1. Introduction
Science and technology are historical drivers of societal change—mostly for good, but sometimes with unintended (often environmental) consequences, many of which we are still struggling to deal with today. The Industrial Revolution of the 18th and 19th centuries, with its fossil-fuel-powered mechanization of mining and manufacturing and its rapid expansion in shipping and land transport, led to increasing urbanization and population growth. Even in the 18th century, it was apparent that the rate of population growth could not be sustained. With more people living in cities and fewer farming the land, how would it be possible to feed and clothe the growing population, unless agricultural productivity could keep pace?
Prior to and, especially, following the Second World War, emphasis was put on improving global agricultural production through international programs spearheaded by the Consultative Group for International Agricultural Research (CGIAR) Consortium of International Agricultural Research Centers. These included the Centro Internacional de Mejoramiento de Maíz y Trigo (CIMMYT, the International Maize and Wheat Improvement Center) and the International Rice Research Institute (IRRI), which were funded by governments, aid agencies, and private foundations. This first “Green Revolution” (GR) was led by the Nobel Prize winner agronomist Norman Borlaug; it began in Mexico, and then moved into Asia and Africa. The subsequent technological and agronomic advances in the growing of wheat, rice, and maize dramatically increased crop yields across the globe. Although it is arguable that these yields have not been equitably or effectively delivered (since poverty and food insecurity continue, particularly in Sub-Saharan Africa), over the last 50 years or so, during which global populations have doubled, the GR tripled the production of cereal crops with only a small increase in the area of land under cultivation [1]. The last 20 years have also seen the widespread adoption of genetically modified (GM) crops that have built on the GR in order to reduce some of the reliance of maize, soybean, canola, and cotton cropping on chemical pesticides and herbicides. These innovations have resulted in considerable economic and environmental benefits by raising yields (by reducing losses to pests and weeds), reducing the environmental load of pesticides, and decreasing inputs, all of which increase economic returns to both large and small landholders [2]. GM crops are not “magic bullets,” and are not without critics; however, on the whole, they have proven to be beneficial [3]. If these technologies can gain broader public acceptance, they will bode well for future agricultural production, particularly in staple food crops; however, genetic modifications continue to be a significant marketing challenge for the biotech industry.
Despite these technological improvements, world population growth continues to advance at a faster rate than food production. It is predicted that 9.8 billion people will inhabit our planet by 2050 (a population 30% larger than today) and that nearly all of that increase will be in low to low-middle income countries [4,5]. Average income will continue to rise, so it will be necessary to feed a larger, more urban, and more affluent population; as a result, cereal and meat production must rise by 70% each in order to feed everyone. Unfortunately, the rate of genetic gain in many of our staple crops is either below what will be required [6] or has begun to plateau. Furthermore, all of this takes place in the midst of a worsening global climate that is already putting significant stress on existing food- and fiber-production systems. Of course, much can be done to ensure a more equitable distribution of current food production and to curb the phenomenal wastage of food that occurs globally (almost a third of all food produced is wasted and never consumed [7]). However, reducing current food wastage by half would only result in a quarter of the food that is necessary to fill the expected gap in food production by 2050; it will not be enough. Do we need another GR? The answer is certainly yes—but this revolution must be a smarter one, and must provide quantum improvements in crop productivity without increasing the arable land required to produce it.
2. Where will the next Green Revolution come from?
2.1. The contributions of “traditional” crop breeding
The first GR was underpinned by the development of high-yielding, disease-resistant, dwarf varieties of cereals that responded well to intensive agriculture. The next GR will continue to use conventional crossing and selection approaches, supplemented by a range of new genetic technologies that include genetic modification. Much of today’s crop breeding and biotechnology innovation in agriculture has shifted from the public to the private sector (and particularly to the large multinational life-sciences companies, with their proprietary GM traits and other integrated management technologies). That is not to say that good, international, public research no longer has a significant role to play in feeding the world. However, public research organizations must reinvent themselves, form more partnerships, and focus more on facilitating breeding in the crops and programs that are already present in their target countries. The CGIAR’s Excellence in Breeding Platform is a model of what is possible, as it provides both training in and access to modern genotyping, bioinformatics, and phenotyping tools to small breeding operations in the developing world. It will be a decade or more before we can assess the impact of such programs, but this initiative is certainly a step in the right direction.
