand is of prime concern today in the global context of plant food productivity.Appropriately perhaps, our story starts with the Book of Genesis, with Adamand his love for a woman in the Garden of Eden. For this error he was thricesentenced, firstly he had his garden confiscated, and then he begat two agri-culturalists.Abel the herdsman was slain rather early in a successful career by hiselder brother Cain, the tiller, who without implements, was unable to comeup with the goods and expended his wrath during a now-infamous brotherlyaltercation. And so for the good of his soul Cain was sentenced to earn hisdaily bread by the sweat of his brow. This he did in the face of great floods,droughts and pestilence, and to this day crop agriculturalists are similarlyafflicted.Here endeth the first lesson!Long before the Book of Genesis was written, ancient scribes told onstone tablets of the earliest agricultural activities. Probably the first 'school-books' were tablets recording farmers' instructions to sons on how to growand harvest the grain (Leonard, 1974). Archaeologists reach back even furtherso that we may use the intriguing quality of hindsight that a sense of historygives us, to revisit the beginnings of the New Stone Age and gain insight intothe activities of the earliest Cains and Abels in the Nuclear Region of SouthWest Asia.One of the archaeological digs dates back to about 9000 B.C. at TellMureybit in Northern Syria (Fig. 1) where under a four-metre mound lie theremains of much of the early kindred of our modern small grains (Darlington,1978). In different ancient village settlements along the nuclear crescent thestory of the earliest tillers of the agricultural revolution has been unearthedto tell of the pre-eminence of grain-growing as the engine of human evolution.The cereals that were swept into growers' baskets were genetically greatlydiverse and variable. They were amenable to selection, change and adaptationwhenever and wherever cultivators took them across the Old World in a waywe tend to forget now after over a hundred centuries of human migration.The history book for this period is the Old Testament. It is the anthro-pological record of an extended and crucial transition from the nomadic wayof our ancestors who had marched and roamed for a million years on the*An inaugural lecture delivered before the University of Rhodesia on 5 July 1979.OUR DAILY BREADFigure 1: SITES OF VILLAGES ASSOCIATED WITH EARLY FARMERS IN THENUCLEAR CRESCENT.frontiers of the last ice age. Bronowski (1973) aptly describes the immemorialnomad's activities as one 'whose most advanced technique was to attachhimself to a moving herd as the Lapps still do'. Civilization took off fromthe cultivator's need to settle: to nurture his grain.Agricultural man's migrations were slow, dominated by the pace thatdomestication of plants and animals dictates. Man, in turn, was dominatedby the plants and animals that he nurtured, for they became more and moreinterdependent on each other for survival. This symbiotic relationship -wasthe physical means of man's extraordinary success, for with his biologicalgifts of hand and brain, he manipulated and moulded selected living forms,and so set himself apart from the cogwheels of the natural ecological system.Man's agri-culture ensured his survival and expansion, but as it turns outwas also the avenue to a direct confrontation with nature and the root of hisdilemma today: that of accommodating his population size to his sustainablefood supplies.Homo sapiens has always been a highly fertile species; he has had to bein order to survive a precarious balance between his high birth rate and highdeath rate for over 99 per cent of the lifetime of his species. Three develop-ments have significantly redressed the balance in his favour, namely the Agri-cultural and Industrial Revolutions which have dramatically increased hisability to wrest bounty from nature, and the brilliant developments of modernmedicine which have greatly reduced his death rate and extended his life span.M. A. SCHWEPPENHAUSER 3And now, suddenly in the last decade, a series of phenomena have cul-minated in the development of an awareness of a possible global confron-tation with Malthusian prediction. It is widely anticipated that populationgrowth will outrun sustainable food supplies within the time-span of one ortwo generations. We need to examine the evidence for this possibility againsta backdrop of two scenarios, namely food-production capacity and populationgrowth.Whereas on a global scale the total human population is expected todouble in forty-six years, the technologically under-developed countries ofAfrica and Latin America will predictably double in about twenty-five yearsŠwhich is three times the population growth rate of technologically developedareas of North America and Europe (Chrispeels and Sadava, 1977). Populationgrowth rate between 1970 and 1975 has slowed down by about one-third inNorth America and East Asia, and by almost one-half in Western Europe(Brown, 1978). In 1976 the United Kingdom and Belgium had achievedpopulation stability whereas East and West Germany, Luxemburg and Austriahad achieved negative growth rates (Brown, 1978). This demographic trend inWest Germany is referred to as 'Der Pillenknick' (the pill pinch). TheScandinavian countries, France,'Italy, Switzerland and the U.S.A. have birthrates below 15 per 1,000, while most Eastern European countries, the U.S.S.R.,Japan, Australia and New Zealand have birth rates between 15 and 20 per 1,000(Brown, 1978)The lowest population growth rates, as well as achievements in decreasingthese rates, generally occur in the temperate regions of the world where agri-cultural productivity is greatest. The highest population growth rates,generally in excess of 30 per 1,000, occur in tropical countries which inci-dentally also have limited agricultural productivity. It is inevitable that thefood situation will considerably worsen in Africa, and Central and SouthAmerica.In a general consideration of humanity's food prospects we may recognizefour biological systems: Croplands, Grasslands, Forests and Oceanic Fisheries.In that these are biologically renewable resources they form a foundation tothe global economic system. It is essentially to croplands that humanity