The DNA Series:
Hello everyone, this is going to be a series of blog posts. Stay tuned so you don’t lose a single one! For this series, the blog posts will be:
- Understanding the code of life
- Conventional breeding
- Mutagenic breeding – a) Introduction to mutation
- Mutagenic breeding – b) Induced mutation
- Transgenic breeding
- Interference RNA
- Gene editing
Mutagenic Breeding: Induced Mutation
While studying the Mendelian pattern of inheritance in 1901, a botanist named Hugo de Vries, found a variation in evening primrose (Oenothera lamarckiana)
that did not follow the Mendelian pattern. He later called that phenomenon ‘mutation’ and indicated that it was a major cause of evolution. De Vries also suggested that radiation like gamma and x-rays could be applied to induce mutations.
It was then in 1927, that a geneticist called Hermann Joseph Muller proved that x-ray radiation could be used to induce mutations in fruit fly (Drosophila melanogaster),
followed by the geneticist Lewis John Stadler in 1928 who used the same technique to prove that induced mutations could be done with plants, specifically corn and barley. Unlike spontaneous or natural mutations that occurs at a low rate, they found out that induced mutations have much higher rates. Mutagenesis using chemicals on the other hand, was only developed in 1941 by Charlotte Auerbach. In 1946, Muller’s research granted him a Nobel Prize in Physiology/Medicine.
Mutagenic Agents
There are physical and chemical mutagenic agents. The physical agents include x-rays, gamma rays, ultraviolet rays, ion beam technology, high hydrostatic pressure, and other radioactive substances, while chemical agents include N-ethyl-N-nitrosourea (ENU), methyl methanesulfonate (MMS) ethyl methane sulfonate (EMS), sodium azide (SA), ethyleneimine, diethylsulphate, formaldehyde, diazomethane, sulfur mustard (or mustard gas), aromatic amines, and polycyclic aromatic hydrocarbons (PAH) such as naphthalene, anthracene, pyrene, etc. The PAHs are present in combustion products of fossil fuels and organic matter (i.e. tobacco smoke and automobile exhaust). Reactive oxygen species (ROS) is also associated with mutations when in high quantities. Transposons, viruses, and some toxins (i.e. Aflatoxin from Aspergillus) can also be the cause of mutations.
How it works
The use of mutagenic agents in seeds improves the genotypic variability in rates much higher than it is in normal crossings. Despite increasing variability, there is a chance that a non-target mutation is produced, so breeders have to screen the mutated plants to choose the one with the desired traits. This is one way breeders can do mutagenic breeding. The resulting plant with the desired characteristics can be directly released into the market or used as parents for crossbreeding.
Let’s use tomato as an example. You have one tomato variety that gives you nice tomatoes, but the plant is susceptible to a certain disease (here we will call it disease X). The breeder would then use the seeds of this tomato plant and apply a mutagenic agent, either chemical or physical mutagenic agent. After treatment, the seeds will be planted and the resulting plants will be screened for desired characteristics. As explained earlier, the resulting desired plant can either be directly released into the market or be used in crossings with elite plant varieties.
Mutagenic Breeding
As of 2022, the Food and Agriculture Organization (FAO) and the International Atomic Energy Agency (IAEA) registered 3365 mutant varieties, belonging to 240 different plant species developed by induced mutation, and three-quarters of them were developed using gamma rays, as shown in the table.
Canada is in 12th regarding the number of mutants (40), the first being China, followed by India, Japan, Russia, Netherlands, and the USA. There is a wide range of characteristics achieved by mutagenesis including improved yield, resistance to diseases, tolerance to abiotic stresses, quality, and maturity.
A lot of times, mutant varieties are not only directly released, but they can also be crossed using conventional breeding to incorporate other desired traits. Rice is a successful example that has 853 mutant varieties worldwide, and Reimei cultivar (see table above) was widely used to produce new varieties from conventional breeding because of its desired characteristic of a short straw, such as Taichung Native-1 and IR 8.
New Mutation Techniques
With the objective of reducing the randomness variable, techniques like oligonucleotide-directed mutagenesis (ODM), targeting induced local lesions in genomes (TILLING), space breeding technology (SBT), endonucleolytic mutation analysis by internal labelling (EMAIL), and site-directed nucleases (SDN) were developed, where the mutation occurs in specific targeted places of the genome. As a result, mutations can be deliberately introduced into specific genes or loci, offering greater control, precision, and reproducibility compared to traditional mutagenesis.
Regulation
After almost a century of mutagenesis with no incidents, the scientists and governments are convinced the technique does not pose any threat to human health. This is one of the reasons why the majority of countries worldwide do not consider this technology as genetically modified (GM). Mutagenesis developed plants are widely used by the organic industry.
New genomic techniques (NGTs), which we will discuss in following blogs of this series, have been considered ‘new directive mutagenesis techniques’ by the European Union (EU) and were regulated as genetically modified organisms (GMOs). The traditional mutagenesis, which we have been talking about in this blog, is exempt from regulation because of its long safety history. It was only in December 2025 that the EU reached a provisional agreement to establish specific rules for NGTs. The agreement guarantees a simplified process for NGTs considered equivalent to conventional crops. The regulations on traditional mutagenesis haven’t changed since then, but we will dive into that on our gene editing blog!
In countries like Argentina, Brazil, Chile, Japan, and the US mutagenic breeding is not regulated as a GM process, but the research and development of crops with this technique usually has to be notified to the inspection agencies or treated on a case-by-case basis. Canada only regulates it if there is a novel trait.
Conclusion
Mutagenic breeding is one of the most established and reliable tools in plant improvement, with nearly a century of safe use and thousands of varieties developed worldwide. By accelerating genetic variation, induced mutagenesis has enabled major advances in yield, disease resistance, stress tolerance, and crop quality across a wide range of species.
Although mutations are generated randomly, careful screening and conventional breeding have ensured that only beneficial traits are retained. This long history of safe application explains why traditional mutagenesis is exempt from GMO regulation in most countries, in contrast to newer genomic techniques that face stricter oversight despite producing similar outcomes.
Mutagenesis has also served as a foundation for modern breeding, providing key traits that continue to be combined and refined through crossing. As newer, more targeted mutation techniques emerge, understanding traditional mutagenic breeding remains essential for informed discussions on innovation, regulation, and the future of sustainable agriculture.
Stay tuned for our next blog post on Transgenics! See you next month.
