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Crop Domestication and Humanity’s Influence on Adapting Plant Species

Crop domestication is the process that transforms “wild plant species into cultivated crops.” This process began approximately 12,000 years ago, independently, in different parts of the world. One method of this domestication consists of farmers selecting traits of the wild plants that are more desirable to human needs and continuing to increase the yield of the desired trait over multiple generations. Thus, domestication of wild plants occurs over a long period of time.

When we talk about crop domestication, we are referring to how wild plants evolve as a result of multiple interactions with humans through cultivation. Farmers wanted to “improve their yields;” making their crops easier to produce on a large scale and improving the quality of the plant. The traits that get domesticated follow simple inheritance patterns, meaning they are controlled by only one or two genes. In the rest of this article, we will: discuss the processes involved in crop domestication, look at two examples, consider its relevance to society, and ponder the ethics of crop domestication.

Crop Domestication and Humanity’s Influence on Adapting Plant Species

Image Source: Shutterstock

How are crops domesticated?

One of the primary methods by which plants are domesticated is selective breeding. To understand this concept, it is imperative to understand the genetic terminology. A trait is a characteristic of the plant that is a result of the genes coding for it. Within a species of a plant, we will see a great deal of variation between individuals. This variation is key to the domestication process.

Two initial plants, referred to as the parent plants or P1 generation, can be bred together to produce multiple offspring. The offspring generation of this initial cross is referred to as the F1 generation. This process of breeding two P1 plants to produce F1 offspring is known as cross-breeding. From the F1 offspring, the plants with the desirable traits, like larger fruit, are crossbred with other F1 offspring possessing similar traits. As generations of plant offspring are produced, an increased yield of the desirable traits will be present.

Using the process of selective breeding, also known as artificial selection, farmers are able to select and increase the frequency of favorable traits and decrease the frequency of unfavorable traits through multiple generations of breeding. Examples of desired traits are those that can “increase [crop] yield, improve grain quality, and [provide]resistance to disease, insects, and environmental stresses.” Additionally, this process can improve the crop’s nutrition, taste, and aesthetics.  Selective breeding is an effective process that allows farmers to gradually repeat the cycle of selection, breeding, planting, harvesting, and reselecting to domesticate wild plants into favorable crops.

Crop Domestication and Humanity’s Influence on Adapting Plant Species

Figure depicting domestication of the wild mustard plant to produce specific modern crops through artificial selection. [Source]

There are multiple methods of breeding crops to aid in crop domestication. One of these processes, called backcrossing, allows breeders to increase desirable traits in their offspring harvests by crossing a plant with a valuable trait A and a plant without this specific trait but valuable in other traits B, C, and D. These parent generation plants produce F1 generation offspring some of which will now possess the desired trait A. These F1 plants with trait A are crossed with the parent plant containing desirable traits B, C, and D. This process of repeatedly breeding a plant with the desirable trait from the F1 generation with a plant possessing all other desirable traits from the parent generation is known as backcrossing.

Crop Domestication and Humanity’s Influence on Adapting Plant Species

Figure depicting the process of backcrossing. Note that the plants in a red box with traits BDC are all the same plant from the P1 generation. The generation name is written in red on the left side. The uncolored plants possess other combinations of traits and are discarded. This diagram was created by Suhani Srihari.

Another process of crop domestication is plant inbreeding, which uses self-fertilizing plants. This ensures that each generation is identical to its predecessor. These plants may serve as parents for hybrid breeding (where two inbred plants from separate family lines are crossed). The plants produced possess more “stable characteristics” and are “more productive than either parent.”

Crop domestication can also occur through the use of genetic mutations. Because genetic mutations naturally occur in all species, farmers can utilize these random mutations to increase the diversity of their stalk. This process may be artificially induced through intentional exposure to specific environmental stressors like chemicals or radiation. Other methods of crop breeding for domestication include the use of scientific methods like molecular markers, genetic engineering, and gene editing.

Specific Examples

Corn

Modern corn, Zea mays, is the third largest calorie source in the world, following wheat and rice. Corn came from the wild plant Teosinte in Southern Mexico. As domestication continued, the crop was spread geographically throughout the Americas. These environmental changes contributed to the adaptation of the crop. Teosinte is a short, bushy, multistemed plant that gradually domesticated into the tall, single-stemmed, modern corn. Early farmers selectively bred for larger, single ears to make harvesting easier and increase the yield of the consumable portion. Thus, the modern corn possesses a large, single, concentrated ear with at least 18 rows of kernels. As opposed to the teosinte’s multiple, small ears with only two rows of kernels each.

An additional trait difference is noticeable in the structure of the seeds. Teosinte seeds are covered by a hard fruit case which allows seeds to be easily dispersed when a fallen case shatters. Seed shattering is a term that refers to the dispersal of seeds once a crop plant is ripe. Farmers opt for domesticated crops with little to no seed shattering ability so that they can harvest seeds themselves and achieve a high grain yield. Modern corn seeds lack this structure and thus are unable to easily disperse their seeds and allow for more easy harvesting.

Crop Domestication and Humanity’s Influence on Adapting Plant Species

A) Modern Corn  [Source]

Crop Domestication and Humanity’s Influence on Adapting Plant Species

B) Teosinte wild plant [Source]

Jatropha

Jatropha, Jatropha curcas L., is a wild plant from the Euphobiaceae family; commonly found in tropical or sub-tropical regions. Evidence today suggests that the jatropha plant was first discovered in the coastal regions of Mexico. Jatropha’s popularity in the agricultural world is partly due to its ability to survive in harsh regions with little annual precipitation.

