Plants, genes & agriculture: sustainability through biotechnology Chrispeels
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Sustainability through Biotechnology & Genes Agriculture Plants,
& Genes Agriculture Plants,
Sustainability through Biotechnology
Maarten J. Chrispeels
University of California, San Diego
Paul Gepts
University of California, Davis
SINAUER ASSOCIATES
NEW YORK OXFORD
OXFORD UNIVERSITY PRESS
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by Val Thoermer/Alamy Stock Photo
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Library of Congress Cataloging-in-Publication Data
Names: Chrispeels, Maarten J., 1938- editor. | Gepts, Paul L., editor.
Title: Plants, genes & agriculture : sustainability through biotechnology / editors: Maarten J. Chrispeels, Paul Gepts.
Other titles: Plants, genes and agriculture : sustainability through biotechnology
Description: New York : Oxford University Press, 2017. | Includes bibliographical references and index.
Identifiers: LCCN 2017045697 | ISBN 9781605356846 (paperbound)
Subjects: LCSH: Crops--Genetic engineering. | Plant breeding. | Sustainable agriculture. | Genetic transformation.
Classification: LCC SB123.57 .P588 2017 | DDC 631.5--dc23
LC record available at https://lccn.loc.gov/2017045697
9 8 7 6 5 4 3 2 1 Printed in the United States of America
Brief Contents
The Human Population and Its Food Supply in the 21st Century 2 A Changing Global Food System 32 Plants in Human Nutrition, Diet, and Health 62 Genes, Genomics, and Molecular Biology 96 Growth and Development 136 Converting Solar Energy into Crop Production 176 The Domestication of Our Food Crops 208 From Classical Plant Breeding to Molecular Crop Improvement 236 Plant Propagation by Seeds and Vegetative Processes 268 Innovations in Agriculture 294 Soil Ecosystems, Plant Nutrition, and Nutrient Cycling 320 Biotic Challenges: Weeds 352 Plant Diseases and Strategies for Their Control 374 Biotic Challenges: Pests 404 Abiotic Stresses and How They Affect Crop Yield 434 Introduced Traits That Benefit Farmers and Industry 466 Introduced Traits That Benefit the Consumer 488 Food Safety 508 Challenges and Solutions for Subsistence Farmers 528 Plants as Chemical Factories 558 Plants as Factories for the Production of Protein Biologics 584 Sustainable Food Production in the 21st Century 604 Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18 Chapter 19 Chapter 20 Chapter 21 Chapter 22
A Changing Global Food System One Hundred Centuries of Agriculture 32 H. Maelor Davies and Paul Gepts 2.1 Hunting and Gathering Were the Methods of Food Procurement for Much of Human History 34 2.2 Agriculture Began in Several Places Some 10,000 Years Ago 35 2.3 Plants Are the Principal and Ultimate Source of All Our Food 38 2.4 Crop Production Today Takes Several Forms That Differ Dramatically in Productivity 41 BOX 2.1 Intensification of Agricultural Productivity in the Brazilian Cerrado 44 2.5 Science-based Agricultural Practices Have Led to Significant Increases in Productivity 46 BOX 2.2 S ome Inventions and Innovations through the History of Agriculture 47 2.6 Farming and the Postharvest Food Delivery Pathway Combine to Provide Consumers with an Abundance of Different Foods 51 BOX 2.3 A gricultural Intensification and New Business Opportunities: The Pacific Fruit Express 53 2.7 Agriculture and Food Production Are Significant Players in the Economic Systems of Developed Countries 55 2.8 Intensive Agriculture Has Environmental Effects That May Limit Its Long-term Sustainability 57
CHAPTER The Human Population and Its Food Supply in the 21st Century 2 Maarten J. Chrispeels and Hanya E. Chrispeels 1.1 Hunger and Malnutrition Persist in a World of Plenty 4 1.2 Human Population Growth Is Slowing 6 1.3 By How Much Does the Food Supply Need to Increase to Satisfy Future Demand? 9 1.4 Agriculture Must Become More Sustainable in the Future 11 1.5 An Uncertain Climate Presents Challenges to Food Production 13 1.6 Urbanization and Rising Living Standards Are Changing the Demand for Agricultural Products and the Way They Are Brought to Market 16 BOX 1.1 Food Deserts in America 18 1.7 Government Policies Play Pivotal Roles in Global Food Production 19 1.8 Agricultural Research Is Vital If We Are to Maintain a Secure Food Supply 20 BOX 1.2 International Agricultural Research Institutes of the CGIAR Consortium 21 1.9 Can Other Agricultural Methods and Policies Contribute to Feeding the Population? 23 1.10 Biotechnology Is Crucial for the Future of Food Production 27
CHAPTER Contents
2
1
3.1 Animals Are Heterotrophs, Plants Are Autotrophs 64
3.2 Carbohydrates Are the Principal Source of Energy in the Human Diet
BOX 3.1 Lactose Tolerance: A Case of Human Evolution in Action 6 8
3.3 Fats Are a Source of Energy, Structural Components, and Essential Nutrients
3.4 Diets High in Energy Are Linked to Major Diseases
3.6 Vitamins Are Small Molecules That Plants Can Make, but Humans and Other Animals Generally Cannot 80
BOX 3.2 Vitamin D: A Vitamin or a Hormone? 81
3.7 Minerals and Water Are Essential for Life 82
3.8 Plants Produce Bioactive Molecules that Can Affect Human Health 85
3.9 The Consequences of Nutritional Deficiencies Can Be Severe and Long Lasting 87
BOX 3.3 Gluten Sensitivity and Celiac Disease 87
3.10 Millions of Healthy Vegetarians and Vegans Are Living Proof that Animal Products Are Not a Necessary Component of the Human Diet 88
