Mutation breeding, sometimes known as “variation breeding”, is the process of exposing seeds to chemicals or radiation in order to generate mutants with desirable traits to be bred with other cultivars. Plants created using mutagenesis are sometimes called mutagenic plants or mutagenic seeds.
From 1930 to 2014 more than 3200 mutagenic plant varieties were released that have been derived either as direct mutants (70%) or from their progeny (30%). Crop plants account for 75% of released mutagenic species with the remaining 25% ornamentals or decorative plants. However, although the FAO/IAEA reported in 2014 that over 1,000 mutant varieties of major staple crops were being grown worldwide, it is unclear how many of these varieties are currently used in agriculture or horticulture around the world, as these seeds are not always identified or labeled as having a mutagenic provenance. There are different kinds of mutagenic breeding such as using chemical mutagens like ethyl methanesulfonate, radiation or transposons to generate mutants. Mutation breeding is commonly used to produce traits in crops such as larger seeds, new colors, or sweeter fruits that either cannot be found in nature or have been lost during evolution.
Exposing plants to radiation is sometimes called radiation breeding and is a subclass of mutagenic breeding. Radiation breeding was discovered in the 1920s when Lewis Stadler of the University of Missouri used X-rays on maize and barley. In the case of barley, the resulting plants were white, yellow, pale yellow and some had white stripes. In 1928, Stadler first published his findings on radiation-induced mutagenesis in plants. During the period 1930–2004, radiation-induced mutant varieties were developed primarily using gamma rays (64%) and X-rays (22%).
High rates of chromosome aberrations resulting from ionizing radiation and the accompanied detrimental effects made researchers look for alternate sources for inducing mutations. As a result, an array of chemical mutagens has been discovered. The most widely used chemical mutagens are alkylating agents. Ethyl methanesulfonate (EMS) is the most popular because of its effectiveness and ease of handling, especially its detoxification through hydrolysis for disposal. Nitroso compounds are the other alkylating agents widely used, but they are light-sensitive and more precautions need to be taken because of their higher volatility.
Plant biotechnologies play an important role in mutation breeding. Plant tissue culture techniques are powerful tools in shortening the time needed to generate breeding mutant lines. This is a bottleneck for the exploitation of induced crop mutations that are recessive (in genetics, when one characteristic of a gene is not expressed because a more dominant one is displayed).
One such plant breeding tool is the doubled haploid technique, which refers to the doubling of chromosomes of a haploid, an organism or a cell that has only one member of each chromosome pair.
Another method is to identify molecular markers closely linked to the desired traits that can then be used to rapidly identify these traits. The development and dissemination of such molecular markers has the potential to further strengthen plant mutation breeding programmes, in particular for main food crops such as rice.
A variety of procedures may be used. Pollen may be mutagenized and then used in pollination. Dominant mutations will be expressed in the next generation, and further generations of selfing reveal recessives.