mustlook for future increases in food supply, particularly in the three staplecereals (wheat, rice and maize) to which over half the world's cultivated landis-devoted and which constitute the largest proportion of plant foods pro-duced (Fig. 2).All plant foods combined provide an estimated 88 per cent of the calories(carbohydrates and fats) and 80 per cent of the protein that .human beingsconsume on a global basis and the balance is derived from animal products(Chrispeels and Sadava, 1977). This situation applies particularly to the under-developed countries, in contrast to the affluent countries of North America,and to some extent Europe, where more or less half of the protein consumedmay come from animal products. When any one of the grains is consumedas a single staple it is likely to lead to protein malnutrition because grainsare generally deficient in one or two of the amino acids essential for growthand health.OUR DAILY BREAD1OO15O2OO 250 300 35O 400Figure 2: APPROXIMATE ANNUAL PRODUCTION OF PLANT FOODS (MILLIONSOF METRIC TONS).In contrast to wheat and rice, which is consumed directly by man, aboutthree-quarters of world maize production is fed to livestock, especially in theU.S.A. and Canada, but also in France, Italy, the United Kingdom and theU.S.S.R. (Chrispeels and Sadava, 1977). Conversion of plant protein toanimal protein for human consumption is expensive, especially for non-affluent societies, as only 10 to 30 per cent of the energy ingested in the grainis available to the next consumer Š man. The rest is used up in metabolic,muscular and nervous activity.M. A. SCHWEPPENHAUSER 5To put this in theoretically quantitative terms the present world plant-food production could at best support either 15 billion (15,000,000,000)vegetarians or about 5 billion people who derived half their energy and protein| from animal products. On a unit of land basis, 1 hectare could support 14'' vegetarians or 4 to 5 people on the mixed diet. Given the present increases, in world populations, humanity's lot will increasingly be with plants as themajor source of food, supplemented with animal food products that will^' differ in each country to the extent that agricultural and population policies'. and good management will allow.I The 'poor man's' meat is the protein-rich seed of legumes which derive'( most of their nitrogen from bacterial fixation in the roots. The most protein-j rich legume is the soya bean which has undergone extensive increase in world1 production in recent years, especially in the U.S.A. where about two-thirds'/ of the world crop is grown. China grows about one-fifth of the world crop of< soya beans and Brazil grows about one-seventh. Soya beans are grown foranimal consumption, while human consumption is at present limited to the]' oil by-products.j. Increased demand for soya beans led to a doubling of the world pricein 1973 and more and more land converted to soya production. For examplej in Brazil a considerable area of land normally devoted to growing table-beans,the staple protein diet of the low-income masses, has been converted to soya( beans in recent years, and exemplifies the fact that world trade is not usuallyconcerned with nutrition. Furthermore any means which promotes the acqui-sition of foreign currency for the purchase of petroleum has become of primeconcern in international trade.I* The Soviet Union has_ become one of the principal importers of soyaI ^ beans although not to anything like the extent of her importation of wheat( from North America. The U.S.S.R., forced by her increasing population toproduce more wheat, opened up new wheat-growing areas north of the forty-ninth parallel in areas which have insufficient rainfall and harsh winters. Aseries of massive harvest failures (Fig. 3) led to the large Soviet purchase ofAmerican wheat in 1972, and brought to an end the era of large surplusworld food stocks. Furthermore subsequent Soviet grain contracts made withf North America, which commands over 96 per cent of the world export wheat|* trade, helped put an end to the era of American food aid to underdeveloped'» nations, and also helped push the world price of wheat from US$2.00 perf bushel in 1972 to nearly US$5.00 per bushel by 1974.," Concerned non-affluent countries of the Third World, now virtuallystarved of North American food aid, demanded increased food handouts atf the 1974 World Food Conference. These same countries, at the World Popu-f lation Conference in the same year, rejected suggestions that they should curbtheir rapid population growth rates. Also at about that time a four-fold in-I crease in the price of petroleum heralded the energy crisis. The food situation* was considerably exacerbated by the serious downturn in world grain reservesL (Fig. 4).OUR DAILY BREADFigure 3: GRAIN PRODUCTION IN THE U.S.S.R. (Source: Chrispeels andSadava (1977), 223).The under-developed countries have been left largely to fend for them-selves in a situation described by ecologist Garret Hardin (1974) as 'lifeboatethics'. This situation depicts a series of lifeboats occupied by the developednations. The people of the Third World, hungry and in deep water, must beprevented from getting into the boats lest everyone drown. The face ofmorality shifts in the light of a transforming world food economy.Meanwhile world grain yield per hectare is levelling off at a time whenit is taking only eleven years to add the fifth billion to the world population,and when the list of food-deficit countries reads like a United Nations roster.The stork has caught up with the plough.Increases in plant food production may be achieved either by increasingyields on the same land area or by expanding the land area. Increased pro-ductivity by yield agriculture has been a fairly widespread world-widephenomenon for the past three decades. The principal areas of high-yieldagriculture are also those with the smallest potential area increases, namelyNorth America, Europe, China, Japan and South-East Asia. A few developingcountries in South America and Africa have achieved relatively modest in-creases in grain production via both avenues.The classic instances of countries turning to yield agriculture are Japanin rice production and the U.S.A in maize production. The Japanese successoccurred as a result of national