History of Plant Breeding

Rolf H. J. Schlegel

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781351588959
• Edition: 1
• Topic: Ciencias biológicas
• Subtopic: Botánica

While there has been great progress in the development of plant breeding over the last decade, the selection of suitable plants for human consumption began over 13, 000 years ago. Since the Neolithic era, the cultivation of plants has progressed in Asia Minor, Asia, Europe, and ancient America, each specific to the locally wild plants as well as the ecological and social conditions.

A handy reference for knowing our past, understanding the present, and creating the future, this book provides a comprehensive treatment of the development of crop improvement methods over the centuries. It features an extensive historical treatment of development, including influential individuals in the field, plant cultivation in various regions, techniques used in the Old World, and cropping in ancient America. The advances of scientific plant breeding in the twentieth century is extensively explored, including efficient selection methods, hybrid breeding, induced polyploidy, mutation research, biotechnology, and genetic manipulation. Finally, this book presents information on approaches to the sustainability of breeding and to cope with climatic changes as well as the growing world population.

1	Introduction

In 1994, German archeologists made a sensational discovery in Anatolia. The place is called Göbekli Tepe. It was a Stone Age settlement with monumental buildings, which are three times as old as the first Egyptian pyramids. Parts of the settlement are 12,000 years old and show 50 tons of heavy megaliths. And this happened during the Middle Stone Age, where only hunters and gatherers were suspected. So, who lived here? How the settlement was built. This leaves only one conclusion. There lived settled inhabitants. And they were able to sufficiently feed themselves on that place.

It is not only a coincidence that one can find in the same region the origin of the einkorn wheat, which is a wild form including a fragile spindle of the spike. Geneticists have now shown that in this group of grasses there was a change in a single (Q) gene, which is located on chromosome 5A, in a single plant, which (among other characteristics) caused a firm attachment of the spikelets to the spindle. This sort of wheat could easily be harvested and was suitable for threshing. It was the prerequisite for preparing bread for the people. This spontaneous mutation in einkorn (Triticum boeoticum) can be traced back to the Göbekli Tepe region. The mutation was not beneficial for the evolution of einkorn wheat. It would have a negative selection value. It benefits people, however. As a result, these early settlers must have selected and multiplied the einkorn wheat with tough spindle, that is, Triticum monococcum. They were probably the first plant breeders on earth.

Thus, more than 12,000 years ago, the first husbandmen started to process grains laboriously from wild grasses—a fateful invention. About 6000 years later, this culture arrived in Europe. It was the beginning of global warming after ice times. In favorable regions, for example, the Fertile Crescent, plant growth “exploded,” including cereals, legumes, and others (Table 1.1).

The use of cereal grains made our forefathers less dependent on hunting and collecting. It offered food to more and more people. This way of life was without alternative, considering bigger population of people in villages and an increase in births. At some point in time then it came to cereal cropping with various types of specialization.

The origin of new information on agriculture, horticulture, and plant breeding derives from two traditions: empirical and experimental. The roots of empiricism derive from the efforts of Neolithic farmers, Hellenic root diggers, medieval peasants, farmers, and gardeners everywhere to obtain practical solutions to problems of crop and livestock production. By the way, the Neolithic populations, which colonized Europe approximately 9000 years ago, presumably migrated from Near East to Anatolia and from there to Central Europe through Thrace and the Balkans. An alternative route would have been island hopping across the Southern European coast. Recent DNA studies on humans point to a striking structure correlating genes with geography around the Mediterranean Sea with characteristic east to west clines of gene flow. The gene flow from Anatolia to Europe was through Dodecanese, Crete, and the Southern European coast, compatible with the hypothesis that a maritime coastal route was mainly used for the migration of Neolithic farmers to Europe (PASCHOU et al. 2014). Before 4500 years they approached northern Europe already as farmers (Figure 1.1). Latest findings, based on diagnostic biomarker lipids and δ¹³C values of preserved fatty acids, revealed a transition at nearly 2500 BC from the exploitation of aquatic organisms to the processing of ruminant products, specifically milk, confirming that farming was practiced at high latitudes (CRAMP et al. 2014).