3.11 Are Organically Grown Plants and Products from Animals Fed with Organic Feed Worth the Additional Price?
3.12 The Intestinal Microbiome Significantly Influences Health 91
4 CHAPTER 3 CHAPTER CONTENTS vii Genes, Genomics, and Molecular Biology The Basis of Modern Crop Improvement 96 Kranthi K. Mandadi and T. Erik Mirkov BOX 4.1 Characteristics and Traits, Phenotypes and Genotypes, Genes and Alleles: Some Vocabulary 98 4.1 Traits Are Inherited from One Generation to the Next 98 4.2 Genetic Information Is Replicated and Passed to New Cells during Cell Division 101 BOX 4.2 Chromosomes, Chromatids, and Meiosis 104 4.3 Genes Are Made of DNA 105 4.4 Gene Expression Involves RNA Synthesis Followed by Protein Synthesis 108 4.5 Gene Expression Is a Highly Regulated Process 114 4.6 Mutations Are Changes in Genes 119 4.7 Much of the Genome’s DNA Does Not Code for Proteins 122 4.8 DNA Can Be Manipulated in the Laboratory Using Tools from Nature 123 4.9 Creating GE Plants Depends on the Application of Naturally Occurring Horizontal Gene Transfer 125 BOX 4.3 Selectable Markers 127 4.10 Genome Sequencing and Bioinformatics Are Important Tools for Plant Biologists and Plant Breeders 129 4.11 Gene Editing Technologies Allow Us to Make Targeted Changes in an Organism’s DNA 131 Plants in Human Nutrition, Diet, and
Health 62 Maarten J. Chrispeels
65
70
74
3.5 To Make Proteins, Animals Must Eat Proteins 76
89
5 CHAPTER
6 CHAPTER
Growth and Development
From Fertilized Egg Cell to Flowering Plant 136
Maarten J. Chrispeels
5.1 The Plant Body Is Made Up of Cells, Tissues, and Organs 138
BOX 5.1 The Structures of a Living Plant Cell 140
5.2 Development Is Characterized by Repetitive Organ Formation from Stem Cells 142
BOX 5.2 Plant Tissue Systems and Cell Types 143
5.3 Gene Networks Interact with Hormonal and Environmental Signals to Regulate Development 148
BOX 5.3 Plant Hormones 150
5.4 In the First Stage of Development, Fertilized Egg Cells Develop into Embryos 151
5.5 Deposition of Food Reserves in Seeds Is an Important Aspect of Crop Yield 155
5.6 Maturation, Quiescence, and Dormancy Are Important Aspects of Seed Development 156
5.7 Formation of the Vegetative Body Is the Second Stage of Plant Development 158
5.8 Secondary Growth Produces New Vascular Tissues and Results in the Formation of Wood 163
5.9 Reproduction Involves the Formation of Flowers with Male and Female Organs 165
5.10 Fruits Help Plants Disperse Their Seeds 169
5.11 Developmental Mutants Are an Important Source of Variability to Create New Crop Varieties 170
5.12 Plant Cells are Totipotent: A Whole Plant Can Develop from a Single Cell 1 72
Converting Solar Energy into Crop Production 1 76
Donald R. Ort, Rebecca A. Slattery, and Stephen P. Long
BOX 6.1 Efficiency of Food Production from Solar Energy to People 17 9
6.1 Photosynthetic Membranes Convert Light Energy to Chemical Energy 180
6.2 In Photosynthetic Carbon Metabolism, Chemical Energy Is Used to Convert CO2 to Carbohydrates 184
6.3 Sucrose and Other Polysaccharides Are Exported to Heterotrophic Plant Organs to Provide Energy for Growth and Storage 188
6.4 Plants Gain CO2 at the Cost of Water Loss 190
6.5 Plants Make a Dynamic Trade-off of Photosynthetic Efficiency for Photoprotection 193
6.6 Abiotic Environmental Factors Can Limit Photosynthetic Efficiency and Crop Productivity 195
6.7 How Efficiently Can Photosynthesis Convert Solar Energy into Biomass? 198
6.8 Opportunities Exist for Improving the Efficiency of Photosynthesis 199
6.9 Global Climate Change Interacts with Global Photosynthesis 201
viii CONTENTS
7 CHAPTER
The Domestication of Our Food Crops 208
Paul Gepts
7.1 Wheat Was Domesticated in the Near East 210
7.2 Rice Was Domesticated in Asia and Western Africa 213
7.3 Maize and Beans Were Domesticated in the Americas 215
7.4 Domestication Is Accelerated Evolution Involving Relatively Few Genes 217
7.5 Crop Evolution Was Marked by Genetic Bottlenecks That Decreased Diversity 2 22
BOX 7.1 Genetic Uniformity and the Irish Potato Famine 224
7.6 Hybridization Plays a Role in the Appearance of New Crops, the Modification of Existing Crops, and the Development of Some Troublesome Weeds 2 26
7.7 Polyploidy Led to New Crops and New Traits 227
7.8 Sequencing Crop Plant Genomes Provides Insights into Plant Evolution 2 29
8.9 Tissue and Cell Culture Techniques Facilitate Plant Breeding
8.10 The Technologies of Gene Cloning and Plant Transformation Are Powerful Tools to Create GE crops 258
8.11 Marker-assisted Breeding Helps Transfer Major Genes 259
BOX 8.3 Karl Sax and the Principle of QTL Analysis 261
8.12 Genome Sequencing Has Become an Essential Tool of Plant Breeding Programs 262
8.13 High-Throughput Trait Measurement Facilitates Phenotyping for Crop Breeding 264
CONTENTS ix
CHAPTER From Classical Plant Breeding to Molecular Crop Improvement 236 Paul Gepts and Todd Pfeiffer 8.1 Plant Breeders Have a Long Wish List 238 8.2 Plant Breeding Involves Introduction of Genetic Diversity, Hybridization, and Selection of New Gene Combinations 241 BOX 8.1 Who Owns the World’s Genetic Resources? 242 8.3 Genetic Variation Manipulated by Selection Is the Key to Plant Breeding 243 BOX 8.2 Johannsen and the ‘Princess’: Defining Variation for Plant Breeders 244 8.4 The Breeding Method Chosen Depends on the Pollination System of the Crop 247 8.5 F1 Hybrids Yield Bumper Crops 249 8.6 Backcrossing Comes as Close as Possible to Manipulating Single Genes via Sexual Reproduction 250
Quantitative Traits Are More Complex to Manipulate Than Qualitative Traits 252
8
8.7
254
8.8 The Green Revolution Used Classical Plant Breeding Methods to Increase Wheat and Rice Yields
257
Plant Propagation by Seeds and Vegetative Processes 268
Kent J. Bradford and Maarten J. Chrispeels
9.1 Commercial Seed Production Is Often Distinct from Crop Production 271
BOX 9.1 Where Do the Seeds to Grow Seedless Watermelons Come From? 27 3
9.2 Seed Certification Programs Guarantee and Preserve Seed Quality 274
9.3 Saving Seeds Securely Is an Important Aspect of Agriculture in Developing Countries 275
BOX 9.2 Storing Seed for the Next Season: Challenges Faced By African Farmers 277
9.4 Seed Germination, Seedling Establishment, and Seed Treatments Are Important Agronomic Variables 279
9.5 Enhancing Microbial Biofertilizers in the Soil Is an Important Technology for Crop Production 281
9.6 Seed Banks Preserve Genetic Diversity for the Future 283
9.7 Sterile Tissue Culture Is Used for Micropropagation and the Production of Somatic Embryos 285
9.8 Grafting Is Widely Used in the Fruit Industry to Propagate Superior Varieties 288
9.9 Apomixis Is a Unique Way in which Some Plant Species Reproduce 289
Innovations in Agriculture
How Farm Technologies Are Developed and How They Reach Farmers 294
10.1 Biological and Technological Innovations Have Improved Farming Practices since the Early Days of Agriculture 295
BOX 10.1 Synergy between Plant Breeding and Technology Development 297
BOX 10.2 The Agricultural Services Industry 298
10.2 Innovations in Agriculture Require Substantial Research in Many Fields 299
10.3 Patents Stimulate Invention and Improvements 303
10.4 Farmers Obtain Seeds in Different Ways 307
10.5 Minor Crops and New Production Methods Are Important 311
10.6 Agricultural Technologies and Practices Are Subject to Oversight and Regulation 313
x CONTENTS
10 CHAPTER 9 CHAPTER
H. Maelor Davies
Soil Ecosystems, Plant Nutrition, and Nutrient Cycling 320
Eric M. Engstrom
11.1 Soil Ecosystems Are Fundamental to Agriculture 322
BOX 11.1 Animal, Vegetable, Mineral? 3 24