mobilization of political, social and scientificM. A. SCHWEPPENHAUSERQ40 i(INCLUDES GRAIN EQUIVALENTOF IDLED U.S. CROPLAND).1960Figure 4:65707580WORLD GRAIN RESERVES AS DAYS OF WORLD CONSUMPTION,1960 - 78 {Source: Brown (1978), 132).resources, whereas the American achievement was mainly due to the breedingof new genetic hybrid varieties backed up by advanced scientific crop-production practices. High agricultural productivity in the temperate and sub-tropical regions of the northern hemisphere is generally the result of advancesin yield agriculture to the extent that yields are closely approaching themaximum biological ceiling for high productivity. In terms of the S-shapedbiological growth curve (Fig. 5) the point of inflection where progressiveacceleration gives way to progressive deceleration appears to have beengenerally reached for grain productivity outside the tropics. It is pertinent tonote that it is in these regions that significant reductions are being achievedin human population growth rates.The most critical situation concerning increasing food deficiency isoccurring in under-developed tropical countries in terms of a widening gapbetween food production and food consumption (Fig. 6). Conversely theseareas, particularly Africa and South and Central America, have by far thelargest world reservoir of uncultivated arable land (Fig. 7) mostly in the formof woodlands and forests. If these areas were brought into crop production itwould be possible to at least double or even triple the existing 1.3 billionhectares of land cultivated in the world today.There are, however, major constraints to crop expansion in.the tropics.Firstly the continuous cropping system so successful in temperate zones isOUR DAILY BREADQLLJDCOWNTIMEFigure 5: THE S-SHAPED BIOLOGICAL GROWTH CURVE.seldom successful in the tropics for a variety of reasons of soil and climate.There is for example an overabundance of highly weathered soil in the tropics,and a disproportionately large share of available nutrients resides in the densevegetation cover. Removal of this cover by deforestation and cultivation leadsto a removal of nutrient supply, loss of residual soil fertility by leaching,rapid oxidization of organic matter in soils exposed to the sun, and a tendencyfor considerable soil compaction.Tropical agriculture also has to contend with a host of pest and diseaseproblems typical of warm climates. Futhermore, particularly in Africa, droughtsare periodic, dry seasons are long and warm, and rainfall is unevenly distri-buted and of high intensity. To these natural constraints must be added theprohibitive cost of converting land to agriculture and the building of a complexagricultural infrastructure with its transport requirements, marketing systems,credit institutions, technical advisory needs, and research and educationorganizations.There are nevertheless a few tropical countries where a sufficiently de-veloped agricultural infrastructure existed along with unusually good irrigationpotential and sufficient Government support to enable the so-called 'greenrevolution' to occur. This was an area in some developing countries charac-terized by the introduction and spread of new high-yielding short-strawedvarieties of wheat and rice. Outstanding plant-breeding achievements gave thenew varieties a package of new genes: (a) for short straw less prone to lodge,(b) for efficient utilization of up to three times higher doses of fertiliserM. A. SCHWEPPENHAUSER500«Ł 4002 300ig 200Ulo15019601961Figure 6:19851986WIDENING GAP BETWEEN FOOD PRODUCTION AND FOOD CON-SUMPTION IN DEVELOPING COUNTRIES.AFRICAS. AMERICACEN. AMERICAU.S.S.R.S.E. ASIAU.S.A.EUROPE0 200 400 600 800MILLIONS OF HECTARESFigure 7: UNCULTIVATED ARABLE LAND IN THE WORLD (Source: Crispeelsand Sadava (1977), 141).compared with the old commercial varieties which sometimes decreased inyield with higher fertilizer inputs, (c) for resistance to several pests and diseases,and (d) for inherent adaptability to a wider range of climatic conditions.By the late 1960s about 13 million hectares had been planted to the new'miracle' varieties and had expanded the Asian food supply by about 16million tons, or enough to feed about 90 million people (Brown, 1978). Massivefamine was further allayed by expansion of the green-revolution into the mid-1970s at a time when food-aid from North America was being effectively cutoff for other reasons.The impact of the green revolution in individual countries was miraculous.10OUR DAILY BREAD+3"-4-1961Figure 8: MEXICO : NET GRAIN TRADE, 1961 - 78 {Source: Brown (1978),149).In India wheat production doubled in the six-year period 1966 - 72, andMexico and Pakistan achieved similar dramatic yield increases in wheat pro-duction. In a similar time period Columbia more than doubled its rice pro-duction on the same hectarage planted, and other green-revolution countriessuch as Sri Lanka, Indonesia, Malaysia, and the Philipines followed suit.Like that celebrated phenomenon in Physics, it was a quantum jump,and rivalled the story of an even earlier miracle when the five thousand werefed with two fish and five loaves of bread. The leader of the green-revolutionteam of plant breeders, Nobel Laureate Dr Norman Borlang, had predicted(Brown, 1970) that the green revolution would buy time, perhaps ten or twentyyears, during which Governments could bridle population growth. Alas, itacted more like a fertility pill! Population is again outrunning food supply incountry after country. For example as Mexico's high population growth ratecontinued its inexorable path she turned from a grain exporter in the lasthalf-decade of the 1960s to a substantial grain importer in the 1970s (Fig. 8),and treads a well-worn path for sustenance to her northern neighbour.Only China used the reprieve as Borlang envisaged, by launching aneffective family-planning programme, boosting its food supply with the miraclevarieties of wheat and rice, and damming and diverting rivers to bring one-third of her arable land under irrigation.The green revolution which took off with such success and optimism, washit by global economic constraints related to energy costs which affectedfertilizer prices in particular, and ran out of countries with the necessaryresource potentials. By this time only Mexico had