This chapter assesses abiotic stresses such as drought, floods, acidic soils, and soil salinity, and how they affect crop yield. Abiotic stresses cause plant cells to more highly express many genes that help the plant cope with the stress so that growth can continue, albeit at a slower rate. The formation of reactive oxygen species (ROS) is a response to many stresses. ROS damage cells but also serve as signals and cause cells to turn on stress-response genes. The chapter then considers water potential, which is the physical property of water that drives water movement from the soil through the plant and into the atmosphere. It also looks at how some common agricultural practices, other human activities, and climate change are leading to soil degradation and increased abiotic stresses.
Abiotic Stresses and How They Affect Crop Yield
Maarten J. Chrispeels
Biotic Challenges: Pests
This chapter examines insects and nematode pests that consume or otherwise destroy plants. Farmers have multiple options for controlling pests: cultural practices, synthetic chemicals, natural genetic resistance, and biotechnology. Plants defend themselves with toxic and deterrent chemicals. Not only do they have constitutive defenses, but they also increase the production of defensive chemicals in response to herbivory. One option for pest control is integrated pest management (IPM). This process requires assessing pest density and then using environment-friendly interventions. Chemicals are only employed as a last resort, and only when the cost of application is lower than expected pest-related losses. The chapter then looks at insecticide sprays, both natural and synthetic.
Biotic Challenges: Weeds
Patrick J. Tranel
This chapter reviews weed management — an enormous problem in all agricultural systems — and highlights the danger of relying entirely on crops that are genetically engineered to resist weeds. Weeds compete with crops for nutrients, water, sunlight, and space, and therefore diminish crop yields. Therefore, farmers have a number of different options to manage their weed populations. Many farmers use chemical weed control as the primary option to control weeds; herbicides target plant-specific biochemical processes. However, overreliance on herbicides results in the emergence of herbicide-resistant weeds. The chapter then considers how herbicide-tolerant crops can be obtained by genetic engineering and can further simplify weed management. It also looks at how sustainable weed management systems require the integration of a diversity of weed control tactics.
Challenges and Solutions for Subsistence Farmers
Manish N. Raizada
This chapter studies the challenges and solutions for subsistence farmers. Subsistence farmers in the subtropics suffer from low food production and malnutrition in the dry season. In order to increase their resiliency, subsistence farmers often cultivate a diversity of crops. Opportunities exist to improve crop yields through breeding and agronomic improvements to the cropping system, leading to agricultural intensification. Other crucial constraints on smallhold farmers include lack of precipitation, infertile or degraded soils, and soil erosion. The chapter then looks at weed and pest control, as well as postharvest food processing. Ultimately, lessons may be learned from the success of agriculture in developed nations which transformed from subsistence farming to wealth through a partnership between the private sector that sold a menu of innovative products and publicly funded agricultural extension to train farmers on a menu of best practices.
A Changing Global Food System
One Hundred Centuries of Agriculture
H. Maelor Davies and Paul Gepts
This chapter examines the changes that have occurred in farming over the past 10,000 years and which continue today. Agriculture and food play an important role in the economic systems of all countries and regions. Indeed, crop and animal domestication — integral to the practices of farming — were essential for the development of human civilizations. Agricultural systems in different regions of the world differ in their productivity, and in the modern world, scientific and technological discoveries are responsible for many of those differences. Whereas modern science-driven agriculture is highly productive, especially in developed countries, a billion smallholder farmers in developing countries are confined to small farms where productivity is low and where they produce just enough food to supply themselves with the bare essentials of life.
Converting Solar Energy into Crop Production
Donald R. Ort, Rebecca A. Slattery, and Stephen P. Long
This chapter focuses on photosynthesis, which is the basis of all life on Earth. Crop plant growth and development are limited by photosynthesis, and so an understanding of the basic chemistry of this process is important to food production. Indeed, increasing food production may depend in part on our ability to make the biochemical processes of photosynthesis more efficient. The chapter begins by looking at how photosynthetic membranes convert light energy to chemical energy. In photosynthetic carbon metabolism, chemical energy is used to convert CO2 to carbohydrates. The chapter then considers how sucrose and other polysaccharides are exported to heterotrophic plant organs to provide energy for growth and storage. It also studies photoprotection and explores abiotic environmental factors which can limit photosynthetic efficiency and crop productivity.
The Domestication of Our Food Crops
This chapter assesses crop domestication, discussing how and where modern crops arose from wild plants. Wheat was domesticated in the Middle East, and domestication resulted in diploid (Einkorn), tetraploid (durum or pasta wheat), and hexaploid (bread wheat) varieties. Meanwhile, three varieties of rice — japonica, indica, and aus — were domesticated in different parts of Asia. The chapter then looks at the domestication of maize and beans, before considering how domestication has accelerated evolution because of selection pressures imposed by humans and farming techniques. Crop evolution has been marked by major genetic bottlenecks that follow domestication, dispersal to new regions, and scientific breeding programs. The result is decreased genetic diversity in most crops. The chapter also studies hybridization, polyploidy, and the sequencing of crop-plant genomes.
