Principles of Plant Genetics and Breeding. George Acquaah
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.
2.2 The “unknown breeder”
Two distinct kinds or groups of people continue to impact plant improvement in significant ways, but with recognition that cannot be personalized.
2.2.1 The “farmer‐breeder”
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‐selected varieties 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.
2.2.2 The “no name” breeder
One of the common practices or traditions in modern plant breeding is to refer to germplasm whose source, name, or breeding history is unknown as simply “No Name.” This casual acknowledgment appears to absolve the breeder of any deliberate and willful infringement on intellectual property. These nameless products are modern‐day examples of cultivars that have fallen victim to improper record keeping.
2.3 Plant manipulation efforts by the early civilizations
Archeological and historical records from early civilizations indicate that some of these communities engaged in rudimentary plant manipulations, albeit in the dark, without knowledge of plant heredity. Whereas it would not be farfetched to assume that, just like farmers of the early civilizations who domesticated crops species would have also continued their selection practices to produce farmer‐selected varieties, evidence of deliberate plant manipulation for the purposes of improvement are few. Archeological findings occasionally reveal some ancient practices that indicate plant manipulation beyond phenotypic selection among natural variability occurred. Babylonians are said to have perceived the role of pollen in successful fruit production and applied it to the pistils of female date palms to produce fruit. The Assyrians did likewise in about 870 BCE, artificially pollinating date palms.
2.4 Early pioneers of the theories and practices of modern plant breeding
Plant breeding as we know it today began in earnest in the nineteenth century. Prior to this era, a number of groundbreaking discoveries and innovations paved the way for scientific plant manipulation. Some of the early pioneers of plant breeding include:
Rudolph CamerariusRudolph Camerarius was a professor of philosophy at the University of Tubingen in Germany. He conducted research that contributed to establishing sexual differentiation, defining the male and female reproductive parts of the plant. His seminal work was published in 1694 in a letter to a colleague, De sexu plantarum (On the sex of plants). Camerarius's work also described the functions of the reproductive parts in fertilization and showed that pollen is required for this key process in heredity.
Joseph Gottlieb KoelreuterGerman botanist, J. G. Koelreuter became professor of natural history and director of the botanical gardens in Karlsruhe in 1764. He was the pioneer in the application of the discovery of sex in plants as a vehicle for their genetic manipulation. He observed that the hybrid offspring generally resembled the parent that supplied the pollen as closely as the parent on which seed was borne. Koelreuter conducted the first systematic experiments in plant hybridization, using the tobacco plant as subject. He recognized the role of insects and wind in pollination of flowers, and also conducted experiments to study artificial fertilization and development in tobacco plants. The golden rain tree genus (Koelreuteria) is named in his honor.
Louis de VilmorinLouis de Vilmorin was a noted French seedsman. His experiments in heredity contributed to our understanding of the cause of variation. Vilmorin conducted studies in plant improvement in vegetables using a method called genealogical selection, which is the modern breeding equivalent of progeny testing. He recognized that one could develop new varieties of plants by selecting certain characteristics which would then be transmitted through genealogy to the progeny. In 1856, he published his “Note on the Creation of a New Race of Beetroot and Considerations on Heredity in Plants,” which laid the theoretical groundwork for the modern seed‐breeding industry. Modern‐day Vilmorin is a major player in the global seed industry, which along with its international subsidiaries is ranked among the top five largest seed companies in the world. The company is also credited with producing the first seed catalog for farmers and academics, among other significant publications.
Thomas Andrew KnightThis British horticulturalist and botanist conducted basic research in plant physiology that led to the discovery of the phenomenon of geotropism, the effects of gravity on seedlings. He also showed how decay in fruit trees was transmitted through grafting. In terms of practical crop improvement, Knight conducted research in the breeding of horticultural plants, including strawberries, cabbages, peas, apples, and pears. The “Downton” strawberry which he developed is noted in the pedigree of most of the important modern strawberries. He is credited with pioneering work in the science of fruit breeding. In 1797 he published Treatise on the culture of apple and pear. Knight is also said to have demonstrated segregation for seed characters of the garden pea, but, unfortunately did not offer an explanation for the event as Mendel eventually did.
Carl LinnaeusA Swedish botanist, physician, and zoologist, Carl Linnaeus