completely converted toM. A. SCHWEPPENHAUSER11JNS<iŁ |LUZUNDERI AGE\CRlWHEAT /100806O4020--PAKISTAN//////MEXICOŁTNDIAFigure 9:O 2 4 6 8 10 12YEARS AFTER INTRODUCING NEW STRAINSCYCLES OF ADOPTION FOR HIGH-YIELDING VARIETIES OF WHEAT(Source: Chrispeels and Sadava (1977), 212).the high-yielding strains (Fig. 9), while other countries such as India andPakistan, having received massive economic support from their Governments,are faltering at the half-way stage, in the face of rapidly increasing productioncosts.Any assessment of the potential of tropical countries in particular, andthe world in general, to increase its plant-food productivity commensuratewith increasing human aspirations must take into account several importantconstraints to crop productivity, such as soil erosion, deforestation, over-grazing, loss of cropland, air pollution, increasing energy costs, and pests anddiseases.In any brief survey of such constraints soil erosion must be accorded afundamental priority. While plants are the primary producers in food chains,the soil is the placenta for their growth. Misuse of soils invariably leads to itsremoval by water and wind Š and this constitutes the oldest lesson in agri-culture, going back to the now desiccated but once most fertile area of thenuclear crescent. It is also the most important lesson to be learned if thefragile ecosystem of tropical agriculture is to be intelligently utilized for sus-tained crop productivity.Often the first step to soil erosion is deforestation. The French philosopher12 OUR DAILY BREADChateaubriand (quoted by Brown, 1978) knew this when he said, 'The forestscome before civilization, the deserts after them'. The global scale of conversionof forests to fields and grasslands by 1970 was estimated (Ehrlich et al., 1977)to be between 18 and 20 per cent of the area of continents, although this hasconsiderably increased during the 1970s by rapid deforestation in tropicalzones.For at least one-third of mankind firewood remains the poor man's oil;and like its liquid cousin, resources are rapidly dwindling, especially wherethe vast majority of the population in developing countries, such as Zimbabwe,are fuel-wood users. Furthermore, unlike the U.S.A.and U.S.S.R,which stillexercise good forest-management programmes, the majority of countries havenot backed long-term national forestry plans with sufficient funds or politicalcommitment. The world-wide escalating cost of newsprint attests to an un-healthy relationship between the level of demand and the sustainable yield offorests. Other than the fact that firewood is still a principal energy source inunder-developed countries, wood is a primary building material everywhere.Furthermore paper is the principal raw material for the bureaucratic world,and for the expanding world of literacy and education.Forests constitute one of humanity's most valuable but most heavilycropped and exploited resources. Throughout the Middle East, India, SouthEast Asia, Africa and Central and South America, in almost every countryundergoing rapid population growth, deforestation is under way on an in-creasingly intensive scale.In many of these areas overpopulation has forced farmers into the hill-sides, and taking agriculture uphill is a losing proposition because soils tendto be marginal and erosion is rapid. As the topsoil washes downhill the peopleare never far behind. One of the first consequences of deforestation is annualdownstream flooding and this is occurring today on a scale as never before,particularly in Iran, India, Pakistan, Nepal, Ethiopia, Nigeria and, morerecently, Brazil; and the result is a considerable loss of croplands and grass-lands.About one-third of the world's remaining natural forest lies in that halfof Brazil which constitutes five million square kilometers of the AmazonBasin. In an attempt to settle about five million peasants on new 100-hectarefarms the Brazilian Government allowed about one-quarter of the forests tobe cleared (Lewis, 1979). Deforested areas which had previously recycledhalf of the rainfall quickly lost their thin humus cover to expose unproductivelaterite soils which the new farmers cultivated unsuccessfully.The scheme floundered in the face of a lack of relevant agriculturaltraining and advisory assistance, which was the only way of coming to termswith a new and difficult tropical environment, and serves as a lesson to alltropical countries under pressure to open new areas for peasant agriculture.The exodus of the Brazilian peasant farmers was assisted by other elements ofa hostile environment in the form of a formidable array of stinging insects,reptiles and unfamiliar sicknesses. Areas cleared and planted to African grassesfor ranching have been successful where annual fertilizer inputs were sufficientto maintain the required level of fertility, but cutbacks in fertilizer applicationsM. A. SCHWEPPENHAUSER 13due to increased energy costs have inevitably led to considerable grasslanddeterioration, overgrazing and soil erosion.The practice of overgrazing is as old as agriculture, and constitutes aserious constraint on world crop productivity, not only in the sense that thebest grazing land is being made over to cropland, but also in that it results ina deterioration of the animal-based industry which provides draft energy forabout one-third of the world's croplands. In arid areas overgrazing oftenleads to desertification as is occurring in parts of the sub-Saharan countriesof Africa where the current ecocatastrophe from overgrazing is making eco-logical refugees of hundreds of thousands of herdsmen as thousands ofhectares of range and cropland are lost each year. It is a formidable task topersuade herdsmen to decrease their herds to suit maximum-carrying capacities.This situation, described by Hardin (1968) as 'The Tragedy of the Commons',is as real and insoluble today as it was when first propounded by Lloyd (1833).Loss of cropland, by whatever means, is also becoming a major con-straint on crop productivity in developed agricultural societies in temperateregions. Thus the United States Council for Agricultural Science is concernedthat loss of cropland due to loss of topsoil will lead to an extensive declinein their agricultural productivity by the end of this century. This loss may bepartly ascribed