World Food Production and Sustainable Agriculture

Summary

Boyce Thompson scientists are making significant contributions to our understanding of how plants grow, how they ward off pests and disease, how they respond to light, how they extract and use nutrients naturally present in soil for their own benefit, and how they produce food nutrients for people. Knowledge generated at BTI may have direct applications for enhancing world food production and making agriculture more sustainable.

The development of hybrid seed, chemical fertilizers and pesticides, and mechanization in agriculture have more than doubled yield on existing acres in our lifetimes. This is an impressive statistic, but increasing world population, drought and other natural factors continue to result in a need for even higher rates of production. Further, increasingly intensive agriculture has exacted a steep environmental price: Soil erosion, run-off of nitrate and phosphate fertilizers, and wide-spread use of broad spectrum chemical pesticides are a serious threat to the quality of the world’s soil and water and to its biodiversity. One way to increase yields and make agriculture more sustainable is to use nature’s own methods developed over millions of years of evolution. But to use nature’s methods, scientists must understand them at the molecular level, which is the role of BTI’s scientists.

The Issue:

• 800 million people in the world currently suffer from hunger and malnutrition.
• Food prices have risen 83 percent in the last three years alone, and soaring food prices could soon push as many as 100 million more people into hunger (World Bank).
• World food production must increase 50 percent by 2030 to meet increasing demand, according to U.N. chief Ban Ki-moon.
• Food stocks are at their lowest in 25 years.
• Every 3.6 seconds someone dies of starvation.

The issue is obvious: The world must produce significantly more food in the future than it does today. The solution is not so obvious because, to meet the world’s need for food, we must increase production by at least another 50 percent over the next 22 years without further negative effects on the environment. Discovering knowledge that will help accomplish this feat is a major goal of research conducted at BTI. Following are a few of the potential, practical impacts of our work.

Potential Impacts

Increasing food supplies by increasing shelf life

If food stayed fresh longer, there would be more of it available for local consumption and for transport to distant markets. This is particularly true in developing countries where the lack of infrastructure impedes timely delivery and where refrigeration is scarce. Making nutritionally valuable, but perishable, fruits and vegetables last longer by controlling the ripening process could effectively increase the availability of these foods for those who need them most.

BTI scientist Jim Giovannoni, Ph.D., is learning how to control ripening in fruit by studying the process in tomatoes. Tomatoes and many other fruits ripen in response to the production and release of a plant hormone, called ethylene. Making fruit less sensitive to ethylene would delay ripening, while making it more sensitive would cause it to ripen more quickly. Identifying the genes that control this sensitivity to ethylene and understanding the regulation of the process are two of Giovannoni’s research objectives. His laboratory also is interested in understanding the events that lead to the production of ethylene in the fruit, and identifying other aspects of ripening that are not controlled by this hormone.

So far, he has discovered a gene, aptly named Greenripe or Gr, which causes the plant to produce a certain protein in its fruit that reduces the fruit’s sensitivity to ethylene. Making the plant under- or over-produce this protein could speed or delay ripening. He also discovered that the fruit is the only part of the plant that responds to ethylene, proving that genetic constituents specific to the fruit interact with the hormone to create the ripening response.

Giovannoni’s team recently discovered a second gene, called greenflesh (gf), that produces another protein important to the ripening process. When the gf gene is inhibited from producing the gf protein, fruit ripening is delayed along with a certain process associated with photosynthesis. The end result is that the fruit ripens slowly to a dark brown color instead of the usual red. Giovannoni also showed that the gf gene is naturally inhibited in pepper varieties, called “chocolate” peppers, that are dark brown in color. Understanding how Gr, gf and other ripening regulator genes interact will facilitate ways to genetically inhibit or accelerate ripening as desired.

The Giovannoni lab is currently identifying additional ripening and nutrient regulatory genes. As interesting candidate genes are identified, they will be assessed for their normal roles in ripening. This will be done through the creation of transgenic test plants in which the genes are altered to see how such alterations impact ripening and fruit quality.

Though Giovannoni’s team focuses primarily on tomatoes, they also are studying ripening in strawberry, melon and banana – research that may have important applications in these and other fruits and vegetables. Extending the shelf life of these foods is only one possible application of Giovannoni’s work. Because fruit flavor, texture and nutrient content are directly related to ripening, his discoveries may also lead to production of higher quality food.

