George Acquaah - Principles of Plant Genetics and Breeding

Please answer the following questions true or false:

1 Rice was the first genetically modified food crop.

2 Cereals tend to be low in lysine.

3 Plant breeding is a lengthy process.

4 Plant breeding is needed to support the growing world population.

Please answer the following questions:

1 Define plant breeding.

2 Give three common objectives of plant breeding.

3 Discuss plant breeding before Mendel's work was discovered.

Please discuss in the following questions in detail:

1 Plant breeding is an art and a science. Discuss.

2 Discuss the importance of plant breeding to society.

3 Discuss how plant breeding has changed through the ages.

4 Discuss the impact of plant breeding on crop yield.

5 Plant breeding is critical to the survival of modern society. Discuss.

6 Discuss the concept of “breeder's eye.”

7 Discuss the general steps in a plant breeding program.

8 Discuss the qualifications of a plant breeder.

9 Distinguish between public sector and private sector plant breeding.

10 Discuss the molecular and classical plant breeding approaches as complementary approaches in modern plant breeding.

1 1Professor Eric Yirenkyi Danquah, Dean of International Programmes, University of Ghana (UG);Professor Samuel Kwame Offei, Dean, School of Agriculture, UG, Professor Ronnie Coffman, Director, International Programs, College of Agriculture and Life Sciences (IP CALS), Cornell University; Mr. Stefan Einarson, Director, Transnational Learning, IP CALS.

Agriculture is the deliberate planting and harvesting of plants and herding animals. This human invention has and continues to impact society and the environment. The players on this stage advanced the industry with innovation, technology, and knowledge available to them during their era. The tools and methods used by plant breeders have been developed and advanced through the years. There are milestones in plant breeding technology as well as accomplishments by plant breeders over the years. In this chapter, individuals (or groups of people) whose contributions to knowledge, theoretical or practical, impacted what has become known in the modern era as plant breeding will be spotlighted. After studying this chapter, the student should be able to:

1 List and describe the contributions of some of the people through history whose discoveries laid the foundation for modern plant breeding.

2 Describe the contributions of Mendel to modern plant breeding.

3 Discuss the advances in plant breeding technologies.

In its primitive form, plant breeding started after the invention of agriculture, when people of primitive cultures switched from a lifestyle of hunter‐gatherers to sedentary producers of selected plants and animals. Views of agricultural origins range from the mythological to ecological. The Fertile Crescent in the Middle East is believed to be the cradle of agriculture, where deliberate tilling of the soil, seeding, and harvesting occurred over 10 000 years ago. This lifestyle change did not occur overnight but was a gradual process during which plants were transformed from being independent, wild progenitors, to fully dependent (on humans) and domesticated varieties. Agriculture is generally viewed as an invention and discovery. During this period, humans also discovered the time‐honored and most basic plant breeding technique – selection, the art of discriminating among biological variation in a population to identify and pick desirable variants. Selection implies the existence of variability.

In the beginnings of plant breeding, the variability exploited was the naturally occurring variants and wild relatives of crop species. Furthermore, selection was based solely on the intuition, skill, and judgment of the operator. Needless to say that this form of selection is practiced to date by farmers in poor economies, where they save seed from the best‐looking plants or the most desirable fruit for planting the next season. These days, scientific techniques are used in addition to the aforementioned qualities to make the selection process more precise and efficient. Even though the activities described in this section are akin to some of those practiced by modern plant breeders, it is not being suggested that primitive crop producers were necessarily conscious of the fact that they were manipulating the genetics of their crops.

Two distinct kinds or groups of people continue to impact plant improvement in significant ways, but with recognition that cannot be personalized.

The term “breeder” is a modern‐day reference to professionals who knowingly manipulate the nature of plants to improve their appearance and performance in predetermined ways. These professionals operate with formal knowledge from the discipline of plant biology and allied disciplines. They are preceded by people who unknowingly and indirectly manipulated the nature of plants to their advantage. This category of “breeders” (to use the term very loosely), or “farmer‐breeders,” continues to impact world crop production today. Of course, the image of the farmer today is variable from one part of the world to another. In developing countries, many farmers still produce crops with primitive technologies, while high‐tech defines the farmer of today in technologically advanced countries.

The age‐old practice is for farmers to save seed from the current year's crop to plant the next season's crop. In doing so, farmers depend on their instincts, intuition, experience, and keen observation to save seed from selected plants for planting the next crop. Performance and appeal are two key factors in the decision making process. For example, seeds from a plant without blemish among a plot of others with disease symptoms would be saved because it obviously had “something” that makes it ward off diseases. This may be described as primitive or rudimentary “breeding” for disease resistance. Similarly, farmers may save seed on the basis of other agronomic features of their preference, such as seed or fruit size, seed or fruit color, plant stature, and maturity, and in the process manipulate plant genetics without knowing it. I call this “unconscious breeding.”

Over time, farmers create varieties of crops that are adapted to their cultural environments, the sole technique being the art of discrimination among variability, or selection as it is called in modern crop improvement. These creations are called farmer‐selectedvarieties and sometimes landraces. The practice prevails in areas of subsistence agriculture, which represent many parts of the developing world. These varieties are highly adapted to local regions and can be depended upon by farmers who produce their crops with limited resources. Farmer‐selected seed continues to sustain agricultural production in these parts of the world while the commercial seed supply system is being developed.

Farmer‐selected varieties or landraces are an important source of breeding material for modern breeders. This primitive or exotic germplasm is heterogeneous and is useful for initiating some plant breeding programs.