11.2 Particles Created by Weathering Are the Medium of Soil Ecosystems 324
11.3 Living Organisms and Their Remains Are Important Components of Soil Ecosystems 329
11.4 Plants Need Six Mineral Elements in Large Amounts and Eight Others in Small Amounts 331
11.5 Productivity May Be Limited by the Availability of Soil Water and Nutrients 334
11.6 Soil Organic Matter Is the Key Determinant of Soil Fertility 336
11.7 Roots Are the Foundation of Soil Food Webs and Soil Adhesion 337
11.8 Phosphorus Is the Rock-Derived Nutrient That Most Commonly Limits Crop Productivity 339
BOX 11.2 Terra Preta Do Indio 3 40
11.9 Nitrogen-fixing Bacteria and Industrial Nitrogen Fixation Drive the Nitrogen Cycle 343
11.10 Mycorrhizae Are Plant–Fungi Mutualisms That Help Plants Acquire Nutrients 347
Biotic Challenges: Weeds 352
Patrick J. Tranel
12.1 Weeds Are Plants Adapted to Environments Disturbed by Humans 353
12.2 Weeds Interfere with Crop Plant Growth 356
BOX 12.1 Weeds That “Don’t Fight Fair” 3 58
12.3 Weed Control Is Achieved by Cultural, Mechanical, Biological, and Chemical Practices
12.4 Herbicides Kill Plants by Interfering with Vital Plant-specific Processes 362
BOX 12.2 Herbicide Properties Depend on Their Chemistry 363
12.5 First Chemistry and then Biotechnology Transformed Weed Control 365
12.6 Weeds Adapt to Our Attempts To Control Them 366
12.7 Herbicide Resistance and a Lack of New Herbicides Are Challenges to Weed Control 367
BOX 12.3 Dioecious Pigweeds Are Particularly Well Equipped to Evolve Herbicide Resistance 368
12.8 New Methods of Weed Control Are Emerging 369
CONTENTS xi
12 CHAPTER 11 CHAPTER
359
Andrew F. Bent
13.1 Microbial Infections Diminish Crop Yields, but Plants Fight Back 375
13.2 Disease Epidemics Occur When Multiple Factors Converge 377
13.3 Viruses and Viroids Have Only a Few Genes 379
13.4 Cellular Pathogens Use Effector Proteins That Act in the Host Plant 382
13.5 Plant-pathogenic Bacteria Cause Many Economically Important Diseases 383
BOX 13.1 The Value of Sequencing a Pathogen Genome 384
13.6 Pathogenic Fungi and Oomycetes Collectively Cause the Greatest Crop Losses 385
Biotic Challenges: Pests 4 04
Georg Jander
14.1 Arthropod Pests Cause Substantial Crop Losses 406
14.2 Parasitic Nematodes Cause Substantial Crop Losses 409
14.3 Plants Have Chemical Defenses against Pests 412
BOX 14.1 Some Legal and Illegal Drugs Are Natural Insecticides 414
14.4 Improved Cultural Practices Can Help Control Pests 415
BOX 14.2 Push-pull Systems for Pest Control 418
14.5 Integrated Pest Management Can Control Outbreaks 419
BOX 13.2 Cereal Rusts Are among the Most Crop-destructive Diseases on the Planet 388
13.7 Chemical Strategies for Disease Control Can Be Effective but Problematic 389
13.8 Plants Mount Defenses to Ward Off Pathogens; Successful Pathogens Elude the Defenses 392
13.9 Resistance to Pathogens Can Be Introduced into Plants by Breeding and Genetic Engineering 397
13.10 The Plant Immune System Can Be Activated So Subsequent Infections Are Met with a Stronger Response 400
14.6 Plant Breeding Methods Accelerate the Development of Pest-resistant Crop Varieties 420
14.7 Properly Applied, Synthetic Chemicals Can Provide Effective Pest Control 42 2
14.8 Genetically Engineered Plants Provide New Opportunities 424
BOX 14.3 Bt Toxins Have Both Positive and Negative Consequences for Farmers 427
14.9 Evolution Keeps Chemists, Plant Breeders, and Molecular Biologists Busy 429
xii CONTENTS
14 CHAPTER 13 CHAPTER Plant Diseases and Strategies for Their Control 374
15.6 Plants Sequester Toxic Ions in Vacuoles 453
15.7 Heat Stress During Reproductive Growth Severely Diminishes Crop Yield 454
15.8 Many Crop Plants That Originated in Tropical Regions Are Sensitive to Cold 456
15.9 The Crops That Feed Humanity Are Not Well Adapted to Alkaline or Acidic Soils 458
15.10 Agricultural Practices and Global Climate Change May Exacerbate Abiotic Stresses 461
Introduced Traits That Benefit Farmers and Industry 4 66
Maarten J. Chrispeels and Eliot M. Herman
16.1 Crops Bred Using Genetic Engineering Approaches Were Introduced in the Mid 1990s 468
BOX 16.1 Genetically Engineered Trees Saved Hawaii’s Papaya Industry 470
16.2 Herbicide-tolerant GE Crops Facilitate Weed Management 471
16.3 Genetic Engineering of Insect Resistance Decreases Pesticide Use on Several Major Crops 473
16.4 Alleviating Water-deficit Stress Is an Increasingly Important Goal of Crop Improvement 474
16.5 Common Bean Provides an Example of Protecting against Virus 476
16.6 Uptake and Assimilation of Nitrogen Can Be Enhanced by Genetic Transformation 476
16.7 Phosphate Uptake Can Be Improved by Transgenic and Traditional Approaches 478
16.8 Pod Shatter-resistant Canola Prevents Seed Losses and Increases Yield 480
16.9 Genetically Engineered Forest Trees Are a New Frontier in Biotechnology 482
16.10 Male-sterile Lines and Fertilityrestorer Genes Facilitate Hybrid Seed Production 485
CONTENTS xiii 16 CHAPTER 15 CHAPTER Abiotic
4 34 Maarten
BOX
Stresses and How They Affect Crop Yield
J. Chrispeels 15.1 Plants Sense Abiotic Stresses and Respond to Them 436 15.2 Plant Growth Depends on an Active Transpiration Stream 4 40 BOX 15.1 The Ogallala Aquifer 4 41
15.2 Water Potential, Osmosis, and Turgor Pressure 443 15.3 The Molecular Responses to Water Deficit Involve Signals from the Root 4 46 15.4 Too Much Water Depletes Oxygen in the Roots and Leads to Cell Death 4 47 15.5 Crops Experience Osmotic Stress and Sodium Toxicity 450
17.1 Enhancing Essential Nutrients or Eliminating Harmful Ones Creates Functional Foods 490
17.2 Golden Rice is the Poster Child for Genetic Engineering in the Service of Humanity 491
17.3 Biofortifying Crops with Iron Is a Major Goal of Nutritionists 494
17.4 Heat-stable Vegetable Oils Are Better Suited for Deep-frying 496
17.5 Biotechnology Can Help Eliminate Food Allergens, But These Innovations May Not Come to Market 498
17.6 Acrylamide Can Be Eliminated from Processed Foods 500
17.7 Genetic Engineering Can Help Reduce Postharvest Food Losses 501
17.8 Conquering Citrus Greening Disease Could Lower the Price of Orange Juice 503
17.9 Are Tastier Tomatoes in Our Future? 504 Food Safety
Are Foods Made from GE Crops Safe to Eat? 508 David Tribe
18.1 Humans Have Continuously Been Exposed to Novel Foods 510
BOX 18.1 Kiwifruit: Entirely New Foods Occasionally Come into Our Stores 511
18.2 The Safety of Genetically Engineered Food Crops Has Been Extensively Debated 513
18.3 Genetically Engineered Food and Feed Crops Have an Excellent Safety Record 514
18.4 Specific Principles of Food Safety Assurance Apply to Foods and Feeds Developed Using Biotechnology 516
BOX 18.2 Internationally Accepted Guidelines for Risk Assessment of Foods 517
18.5 Evaluation of Variability Is a Major Tool to Limit Unintended Changes in GE Crops 517
18.6 Molecular Characterization of Intended Changes and Added Proteins Is a Necessary Component of Safety Assessment 520
18.7 Chemical Risk Evaluation Involves Investigating the Relationship between Degree of Exposure and Harmful Effects 521
18.8 Food Safety Experiments Demand High Standards of Experimental Design and Interpretation 523
18.9 Perspectives on the Impacts of Crop Biotechnology on Human and Animal Health Are Changing 524
xiv CONTENTS
CHAPTER 17 CHAPTER
18
Introduced Traits That Benefit the Consumer 4 88 Maarten J. Chrispeels and Eliot M. Herman
Challenges and Solutions for Subsistence Farmers 528
Manish N. Raizada
19.1 Subsistence Farmers Grow a Diversity of Crops to Maintain Resiliency 530
BOX 19.1 The Orphan Crops of Smallholders 531
19.2 Intensifying Agricultural Output on Smallholds Must Be a Priority 535