Sustainable agriculture in spite of global warming

Global warming will bring a double whammy when it comes to crop damage from insect pests. First, winter temperatures will increase, so there will be more insects to contend with. Second, each insect will need to eat more, causing crop yield losses to escalate.

Rising carbon dioxide (CO2) levels are the reason for both. Insects flourish in warm climates – that’s why there are more of them in the tropics than in the temperate zone. Worse, scientists studying fossil plants from the last major climate change say that increased CO2 will cause plant leaves to contain less protein, which is nutritionally important for insects. So, even though plants will grow faster when CO2 levels rise, each insect will need to eat more of each plant to survive. These scientists predict a disproportionate increase in crop damage just at the time when we’ll need much more food to feed the extra three billion people who will be living at the end of this century.

Given that using more pesticides is not the answer, what can be done to combat the insects and increase production in a sustainable way? One solution is to use nature’s own methods of protecting plants from insects, and that’s the goal of two BTI research projects.

• Using naturally occurring viruses that kill insects is one option being studied by Gary Blissard, Ph.D. His work on baculoviruses could lead to a new way to control pests without using chemicals. Baculoviruses are expert at entering insect cells, depositing viral DNA there that kills the cell, multiplying, and then leaving the cell in a cycle that eventually kills the insect. Understanding exactly how this viral infection process works at the genetic level could enable scientists to improve the virus’ insect control capabilities. Another plus is that baculoviruses are specific to the insects they infect and they do not infect mammals, birds or even other insects. Because of this, using baculoviruses for pest control would be safer for humans, animals and the environment than chemical pesticides.
• Another way to approach the insect pest problem is to better understand how plants naturally protect themselves from insects and then enhance this capability in crops. To that end, Georg Jander, Ph.D., is studying certain chemicals, called glucosinolates, that plants produce in response to insects. Glucosinolates help the plant recognize that insects are feeding on it, and they are important for plant self-defense. Using white cabbage butterflies and Arabidopis plants as a model system, Jander found that glucosinolates have two different effects on the insects: One form of the molecule deters the butterflies from laying eggs on the plant’s leaves, effectively reducing the damaging caterpillar population on the plant; the other form is converted in the caterpillar’s gut (after the caterpillar eats a portion of the plant) into a molecule toxic to the insect. Which form of glucosinolate the plant produces seems to depend on the plant’s habitat and the prevalent insect threat.
• Jander also found that feeding by green peach aphids causes Arabidopsis plants to develop a more toxic chemical profile, and that plants that had previously been infested with the aphids were more resistant to subsequent insect attack. More study is needed to fully understand this self-protection mechanism in plants, but Jander believes it has positive implications for future natural insect pest control.

Boosting plant immunity to disease

Worldwide crop losses due to plant diseases amount to billions of dollars each year because infected plants yield less, and the problem is getting worse. For example, the loss of soybeans from disease in 1994 in the U.S. Sunbelt amounted to $266 million, according to official estimates. But by 2002, U.S. soybean farmers experienced epidemics of soybean sudden death syndrome, and various viral diseases, that cost them nearly $2 billion dollars.

Because the majority of plant diseases are caused by fungi or by viruses carried by insects, chemical fungicides and pesticides have traditionally been used to control or reduce diseases to increase yields. At BTI, however, scientists are looking at ways to boost the plant’s natural immunity to disease as a safer, less toxic way to increase production.

