Origin, Evolution and Domestication of Crop Plants | Agriculture Optional Notes for UPSC PDF Download

Introduction

Throughout history, humans have coexisted with plants, relying on them for their survival. Our ancestors gathered a wide variety of wild plants from all corners of the world, experimenting with their uses through trial and error. This deep knowledge of plants has had a profound impact on the evolution of human societies. The domestication of plants has brought about significant changes in the course of human history. The adaptation of plants for agriculture played a pivotal role in the transition from a hunter-gatherer lifestyle to settled agricultural communities, paving the way for the development of cities and the modern civilization we know today. If you want to delve further into the topic, continue reading to explore the origins, consequences, and importance of plant domestication.

Domestication of Plants: Definition

Domestication involves the hereditary transformation of wild plants into domesticated and cultivated varieties to meet human requirements. It's the process of taking control of a plant species and gradually modifying it through careful selection, genetic manipulation, and cultivation to enhance its usefulness to humans. These domesticated plants encompass resources like food and fuel, providing various benefits to humanity.

In its purest form, domestication represents the initial phase of humans gaining control over wild plants. Domesticated plants differ from their wild ancestors because they have been deliberately bred by humans to serve specific purposes or desires and have been adjusted to thrive under the constant care and attention provided by people.

Origins of Domestication

• Plant domestication in the Old World began during the Mesolithic Period, preceding 9500 BCE. The true onset of the Neolithic Period, marked by the successful domestication of both plants and animals, occurred around this time.
• Primitive agriculture, as a social activity, didn't emerge until the Neolithic Period, by which point domestication had become well-established. The Neolithic Period had varying start times worldwide, but it is commonly accepted to have started between 10,000 and 8,000 BCE.
• While most of the plants we currently cultivate were selected and grown during the Neolithic Period, there were some exceptions to this rule.

N. I. Vavilov proposed that crop plants originated from wild species in various locations, which he referred to as "primary centers of origin." These crops then spread to other areas as humans moved. Interestingly, certain crop species display a wide range of characteristics in specific regions, even if they didn't originate there. These additional regions where these characteristics developed are known as "secondary centers of origin."

Vavilov has suggested eight main centres of origin:

Domesticated Plants

• Sugar beet became a sugar-producing crop only in the 19th century, while mint was cultivated as an agricultural crop in the 20th century for the first time.
• The domestication of plants that reproduce vegetatively, like tubers, likely predates the domestication of seed plants such as cereals, legumes, and other vegetables.
• Certain plants were domesticated primarily for the strong fibers found in their stalks, which were used for making various products, including fishing nets.
• Hemp, one of India's earliest cultivated plants, is a versatile example because its seeds yield oil, its stalk provides fibers, and its flowers and leaves produce the narcotic hashish.
• Some plants were domesticated specifically for the production of opioids; an example is tobacco, which was likely initially used by Native American tribes to create a narcotic drink and later for smoking.
• The opium poppy is another instance of a plant that has been cultivated solely for the purpose of producing a narcotic substance.
• Beverages like tea, coffee, and cola are a few examples of plants that have been identified and cultivated for human consumption. The domestication of plants for aesthetic reasons, focusing on their beauty and uniqueness, began after a certain level of cultural development had been reached.

Effects of Domestication

Domestication has influenced the characteristics of most wild species through three key processes: mutation, hybridization, and genetic recombination, all of which are driven by human or natural selection.
During the process of domestication, certain traits have undergone changes, some have disappeared entirely, and many have evolved.
Notable characteristics that have been affected include:

• Reduction or elimination of spines, pods, or spikes.
• Elimination of dormancy periods.
• Reduction in toxins or other undesirable substances.
• Increase in the size of grains or fruits.
• Changes in plant type, including alterations in height, the number of tillers, leaf size, branching patterns, and more.
• Acceleration of maturity.
• Increased economic yields.
• Alterations in photoperiodic behavior.
• Changes in the mode of reproduction.
• Adjustments in pollination habits.
• Synchronization in flowering.
• Loss of defensive adaptations like hairs and thorns.
• Selection of bisexual varieties over dioecious ones.
• Reduction in variability.
• Selection of polyploidy.

Through the domestication process, various crops, including rice, wheat, barley, sugarcane, cotton, potato, tobacco, and arhar, have transformed from their wild origins into domesticated forms.

Origin of Crop Plants

Origin of Rice

• Rice (Oryza sativa) was initially grown in South and Southeast Asia approximately in 300 B.C.
• The cultivated forms of rice likely originated from wild rice species like O. perennis.
• Rice cultivation spread from India to China, Africa, and the Americas, leading to its domestication into three distinct varieties: indica, japonica, and javanica.
• The process of domestication brought about numerous morphological and physiological changes, including adaptation to diverse environments, transitioning from typical open fields with sunlight to dark, waterlogged wetlands.
• O. sativa was categorized into three types based on differences in leaf shape and size, grain characteristics, and other plant type traits.

Origin of Wheat

• Triticum likely had its origins around 6000 years ago in Afghanistan and the South-Western Himalayas and subsequently spread with human migration both to the west and east.
• India cultivates four species of Triticum: T. durum, T. aestivum, T. dicoccum, and T. turgidum, all of which are allopolyploids.
• Through the domestication process, there have been changes in the plant's characteristics, with one of the most significant alterations being the transition to a non-brittle rachis.

Origin of Cotton

• Among the four cultivated cotton (Gossypium) species, two are diploid, and the remaining two are tetraploid.
• The diploid cotton species had their origins during the time of the Indus civilization, dating back to around 2000 B.C. These two species migrated from India to Africa and the Americas, where tetraploid species emerged during the process of domestication.
• During domestication, two noteworthy characteristics that evolved are the complex lint and its suitability for spinning.
• The diploid cotton species include G. arboreum and G. herbaceum, while the tetraploid species consist of G. barbadense and G. hirsutum. The New World cotton is an allotetraploid variety.

Origin of Tea

• The belief is that this crop had its beginnings in Central Asia and then split into two varieties: the small-leaved China type and the broad-leaved Assam type.
• The China type (Camellia sinensis) underwent further distinction and domestication in South China before eventually being introduced to India during the early 19th century. Meanwhile, the Assam type (Camellia assamica) originated as a secondary source in North East India.

Significance in Domestication of Plants

The following is a list of possible modifications in plant species as a result of domestication:

• Enhancing adaptability to a broader range of environments and geographic locations.
• Achieving uniform and simultaneous flowering and fruiting.
• Preventing the shattering or dispersal of seeds.
• Enlarging the size of fruits and seeds.
• Transitioning from a perennial growth habit to an annual one.
• Altering the plant's breeding system.
• Boosting yield and productivity.
• Increasing resistance to diseases and pests.
• Developing parthenocarpic fruits that do not contain seeds.
• Enhancing the color, appearance, taste, and nutritional content of the produce.

Conclusion

Domestication involves the gradual transformation of a plant species under human influence through processes like selective breeding, genetic manipulation, and cultivation to enhance its utility to humans. Selective breeding is employed as a method for domestication, where individuals with advantageous traits are deliberately chosen for breeding, thus passing on these desirable characteristics to successive generations. Crop domestication has had notable effects on the dynamics between plants, herbivores, and their natural adversaries. It is observed that domestication consistently reduces the chemical resistance of herbivorous insects, resulting in improved performance of herbivores and their natural enemies on cultivated plants.