The accumulated successes and improvements passed orally from parent to child, from artisan to apprentice, have become embedded in human consciousness via legend, craft secrets, and folk wisdom. This information is now stored in tales, almanacs, herbs, and histories and has become part of our common culture.

TABLE 1.1
Major Steps in Plant Breeding over 12,000 Years of Development and Continuous Influence by Scientific Achievements

FIGURE 1.1 Distribution of agriculture from Near East to Europe until 5000 BC. (Courtesy of R. SCHLEGEL.)

More that practices and skills were involved as improved germplasm was selected and preserved via seed and graft from harvest to harvest and generation to generation. The sum total of these technologies makes up the traditional lore of agriculture, horticulture, and breeding. It represents a monumental achievement of our forebears.

Without the knowledge about the development of a scientific discipline, nobody is able to judge the recent achievements and to weigh the future chances. Otherwise, one could overestimate the presence too much. The plant breeding does not form any exception at this. Who traces its way back recognizes that the performances and breeding of crop plants are based on centuries- and even millennium-old experiences, such as, for barley (Table 1.1).

Crop plants are a wide and somewhat ambiguous term for many plants grown for food and other purposes regardless of their status as domesticate. The total number of plant species, which are cultivated as agricultural, forest, or horticultural crops, can be estimated to be close to 7000 botanical species. Nevertheless, it is estimated that 30 species only “feed the world” because the major crops comprise a very limited number of species. The basic types of recent crops have arisen this way. Of course, for other crops—such as sugarbeet or triticale—this step cannot be dated back so long. On the other hand, one can follow how some plants will just in the real meaning become cultivated plants (some fodder, ornamental, or industrial crops).

Most of the crop plants are thus the result of a long development process. They are derived from wild types, which are known quite well. Others are the result of spontaneous crosses unifying the genes of two independent species within a hybrid. Under specific circumstances, the linkage of genes remains stable without a following segregation or dissociation. Bread wheat, domesticated plum, and rapeseed have evolved in this way.

The wild types differ from the cultivated plants not only in terms of yield but also in terms of many characteristics important for their existence under growing conditions untouched by man. So, wild cereals show a brittle rachis of the spike and special shaped awns in order to dig in the soil segments of the spike or panicle. Seeds and fruits of wild species are commonly small. The ripen fruits shatter the seeds, such as legumes, linseed, or poppy.

To prevent post-ripening sprouting in dry areas or frost-endangered climates, some wild species form hard-shelled seeds or show dormancy, a resting condition with reduced metabolic rate found in nongerminating seeds and nongrowing buds. Some seeds contain bitter substances against damage caused by game (lupines). Typical are also small and badly shaped tubers or beets of root crops. The wild forms are substantially more unpretentious than the cultivated plants in their requirements of climate and soil. They grow slowly and ripen more unevenly. Wild species are pubescent more frequently. This awards them the characteristics of a very rough, resistant, and solid plant already externally. However, they are not in principle more resistant than crop plants. There are also susceptible wild plants and resistant crops.

It can be summarized that wild plants are adapted to produce sufficient offspring, that is, to maintain the species. A luxuriant shape usually is not required for this—often it is even adverse.

In general, the crop plants are differentiated from wild species by missing of typical wild characteristics, such as seed shattering, brittle spikes, bitter fruits, or branched roots, in addition to traits useful in agriculture, horticulture, or forestry.

The resulted cultivated plant is no longer able to exist under natural environments because of such changes. It is now more or less dependent on man to look after its propagation by sowing, harvesting, and threshing. In some crops, the grade of dependence has progressed particularly far. For example, in maize, the seeds sit so tightly at the cob that self-seeding is impossible, whereas other cereals still shatter the grains when overripe or late harvested. On the other hand, this shows that crop plants still can have wild features, for example, burst of pods in legumes or rapeseed, seed shattering in cereals, dropping of fruits in fruit trees, long germination period in parsley, bitterness in cucumbers, deep rooting, or multigerms in sugarbeet.