19.3 Water Is a Challenge for Smallhold Farmers 538
19.4 Degraded Soils and Soil Erosion Are Lifethreatening Issues for Smallholders 543
19.5 Weed Control Is a Major Burden on Women and Girls in Developing Countries 547
19.6 Indigenous Farmers Have Strategies to Combat Pests and Diseases 549
19.7 There Are Hazards and Drudgery in Harvest and Postharvest Work 551
19.8 Maximizing Profit after Harvest Is Critical 552
19.9 The Public–Private Sector Job Creation Model Can Apply to Smallholders 554
Plants as Chemical Factories 558
Krutika Bavishi and Birger Lindberg Møller
BOX
20.1 The Elixir of Poppies 5 60
20.1 Plant Secondary Metabolism Is a Treasure Chest of High-value Chemicals 560
BOX 20.2 Cannabis, Cannabinoids, and the “Entourage Effect” 5 64
20.2 Several Different Platforms Are Used to Produce Plant Secondary Metabolites for Human Use 565
BOX 20.3 “Hairy Roots” Produce Novel Chemicals 568
20.3 Plant Cells Cultured in Bioreactors Constitute Sustainable “Green Factories” 568
20.4 Metabolic Engineering of Plants Results In Higher Yields And Superior Quality Chemicals 571
BOX 20.4 Pink or Blue? Economics in the Floral Industry 573
20.5 Transferring Metabolic Pathways into Microorganisms Is a Promising Approach to Producing Secondary Metabolites 575
20.6 Microalgae Are Potentially Renewable Resources for a Bio-based Society 576
20.7 The World Needs Biodegradable Plastics 579
CONTENTS xv
19
20 CHAPTER
CHAPTER
Plants as Factories for the Production of Protein Biologics 5 84
Qiang Chen
21.1 Plants Can Be Used as Factories for Protein Biologics 585
21.2 There Are Several Production Strategies for Making Protein Biologics in Plants 587
21.3 Agroinfiltration Is an Effective Way of Delivering Transgenes into Plants 588
21.4 New Vectors for Gene Delivery Are Being Developed 590
21.5 The Plant Host and Plant Organs Used to Produce Biologics Must Be Chosen Carefully 592
BOX 21.1 A Primer on Adaptive Immunity, Immunoglobulins, and Monoclonal Antibodies 594
21.6 Monoclonal Antibodies and Vaccine Candidates Can Be Produced in Plants 596
BOX 21.2 Plant-produced MAbs Show Promise in the Fight against Ebola 598
21.7 A Plant-manufactured Biologic Has Been Approved to Treat a Genetic Disease in Humans 600
Sustainable Food Production in the 21st Century 604
Maarten J. Chrispeels
22.1 Agricultural Intensification and Sustainability Are Equally Important 606
22.2 Can We Decrease the Yield Gap? 608
22.3 Smarter Agronomy Can Deliver Higher Yields 611
22.4 Wider Acceptance of GE Technology Is Essential if We Are to Increase Food Supplies 615
22.5 Research Is Key to Increasing the Intensity of Crop Production 616
22.6 Education at All Levels Is Essential if We Are to Increase Food Production 618
22.7 Maintaining the Resource Base Is Essential for Food Production 619
22.8 We Must Diminish Agriculture’s Contribution to Climate Change and Global Pollution 622
22.9 Sustainability Will Require Greater Attention To Food Waste 623
Glossary G-1
About the Chapter-Opening Photos COP-1
Illustration Credits C-1
Index I-1
xvi CONTENTS
21
22 CHAPTER
CHAPTER
Contributors
Krutika Bavishi
Plant Biochemistry Laboratory
Center for Synthetic Biology
University of Copenhagen
Copenhagen, Denmark
Andrew Bent
Professor of Plant Pathology
University of Wisconsin
Madison, Wisconsin
Kent J. Bradford
Distinguished Professor of Plant Sciences
Director, Seed Biotechnology Center
University of California
Davis, California
Qiang Chen
Professor of Molecular Biology
The Biodesign Institute
School of Life Sciences
Arizona State University
Tempe, Arizona
Maarten J. Chrispeels
Distinguished Professor of Biological Sciences, Emeritus
University of California, San Diego
La Jolla, California
Hanya E. Chrispeels
Assistant Research Professor
Department of Biology
Wake Forest University
Winston-Salem, North Carolina
H. Maelor Davies
Professor of Plant & Soil Sciences, Emeritus
University of Kentucky
Lexington, Kentucky
Eric M. Engstrom
Associate Professor of Biology
Global Food Security Initiative
Monmouth College
Monmouth, Illinois
Paul Gepts
Distinguished Professor of Plant Sciences
Department of Plant Sciences
Section of Crop & Ecosystem Sciences
University of California
Davis, California
Eliot Herman
Professor of Plant Sciences
School of Plant Sciences
University of Arizona
Tucson, Arizona
Georg Jander
Professor
Boyce Thompson Institute
Ithaca, New York
Stephen P. Long
Gutgsell Endowed Professor
Departments of Plant Biology & Crop Sciences
University of Illinois
Urbana, Illinois
and
Distinguished Professor of Crop Sciences
Lancaster Environment Centre
Lancaster University
Lancaster, United Kingdom
Kranthi Mandadi
Assistant Professor of Plant Pathology & Microbiology
Texas A&M AgriLife Research & Extension Center,
Texas A&M University System
Weslaco, Texas
T. Erik Mirkov
Professor of Plant Pathology & Microbiology
Texas A&M Agrilife Research & Extension Center
Weslaco, Texas
Birger Lindberg Møller
Professor of Plant Biochemistry
Plant Biochemistry Laboratory
Center for Synthetic Biology
University of Copenhagen
Copenhagen, Denmark
Donald R. Ort
Robert Emerson Professor of Plant Biology & Crop Sciences
USDA/ARS Global Change & Photosynthesis Research Unit
University of Illinois
Urbana, Illinois
Todd Pfeiffer
Professor of Plant Breeding & Genetics
Department of Plant and Soil Sciences
University of Kentucky
Lexington, Kentucky
Manish N. Raizada
Professor of Plant Agriculture
University of Guelph
Guelph, Ontario, Canada
Rebecca A. Slattery
Research Associate
USDA/ARS Global Change & Photosynthesis Research Unit
University of Illinois
Urbana, Illinois
Patrick J. Tranel
Ainsworth Professor of Crop Sciences
Department of Crop Sciences
University of Illinois
Urbana, Illinois
David Tribe
School of Biosciences
University of Melbourne
Parkville, Australia
Preface
Feeding the human population in a sustainable way is one of the most important problems societies face in the 21st century. Fortunately, the field of agriculture has benefitted from strides in biotechnology made in the last three decades. During this period our knowledge of how plants grow, develop, and function in the environment has greatly increased, and the tools and achievements of biotechnology have considerably changed plant breeding and crop improvement practices. Here we present biotechnology as including all the laboratory-based methods that are used to improve crops and help farmers feed the world. These methods include genome sequencing, identification of individual genes and their functions, marker-assisted selection, genome-wide association of traits with variations in DNA, genetic transformation of plants by the insertion of foreign genes, gene editing using techniques such as CRISPR, high-throughput phenotyping, and more.
It is important to note that we use the term “genetic engineering” (GE) only for the introduction of a foreign (often bacterial) gene into a plant to give it a new characteristic. We take the term “genetic modification” literally—all crops have been genetically modified from their ancestors—and we do not use the colloquial term GMOs (“genetically modified organisms”) to describe genetically engineered plants. All plant species, like all animal species—including humans—are continually being genetically modified as they evolve. Millennia before our knowledge of genetics, DNA, biochemistry, and molecular biology, our ancestors genetically modified crops. Indeed, the process began when the earliest farmers chose plants with specific, recognizable characteristics that facilitated their cultivation and consumption.