• One BTI research group, led by Dan Klessig, Ph.D., has made major discoveries about how plants acquire systemic immunity to a disease when only a small portion of the plant, say one leaf, has been infected. He recently found a molecule that acts as a messenger: It carries a signal from the infected site on the plant to distant plant tissues, which mobilizes the plant’s defense system in those tissues. He and his team have explained how this phenomenon works at the molecular level – knowledge that will one day assist scientists in making this natural defense system work better or more quickly in crop plants.
• Peter Moffett, Ph.D., is attacking the disease problem in another way. He knows that all plants have a repertoire of disease resistance genes, each of which recognizes a specific virus, bacterium or other disease-causing organism (pathogen). When this recognition occurs, the gene triggers the production of unique proteins that protect the plant from the disease. He’s working to understand exactly how the gene recognizes the pathogen at the genetic level, and he and his team have made significant advances in unraveling the process. The knowledge he gains may enable scientists to adjust a plant’s defense system to mobilize against a pathogen it couldn’t previously recognize, or to transfer naturally occurring resistance to a particular disease from one plant to another.
• In an opposite approach, Gregory Martin, Ph.D., and his research team are working to understand how plants lose their natural resistance to a disease by studying the relationship between certain bacteria and the plants they infect. It’s a plant/bacteria arms race, and understanding it at the molecular level could have significant positive applications in agriculture. The bacteria Martin is studying, which cause speck disease in tomatoes, have evolved a way to sabotage the plant’s normally effective defense system. Discovering exactly how the bacteria accomplish this feat at the genetic level is one of Martin’s research goals. The knowledge he contributes could lead to crops that yield more because they have more effective, longer lasting resistance to disease.

Here comes the sun

As any gardener knows, some plants require more sunlight for optimal growth and flowering than others. Farmers know that to yield their best, crop plants require full sun, all day. In fact, just the minimal shade cast by its neighbors or shorter days can reduce a crop plant’s yield. Sunlight is important not only because plants use light to carry out photosynthesis, but because all plant growth and development is dependent on the plant’s physiological response to light.

Understanding how plants “see” and respond to light has been an enduring scientific mystery –one that BTI’s Haiyang Wang, Ph.D., is working to explain. His discoveries could lead to ways to fine tune a plant’s response to light – an ability that could increase the plant’s tolerance of shade from its neighbors or enable it to grow in places where the days are shorter.

Wang is studying how plants sense and respond to a particular wavelength of light, called far-red, which is the wavelength of light that predominates at sunrise and sunset. When light falls on a plant leaf, special receptors in the leaf’s cells “see” the light, meaning that the light activates certain molecules in the cell. These molecules then move into the cell nucleus where they tell the plant’s genes to respond. The color of the light, it’s intensity, direction and duration all influence when, how fast, how tall and in what direction a plant will grow, and when it will flower. For instance, it’s this chain of events that causes all the sunflowers in a field to turn throughout the course of the day so that they always face the sun.

Discovering exactly what causes this chain of events and how it works is the goal of the Wang laboratory. Knowledge gained from this research could increase food production by enabling farmers to grow more plants in a single field or to grow plants in climates where they couldn’t be grown before.

Natural nourishment from the soil

According to the U.S. Department of Agriculture, four million tons of mineral phosphate fertilizers are applied each year in the U.S. alone to enhance plant growth. Phosphorus is a primary ingredient in lawn and agricultural fertilizers. It promotes greener, thicker grass and higher crop yields, but it has a dark side: Soil erosion and other factors can cause phosphorus run-off into lakes and streams, which can kill fish and cause harmful algae blooms. Mined phosphorus is also a non-renewable resource, which is rapidly running out.

The good news is that the majority of plants can access naturally occurring phosphorus from the soil due to a very special symbiotic relationship with certain types of soil fungi. It’s a win-win for both: The plants provide the fungi with essential carbon while, in turn, the fungi provide the plants with phosphorus. Understanding this relationship and how it works at the molecular level is the work of BTI scientist Maria Harrison, Ph.D.

Harrison and others know that the fungi live in close proximity to plant roots and grow on their surface. In response to a signal from the plant, the fungus enters the cells of the root. The plant then forms a specialized structure around the fungus that facilitates the transfer of phosphate from the fungi to the plant. Recently, Harrison proved that certain proteins produced by the plant play a critical role in the ability of phosphate to transfer into the plant’s cells from the specialized structure. There are many different fungi that can establish this relationship with any particular plant, and Harrison discovered that some plant/fungi combinations yield more phosphorus to the plant than others.

Continuing work in her laboratory will further explain this plant/fungi relationship, exactly how the specialized structure facilitates phosphorus transfer, and why some plant/fungi relationships outperform others. What Harrison and her team discover may well enable the production of crop plants that also can enjoy this relationship, which could reduce the use of potentially polluting, non-renewable phosphate fertilizers.