to putting fallow land back into production to help meet in-creasing world demand for grain. In the American Mid-West severe duststorms, reminiscent of the Great Dust Bowl of the 1930s are not infrequent.Furthermore thousands of hectares of arable cropland are lost each year tohighways and urbanization, particularly in North America and Europe.The human prospect is tied to the size and condition of its cropland base.It is the foundation not only of agriculture but of civilization itself, and eachyear a part of this life-support system is washed away, blown away, scrapedaway or covered away. In technologically developed countries another way ofcovering croplands is with polluted air. Resultant declines in yields can behigh and tend to vary from crop to crop as shown in Table I derived fromCalifornian data (Brown, 1978). Potential damage of this kind to crop yieldsin the U.S.A. is predictable to the extent that data is available concerningnumber of potential days of air pollution and the extent and concentrationof acid rain (Ehrlich.e/ al.).The most serious recent constraint on crop productivity is that of risingenergy costs. Over half of world agriculture is highly energy-intensive in thatmass production is achieved by mechanical means in land preparation, planting,cultivating, irrigating, and harvesting. The most energy-demanding require-ments in crop production are concerned with the manufacture of nitrogenousfertilizer and pesticides. Compared with agriculture in the developed countriesof North America and Europe, the agriculture of Africa and South Americauses an almost negligible amount of fertilizer. With rising costs of fertilizerthe trend in the Third World is actually to import less fertilizer than before.The energy crises will predictably adversely affect potential grain pro-ductivity in North America. For example in the U.S.A.,where the energyconsumption per capita is double that of the next highest consumer, thepattern of energy consumption is rapidly increasing despite decreasing U.S14 OUR DAILY BREADcrude oil production. The U.S.A. is thus in a real energy predicament andfaces an uncertain future with only a small share of proven world reserves ofcrude oil. Canada is no better off. The ability of North America to continueto be the breadbasket of the world, and to continue to export large quantitiesof grain, particularly to the U.S.S.R., is questionable.Table IYIELD DECLINE DUE TO AIR POLLUTION(CALIFORNIA 1977)Crop % Decline in YieldAlfalfa 38Beans 32Lettuce 42Sweetcorn 72Radishes 38Ponderosa Pines 75 (over 30 years)TOTAL ANNUAL CROP DAMAGE = US$25 millionSource: Brown (1978), 42.Even though over half of world agriculture is energy-intensive only aboutone-quarter of the energy used in the food system goes into the on-the-farmproduction phase. The rest Š and this is where some opportunity exists forconserving energy used in food production Š goes into the distribution endof the system: transport, processing and packaging. It is not unusual thatthe package in which the food is wrapped embodies more energy than thefood itself. The cost of superficial glitter in packaging is a form of waste ofenergy that applies to many commodities besides food.Nevertheless the largest constraint on crop productivity is not energy butpests and diseases. At least 50 per cent of the world's total crop productionis lost each year (Russell, 1978) through insects, nematodes, fungi, bacteria,viruses, vertebrate pests and parasitic weeds. Each crop has its share of pestsand diseases; rice, for example, has sixty-six diseases (Table II), and isprobably typical of most major crop species. Pests and diseases tend to benatural parasites which have evolved with the species.Modern crop agriculture rests on vast acreages of homogeneous plantsgrowing close together, with a genetic rigour that makes 100 million plantsshoot on the same day, be ready for harvest on the same day, and each havethe same innate capacity for a host of morphological and physiologicalcharacteristics that regiment yield and quality.M. A. SCHWEPPENHAUSER 15Table IIDISEASES OF RICEAgent Plant Organ Attacked No. of DiseasesVirus leaf 12Bacteria leaf 4Bacteria grain 3Fungus leaf 11Fungus stem, root 10Fungus seedling 5Fungus grain 10Nematodes root 11Source: Chrispeels and Sadava (1977), 162.And yet, this very hard-won genetic uniformity, so essential for com-mercial agriculture and the daily bread of billions of people, constitutes theAchilles heel of crop productivity. Diseases can spread like wildfire, attainepidemic proportions, destroy homogeneous plant-food supplies within days,and persist from season to season. Agricultural literature abounds withexamples of crop destruction by diseases, such as blight epidemics in potatoesand oats, and more recently in maize, and numerous rust epidemics in wheat.There are many instances of disease epidemics in many crops in manycountries.Breeding disease-resistant varieties has greatly put the brake on thedestruction of crops, but some disease organisms, particularly fungal types,have their own genetic equipment for survival which can more than matchman's attempts to outwit them in the process of engineering resistant genesinto previously susceptible cultivars. The parasite has all too frequentlydemonstrated an ability to selectively side-step such breeding achievements ona gene-for-gene basis. Like chess, it is a tit-for-tat reaction, but with theparasite always one step ahead owing to its chameleon-like mutational armoury.For over half-a-century North American wheat breeders in particular havewaged this battle, and always on the defensive. Fortunately this chain-reactionsituation does not apply to all plant diseases.But of all the long-term goals in crop science which could result in foodproductivity, no investment will pay greater dividends in raising the standardof living and health throughout the world than the continued development ofdisease-resistant crop varieties. Inevitably this will go hand in hand with theuse of pesticides but, it is hoped, chemical control can be minimized. Althoughoften essential, pesticides tend to be increasingly expensive, have inherentproblems concerned with residues and pollution, and demand high standards16 OUR DAILY BREADof control and monitoring.From instances of breakdown in