As teachers, we believe that textbooks are valuable teaching tools, especially when they bring together many different strands of knowledge. We strive to integrate different scientific disciplines, and our approach is seen in the diverse subject matter described in the chapters of this book. This integrative approach is especially important at the introductory undergraduate level.
Overview
This book highlights that feeding people—growing crops and producing food— is a complex challenge. Many undergraduates have grown up in cities and have no idea of the complexity of producing food and of the numerous issues that crop up (no pun intended) between farm and fork. By learning about the challenges associated with food production, we hope that students take an interest in and perhaps become involved in solving the problem of sustainably feeding the human population.
Chapter 1 deals with 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. 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.
Chapter 2 discusses the changes that have occurred in farming over the past 10,000 years and continue today. Agriculture and food play an important role in the economic systems of all countries and regions. 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.
Chapter 3 deals with food not from a production standpoint, but from the point of view of human nutrition. We describe 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. How do these molecules affect us and the microbes in our intestinal tract?
Chapter 4 begins our 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.
In Chapter 5, we describe 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. Raising plants from single cells in culture and the importance of this technique for micropropagation and genetic engineering are also discussed.
Photosynthesis is the basis of all life on Earth, and Chapter 6 is devoted to this subject. 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.
With the basic science under our belts, we turn in the next chapters to crops, their improvement, and how improved crops reach farmers. Chapter 7 on crop domestication discusses how and where modern crops arose from wild plants. Chapter 8 describes plant breeding, where humans deliberately make crosses and choose specific plant varieties with characteristics that are desirable for food, feed, fiber, and fuel production. Concepts of hybridization and selection are explored, as are the molecular methods we use to accelerate selection among the crossbred progeny, such as marker-assisted genomic selection and high-throughput progeny evaluation. Both chapters emphasize the concept of genetic variability and its importance in the accelerated evolution—changes in crop plant characteristics over time—that humans cause when they practice agriculture.
xx PREFACE
Seeds are crucial not only because they are food; they are also a primary means of plant propagation. We return to the study of seeds in Chapter 9 as the means by which improved varieties are distributed and how we make sure that farmers receive “certified” seeds. In addition to seeds, some improved varieties are propagated as cuttings, grafting, or other vegetative means including tissue culture, all of which are described in Chapter 9. Chapter 10 deals with the difficult questions of proprietary plants and patented seeds. Why do private companies that create new varieties of fruits or genetically engineered seeds not allow farmers to freely distribute the progeny? What are the legal bases for this proprietary status? Who owns the genetic resources of the world?
The next five chapters deal with the many very real problems encountered by farmers. These include keeping soils fertile and fighting weeds, diseases, and pests, as well as coping with the abiotic effects of extreme temperatures, droughts, and floods, to name a few. Chapter 11 discusses the soil as an ecosystem and a renewable resource. What are the components of a fertile soil, and how do these components interact with one another? How are the major nutrients such as nitrogen and phosphate used by crop plants, and how do they cycle in the soil ecosystem? Chapter 12 discusses weed management—an enormous problem in all agricultural systems—and emphasizes the danger of relying entirely on crops that are genetically engineered to resist weeds. Chapter 13 covers plant diseases caused by viruses, bacteria, fungi, and oomycetes, and discusses how understanding the mechanisms of these diseases can be used to breed more durable resistance into crops. Insects and nematode pests that consume or otherwise destroy plants are discussed in Chapter 14, and once again we stress how understanding biology can be applied to controlling crop losses. Abiotic stresses such as drought, floods, acidic soils, and soil salinity are the subjects of Chapter 15, which also describes examples of how crops are being bred to mitigate those stresses.
Chapters 16 and 17 provide two perspectives on some of the important crop-plant traits that have been introduced in the last two decades by markerassisted selection and genetic engineering. In Chapter 16, the emphasis is on traits that primarily benefit farmers and the food production and processing industry. In Chapter 17, the traits described primarily benefit consumers. We are aware that these are just a few examples, and that within a few years many more such examples will be available for classroom discussion.
How do we know the food we buy is safe to eat? This is the question addressed in Chapter 18. How do governments assess and regulate the safety of the food supply? Given the extensive public discussion and concern over this issue, the chapter places great emphasis on genetically engineered crops and the evidence that they are safe for human and animal consumption.
Although large “factory farms” dominate food production in the 21st century, millions of subsistence farmers cultivate just a few hectares, and increasing their productivity is a pivotal key to eliminating food insecurity. Chapter 19 spotlights the contributions these smallhold farms make to feeding the human population. What are the specific problems of increasing smallhold productivity and reliability, and how might these problems be addressed sustainably?
For centuries, various biochemical compounds produced by plants have been sources of both medications and stimulants. As demand for these products increases, harvesting them from plants growing in nature becomes less
PREFACE xxi
feasible in the long term, and the idea of “green factories” for making these chemicals has emerged. Two chapters view plants as production platforms for specialty chemicals (usually small molecules; Chapter 20) and for biologics (large-molecule compounds such as therapeutic proteins; Chapter 21). These are fast-developing fields, unrelated to conventional agriculture and food production, but very much a part of sustainability.
The final chapter attempts to summarize what needs to happen to feed the world, and to put that summary in a context of sustainability.
Acknowledgments
We thank the many people who made this book possible, especially the authors who contributed chapters and responded so enthusiastically to our call for a uniquely readable and up-to-date synthesis of these important topics. This is their book, really. We also thank all those scientists who sent us their photographs and other graphic material to include in the book. Most importantly, we thank our colleagues who donated their time to read and review chapters and give us feedback.
Illustrations are the lifeblood of today’s science textbooks, and we appreciate the efforts of photo researcher Mark Siddall and artist Jan Troutt and their contributions to the book’s remarkable illustration program. We also thank Michele Beckta for her Herculean work in verifying sources and confirming permissions for all the illustration material. We are grateful for the professionalism and diligence of Chris Small, Beth Roberge Friedrichs, and the entire Sinauer/Oxford production staff.
Research scientists generally are not used to writing for beginning undergraduates, and we are very grateful to David Sadava and Hanya Chrispeels for their help in transforming what we and the other authors submitted into a text that we have attempted to make accessible to any motivated reader, whatever their scientific background. However, by far the greatest accolades must go to Carol Wigg, the outstanding development editor at Sinauer/Oxford. Her diligence and professionalism far exceeded anything that anyone writing a book like this one could expect. If you like this book, thank Carol Wigg.
And finally, we thank Rachel Meyers and Andy Sinauer for having faith in us and believing that we could deliver a quality product.
Maarten Chrispeels La Jolla, California
Paul Gepts Davis, California
xxii PREFACE
Sustainability through Biotechnology & Genes Agriculture Plants,
Chapter Outline 1.1 Hunger and Malnutrition Persist in a World of Plenty 4 1.2 Human Population Growth Is Slowing 6 1.3 By How Much Does the Food Supply Need to Increase to Satisfy Future Demand? 9 1.4 Agriculture Must Become More Sustainable in the Future 11 1.5 An Uncertain Climate Presents Challenges to Food Production 13 1.6 Urbanization and Rising Living Standards Are Changing the Demand for Agricultural Products and the Way They Are Brought to Market 16 1.7 Government Policies Play Pivotal Roles in Global Food Production 19 1.8 Agricultural Research Is Vital If We Are to Maintain a Secure Food Supply 20 1.9 Can Other Agricultural Methods and Policies Contribute to Feeding the Population? 23 1.10 Biotechnology Is Crucial for the Future of Food Production 27
The Human Population and Its Food Supply in the 21st Century
Maarten J. Chrispeels and Hanya E. Chrispeels
A visit to a grocery store in a metropolitan area in a rich country reveals aisle after aisle of food—fruits, vegetables, meat, dairy, baked goods, frozen foods, drinks, spices, and thousands of pre-packaged, ready-to-eat foods. A typical grocery store in the United States carries over 40,000 items in an incredible variety of choices. With all the bounty on display, it may seem impossible that feeding the world’s population would be a problem. Yet the world faces the enormous dual challenges of addressing existing food insecurity— defined as either a lack of available food or a lack of resources to buy or trade for it—and increasing food production to meet the needs of a growing population with increasing economic resources and expectations.