Actual on-farm yields are often considerably below the potential yield [6] because of losses caused by pests, pathogens, and various abiotic stresses such as drought, high temperatures, and waterlogging, all of which reduce crop yield. Pests and pathogens continue to co-evolve with their hosts and overcome the pre-existing resistance mechanisms assembled in our crops by past plant breeders. These old enemies have not gone away with the GR; in many cases, their impacts are exacerbated with the rising temperatures and less-predictable climates that are induced by global warming. Closing the gap between potential and actual yield by breeding more disease- and pest-resistant varieties remains a cost-effective way to increase global food production. Examples of utilizing new sources of host plant resistance to powdery mildew in wheat, Aphanomyces root rot in field peas, and soybean cyst nematode in soybean are illustrated in this issue. Although biotechnology will continue to have a major role in protecting crops against insect pests and some viruses [3], it has been less successful in producing resistance to fungal and bacterial diseases; therefore, more traditional approaches will still be needed. Of course, biotechnology will have other uses than crop protection, such as increasing the nutritional value or quality of our food crops. However, experience with “Golden Rice,” which is bio-fortified with pro-vitamin A, shows that bioengineered foods will be difficult to market for a while yet, due to public attitudes toward GM foods [8].
Targeted breeding and biotechnology approaches for greater adaptation to variable climates have been widely adopted in the last few decades. More recently, they are being combined with high-throughput phenotyping in order to capitalize on new techniques of hyperspectral imaging [9] to rapidly assess plant responses to abiotic stresses. However, progress in this area has been slow, partly due to the complexity of the physiological responses of crops to water limitation. In today’s genomic age, accumulated knowledge of the underlying genes involved in crop phenology and performance under stress is now available. This may help to better focus breeding on the alleles or allele combinations that contribute most to crop performance under drought stress, as may utilizing crop relatives as intraspecific hybrids or synthetic polyploids (e.g., wheatgrass relatives of wheat that are perennial and drought tolerant), because wild species are often better adapted to water-limited conditions, or possess novel agronomic traits.
New gene-editing technologies [10] that allow targeted small base changes or deletions to plant and animal genomes now offer a greater diversity in approaches to crop improvement. Since the results of such technologies may not carry the stigma of being “genetically modified,” they may be more palatable to consumers than conventional GM crops—although time will tell. The first products (e.g., gene-edited non-browning mushrooms) are beginning to enter the food chain in the United States. Gene editing also offers the potential to quickly “domesticate” new crop species with desirable characteristics such as drought and disease tolerance, as it should be possible to quickly “edit” endogenous genes in order to enhance traits that are known to be important for domestication (i.e., non-shattering seed pods, insensitivity to day length, etc.). Such traits would otherwise take decades to achieve by conventional breeding, so gene editing can bring novel crops into production more quickly.
Genome sequencing has become mainstream in plant and animal breeding; as the cost of sequencing plummets, new genomic-enabled breeding approaches will become more affordable and accessible. Such approaches have already made significant inroads into the commercial production of improved breeding stocks in domesticated animals such as cattle, but they are only just beginning to be applied in plant breeding [11]. Despite their enormous potential, the cost, complexity, and infrastructure requirements for many of these genomic breeding tools are still relatively high; thus, these tools are predominantly being used in the private sector. Nevertheless, movement toward the increased use of such approaches is occurring in public research agencies as well.