Crop Domestication and Humanity’s Influence on Adapting Plant Species

A) Jatropha fruits [Source: Shutterstock]

Crop Domestication and Humanity’s Influence on Adapting Plant Species

B) Jatropha plantation layout in the Thailand countryside. [Source: Shutterstock]

Unlike some popular wild crop plants such as corn, sunflower, or the common bean, the domestication of Jatropha is not widespread. This is due to the low genetic variability of the Jatropha plant species found in China and India– the top countries where the plant is recorded to have been studied the most for domestication potential. At least 20 generations of a wild plant is cited as a requirement for successful wild crop domestication.

The simplest domestication method for Jatropha is Line breeding. This method begins with a cross between two parents of genetically distinct types of Jatropha plants. The type of parents chosen to begin this process is dependent on the breeding objective. For example, a desire to cultivate Jatropha crops with a higher tolerance to drought, increased product yield, and high disease resistance led to the initiation of Plantation field trials to produce elite lines of Jatropha in Samarlakota town in India.

 

Crop Domestication and Humanity’s Influence on Adapting Plant Species

Plantation field trials create an elite line of Jatropha that were tested and found to have a minimum yield potential of 3.5 ​tons per hectare per year under rainfed conditions. The average yield of Jatropha prior to breeding (in India) is 0.5 to 1 ton per hectare per year. [Source Oil Crop Science]

The discovery that every Jatropha seed consists of ~36% oil content has made the plant a topic of interest in the bioenergy world. Within each Jatropha seed is a core element called a kernel, and within this are phorbol esters which are useful for bioenergy production, but toxic if ingested. The kernel types grown in Mexico do not contain these phorbol esters and are safe for consumption and sale in the agricultural market.

Today, research is underway to map the numerous pathways possible for converting Jatropha into other, more common, food products. The figure below illustrates the various products that can be grown or manufactured using a natural supply of Jatropha plants.

 

Crop Domestication and Humanity’s Influence on Adapting Plant Species

Meeting Future Agricultural Goals using Jatropha [Source]

Relevance to society 

Crop domestication is an agricultural practice that began after the Neolithic Revolution and is regarded today as a viable option for meeting human crop breeding objectives. Over the last few decades, some breeding objectives prioritized by agricultural farmers have included:

  • Seed size and weight
  • Growth habit
  • Loss of Seed shattering*
  • Adaptability to local climate
  • Physiology preferences
  • Fruit size and shape

These breeding objectives have seen wheat, rice, and maize crops become the leading agricultural products consumed at dinner tables worldwide.

Crop Domestication and Humanity’s Influence on Adapting Plant Species

Common cereal crop types consumed around the world. [Source: Shutterstock]

A Solution to Food Insecurity?

Today, food insecurity is on the rise and directly results from biodiversity loss, climate change, and rising economic inequality, amongst other factors. In the thick of this, crop domestication offers farmers a silver lining by providing them with more agency in selecting crops to breed and supply to the global market.

Genome selection technologies can now be used to create climate-resilient crop plants. One means of achieving this is de-novo domestication, which employs advanced genome editing in selective crop breeding.

Another is neo-domestication, which broadly refers to sustainably achieving full crop domestication by identifying climate-resilient traits based on the local environment, determining the availability of crop seeds with these climate-resilient traits, and scaling up production of the selected crop seed types. Neo-domestication is commonly used today for wild tomato and wild Oryza alta (O. alta) – a relative of wild rice. In the case of these two wild plant species, the neo-domestication process creates new crops of larger grain size and optimized flowering time. Yet, successful neo-domestication to produce climate-resilient crops of the future is not always straightforward. The availability and suitability of wild plant species is an important factor and challenge.

Challenges Ahead and Ethical Considerations

Our human needs are constantly changing. The crops of the future do not have to look the same as the crops we consume today. The potential in what can be created from crop domestication is a testament to this.

As crop domestication practices continue around the world, there are some ethical considerations to ponder. These include respecting the ownership rights of locally grown wild plant species and maintaining natural ecosystems by preserving the genetic survival traits of rare wild crop species.

A side effect of disrupting the balance of a natural ecosystem is biodiversity loss. Crop domestication changes how animals interact with crops in their shared environment. In the case of cultivated olives, prioritizing genetic traits that induce fast growth came at a cost. According to a 2000 study released by the Institute of Terrestrial Technology, cultivated olives are shown to have fewer amounts of phenols and tanning than wild olives. These compounds are important tools for plant self-defense against pests, herbivores, and microbial pathogens. Thus, the domestication of wild olives renders the species defenseless against invasive organisms, reducing their survivability in the wild. As these types of domestication practices continue, these plant species become more reliant on human intervention.

Crop Domestication and Humanity’s Influence on Adapting Plant Species

Aphids, also commonly known as greenfly, suck sap from olive tree. [Source: Shutterstock]

Conclusion

The crop domestication process that started 12,000 years ago continues to allow farmers to improve their crop yields and diversify the foods that make it to our dinner tables. This domestication process allows us to alter the genetics of the crop species for human use. These alterations include increasing tolerance to harsh environmental conditions and adapting its morphology. Domestication of Jatropha is currently underway to explore its potential usage as a sustainable food source, and biofuel alternative.

Crop Domestication and Humanity’s Influence on Adapting Plant Species

Image Source: Freepik

It is evident that human interaction has and will continue to play a large role in shaping the crops of today and, as a result, the environment. Through years of domestication, we have changed the structure of modern corn to the point where it barely resembles its ancestral species, teosinte. As we continue these practices, it is vital that we consider the permanence of human influence on these species and the environment as a whole. More research is needed on how wild plant species are affected by the domestication process and the possible long-term effects of increased dependence on these crops on human interactions. Lastly, it is worth speculating what today’s crops will look like 10, 20 years from now as domestication continues.

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