The concept that the human population might outstrip food production was formally laid out in 1798, when Thomas Malthus, a political economist and minister of the Church of England, published An Essay on the Principle of Population. In his essay, Malthus stated that, unless kept in check, the human population would increase faster than the world’s food supply. He predicted at that time that a major crisis was just a few decades away unless society took drastic steps to control population growth. Although he was incorrect in his timing, Malthus raised awareness of the need to balance the population size with food resources.
In the past 100 years there has been impressive progress in providing the human population with an assured supply of food through increased production (more food per hectare area per year) and trade (for example, the US began exporting food to Russia, China, and many other countries). To be sure, major famines, mostly the result of wars, have not been eliminated. However, the number of food-insecure people has dropped steadily in the past 50 years and diets in many parts of the world have improved. But progress is not as fast as we would like, and we are not entirely sure that the food production systems currently in place are sustainable into the future.
food insecurity Refers to a lack of available food and/or a lack of resources to buy or barter for it.
CHAPTER 1
The challenge of feeding the world of the future has at least three important facets:
1. Feeding everyone at current levels will require a 70% increase in available calories in our crops by 2050. We must continue to strive to end existing food insecurity, which is primarily a matter of complex policies in developed and developing countries rather than supply. At the same time, we must increase food production (overall amount produced, e.g., tons of wheat/ yr) and crop productivity (food produced per unit area per unit time, e.g., tons of wheat/ha/yr). The world’s population is not only increasing, but in many countries also becoming more economically secure. People with an adequate food supply and more money to spend on food often change their diet, especially to include more meat.
2. We must protect the environment so food production is sustainable. Almost by definition, crops are grown on land which has been fundamentally changed. And growing itself also changes the environment: for example, plants remove substances from the soil and may allow insect pests to multiply. Activities such as deforestation and overuse of water resources to grow crops cannot continue indefinitely. Sustainability needs to be achieved in a world with a changing and unpredictable climate.
3. To eliminate food insecurity in poor countries, economic development and agricultural investment are needed. When governments help farmers by investing in roads, markets, and the resources needed to grow crops, farmers have an incentive to grow crops, and more food becomes available to citizens.
1.1 Hunger and Malnutrition Persist in a World of Plenty
In 2001, the United Nations defined food security as existing “when all people, at all times, have physical, social and economic access to sufficient, safe and nutritious food that meets their dietary needs and food preferences for an active and healthy life.” While there has been great progress in the past 25 years, about 800 million people, or about 11% of the 7.5 billion people on Earth, are still food-insecure (Figure 1.1). The major reason for food insecurity is poverty caused by a lack of gainful employment, not that there is not enough food produced in the world. Poverty has a twofold, circular effect: poor people cannot afford to buy existing food, and when people do not have money to buy food, local farmers have no incentive to produce it or bring it to market. Poverty is not the only reason for food insecurity, however. During the last 25 years the global gross national product (GNP) has seen an annual increase of 3.6%, cutting the poverty rate substantially. However, food insecurity decreased at only half that rate, showing the complexity of this interrelationship.
Food insecurity is not limited to developing countries but is also widespread in countries that produce plenty of food. For example, in the United States since 2000, levels of food insecurity and poverty have fluctuated between 12% and 15% of the population—about average for the entire world. The highest rates of food insecurity occur in the states of Texas, Mississippi, and Arkansas. In the US, 90% of the counties with the highest food insecurity are in the South, where average incomes are lower than in other parts of the country and a large
4 CHAPTER 1 T he Human Population and Its Food Supply in the 21st Century
Both the number of undernourished people…
…and the percent of the world’s population that is undernourished are declining.
Note:
proportion of the population lives in rural areas (another risk factor for food insecurity). About one in seven Americans—around 45 million people—relies on food banks and food kitchens on a daily basis. The principal reasons for food insecurity in the US are low wages, unemployment or underemployment, and an insufficient social safety net for those with no or low income, especially single-parent families.
In developing countries, many food-insecure people are subsistence farmers living in small villages, but food insecurity is also widespread in cities. Food insecurity in cities is related primarily to a lack of gainful employment (especially for women) and inadequate public food distribution systems. A study of food insecurity in India, published in 2010 by the Swaminathan Research Foundation, showed that “about half the women in urban areas are estimated to be anemic, and under-nutrition among women, indicated by chronic energy deficiency, is increasing. Despite rapid economic growth since the early 1980s, and especially since the 1990s, the access and absorption indicators of urban food insecurity tell a dismal story of relatively little improvement in nutritional intake and worsening in terms of livelihood insecurity.” The Swaminathan study also concluded that the situation was worse in small and medium-sized towns compared to large cities.
In rural areas, broad-based agricultural and infrastructure development is needed to alleviate food insecurity. Farmers on small rural farms face the many obstacles that affect all farmers—including the weather, insect pests, and plant diseases—and if there are no roads, no public transportation system, and no markets at which to sell their crops, then they have no incentive to grow more, because the lack of infrastructure means they will not be able to sell their extra produce. Rural development makes it possible for farm families to raise crops and to have off-farm employment. Governments and private industry can play a role to ensure that rural farmers have access to the resources they need for crop production and the sale of what they produce. This includes both infrastructure, such as irrigation canals and roads; and legal and financial systems, such as access to bank loans and land tenure laws that are equitable and do not discriminate against women or poor people (who may be illiterate).
1.1 H unger and Malnutrition Persist in a World of Plenty 5
Chrispeels Plants, Genes, and Agriculture 1E Sinauer Associates Troutt Visual Services Chrispeels1E_01.01.ai Date 02-28-17 Number of food-insecure people (millions) Percent undernourished 1990–92 2000–02 995 939 893 863 827 23.6% 18.8% 16.7% 15.5% 14.3% 795 12.9% 2005–07 Years 2008–102011–132015 300 0 500 400 700 600 1100 1000 900 800 5 0 15 10 25 20 45 40 35 30
I added horizontal grid lines since both side axis tics aligned.
Figure 1.1 Changes in the total number of food-insecure people in the world for the period 1990–2015. (After FAO 2015, 2013.)
Green Revolution Refers to the dramatic increase in the productivity of rice, wheat, and corn in developing countries, especially Mexico, Brazil, India, Pakistan, and the Philippines. Beginning in the late 1940s, it was the result of (1) improved crop varieties developed from known principles of genetics and plant breeding, and (2) the application of inputs such as fertilizer and irrigation.
Progress has been made in decreasing the number of undernourished people in the past 25 years, especially in Southeast Asia. The greatest concentration of undernourished people is now in sub-Saharan Africa, where agricultural development has been slow and population growth is high. Environmental degradation—notably soil salinization, overgrazing, and soil erosion caused by logging—is making it increasingly difficult for people in this region to produce sufficient food consistently, a situation that may become worse as climate change makes the weather even less predictable (see Section 1.5).
Lack of education can be another cause of undernutrition. If most children in a village are stunted in their growth due to inadequate food intake, parents may not even realize the cause because there are no healthy children for comparison. It may not occur to the parents that the food they are providing is insufficient. Nutrient deficiency is often a side effect of food insecurity. As many as 2 billion worldwide suffer from specific nutritional deficiencies such as insufficient vitamin A, iron, or zinc. Lack of sufficient amounts of vitamins and minerals can lead to increased risk for certain diseases, and can cause reduced physical and mental development in children.
