What is Mutation Breeding?

Mutation induction is a process through which natural spontaneous mutation is sped up through biological, chemical or physical factors to improve desirable or targeted characteristics of a plant. Those include, but are not limited to, viruses and bacteria (biological), antibiotics and alkylating agents (chemical) or exposure to ionizing radiation (physical). Plant seeds are most commonly irradiated to induce mutations. However, for certain experiments whole plants, seedlings or only parts of the plant— pollen, spores or the stem of a plant — are irradiated. If the resulting mutations are not eliminated by the cell’s own repair mechanism, a heritable mutation is generated. The plants with the most promising mutations are bred further, until the researchers arrive at a substantially improved variant that can address the farmers’ needs.

Typically, scientists use specific technologies such as cobalt-60 radioactive sources or an X-ray machine for plant irradiation. Gamma rays from cobalt-60 have been the most commonly used mutagenic agent in the past decades. Other types of radiation such as α- and β-particles, fast neutrons or UV light have also been useful for plant mutation induction. Ion beam radiation and cosmic radiation are increasingly being used for this purpose as well, in order to explore the advantages of these methods in comparison with other types of radiation.

Mutant selection is the process of identifying plants that have been improved by induced mutation through irradiation. Mutations occur in such low frequencies that large numbers of seeds must be irradiated, grown and bred over different generations, until a desirable trait is developed. The time this process takes varies, since the development and analysis of mutant populations with, often, many thousands of individual plants, is a large undertaking and depends on the crop.

The process of identifying and selecting new plant varieties with improved traits involves two major steps: screening and validation. Screening and validation of visible and readily scorable characteristics of a new crop variety, such as early flowering or short stature, is straightforward. Other characteristics that are not so easily identifiable require the development and application of screening procedures specifically for the target characteristic, for example, salt tolerance in hydroponics or disease screening.

Space can be considered the harshest growing environment, since seeds, plants and plant materials in space are affected by cosmic radiation and microgravity. On the other hand, cosmic rays can help to produce mutations that could make plant varieties more enduring to the conditions on Earth, which are worsening because of climate change and other stressors.

Space mutagenesis, is a method that involves the use of cosmic rays in outer space to induce spontaneous mutations. Scientists typically send plant seeds into space, and then grow, screen and breed them once they return to Earth. As in conventional mutation breeding, scientists try to identify the plants with the most useful traits, and those which may provide an advantage over more traditional crop varieties. Wheat, rice and cotton have already visited space.

Moreover, cosmic rays and microgravity affect plant biology itself. This is being explored in astrobotany studies for a different purpose — to determine the best ways of growing plants in space.

You can read more about this technology here.