Are Foods Made from GE Crops Safe to Eat?
This chapter explores food safety. All novel foods (crops or processed foods) may carry toxicity hazards, and governments have set up regulatory agencies for the purpose of examining these hazards. The safety of genetically engineered (GE) crops has been examined by many scientists and health organizations and they have an excellent safety record. Safety evaluation begins with analysing the components present in a GE crop and comparing the levels with a non-GE variety of the same species that has a history of safe use. Molecular methods make it possible to examine the chromosomal site where DNA is inserted, and the presence of novel proteins and metabolites. The chapter then looks at how gene editing allows scientists to create novel varieties that do not contain foreign DNA.
From Classical Plant Breeding to Molecular Crop Improvement
Paul Gepts and Todd Pfeiffer
This chapter addresses plant breeding, where humans deliberately make crosses and choose specific plant varieties with characteristics that are desirable for food, feed, fibre, and fuel production. Crop improvement requires a never-ceasing pursuit of genetic diversity to introduce new alleles and new gene combinations into elite cultivars. This diversity originates in a wide range of sources, including other cultivars, landraces, wild progenitors, other crossable species, and transgenes. Plant breeding is a well-established science that, since the 1930s, has adopted approaches aimed to increase the efficiency of selection. These approaches include the use of quantitative genetics, artificial mutagenesis, and marker-assisted selection. More recent tools include genome-wide association studies, genomic selection based on extensive genome sequencing, and high-throughput phenotyping.
Genes, Genomics, and Molecular Biology
The Basis of Modern Crop Improvement
Kranthi K. Mandadi and T. Erik Mirkov
This chapter begins the consideration of the basic biology that is the foundation of crop-plant improvement by describing genetics, heredity, and molecular biology. The basics of DNA, RNA, and protein synthesis are necessary to an understanding of genes and how/when/where they are expressed; a crucial prerequisite for crop improvement. Gene expression encompasses all the steps from transcription of the DNA to the formation of the final protein. The chapter looks at mutations, which are the basis of polymorphism in the DNA, leading to polymorphism in the individuals of a population. Plant breeders are interested in understanding which polymorphism is associated with which trait. The chapter then highlights the importance of genome sequencing, bioinformatics, and gene editing technologies for plant biologists and breeders.
Growth and Development
From Fertilized Egg Cell to Flowering Plant
Maarten J. Chrispeels
This chapter details the structure and function of plant cells and organs and how an entire plant develops from a single fertilized egg cell. There is considerable emphasis on seed development, because most of the foods we eat are, at their core, made from the seeds of rice, wheat, and corn, as well as the seeds of legumes such as soybeans, peas, and beans. The chapter differentiates between shoot apical meristem (SAM) and root apical meristem (RAM). SAM is responsible for forming leaf and stem tissues, while RAM contains stem cells for the different root tissues and for the root cap, a small thimble-shaped mass of cells that protects the RAM as the root pushes through soil. The chapter also discusses the practice of raising plants from single cells in culture and the importance of this technique for micropropagation and genetic engineering.
The Human Population and Its Food Supply in the 21st Century
Maarten J. Chrispeels and Hanya E. Chrispeels
This chapter discusses the past, present, and future of the human population and its relationship to food production. In the past, the uncertainties of food production too often have led to food insecurity, and the future holds further uncertainties posed by climate change. Rapid urbanization in developing countries is changing where vegetables are grown and how they are made available to consumers. The depopulation of the land means that farming will have to become more efficient and less labour intensive. There is agreement among agricultural scientists that the way forward is to increase the productivity of farmland everywhere and to do this sustainably, reducing the impact of agriculture on the environment. The chapter then looks at how government policies play pivotal roles in global food production, as well as the importance of agricultural research and biotechnology.
Innovations in Agriculture
How Farm Technologies Are Developed and How They Reach Farmers
H. Maelor Davies
This chapter explores how farm technologies are developed and how they reach farmers. Farmers obtain seeds in one or more of four different ways. They may obtain seed freely through sharing with other farmers; purchase from seed companies with no restrictions on their future propagation; purchase seed of varieties suitable for only one crop-production cycle; and/or purchase with formal agreement that limits use to a single crop-production cycle. The ability to patent plant varieties combined with the development of advanced plant genetics led to considerable consolidation of the seed-supply industry. The chapter then looks at how domination of the seed-supply for the major crops by just a few large companies has led to concerns about limited genetic diversity among the major crops, and debate about who actually owns plant varieties. It considers how agricultural technologies and practices are subject to oversight and regulation.