Even without factoring in the projected increase in population, addressing the present food insecurity is a significant challenge. Given the different causes of food insecurity and the different locations where it occurs—urban versus rural, developed versus less developed countries—different strategies will be needed to combat it. Some solutions are more sociopolitical than purely agricultural. However, some of the strategies for solving food insecurity are similar to those needed to increase agricultural production.
1.2 Human Population Growth Is Slowing
How many people will there be in the year 2100? Making predictions about the future size of the human population and its relationship to the food supply is challenging. Malthus was wrong about long-term trends in human population growth; he could not have foreseen that in the 21st century a majority of families in developed countries would have two, one, or no children. In the 19th and 20th centuries the human population did rise very rapidly. In fact, in 1968, Paul Ehrlich, a Stanford University professor of ecology, published a bestseller entitled The Population Bomb. He predicted that millions would die of starvation in the 1970s and 80s because of excessive population growth. At the time Ehrlich was writing, the Green Revolution, which raised food production substantially in developing countries, was in full swing, but birthrates had not yet declined. Since 1970, birthrates have declined and are continuing to decline and food production continues to increase at a steady pace.
The human population in 2017 stands around 7.5 billion and is increasing. The global population doubled between 1960 and 2000, going from 3 billion to 6 billion ( Figure 1.2 ). That is a doubling time of 40 years. If it happens, the next doubling—to 12 billion—is expected to take at least 200 years. The United Nations (UN) calculates projections for the future human population based on historical estimates of population size as well as fertility (the number of children a woman has) and mortality trends. For the year 2050, the UN’s low projection is 8.1 billion, the middle projection is 9.6 billion, and the high projection is 10.4 billion. Currently, the world population is growing by 80
6 CHAPTER 1 T he Human Population and Its Food Supply in the 21st Century
9 billion (2041, projected)
8 billion (2024, projected)
7 billion (2011)
6 billion (1999)
5 billion (1987)
4 billion (1974)
3 billion (1959)
2 billion (1927)
1 billion (1804)
12332151312121713
180018501900195020002050
million people each year. To put this number in perspective, Germany and Iran each has about 80 million people, and the five boroughs of New York City are home to about 8.2 million people (picture almost 10 New York Cities added to the planet each year).
Just 15 years ago, demographers predicted that the global population would probably stabilize by 2100, but now they are not so sure. If fertility in subSaharan Africa remains high, the global population may continue to climb into the 22nd century. The UN’s middle projection estimates an increase of 30–35% by 2050, but not all regions of the world are projected to increase to the same extent (Figure 1.3). Most of the increase will occur in Africa and Asia (which includes India). On the other hand, Europe’s population will remain the same or possibly decrease, depending on immigration trends. The population of Russia has been declining since 1991 at a rate of 0.5% per year. There are also big differences within continents. In Asia, Japan’s population is declining and will continue to decline, while India, which currently has 1.25 billion people, could become the most populous country on Earth by 2028, according to new UN projections.
China is currently the world’s most populous country, with 1.4 billion people, and it is uncertain how its population growth rate will change in the future. Over the years, China’s government has implemented multiple policies to regulate its population growth. Between the 1940s and the 1970s, the population approximately doubled, due in part to encouragement from the Maoist government for women to have large families. By the
Figure 1.2 Growth of the human population since the year 1800. The graph shows how long it took to add each additional billion people. Today the population stands at approximately 7.5 billion. The eighth billion is expected to take 12–13 years, after which the rate of increase is expected to slow. (After United Nations Population Division 1999.)
Figure 1.3 Projected increases in population in each world region between 2015 and 2050 according to the middle projection of the United Nations. Most of the change will occur in Africa, where female fertility is still high. (Data from United Nations Population Division 1999.)
1.2 Human Population Growth Is Slowing 7
Chrispeels Plants, Genes, and Agriculture 1E Sinauer Associates Troutt Visual Services Chrispeels1E_01.02.ai Date 10-16-17
Population
The distance between dashed lines represents the number of years to add 1 billion people.
(billions)
3 5 4 2 1 7 6 10 9 8 Year
Population (billions) 2015202520352045 Year 2055 Asia Africa Europe Latin America/Caribbean USA/ Canada Oceania 3 0 5 4 2 1 6
fertility rate
The average number of children born to a woman of childbearing age (15–44).
1970s, it was feared that the economic growth would be unable to keep up with the large population growth, and in 1980 the Chinese government implemented a one-child-per-couple policy in an effort to limit population growth. Although there were exceptions for certain groups, approximately 65% of the population was subject to the one-child restriction. The rate of China’s population growth did decrease after this policy was put into effect. In 2015, the government announced an end to the one-child policy, replacing it with a policy that would allow two children per family, because of fears that the aging population would not be able to maintain the country’s economic growth. Despite the lifting of the restrictive policy, economic and social factors may prevent many married couples from having more than one child. Thus an immediate effect on China’s rate of population growth is not expected from the change in policy. Demographers predict that China’s population will peak in 2030, just one year later than if the one-child policy had remained in effect.
While China’s one-child policy was successful at controlling population growth, other Asian countries such as North Korea, South Korea, and Thailand, have achieved a similar result without such a restriction, so other factors may be influential in reducing population growth. The fertility rate—the average number of children a woman is expected to have in her lifetime—has been steadily declining in many developed countries since the middle of the 20th century. Two important factors are (1) the desire of parents to have fewer children, and (2) the availability of affordable family planning options and education about their use.
Bringing down the rate of population growth in developing countries has been high on the agenda of the United Nations and other development agencies for several decades. In the 1960s and 1970s, developed countries attempted to lower population growth in developing countries through a supply side approach, by supplying contraceptives and sex education. The thinking was that with contraception, women would have control over reproduction, which would lead to lower birthrates. We now realize that, although access to contraceptives is crucial, their availability does not guarantee a lower birthrate unless there is a desire to have smaller families. The approach of development agencies therefore shifted to include the demand side of controlling births. Economic development coupled with the empowerment of women is now seen as the best way to reduce the fertility rate and slow population growth.
There is a clear inverse (negative) correlation between female literacy and the number of children a woman has, with higher literacy rates correlating with fewer children (Figure 1.4A). According to figures from the United Nations Educational Scientific and Cultural Organization (UNESCO), global female illiteracy declined from 55% in 1970 to just over 30% in 2000. In the same period, the global fertility rate dropped from 4.1 to 2.9 children per woman. We are familiar with this phenomenon in developed countries, but it has also become apparent in Africa and elsewhere in the developing world, and appears to be true irrespective of the major religion of the country.
Why has this occurred? One possible explanation is education. In many developing countries, when a girl reaches puberty she enters the world of adults and is considered by society to be marriageable and ready to bear children. If she stays in school, however, she will be less likely to be married at a young age, and more likely to have employment outside the home. When she does marry, she is likely to have a different relationship with her husband than if she had
8 CHAPTER 1 T he Human Population and Its Food Supply in the 21st Century
1.3 By How Much Does the Food Supply Need to Increase to Satisfy Future Demand?
not had several years of education. She is more likely to control her own fertility and to determine together with her husband how many children they want to have. Thus, educating girls (Figure 1.4B) leads to their empowerment. Unfortunately, many developing countries do not have universal free public education at even the primary school level. Even when a country has such a system, it does not guarantee that children will actually attend school, because they may be needed to help support the family financially. In many countries, educational opportunities are strongly tied to economic status. If education costs money, parents generally favor boys over girls.
Multiple United Nations conferences dealing with the status of women have stressed the need to increase investments in the education of girls, to encourage practices that lead to the postponement of the first pregnancy, and to provide opportunities for women other than child bearing and child rearing. Education and empowering women may satisfy our sense of social justice, but does it also help to reduce population growth? Indeed it does. Educated women who are employed outside the home are in control of their own fertility. They decide—in agreement with their partners—when to become mothers and when to wait.
1.3 By How Much Does the Food Supply Need to Increase to Satisfy Future Demand?
Each data point represents a different country.
