Plant breeding is the process of changing plant traits to create desired features. It helps improve the quality of plants so they can be used by people and animals. The goal is to develop crops with special traits that are useful for many purposes. Common traits that are improved include resistance to pests, diseases, and environmental challenges like drought or poor soil, as well as higher crop yields, better taste, and higher levels of important nutrients like proteins, sugars, and vitamins. Traits that make plants easier to grow, harvest, and process are also important.

Plant breeding can be done in many ways. Simple methods include choosing the best plants to grow more of. More advanced methods use knowledge about plant genetics and chromosomes. Even more complex techniques involve working with the specific genes that control a plant’s traits. Plant breeders aim to create plants with certain features, which may lead to new plant varieties. This process can reduce the variety of plant types within a species to a few specific kinds.

People around the world, including gardeners, farmers, and professional plant breeders working for organizations like government agencies, universities, and research centers, practice plant breeding. International groups believe that creating new crop varieties is important for food security. These varieties can produce more food, resist diseases, survive droughts, and grow well in different environments.

A 2023 study found that without plant breeding, Europe would have grown 20% less food from crops over the past 20 years. This would have required an extra 21.6 million hectares (53 million acres) of land and released 4 billion tonnes (3.9 × 10 long tons; 4.4 × 10 short tons) of carbon. Scientists are currently crossing wheat varieties developed for Morocco with plants to create new types that grow well in northern France. Soybeans, which were once mainly grown in southern France, are now being grown in southern Germany.

History

Plant breeding began with settled farming and the domestication of early agricultural plants. This practice is believed to have started about 9,000 to 11,000 years ago. Early farmers chose plants with useful traits and used them to grow future generations, gradually improving these traits over time.

Grafting, a technique where parts of plants are joined together, was used in China before 2000 BCE. By 500 BCE, this method was widely practiced.

Gregor Mendel (1822–1884) is known as the "father of genetics." His experiments with plant crossbreeding helped him discover rules about how traits are passed from plants to their offspring. These discoveries encouraged research to improve crops through breeding.

Selective breeding was important during the Green Revolution of the 20th century.

Modern plant breeding uses genetic science but includes many other areas of study, such as molecular biology, cell structure, classification, plant function, disease, insect study, chemistry, and statistics. It also involves specialized tools and techniques.

Classical plant breeding

Plant breeding often uses a method called selection. This involves growing plants that have good traits and not growing plants that have poor traits. Another method is crossing plants that are closely or far apart in relation. This helps create new plants with useful traits. For example, a pea that resists mildew might be crossed with a pea that produces a lot of food but is not resistant to mildew. The goal is to get the mildew resistance without losing the high food production. The offspring from this cross would be crossed again with the high-yielding pea (a process called backcrossing) to make sure they look like the high-yielding parent. These offspring would then be tested for mildew resistance and food production. Plants can also be crossed with themselves to create inbred plants. To control pollination, breeders might use bags to keep pollinators away.

Classical breeding depends on mixing genes between chromosomes to create genetic variety. Breeders may also use techniques like protoplast fusion, embryo rescue, or mutagenesis to create hybrid plants that do not exist naturally.

Plant breeders aim to improve crops by adding traits such as:
1. Better quality, like more nutrition, better taste, or more beauty
2. Higher food production
3. Better ability to survive in tough environments, like salty soil, extreme heat, or drought
4. Resistance to viruses, fungi, and bacteria
5. Better ability to survive insect attacks
6. Better ability to survive herbicides
7. Longer storage time for harvested crops

In 1880, Gartons Agricultural Plant Breeders was started in England by John Garton. He was one of the first to sell new crop varieties made through cross-pollination. The company’s first product was the Abundance Oat, a type of oat created from a controlled cross and introduced in 1892.

In the early 1900s, breeders used Gregor Mendel’s work on inheritance to predict traits in seedlings. In Italy, wheat hybrids helped increase food production during the "Battle for Grain" (1925–1940). George Shull explained heterosis, a process where the offspring of a cross outperform both parents. This led to the creation of inbred lines that produce better hybrids when crossed. Maize was the first crop where heterosis was widely used.

