Mutation breeding process and points
Mutation breeding can be defined as the process of exposing seeds to chemicals or radiations in order to produce mutants with desirable traits, that can be bred with other cultivars. Plants generated by induction of mutagenesis are called mutagenic plants or mutagenic seeds. Thus, crop improvement through induced mutation is mutation breeding.
Process of mutation breeding:
There are different methods for mutation breeding. For the induction of mutation in plant varieties fol- lowing mutagens are used to generate mutants. The main objective of mutation breeding is to produce traits in crops such as larger seeds, new colors, or sweeter fruits, which are not available in nature or have been lost during evolution.
(1) Use of chemical mutagens:
There are different chemicals, that can induce mutations. During the Second world-war, C. Auerbach (1847) was the first lady, who discovered some chemicals such as Mustard gas, Ethylene urethane, Phenol, Formaldehyde, etc., which can induce mutation or cause chromo- somal aberration in plants. Amongst these mustard gas is the most effective mutagenic agent. Some mutagenic agents are as follows-
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(i) Mustard gas
(ii) Nitrogen mustard
(iii) Sulphur mustard These are highly mutagenic
(iv) Chloroacetone
(v) Di-chloroacetone
(vi) Mustard oil
(b) Base Analogue Chemicals:
These chemicals are similar to the 4 bases of DNA, e.g., 5-bromo Uracil and 5-bromo-de-oxy uridine, which are equivalent to Thymine, which can substitute for DNA base Adenine during replication and cause transition mutations. Similarly, Amino-purine is equivalent to Adenine & it can substitute with Thymine and Cytosine.
(c) Antibiotics:
Some antibiotics, like Azasorine, Mitomycine-c Streptonigrin, etc. have the capacity to break Chromo- some.
(d) Alkylating agents:
A large number of chemicals may interact directly with DNA. For example- Ethyl-nitrosourea is an alkylating agent. The alkylating compounds transfer methyl or ethyl group to bases or the backbone phosphate group. Guanine when alkylated may be mispaired with thymine, some may cause DNA cross-linking and breakages. Nitrosamines are an important group of mutagens found in tobacco. Other alkylating agents include musted gas. Vinyl chlorides, Epoxide, Methylmethane sulphonate (MMs, Ethyl methane-sulphonate, Ethylamine, sulfur, etc.,) are the alkylating agents that are sex-linked lethal.
(e) Other Chemicals-
Some chemicals like Hydroxylamine, Nitrous acid, Acridines dye, Alkaloids, etc. Have mutagenic properties. Phyto-chemical colchicine is used for the induction of mutations i.e., polyploidy.
(2) Mutagenic Radiations:
The induction of mutation in plants through radiation is known as radiation breeding. Mutagenic radiations are mainly of the following types-
(i) Ionizing radiations- These Types of radiations are of two types-(a) Nonparticulate or electromagnetic radiation, Examples- X-ray & 7-rays (Gamma rays) and (b) Particulate radiation, Examples a-rays (Alpha rays), B-rays (Beta rays), High-Speed neutrons and Thermal Neutrons. Ionizing radiations may cause DNA breakage and other damage.
(ii) Non-Ionizing radiations- Ultra-violet radiations are long wavelength (above 260 nm) radiation, with less energy & less penetrating power. They are strongly absorbed by DNA bases, Producing pyrimidine dimers, which can cause errors in replication if left uncorrected.
(iii) Radio-active decay- Radioactive decay such as 14 C in DNA which decays into nitrogen.
The technique of Mutation breeding: Genetic variations are required for crop improvement. In mutation breeding variations are brought about by the mutagenic agents & radiations.
The technique of mutation breeding completes by following steps:
(1) Selection of plant material for irradiation: For this soaked seeds, seedlings, pollen grains, vegetative propagules, or even complete flowering plants or cut portions of the plant are treated or irradiated with an appropriate dose of the mutagen.
(2) Raising of M, or R, generation: For raising M1 or R1 generation, the mutagen-treated seeds are sur- face dried with blotting paper & immediately space planted in the field to rise M1 generation. And in the case of irradiated plants are immediately planted to rise R1 generation. (If pollen grains are treated they are used for pollination. Seeds from individual plants are harvested separately.)
M1 is the generation that is directly produced from the mutagen-treated plant parts without the involvement of sexual or asexual reproduction. But when pollen grains are treated, then the generation (seeds) produced after pollination would be M1 By selfing or clonal propagation M2, M,, M, etc. Can be derived.
(3) Raising of M2 or R2 generation- Population of plants grown from seeds of M, or R, or vegetative parts harvested from M1 selection of desired mutants may start in this generation or later.
(4) Screening or selection in M3-M8 or R,- R, generation- During this selection is continued, Followed by genetic confirmation, multiplication, and stabilization of field performance of mutant lines.
(5) Next 2-3 generations- During this comparative analysis of mutant lines is done during different years and at different locations.
(6) Next 2-3 generations- Official testing is done before releasing it as a new variety.
Let's have some questions on Mutation breeding:
1. Which term best describes the process of exposing seeds to chemicals or radiation to produce mutants with desired traits?
a) genetic modification
b) selective breeding
c) mutation breeding
d) clonal propagation
Answer: c) mutation breeding
2. Which of the following is not a chemical mutagen used in mutagenic breeding?
a) mustard gas
b) nitrogen mustard
c) chloroacetone
d) X-ray
Answer: D) X-ray
3. What is the main purpose of mutation breeding?
a) To produce genetically modified crops
b) Creating new varieties of plants through selective breeding
c) Inducing mutations for crop improvement
d) To preserve the natural qualities in crops
Answer: c) To induce mutations for crop improvement
4. Which type of radiation is strongly absorbed by DNA bases and can cause errors in replication?
a) alpha rays
b) beta rays
c) gamma rays
d) Ultra-violet rays
Answer: d) Ultra-violet rays
5. What is the purpose of increasing the M1 or R1 generation in mutation breeding?
A) to select the desired mutants
b) harvesting seeds for future generations
c) Comparative analysis of mutated lines
d) to confirm the genetic stability of the mutants
Answer: a) To select the desired mutants
6. At what stage of mutation breeding are the mutant lines genetically confirmed, multiplied and stabilized for their field performance?
a) M2 or R2 generation
b) M3-M8 or R3-R8 generation
c) M1 or R1 generation
d) next 2-3 generations
Answer: b) M3-M8 or R3-R8 generation
7. What is the last step in the mutation breeding process before the mutant line is released as a new variety?
A) Comparative analysis of mutant lines
b) official test
c) selection of plant material for irradiation
d) raising the M2 or R2 generation
Answer: B) official test
Reference:
- Bsc 2nd year botany 3 dots.