The average number of children a woman has decreases from 7 to 1.2 as the percentage of girls in secondary school rises from 5% to 95%.
Figure 1.4 (A) The effect of a woman’s education on the number of children she has. The graph shows the relationship, for individual countries worldwide, between the percent of girls enrolled in secondary school and the country’s fertility rate. (B) Young women in school in the Mideast. (A, data from the Earth Policy Institute 2014; B, © UN Photo/Eskinder Debebe.)
Although population growth is slowing, the world’s population is still increasing, and we will need to produce more food to ensure food security for all. Between 1950 and 2000, when the human population more than doubled, the supply of food increased even more rapidly. This is an amazing achievement, and is the opposite of what Malthus had predicted. Hundreds of millions of people were lifted out of poverty and were able to produce or purchase sufficient food for a healthy life. This Green Revolution was possible because (1) plant breeders produced genetically improved varieties of grains, and (2) farmers adopted new agricultural technologies including improved irrigation, fertilizers, and pesticides that enabled them to get the most out of the new varieties. Governments encouraged these changes in agricultural practices
grains As used here, refers to the major crops on which humans and their livestock depend. Broken down as two small grains—wheat and rice—and what are referred to as coarse grains, including corn, sorghum, and oats. The US Department of Agriculture also considers soybeans to be a grain.
9
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Troutt Visual
Fertility rate 0 20 40 60 80100 Percent of girls enrolled in secondary school 2 1 4 3 8 (A) (B) 7 6 5
Chrispeels Plants, Genes, and Agriculture
Associates
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Figure 1.5 Per capita demand for meat products, 1995–2020. Meat consumption is highest in developed countries but the growth and projected growth is modest. Meat consumption in China (included in the numbers for “East Asia”) has been growing rapidly and will continue to do so. Since China has more than a billion people, this growth accounts for the lion’s share of the growth in world demand for meat products. (After PinstrupAndersen et al. 1999, with permission of the International Food Policy Research Institute. Original figure at www.ifpri.org/ publication/world-food-prospects-0.)
by providing subsidies. On a global scale, food is now cheaper, safer, and more widely available than ever before in human history. Can this continue? Should we be optimistic or pessimistic about the future of food?
Forecasting future food needs is just as difficult as projecting the future population. The expected increase in the human population by 2050 (30–35%) presents us with a double challenge. First, food production has to increase by at least that much. Additionally, there is the burden of increased expectations. Affluence in our globalized economy has resulted in rising incomes for many people in populous countries such as China, India, Brazil, and Mexico. As people have more money and can buy food beyond just getting enough to survive, they usually want to eat a more diversified diet, including more varieties of fruits and vegetables, more dairy and meat products, and more processed foods (this scenario will be familiar to people in developed countries). Producing animal products requires growing corn and soybeans to feed the animals rather than growing staple grains (e.g., wheat and rice) and other starch crops that people eat directly. Meat consumption in mid-development countries like China has been increasing rapidly (Figure 1.5). In China, this increase in meat consumption parallels the import of soybeans from the US, Argentina, and Brazil (see Figure 2.3). Protein-rich soybeans are essential in the formulation of animal feed.
past 50 years.
Figure 1.6 World yield of wheat, rice, and corn (arithmetic average) and the annual relative yield increase between 1960 and 2010. Grain yields now stand at 4.2 tons/hectare and have been increasing for 50 years at a rate of 52.6 kg/hectare. (Data from FAOSTAT 2013; after Fischer et al. 2014.)
Taking these trends into account, the Food and Agriculture Organization (FAO) of the United Nations projects that demand for grains will increase by 44% by 2050. The greatest expected increase is for soybeans (80%) and corn (60%), most of it to feed animals. Indeed, by 2050 animal feed production is projected to increase by 70%. Projected increases for wheat (40%) and rice (28%) are lower, in part because diets are changing and also because the population increase of Southeast Asia, the largest rice-eating area of the world, has slowed considerably. These figures may be underestimates, with some studies suggesting a 100% increase for demand for grains over the next few decades.
Can farmers produce enough food to meet the projected demand? One way to estimate this is to look at how farmers have been doing recently. The data show that the increase in the grain production has increased linearly since 1960, with an annual increase of just over 52 kg/ha/yr ( Figure 1.6 ).
10 CHAPTER 1 T he Human Population and Its Food Supply in the 21st Century
Chrispeels Plants, Genes, and Agriculture 1E Sinauer Associates Troutt Visual Services 0204060 Per capita meat consumption (kg) 80100 Latin America Developed countries Southeast Asia East Asia South Asia Sub-Saharan Africa West Asia and Northern Africa 64.3 85.3 26.5 63.7 8.5 11.2 26.4 As of 1995 Increase, 1995–2020 Grain yield (tons/hectare) 196019701980199020002010 Year 0 1.5 1.0 0.5 2.5 2.0 4.5 4.0 3.5 3.0
World yield of the three major grains (corn, wheat, and rice) has increased linearly over the
Given that the average of grain production in 2010 was about 4.2 tons/ha, we could expect an increase of 2.08 tons per hectare by 2050, or about 50%—a bit more than the 44% projected by the FAO. This projection suggests that if we can stay on the present trajectory, using current methods of plant breeding and agricultural technology, we can probably feed the future human population. But remember, just producing enough food does not eliminate food insecurity. People need to have the food available and affordable.
Agricultural scientists develop and test new crop varieties on experimental farms, under carefully controlled environmental conditions, and using the best practices of soil management, irrigation, fertilizer enrichment, and pesticide application. It is not surprising that in the “real world,” farmers get lower yields of food than do the managers of these experimental farms. The difference between optimal crop yield and actual yield is called the yield gap Raising yields worldwide requires an analysis of the reasons for the yield gap in each production area (country or region) for each of the major crops. For example, the current wheat yield in France is 8.6 tons/ha, in Kansas 2.8 tons/ha, and in Western Australia 1.7 tons/ha. These are the actual yields obtained by farmers using good farming practices and all technologies they can afford. What would be the potential yield in each of these areas if we eliminated all the constraints on production given present day technologies? Would they be the same? The three areas have very different climates and soils, so their potential yields are not the same. In France, the current potential yield for wheat is calculated to be 10.8 tons/ha, so the shortfall or yield gap is 2.2 tons/ha, or 26%. For Western Australia the yield gap is 45%; for Kansas it is 36%. “Eliminating the constraints” means using the best wheat varieties, applying optimum amounts of fertilizer, using the most effective pest control procedures, and using irrigation when needed. These practices, of course, are easier to carry out in developed countries with modern agricultural systems. Countries in sub-Saharan Africa have the lowest crop productivity, the largest yield gap, and the highest birth rates. Improving agricultural productivity in Africa is therefore an absolute must if we are to bring population and food into balance. Although closing the yield gap in developing countries is more challenging than in developed countries, it has the potential to have a larger impact on increasing food security.
1.4 Agriculture Must Become More Sustainable in the Future
Modern agricultural techniques are essential for feeding the world’s population. But by definition, a farm is ecologically disruptive. Cutting down a forest or plowing up a prairie and replacing these with fertilized, irrigated, and pesticide-treated fields means replacing natural ecosystems with an artificial one. After the crop is harvested, the ecosystem has been changed (e.g., crop plants use up the nutrients in the soil and these are removed when the crop is harvested). Even sustaining the conditions of the field for optimal crop growth in subsequent years is a challenge. In addition, the farming process itself is environmentally destructive. Agriculture uses up fresh water from rivers, aquifers, and other sources. It applies chemicals that pollute groundwater, rivers, and oceans, and releases large amount of greenhouse gases that contribute to climate warming.
yield gap The difference between the potential crop yield achievable under optimal conditions and the yield actually achieved by farmers.
1.4 Agriculture Must Become More Sustainable in the Future 11