disease resistance we are learning thatman is not the supreme ruler of living matter. It is not possible to obliteratediseases at will by breeding for immunity against them. Our humility hasbeen hard-won in this respect and has led us to learn to live with our plantparasites. Nevertheless instead of giving them free rein to live and reproduce,the aim is to achieve a level of genetic resistance in the host plant so thatsmall populations of parasites may survive in circumstances where their repro-ductive potential is limited. Would that we could find a similar recipe forhuman populations!The hope and promise of achieving increased productivity, particularlyin food crops, is greatest when disease resistance is sought against manyeconomically important pests and diseases simultaneously. Hence multiple-disease resistance must head the list of long-term crop-science goals:Multiple disease resistance,Increase nutritional quality,Rechannel primary productivity,Improve nitrogen fixation,Maximize photosynthesis,Aqua-culture of kelp,Processing of plant proteins,Substituting animal product analogues,Processing leaf protein.In all the centuries of plant manipulation we have consciously or un-consciously shuffled and reshuffled the gene pools of plants and subjectedan infinite diversity of gene combinations to the formidable forces of artificialselection. Man and not nature has been the arbiter of fitness and has developedplant architectures that nature would not tolerate on her own. In the processwe have unwittingly discarded a multitude of genes that could now be usefulto us in pursuing our long-term crop-science goals. And so we are retracingour steps now, back to the centres of origin and diversity in different continentsto collect the ancient and possibly valuable weed parents of our modern cropspecies.On creating these germplasm banks we are beginning to rediscover thebounty of nature, by finding genes for multiple-disease resistance and greaternutritional quality. We are already producing varieties of maize and sorghumwith increased concentrations of the generally deficient amino acids, lysineand tryptophan (Table HI).The man-made evolution of crop plants has largely been an exercise inchannelling a higher proportion of primary productivity into the reproductiveorgans, such as increasing the size of the maize cob from about one inch tomore than one foot in length over a period of three thousand years. Usingmodern knowledge in plant physiology and genetics this re-channelled develop-ment process is continuing even although it may seemingly be at a comparativecrawl on the frontiers of scientific knowledge.Because yields are approaching maximum ceilings of known geneticpotential in many crops cultivated in the best agricultural regions, and becauseM. A. SCHWEPPENHAUSER 17these same crops are in fact being grown and will increasingly be grown inmarginal areas throughout the world, the emphasis in research is now startingto incorporate this hitherto largely neglected area. One aim is to breed plantstrains with an improved plant - water efficiency, where for example asmaller transpiration ratio might be useful. There is considerable potentialfor research gains in this area of investigation.Table IIIAMINO ACID CONTENT(% OF PROTEIN IN MAIZE AND SORGHUM)Lysine TryptophanNormal Maize 2.7 0.7Opaque - 2 Maize 4.0 1.3Normal Sorghum 2.0 0.9High-Lysine Sorghum 3.3 1.7Source: Chrispeels and Sadava (1977), 201.A difficult but exciting area now being researched, is the increase inefficiency of nitrogen-fixing organisms in the roots, even in non-leguminousplants. Some grasses are now known to be capable of this symbiosis, andsince our major crops are essentially grasses, the argument goes, why not givethem the relevant genetic ability for nitrogen fixation? The consequenceswould be revolutionary in terms of reduced nitrogenous-fertilizer requirement.At this stage it is a theoretical possibility rather than a probability, as manycomplex problems will first need to be resolved.One of the most important advances that might be made would be tomaximize photosynthesis. All living entities are in a sense heliophagus (sun-eating), for we ingest daily, or burn as fuel, products of the radiant energythat has flashed across the void of space since, as Genesis correctly puts it,the earth was without form and void.We are predominantly a water-covered planet, and the sea traps three-quarters of incoming solar energy. The chain of life begins here in nutrient-rich coastlines Š that lambent-blue-green area about one-fifth the size of theland masses. Energy conversion by photosynthesis begins with the tiniest ofplants, phytoplankton, which are consumed by zooplankton and then in turnby crustaceans and fish, and so on up the trophic scale. Life and death at alllevels creates a rain of organic detritus which over millions of years formsthick blankets of globugerina ooze on the ocean floor. Under great pressureand heat these layers form into gas and the oil that provides petroleum energy.18 OUR DAILY BREADIn 1818, the poet Byron could write:Man marks the earth with ruin,His control stops at the shore.But in this century we have breached and extended our boundaries to embracethe underwater resources contiguous to our coastline. Today we go down tothe sea to acquire this ancient energy, for we need it to win our daily bread.With optimism we had thought in the 1950s and 1960s that the largessof the sea would provide almost unlimited food for humanity's future needs,but in 1970 we achieved the maximum sustainable yield from the ocean. Theseoff-shore and upwelling zones which provide our fish catch (90 per cent ofthe ocean is a biological desert in this regard) also comprises humanity'slargest dumping ground for waste products, and the highway for oil tankerswhich have been described as 'accidents looking for a happening'. Withoutsuch pollution it is possible that commercial fish yields could double, butsuch a prospect is unlikely to eventuate.Meanwhile overfishing of the oceanic 'commons' has become a pervasiveglobal problem since catches of most of the thirty-odd leading species oftable-grade fish has either attained or passed the point of inflection on the S-shaped biological growth curve. Despite their large fishing fleets, Japan andthe U.S.S.R. are