Scientists also developed methods to study genes and separate genetic differences from environmental ones. In 1933, Marcus Morton Rhoades described cytoplasmic male sterility (CMS), a trait that stops plants from making pollen. This allows hybrid plants to be made without needing to remove pollen manually.

These early methods helped increase crop yields in the United States in the early 1900s. Similar increases happened later, especially after World War II, when the Green Revolution boosted food production in developing countries in the 1960s.

After World War II, breeders found ways to cross distant species and create genetic variety. When distant species are crossed, tissue culture techniques help produce offspring that would not normally grow. These crosses, called wide crosses, include hybrids like triticale, a mix of wheat and rye. These hybrids often have uneven chromosomes and are sterile, but chemicals like colchicine can help make them fertile.

If a hybrid does not form, it might be because of problems before or after fertilization. If an embryo stops growing, it can sometimes be saved and grown into a plant through embryo rescue. This method helped create new rice varieties in Africa by crossing Asian and African rice.

Another method is protoplast fusion, where plant cells are joined using electricity. This can create new plant combinations. Chemicals, radiation, and transposons are used to cause mutations. Breeders hope these mutations lead to useful traits. Classical breeders also use somaclonal variation, which happens in plants grown from tissue culture, and chromosome engineering to change the number of chromosomes.

When a useful trait is added to a plant, breeders cross it with the preferred parent many times to make the new plant look like the parent. For example, mildew-resistant pea offspring are crossed back with the high-yielding parent multiple times (backcrossing) to remove the mildew-resistant parent’s genes. This shows that classical breeding is a repeated process.

Classical breeding does not always reveal which genes are added to a new plant. Some scientists say plants made this way should be tested like genetically modified plants. For example, some potato varieties had too much solanine, a harmful chemical, due to breeding. New potatoes are tested for solanine before being sold.

Even with modern tools, adding a trait to plants takes many generations: seven for clonally grown plants, nine for self-pollinating plants, and seventeen for cross-pollinating plants.

Modern plant breeding

Modern plant breeding may use molecular biology techniques to choose or add useful traits to plants. This process, which uses tools from biotechnology, is also called molecular breeding.

In plant breeding, many genes can affect a single desired trait. Scientists use tools like molecular markers or DNA fingerprinting to identify thousands of genes. These tools help breeders find plants with the desired trait by checking for specific genes in the lab, not by looking at the plant’s visible features. This method, called marker-assisted selection, helps locate and understand the roles of genes in a plant’s genome. If all genes are identified, it leads to a complete genome sequence. All plants have different genome sizes and genes that make proteins, but many genes are shared between species. If a gene is found in one plant, a similar gene may be in a related plant in the same location.

Homozygous plants with useful traits can be created from heterozygous plants if a haploid cell with the desired traits is made and then used to create a doubled haploid. A doubled haploid will have two identical copies of the desired traits. Two homozygous plants made this way can be crossed to create F1 hybrid plants, which have the benefits of genetic diversity and a wide range of traits. This method, called "reverse breeding," allows breeders to create hybrid plants without needing to grow many generations of plants. Plant tissue culturing can make haploid or doubled haploid plants, reducing the time and genetic diversity needed to find useful traits. Microspore culturing is currently the most effective method for creating large numbers of haploid plants.

Genetic modification adds specific genes to a plant or uses RNAi to reduce the activity of a gene, creating a desired trait. Plants with added genes are called transgenic plants. If genes from the same species or a closely related plant are used with their natural promoters, they are called cisgenic plants. Genetic modification can sometimes create plants with desired traits faster than traditional breeding because only a small part of the genome is changed.

To modify a plant, scientists design a genetic construct that includes the gene to be added or removed, along with a promoter to start gene activity, a stop signal, and a marker to identify successful changes. In labs, antibiotic resistance is often used as a marker: plants that absorb the new gene grow on antibiotic-containing media, while others die. Sometimes these markers are removed before selling the plants.

Genes can be inserted into a plant’s genome using bacteria like Agrobacterium tumefaciens or A. rhizogenes, or through direct methods like gene guns or microinjection. Plant viruses can also be used, but this method is limited to specific plants, like cauliflower. Viral methods also require re-infecting each plant, as the virus is not passed to offspring.