Introduced Traits That Benefit Farmers and Industry
Maarten J. Chrispeels and Eliot M. Herman
This chapter addresses the crop-plant traits that primarily benefit farmers and the food production and processing industry. Genetically engineered (GE) crops were introduced in the mid-1990s and have been extensively planted in many developed and developing countries by millions of farmers. Herbicide-tolerant genes make GE plants tolerant of herbicides that were already in use when the GE crops hit the market, while insect-resistant GE crops rely on the effects of Cry proteins, encoded by Bt genes, on insect larvae. The chapter then looks at nitrogen assimilation and phosphate starvation tolerance. It also considers pod shatter-resistant canola, genetically engineered forest trees, and hybrid seed production.
Introduced Traits That Benefit the Consumer
Maarten J. Chrispeels and Eliot M. Herman
This chapter describes crop-plant traits that primarily benefit consumers. Functional foods can be made in several ways: by traditional plant breeding, by genetic engineering, or by the addition of ingredients as foods are being processed. The Golden Rice Project shows an example of what can be achieved scientifically to address nutritional deficiencies by plant genetic engineering, but also how difficult it can be to bring the benefits to consumers. The chapter then looks at how biofortifying crops with iron is a major goal of nutritionists. It also considers heat-stable vegetable oils, particularly soybean oil; hypoallergenic foods; and the use of genetic engineering to reduce postharvest food losses.
Plant Diseases and Strategies for Their Control
Andrew F. Bent
This chapter discusses plant diseases caused by viruses, bacteria, fungi, and oomycetes, and explains how understanding the mechanisms of these diseases can be used to breed more durable resistance into crops. Genetic diversity of a crop species can minimize the threat of severe disease epidemics. Disease problems can be reduced by plant cultivation practices such as crop rotation or altered irrigation, by use of fungicides and other chemicals, and especially by planting disease-resistant plant varieties. The chapter then looks at how plants have a sensitive pathogen-detection system — the innate immune system — that allows early and strong activation of defenses. It also considers how molecular biologists use genetic engineering to protect plants from pathogens. A particularly effective method is called HIGS or host-induced gene silencing.
Plant Propagationby Seeds and Vegetative Processes
Kent J. Bradford and Maarten J. Chrispeels
This chapter describes plant propagation by seeds and vegetative processes. Plants propagate both sexually and asexually (vegetatively) and people exploit both types for plant propagation. The chapter looks at seed germination, seedling establishment, and seed treatments. Seedling establishment in the field is an important agronomic variable for crop-production; sowing healthy seeds at the right time ensures a good stand of the crop. To improve seed germination and crop growth, seeds are coated with chemicals to prevent diseases. The chapter then considers the role of seed banks in preserving the genetic diversity of crops, before studying micropropagation, grafting, and apomixis. Understanding the genetic control of apomixis could result in significant breakthroughs in crop improvement.
Plants as Chemical Factories
Krutika Bavishi and Birger Lindberg Møller
This chapter reviews plants as chemical factories. We obtain a vast array of chemicals such as flavours, fragrances, and drugs from plants that are products of their metabolism. Plant metabolism can be classified as primary or secondary. The products of primary metabolism are crucial for the life processes, while those of secondary metabolism mostly help in environmental adaptation and survival. There are tens of thousands of secondary metabolites, which can be broadly classified based on their chemical structures into terpenoids, alkaloids, and phenolics. The chapter then looks at the practice of culturing plant cells in vitro, plant metabolic engineering, and microalgal cultures. Co-production of valuable chemicals like secondary plant metabolites is essential to the commercial success of microalgal cultures as a source of biofuel.
Plants as Factories for the Production of Protein Biologics
This chapter examines plants as factories for the production of protein biologics. Plants have been used as a source of natural pharmaceuticals for a long time, and still provide a quarter of all prescription pharmaceuticals. They are not used as a source of protein pharmaceuticals, but can be modified to produce protein-based biologics. Genes for biologics can be delivered into plant cells either directly by particle bombardment with a gene gun or indirectly through infection with modified plant viruses or Agrobacterium-mediated transformation of the nuclear genome. The chapter then looks at agroinfiltration, new vectors for gene delivery, and how a plant-manufactured biologic has been approved to treat a genetic disease in humans.
Plants in Human Nutrition, Diet, and Health
Maarten J. Chrispeels
This chapter looks at food not from a production standpoint, but from the point of view of human nutrition. It describes nutritional biochemistry in terms of some familiar molecules: carbohydrates, fats, proteins, and vitamins. In addition to being the ultimate source of all our food, plants also contain non-nutritive molecules that affect other organisms by defending the plants against herbivory or attracting pollinators. The chapter then considers the consequences of nutritional deficiencies, before exploring organically grown plants. Although humans are omnivores, millions of vegetarians and vegans attest to the fact that animal foods are not essential to our health. The chapter also studies how the intestinal microbiome significantly influences human health.