Mutation induction

To artificially induce hereditary changes in plants, either physical or chemical agents are used. Ionizing radiation is a widely used physical agent to treat the seeds and other plant material of crops to create heritable mutations.

Natural means to induce genetic diversity have been exploited for many millennia to improve major food crops. However, the frequency of such mutations is insufficient to meet current needs. One of the most important breakthroughs in the history of genetics was the discovery that mutations can be induced by physical and chemical mutagens (agents that change the genetic material of an organism). Mutation induction, together with mutation detection a key element of mutation breeding, has been an important tool for plant breeders for more than 70 years to increase the genetic diversity of plants and derive new mutant lines with improved characteristics.

Jointly with the FAO, the IAEA helps Member States develop and adopt nuclear-based technologies that optimise mutation induction practices, with the goal to intensify crop production and preserve natural resources.

Irradiation to bring about heritable genetic changes

Whether spontaneous or induced, mutations generally are a result of large-scale deletions, inversions or translocations of chromosomes, or from point mutations (a type of mutation that causes a single change, insertion or deletion of the genetic material) in the DNA. Physical mutagens most often result in chromosome changes and larger DNA deletions while mutagenic chemicals typically cause point mutations.

The degree of mutation also depends on the tissue and the time and dosage of exposure. DNA mutations are generally of the most interest to breeders. However, mutations that alter chromosome structure to increase the number of recombination events (the production of offspring with combinations of traits that differ from those found in either parent) and break undesirable linkages are also extremely valuable.

Physical mutagens, mostly ionizing radiation, can increase the natural mutation rate by 1,000 to 1 million fold, and have been widely used to induce heritable genetic changes. More than 70 per cent of induced and released mutant crop varieties have been developed using physical mutagens. Since the 1960s, gamma rays have become the most commonly used mutagenic agent in plant mutation breeding. 
Seeds or other plant propagules (such as pollen, spores or stem cuttings) are typically treated for seconds or minutes with a cobalt-60 source, or are irradiated in X-ray machines. Whole plants or seedlings can also be irradiated, either in a gamma greenhouse or a gamma field. This process is called chronic irradiation. If the resulting mutations are not repaired by the cell’s own repair mechanism, a heritable mutation has been generated.

During the past two decades, ion beam radiation has emerged as an effective and unique mutagen. Other types of mutagenic radiation, such as X-rays, α- and β-particles, fast neutrons or UV light  have also demonstrated their usefulness in plant mutation induction, either for particular types of material or for particular purposes. One example is the use of fast neutrons to induce large deletions of genetic material).