Most commercially available transgenic plants have traits like insect resistance or herbicide tolerance. Insect resistance is achieved by adding a gene from Bacillus thuringiensis (Bt), which produces a toxin harmful to pests. Herbicide resistance is created by altering the target site of the herbicide, such as in glyphosate-resistant ("Roundup Ready") crops.

Genetic modification can improve crop yields by helping plants survive environmental stress. Stress signals trigger a series of reactions that activate genes involved in survival, such as those that help plants resist freezing.

Genetically modified plants can also produce medicines or industrial chemicals, a process called "pharming."

Debates about genetically modified food began strongly in the 1990s and continue today. For example, Germany banned a widely used pest-resistant corn variety. Concerns include ecological effects, food safety, and methods like "substantial equivalence" used to evaluate safety. These issues are not new to plant breeding, as most countries have regulations to ensure new crops are safe and meet farmers’ needs.

Plant breeding has changed how crops interact with their microbiomes. For example, modern maize lines have fewer nitrogen-fixing bacteria and more bacteria that process nitrogen in the soil. Hybrid plants often share similar bacteria with their parent plants, such as in cucurbits and apple shoots. The proportion of bacteria passed from parents to offspring depends on how much genetic material each parent contributes.

As of 2020, machine learning, especially deep learning, is increasingly used in plant phenotyping. Computer vision with machine learning has improved tasks like analyzing leaf traits, which were previously done by humans. Studies by Pound et al. (2017) and Singh et al. (2016) show how this technology can be applied across many plant species.

Participatory plant breeding

Participatory plant breeding (PPB) is a method where farmers take part in crop improvement programs. They have the chance to make choices and help with research work at different stages. These methods can also be used when plant biotechnology is involved in improving crops. Participatory programs support local farming systems and increase genetic diversity. Farmers' knowledge about the qualities needed for crops and their understanding of the environment where crops grow help improve the results of these programs.

A 2019 review of participatory plant breeding found that it was not widely accepted, even though it has a history of successfully creating crop varieties with better diversity and nutrition. These improved varieties are more likely to be used by farmers. The review also noted that PPB has a better balance between costs and benefits compared to non-participatory methods. It suggested combining PPB with evolutionary plant breeding to improve outcomes.

Evolutionary plant breeding

Evolutionary plant breeding involves using large groups of plants with different genetic traits grown in natural conditions where competition occurs. The main way plants are selected is based on their ability to survive in typical farming environments, rather than being chosen directly by farmers or breeders. Plants that thrive under current growing conditions, such as weather and soil quality, produce more seeds for the next generation than plants that are less adapted. This method has been used successfully by the Nepal National Gene Bank to protect the variety of Jumli Marshi rice while making it less likely to get blast disease. Similar practices have also been applied to bean varieties in Nepal.

In 1929, Harlan and Martini suggested a way to breed plants by combining equal numbers of F2 seeds from 378 crosses between 28 barley types from different regions. In 1938, they showed that natural selection in mixed plant groups can lead to some varieties becoming dominant in certain areas while disappearing in others. Varieties that are not well-suited to the environment often disappeared completely.

Evolutionary breeding has been used to create self-regulating systems between plants and their diseases. For example, barley breeders improved resistance to a disease called Rynchosporium secalis scald over 45 generations. In another project, F5 hybrid soybean populations were grown on soil with soybean cyst nematodes, increasing the proportion of resistant plants from 5% to 40%. The International Center for Agricultural Research in the Dry Areas (ICARDA) combines evolutionary breeding with methods that let farmers choose plant varieties best suited to their local conditions.

In 1956, Coit A. Suneson helped define this method and named it evolutionary plant breeding. He found that 15 generations of natural selection can create results as strong as traditional breeding methods. Evolutionary breeding works with much larger groups of plants than traditional methods. It has also been used together with traditional practices to develop both diverse and uniform crop lines for farming systems with unpredictable challenges.

Evolutionary plant breeding is divided into four stages:

• Stage 1: Genetic diversity is created by crossing plants that usually reproduce by self-pollination or mixing different types of plants that rely on cross-pollination.
• Stage 2: Seeds are multiplied to increase their numbers.
• Stage 3: Seeds from each cross are mixed to form the first generation of the Composite Cross Population (CCP). All offspring are planted to grow and produce seeds. As the population grows, some seeds are saved for future planting.
• Stage 4: The seeds can be used for further evolutionary breeding or as a starting point for traditional breeding efforts.

