Breeding of Fruit and Plantation Crops 2 + 1

Mutation

• Sudden heritable change in the genotype of an organism is termed as mutation. It may be spontaneous (without any treatment by man) or induced (artificially induced by a treatment with certain physical or chemical agents) in plant population. The process through which mutants get induced is called mutation and the mutated individual is called a mutant. Mutants have variously been classified as spontaneous and induced, natural and artificial based on their origin; germinal and somatic based on the tissue involved; chromosomal, genic and cytoplasmic etc.

Kind of mutations

• Macro mutations are large mutations and can be recognized on a single plant basis, e.g., changes in colour, shape, etc., Micro mutations are mutations with small effects and can be recognized only when a group of 30 or more mutant plants are compared with a normal one. Micro mutants differ with normal only quantitatively; for example, mutants with larger or smaller grains or higher yield, etc., Micro mutations are more important for direct use in plant breeding.


• Point mutation is another term often used to designate gene mutation but it comprises of group of changes at individual loci (point) including micro structural change, micro-deficiencies and gene mutation.


• Somatic mutation refers to mutants appearing in vegetative part in M1 generation. It also refers to ‘bud-sport’ in the case of vegetatively propagated plants. This may occur either due to dominant mutation (aa Aa), recessive mutation in a heterozygote (Aa aa), removal of epistatic factor of chromosomal aberrations.

a. Spontaneous mutations

• These are naturally occurring mutations, which arise somatically. They arise in nature continuously without any human control and create variability, which forms the basis of conventional crop breeding methods. Their frequency is extremely low (one in a million).

b. Induced mutations

• Contrary to spontaneous mutations, these are induced by using various agents.Physical or chemical agents, which cause mutation, are known as mutagens or mutagenic agents.