supplementing their declining yields of oceanic protein withlarger imports of feed grains and soya beans to sustain their livestockproduction.Fishing is achieved by hunting, and on land this is a paleolithic occupation.Not surprisingly, some claims have been made that an aquaculture revolutionŠshades of its agricultural predecessors perhapsŠis in the making. Atpresent aquaculture provides about four per cent of the global fish harvestbut estimates are that not more than a tenfold increase is possible (Bardach etal., 1972). Aquaculture for plant production is a further possibility by pro-cessing kelp into carbohydrate-based foods. The U.S. Navy is working on a100,000 acre kelp farm to be in operation by 1985 (Chrispeels and Sadava).Seaborne enterprises notwithstanding, the earth is a plant-oriented planet,and the land will continue to be the traditional supplier of most human food.As pressures of exploitation of arable land increase man will turn to usingmore processed foods. In terms of processing protein-rich foods, the mostpromising are soya beans, groundnuts and cottonseed. When man learns toprocess a better quality flour for cooking, this food source could theoreticallydevelop into a multi-million-ton industry, especially in the more under-developedcountries. However, as experience has shown to date in South America andSouthern Asia, we have a long way to go before we learn to make thesefoods acceptable even to hungry people.Animal-product analogues are also catching on, following the successfulsubstitution of margarine for butter, vegetable oils for lard and plantproducts for dried milk, cream and whipping cream. The production of plant-derived meat analogues is experiencing early successes in terms of consumeracceptability, costs of production, nutritional value and long refrigeration-freeshelf-life. One method is to heat mixtures of wheat, soyas and milk solidsM. A. SCHWEPPENHAUSER 19and form them into frankfurters or bologna. Another method is to gel anaqueous paste from soya bean protein, wheat, oils and flavours and use as asandwich spread. A third method involves producing soya protein fibres coatedwith proteins, fats, vitamins, minerals, colouring and flavourings and bindthem together into nutritious cubes, slices or granules. As much as 20 per centof all processed meat in the U.S.A. will probably be replaced by soya bean-based meat analogues within the next year.Another promising recent food-source innovation is the processing ofprotein from leaves. Leaf protein is the world's largest source of readily avail-able protein and is already being processed for use in animal feeds. Further-more a colourless, tasteless leaf-derived 95 per cent protein powder is nowbeing tested as a nutritious additive in beverages and foods (Chrispeels andSadava). Yields of 25 tons of protein per hectare are possible from wheatand barley leaves and this food source could have a significant impact onhuman nutrition. No doubt we will be consuming such protein in one way oranother in the near future, relatively cheaply, and probably without undueknowledge or concern as to its source. Such protein is also likely to arrive inhuman foods long before single-cell protein from micro-organisms, whereconsiderable research remains to be done before large-scale commercialfeasibility can be achieved.In the face of rapid population growth, and given that long-term crop-science goals and food additives could achieve a significant measure of increasedfood productivity and nutrition, what are the food prospects for humanity?There is no unequivocal answer and can be none until populations stabilize.If the projected United Nations pattern of population growth in the majorareas of the world (Fig. 10) is anything to go by, then it would mean feedingabout twelve billion people, that is three times the existing population. Ifevery hectare of arable land in tropical countries were brought into full-scalehigh-level production, it might be theoretically possible to feed such a worldpopulation. However, the practical realities of the 1970s belie such aneventuality on a world-wide scale.In the first place international constraints, economic and physical, haverapidly reduced world food trade, and this trend will inevitably continue.Each country will therefore be increasingly pressurized to achieve its ownfood - population balance, and create its own food reserves to meet inevitableharvest failures. Greater priority will be given in national budgets forrationalized agricultural development. Furthermore, irrespective of any successin population policies, there will be a long lag-period during which the rapidlyincreasing population will need to be fed, and the soil will be the majorsupplier of such food.During our lifetime, cheap energy has shaped the global economic system,helped multiply and remultiply the output of food, and goods and services,and generally sighted the aims and expectations of the masses at levels whichcannot be sustained. In every sense it has been a growth ethic. The 1970s have,however, proved to be the hinge-period in modern history. It has been adecade of discontinuities, in terms of the energy crises, food shortages,20OUR DAILY BREADSOUTH ASIAAFRICAEAST ASIALATIN AMERICAEUROPEUSSRN. AMERICA1001925 50 7525 50 752000YEARFigure 10: PROJECTED POPULATION GROWTH IN MAJOR AREAS OF THEWORLD (Source: Ehrlich et al. (1977), 226).rapidly increasing food prices, the levelling off of the world fish harvest,excessive deforestation, loss of cropland through flooding and urban sprawl,a turnabout in the international political power structure, and excessively highglobal inflation and economic decline.The new international ethic that is emerging is one of accommodationto the earth's biological systems. Unrestrained materialism is giving way toconservation. Profound social changes are in the making and will exerciseincreasing pressure for the implementation of more effective political manage-ment. Food will stand alongside energy in terms of power. The origins ofthis change are to a large extent ecological, but the impact of such changewill be in the social and economic fields. The processes of achieving change,as has been demonstrated in the agriculture of Japan and China, are political.M.A. SCHWEPPENHAUSER 21, The tools of Government have no rivals, in terms of legislation, budgetarytaxation, fiscal policies, and the analytical and eduational capacities of itsinstitutions. Power now walks side by side with responsibility as never before.If history is anything to go by, there will continue to be a succession ofscientific developments and inventions which other men can learn, copy andutilize for the creation of rewarding environments. It is the variables in humanintelligence and skills that make it difficult to predict the future of anycountry with any accuracy. Those who cannot learn will be at a disadvantage.The cost of the frequent lack of brains at the bottom of society will beborne by the individual, but when brains are lacking, as they often are, bythose who are at the helm of society then the whole society will pay the price.