The oldest plant breeder is already mentioned in the Bible. “Noah, a man of the soil, proceeded to plant a vineyard…” after surviving the Flood. (Genesis 9:20–27)

To be classified as a cultivar, it is important that the plant shows either the majority or the essential traits different from the wild characteristics and/or modified for human utilization. What it is still missing can or has to be improved by subsequent breeding.

FIGURE 1.2 The development of average yields in grain maize (USA), wheat, and oats (Germany) over a 100-year period (compiled from data of Schmalz 1969 and Allard 1999a): during 1860–1900, almost no progress by utilization of allogamous populations in maize and landraces in wheat and oats; during 1900–1930, slow progress by utilization of cross and combination breeding; and during 1940–2000, continuous yield progress by using combination and mutation breeding of wheat and oats; during 1940–1960, significant progress in maize using double crosses; during 1970–2000, tremendous progress in maize by the application of single crosses. (Courtesy of R. SCHLEGEL. With Permission.)

Plant breeding, however, does not confine itself to the supplement of useful traits but also on the improvement of already available characteristics. Genetic engineering makes feasible even an interspecific and an intergeneric transfer of alien characteristics, as well as the creation of novel traits (Chapter 5).

In some cases, intensive breeding has led to the situation in which cultivars lost too much of the original wild characteristics. Breeding toward re-introgression of wild characteristics is one way out of the dilemma. The enhancement of the dormancy in order to reduce preharvest sprouting became such a task in rye or oat improvement.

The origin of cultivated plants is basically a process of displacement of wild characteristics and an enrichment of suitable traits—a process that began before thousands of years, for example, for wheat, barley, or millet. Nevertheless, plant breeding as an artificial version of natural evolution, involving artificial selection of desired plant characteristics and artificial generation of genetic variation. It complements other farming innovations (such as introduction of new crops, grafting, changed crop rotations and tillage practices, irrigation, and integrated pest management) for improving crop productivity and land stewardship. During the period from 1930 onward, crop breeding, in concert with these other innovations, has led to spectacular increases in crop yields especially of cereal grains (Figure 1.2). Plant breeding is now practiced worldwide by both government institutions and commercial enterprises. International development agencies believe that breeding new crops is important for ensuring food security and developing practices of sustainable agriculture through the development of crops suitable for minimizing agriculture’s impact on the environment.

2	Plant Breeding Since 10,000 Years BC

Recent archaeological evidence has begun to undermine this model pushing back the date of the first appearance of plant agriculture. The best example of this being the archaeological site Ohalo II in Syria, where more than 90,000 plant fragments from 23,000 years ago show that wild cereals were being gathered over 10,000 years earlier than previously thought, and before the last glacial maximum (18,000–15,000 years ago).

Agriculture had begun in only a very few places around the world: at least four places in the Old World and three in the New World have been identified. The migration of the early people around the world has, of course, also spread their efforts for food as well as agriculture (Figure 2.1). The oldest region is in the Old World at the eastern end of the Mediterranean Sea extending through Syria, Turkey, Iraq, and Iran. Two separate places are located in China, one in the south along the Yangtze River and another in the north in the valley of the Yellow River.

The fourth region is in a band in Africa extending south of the Sahara. The transition was gradual in each separate case, and the plants that were domesticated were distinctive of the particular region. These places were called Centers of Origin, but it is now clear that there are at least 10 such centers instead of 6 claimed by N. I. VAVILOV (Chapter 9). Wheat was developed in the Middle East, apparently in the northern portion of the Fertile Crescent: the lands immediately east of the Mediterranean Sea. It was apparently brought to the western hemisphere in historic times by Europeans, post-Columbus. Current dating puts its origin at 10,000–10,500 years ago. The same area seems to have given rise to rye maybe even as early as 13,000 (at Abu Hureyra, Euphrates), barley at 10,000, and figs at 11,400 years ago.

RIEHL et al. (2013) concluded that the first peasants settled in the Fertile Crescent between Euphrates, Tigris, and the Mediterranean over 11,000 years ago. There they began to grow grain for the first time. From there, agriculture spread over large parts of Europe and Asia.

It was unclear, however, where our ancestors first began to make wild plants into crops by breeding. The German–Iranian researcher team has discovered decisive indications in ...