2.2. Quantum leaps in agricultural production
Even with all these new genetic and biotechnology solutions, it will be difficult to reach the food production targets that are needed over the next 30 years. Real innovation will be required to achieve quantum changes in the productivity of plants and animals; these types of innovations are likely to be inherently risky, and therefore not easily accommodated by our current models for funding agricultural R&D in the public or private sectors. New funding paradigms will be needed, and are already occurring at two levels—through large philanthropic foundations (e.g., the Bill & Melinda Gates Foundation’s Grand Challenge Explorations, the Rockefeller Foundation’s Food Waste and Spoilage Initiative, and the Two Blades Foundation) that are funding large international transformative research initiatives; and through online crowd-funding platforms (e.g., AgFunder: https://agfunder.com/) that are connecting good ideas in agriculture (both in research and production) with both larger institutional and smaller or individual investors in order to move the ideas from the drawing board into practice.
The explosion in available genomic information and an increased understanding of genetic and metabolic networks in living cells have spawned the new discipline of synthetic biology, and have opened up previously unthinkable new avenues for improving food and food productivity [12]. Many social, ethical, and regulatory implications still need to be sorted out for synthetic biology. In many cases, the basic “chassis” (minimal genomes) and “biobricks” that can be assembled into new genetic pathways to produce synthetic biological organisms are only just being developed. At present, the focus is on more modest targets than the total redesign of organisms—albeit one that may be just as difficult. Large international consortia (many of which are co-funded with the Bill & Melinda Gates Foundation) are attempting to redesign crops using gene technology in order to achieve the following goals, among others: ① to design crops that can fix their own nitrogen, rather than relying on symbiotic relationships with bacteria or synthetic fertilizers; ② to enhance the photosynthetic efficiency of temperate crops, such that they become more like fast-growing tropical grasses (e.g., C4 rice); and ③ to produce seeds without sexual reproduction (apomixis) in order to fix the productivity benefits that are delivered in hybrid seeds and that are normally lost in the next generation. Others are redesigning metabolic pathways in plants and microbes in order to produce novel products such as cow’s milk from yeast, or oils in the leaves of plants to replace some of the demand for petrochemical oils, which are predicted to run out in the not-too-distant future. Success in any of these attempts will have a significant impact on our ability to produce foods more efficiently or sustainably.
2.3. Digital agriculture and farm automation
“Better” plants were only one aspect of the GR; the enhanced production of the GR was equally due to improved farm machinery and to management enabled by technological advances. The next Green Revolution, GR 2.0, will likely depend even more on technology, in order to allow farmers to make better management decisions, and even more on automation, in order to require fewer people to run farms. Catalyzed by the availability of cheap, Internet-connected sensor technologies, we are beginning to be able to collect vast amounts of real-time data from farm machinery, in-field sensors, irrigation pumps, and even farm animals—all supplemented by increasingly detailed image data collected by satellites and drones across a range of spectral frequencies. At present, the huge volume of data quickly outstrips our ability to convert it into usable information; nevertheless, the development of quick and simple predictive analytic tools utilizing artificial intelligence (AI) and machine learning will undoubtedly increase farm productivity. Given all of this information, along with precise satellite and wireless navigation, there is really no reason for a farmer to have to sit in the cab of a tractor or harvester in order to drive and operate it. Increased farm automation at all levels will significantly increase farm efficiencies in planting; the applications of fertilizers, pesticides, and fungicides; harvesting; and irrigation, in order to maximize the yields from existing arable lands and available water [13].
3. Conclusion
Farming and food production have traditionally benefited from innovative solutions that solved the challenges presented by nature and society. Now, more than ever, we need to embrace new science and technology and new funding models for agricultural research, so that we can continue to put food on our tables and clothes on our backs into the future. Everyone would agree that serious challenges lie ahead, which are not limited to climate change; however, our species has the ingenuity that is required to tackle these major challenges in order to ensure that we can equitably feed our growing population in a sustainable manner. The first GR was a game changer, and GR 2.0 needs to be even better; however, we must learn from our earlier mistakes and ensure that the GR 2.0 will not have the deleterious impacts on soil health, water health, biodiversity, or human health that resulted from the massive intensification of agricultural production over the last few centuries.