* The saga of establishing an equilibrium between sustainable food suppliesand population size is an ongoing problem that will have to be faced by eachnation. In Zimbabwe we have on occasions been euphorically and erroneouslyled to suppose that we are the breadbasket of Central Africa. The truth isthat we are of Africa, with all the inherent realities, problems, limitationsand constraints on sustaining high productivity in a tropical environment.Our agricultural infrastructure varies from a sophisticated energy-intensivesystem to that of subsistence community plot-holders where the land is tilledfor the retention of usufruct rights, social and old-age security and, aboveall, survival. Like the vast majority of tillers the world over, life consists ofi making rational economic decisions relative to hard realities and a spartanlife-style. At this level, parameters for growth are almost impossibly restrictive.At both levels of agricultural productivity, commercial and subsistence,, there is reason for deep concern for sustained viability for different reasons.We walk an economic tightrope made slippery by rising costs of energy and theresults of civil war. For various political reasons we are in a unique petroleum-energy predicament in terms of procurement costs compared to the rest of theworld (Fig. 11). For this reason alone the productivity squeeze for future harvestshas tightened considerably for commercial agriculture.Ł There is a parallel predicament in peasant agriculture where draughtanimals constitute the appropriate tillage technology for crop production. This1 arises because of large-scale war-induced stock thefts, and partly because ofwidespread decimation by diseases and the effects of an increased incidenceof tsetse fly and foot-and-mouth disease.There are no short-term non-political remedies. There are neverthelessy promising innovations such as the use of expressed plant oils, particularly fromsunflowers, as a substitute for imported dieseline to help power the tractorsof commercial farmers. There is also the beginnings of a startling innovationof cropping the wild African buffalo population instead of culling it, andthen raising and training a regularly cropped buffalo-calf population to theyolk (Condy, 1979). Immune to the crippling diseases that decimate cattle,the African buffalo, even though a carrier of foot-and-mouth disease, mayyet be Africa's answer to the Indian buffalo. Furthermore, the population ofAfrican buffalo is totally unexploited in terms of its potential genetic! variability, either in the form of selection among the wild population or in22OUR DAILY BREADR.S.A. &Z.R.INTERNATIONALPRICES1953196019701979Figure 11: WORLD PRICE OF PETROLEUM.domesticated breeding stock. This animal may well help provide an appro-priate technology in small-scale agriculture.And yet the largest untapped resource in this and other developingcountries is, and will increasingly be, the vast potential labour force in theschool and the gestation pipe-lines. Of the 922 million additional estimatedjobs required in the world between 1970 and 2000 (Table IV), possibly 41488Oil1(millions)649933161922(per cent)+ 33+ 91M. A. SCHWEPPENHAUSER 23Table IVPROJECTED GROWTH IN WORLD LABOUR FORCE, 1970 - 2000Additional Change1970 2000 Jobs Required 1970 - 2000More Developed NationsLess Developed NationsSource: Brown (1978), 186.million will be in Zimbabwe, and with good management many of these willfind productive employment on the land. If we are not to emulate thefailure of agriculture to keep pace with food requirements in so many tropicalcountries in Africa and Central and South America, it will be necessary totrain and utilize, at certificate, diplomate or degree level, our potentialhuman skills.Whenever and wherever settled agriculture has developed, it has providedthe infrastructure of civilizations, and this process will need to be re-enactedbetween Capricorn and Cancer. In what has come, after 120 centuries ofagricultural revolution, to be our little universe, we have returned to the basicsof an old human agenda: food, population and energy.AcknowlegementIt is a pleasure to acknowledge the valuable assistance of Mrs Desiree' Palmerwho prepared the illustrative material.1.24 OUR DAILY BREADReferencesBARUACH, J. R., RYlHhR, j. and MCLARNL-Y, W. 1972 AquacuUure (New-York, Inierscienee).BRONOWSKI, J. 1973 The Ascent of Man (London, British BroadcastingCorporation).BROWN, L. R. 1970 'Nobel Peace Prize: A developer of high-yield wheatreceives award', Science, CLX1I, 518 - 19.BROWN, L. R. 1978 The Twenty Ninth Day (New York, Norton).CHRiSPbhLS, M. J. and SADAVA, D. 1977 Plants, Food and People (SanFrancisco, hreeman).CONUY, J.B. 1979 Personal Communication (Salisbury, Zimbabwe).DARLING ION, c. D. 1978 The Little Universe of Man (London, Allen andUnwin).EHRLICH, P. R., LHRLICH, A. H. and HOLDREN, J. p. 1977 Ecoscience:Population, Resources, Environment (San Francisco, 1-reeman).HARDIN, G. 1968 'The tragedy of the commons', Science, CLX11, 1243 - 8.HARDIN, G. 1974 'Living on a lifeboat', Bioscience, XXIV, 561 - 3.LEONARD, J. N. 1974 The Emergence of Man: The First Farmers (Amster-dam, Time Life).LEWIS, N. 1979 'The rape of Amazonia', Observer, 22 April, 46-61.LLOYD, W. K 1833 Two Lectures on the Checks to Population (Oxford[Univ.]), reprinted in part in G. Hardin (ed.), Population, Evolution andBirth Control (San Francisco, Freeman).RUSSHLL, G. E. 1978 Plant Breeding for Pest and Disease Resistance(London, Butterworths).