Issues and concerns

Plant breeding faces several challenges in the future. These include limited land available for growing crops, harsher growing conditions, and the need to ensure enough food for the world's growing population. Crops must be able to grow in many different environments so people everywhere can access food. This requires solving problems like making crops more resistant to drought. Scientists believe that plant breeding can help solve these global issues by selecting specific genes that allow crops to produce better results. One problem in agriculture is the loss of local crop varieties, which may contain useful genes for adapting to future climate changes.

Traditional breeding methods reduce the ability of plants to change their traits and limit differences between plant types. This lack of variety makes it harder for crops to survive changes in climate and other environmental stresses.

Plant breeders' rights are an important but debated topic. Most new crop varieties are developed by commercial breeders who want to protect their work and earn money through agreements based on intellectual property laws. This topic is complex. Some people argue that strict rules and economic pressures are causing commercial breeders to reduce the variety of crops, making it harder for farmers to grow and trade seeds locally. Efforts to strengthen breeders' rights, such as extending the time new varieties are protected, are still happening.

Laws about plant intellectual property often define stability as having the same appearance and genetic makeup across generations. This contrasts with traditional farming practices, which define stability as how consistently a crop’s yield or quality remains across different locations and over time.

As of 2020, Nepal’s laws only allow crops that are uniform in appearance to be registered or released. Many traditional crop varieties, which are naturally diverse, do not meet these standards.

Uniform and genetically stable crops may not be enough to handle unpredictable environmental changes or new stress factors. Breeders are working to find crops that can grow well under these conditions, such as strains that resist drought and require less nitrogen. This shows that plant breeding is essential for future agriculture, as it helps farmers grow crops that can withstand stress and improve food security. In countries with harsh winters, like Iceland and Germany, breeders are developing crops that can survive frost, heavy snow, and high soil moisture.

Plant breeding is a slow process, especially when addressing diseases. It typically takes at least 12 years from the discovery of a new fungal disease to the release of a resistant crop.

When new plant varieties are created, they must be carefully maintained. Some plants are grown without seeds, while others use seeds. Seed-based crops require strict control over where seeds are grown and how they are handled to keep the variety’s traits consistent. Plants must be isolated from other plants to avoid cross-pollination or mixing of seeds after harvest. This is often done by keeping plants far apart or using greenhouses or cages, especially for hybrid crops.

Modern plant breeding, whether through traditional methods or genetic engineering, raises concerns, especially about food crops. There is debate about whether breeding might reduce the nutritional value of crops. Some studies, like one from 2004, found that certain nutrients in vegetables, such as protein and riboflavin, decreased between 1950 and 1999. The study suggested these changes may be linked to the development of new crop varieties that prioritize yield over nutrition.

Plant breeding can help improve food security by increasing the nutritional value of crops and forage. Since the 1960s, advances in science have allowed breeders to improve traits like digestibility in forage crops. These improvements have helped increase livestock growth rates. This shows that plant breeding is a valuable tool for advancing agriculture.

As the world’s population grows, food production must increase. It is estimated that food production must rise by 70% by 2050 to meet global food needs. However, degraded farmland limits the ability to grow more crops. Plant breeding can help by creating new crop varieties that produce more food without needing more land. For example, in Asia, food production per person has doubled through better crops and the use of fertilizers.

Some critics argue that organic farming may not produce enough food because it often uses crops adapted to conventional farming, which are not suited to organic conditions. Organic farming has fewer tools to manage the environment, so breeding crops specifically for organic conditions is important. These crops need traits like efficient water and nutrient use, strong weed resistance, and tolerance to pests, diseases, and environmental stresses. Few breeding programs focus on organic agriculture, and those that do often rely on indirect methods.

List of notable plant breeders

• Yvonne Aitken
• Norman Borlaug
• Luther Burbank
• Keith Downey
• Thomas Andrew Knight
• Niels Ebbesen Hansen
• Nazareno Strampelli
• Nikolai Vavilov